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Phil Pilgrim (PhiPi)
08-14-2008, 02:15 PM
Okay, the title's a bit of a come-on, since it's not a very good radio; but it's an AM radio, nonetheless, with digital tuning to boot. Moreover, it can be built without any additional active components. If you have a Propeller Demo Board, a resistor, cap, inductor, wire antenna, and a decent ground are all you need.

THEORY

Now that I've got your attention, here's the theory behind it. Most consumer radios on the market are superheterodynes (http://en.wikipedia.org/wiki/Superheterodyne). In such receivers, the incoming RF signal is "mixed" with a sinewave coming from a tunable local oscillator (LO). Mixing is basically analog multiplication, which produces, in addition to the original RF and oscillator signals, signals which are at both the sum and difference frequencies of the two. The output of the mixer is filtered to a single, fixed, "intermediate frequency" (IF) and then amplified. In AM (amplitude modulation (http://en.wikipedia.org/wiki/Amplitude_modulation)) broadcast radios, which tune from 550KHz to 1600KHz, the IF is usually at 455KHz. So, by varying the frequency of the local oscillator from 1005KHz to 2055KHz, one can obtain a 455KHz difference signal from the mixer for the entire broadcast band. The output of the IF amplifier is then introduced to a "detector", which rectifies and low-pass filters the IF signal to produce an audio waveform.

A receiver similar to the superheterodyne is the direct conversion receiver (http://en.wikipedia.org/wiki/Direct-conversion_receiver). In such a receiver the "intermediate frequency" is zero. In other words, the LO is tuned to the exact frequency you want to listen to, and the difference signal is simply the detected audio, which can then be lowpass filtered and amplified. But there's a catch: the local oscillator must not only have the same frequency as the desired signal, it must also have the same phase. To understand this, suppose the incoming RF carrier and the LO were 90° out of phase with each other. When multiplied together, these two signals would effectively cancel each other out, and you'd hear nothing. When they're in phase, the positive swings would multiply, returning positive results, and the negative swings would multiply, also returning positive results. But getting the LO to lock onto an incoming carrier can be tricky — especially if that carrier is weak.

One way around this is to have two LOs, 90° out of phase with each other, and two mixers. The idea is, what one LO oscillator misses by having the wrong phase, the other will catch. In fact, the outputs from the two mixers can be combined in such a way that the actual LO phases are irrelevant, so long as they're 90° apart. The formula for doing so is:

····Audio Amplitude = sqrt(I2 + Q2),

where I is the output of one mixer (from the "In-phase" LO), and Q is the output of the other mixer (from the "Quadrature-phase" LO).

Well, that's enough theory to lay the groundwork for the Propeller receiver. I've really glossed over a lot of stuff, but this is a forum post, not a book, and I want to get to the actual hardware and software.

APPLICATION

The use of a Propeller counter as the basis for an analog-to-digital converter (ADC) is now well-established. So why not simply attach an antenna to the input of one of these ADCs and see what comes out? Basically, that's what I've done. Here's a schematic:

http://forums.parallax.com/attachment.php?attachmentid=55182

The antenna (a wire strung across the ceiling of my shop) is connected, through an inductor to both digital ground and earth ground. I used a 330uH power inductor I found in my junkbox. It actually worked better than the ferrite antenna scavenged from a cheap transistor radio. A bunch of enameled wire wound on a plastic sewing machine bobbin worked almost as well, too. I'm sure Beau Schwabe (i.e "He Who Understands Inductors and Knows What to Do with Them") can shed a lot more light on the choice of inductors and why one is needed here. I just grabbed what I had until I found something that worked. My "earth ground" consists of the ground clip from my scope attached to the ground stud on the Demo Board. My scope input return ground and its AC protective ground are connected together, thence back to the breaker box and to a metal grounding rod. (By the way, I live in a fringe area for AM reception. If you live in a city with strong AM transmitters, you may not have to go to all this trouble.)

The antenna also connects, through a capacitor, to pin A3 of the Propeller. This is the "analog" input terminal. The feedback comes from A4 through a 470K 0805 SMD resistor, which I soldered between pins A3 and A4 right on the chip itself. I've omitted the usual filter caps to Vdd and Vss (Gnd), choosing instead to let the inherent input capacitance of A3 do the filtering. This keeps both the input impedance and frequency response of the ADC high, which is necessary for detecting weak RF signals. During positive swings of an incoming signal, A4 will be sending more 0s than 1s to counterbalance it; during negative swings, more 1s than 0s. One counter can do this, set up in the "positive-with-feedback" special analog mode. Unlike the usual ADC usage, though, we're never going to read this counter again. It's just that string of 1s and 0s fed back from A4 that we're interested in.

I love the Propeller's counters! I don't know if Chip knew what all could be done with them when he designed them, or if he just had an inkling that, with the right set of features, almost anything could be accomplished. In any event, the counters make ideal local oscillators and mixers! The oscillator part is pretty easy: just configure two counters as numerically-controlled oscillators (NCOs) in quadrature with each other. The frequency will be the frequency of the station you want to tune in. So, if I want to receive KIXI 880 in Seattle, I set up both counters to output 880KHz square waves, 90° out of phase with each other (i.e. PHSB = PHSA + $4000_0000).

Now comes the magic part: the mixers. The counters can be configured to count up whenever two inputs satisfy a Boolean conditional. The Boolean equation can be anything you want: AND, OR, NAND, NOR, XOR, you name it. I used XOR. Each "mixer" counter gets two inputs: the feedback from A4 and one of the LO outputs. If the LO output is low when A4 is feeding back 1s, predominantly (i.e. when the antenna signal is low), the counter will count up at a fast clip. Likewise, if LO is high when A4 is feeding back 0s, predominantly, the counter will, again, count up at a fast clip. In other words, the counter will count up faster when an incoming RF signal is in phase with the LO than when it's not. Moreover, the rate at which it counts up will be proportional to the amplitude of that signal. So, to read the amplitude of a signal in phase with the LO, one need only zero the mixer counter, wait awhile, then read it to see how far up it counted. On average, there will be as many increments during the sample period as non-increments, so the mean (average) count will be half the number of system clocks occurring during the same period. Any signal that's out of phase with LO, or of a different frequency, will contribute as many increments as non-increments, thus having no effect on driving the net count away from the mean.

Therefore, after each sample period, we can subtract the actual count from the mean count to get the instaneous amplitude of the signal. By doing this for both the I mixer and Q mixer, squaring the individual amplitudes, adding them, and taking the square root, we get the signal's amplitude, which can then be fed to the audio output: another counter in DUTY mode, feeding a lowpass filter. (I used A10 on the Demo board, which has the filtering hardware already in place.)

The length of the sample period will affect two things: the audio frequency response and the signal-to-noise ratio. Like most things in life, each of these two desirable qualities increases at the expense of the other, so you have to strike a balance. I got the most pleasing results with a 16KHz sample rate, which yields an 8KHz audio bandwidth. This is about as good as AM radio audio can get anyway, since the stations are spaced 10KHz apart. You can lower the sampling rate to get less static, but the audio starts to sound more "boomy".

SUMMARY

To summarize, the receiver uses six counters (spread over four cogs), as follows: (1) ADC (actually just a digitizing RF amplifier), (2) Local Oscillators in quadrature, (2) Mixers, and (1) Audio Output. Here's a block diagram:

http://forums.parallax.com/attachment.php?attachmentid=55118

The counters do virtually all the work. There's not a lot of code required, outside of setting up the counters, reading them, and shuffling data between them via the hub. The attached program is configured as a scanner for the AM broadcast band. It increments continuously by 10KHz steps from 550KHz to 1600Khz, pausing at each frequency for three seconds, which is long enough to tell if something's there. It displays the frequency on a TV monitor, via tv_wtext (included). I've also used it for LF reception below the broadcast band with some minor success. As I stated in the intro, it's not a very good receiver — in fact it sounds pretty crappy and noisy. If, like me, you live in a fringe area, you may be disappointed by its performance. But, even then, it does illustrate the capabilities of those amazing Propeller counters. And that, really, was the main point.

-Phil

Update: Owing to advice received from Beau Schwabe, based on his own testing, I've changed some component values. The inductor is now 500uH; the feedback resistor, 10M; the coupling cap, 0.047uF; and the antenna, a 2-meter-long vertical wire. The attached schematic reflects these changes, which did lead to an improvement in performance.

Also, I've corrected a bug in the program's square routine. The bug should have had no effect on the small values involved, but could cause trouble if adapted for other uses.

In a later post (17 Aug 08), I show how to wind the required inductor using readily-available parts. There's also a photo of the complete setup, with a detailed look at the feedback resistor.

Post Edited (Phil Pilgrim (PhiPi)) : 6/11/2010 11:11:36 PM GMT

Leslie (HA4WV)
08-14-2008, 02:40 PM
Phil,

We experimented with the Propeller on the Technical University of Budapest. Unfortunately, the synthesiser of the propeller is very noisy.
Now I ordered an AD9951 DDS chip (sample) from Analog Devices.
Would it be possible to produce right radio reception with the DDS and a 90 degree phase shifter according to his opinion?

Leslie

VIRAND
08-14-2008, 02:51 PM
Very nice work. I have been very slowly contemplating if and how I can make a ham radio with a Propeller.
edit:
I haven't done enough to have the noise yet but I hope I think of a way to stop the noise.
Also thanks for reminding me about the other chip just in case it is needed.

Post Edited (VIRAND) : 8/14/2008 8:09:43 AM GMT

Leslie (HA4WV)
08-14-2008, 03:12 PM
Phil,

I planned a logo last year to a similar project. I asked in e-mail the Parallax's officers, that I am allowed to use this logo for the project.
They were glad that somebody deals with this topic very much. Allowed the usage of the logo!

Let you make use of it for this work if he believes it in that manner.

Leslie

jazzed
08-14-2008, 03:33 PM
Good work Phil. Can't wait to try it.

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Drone
08-14-2008, 04:01 PM
Hi Phil, Very nice work indeed. Note however, I believe this technique of deriving the 90 degree I/Q phase shift after-the-fact can be troublesome when the modulation bandwidth is a significant percentage of the carrier frequency. Your I/Q phase shift is 90 degrees at the carrier frequency, but deviates away from 90 degrees as you move away from the carrier. But if it works, the proof's in the pudding!

Rgds, David

Drone
08-14-2008, 04:40 PM
Leslie,

At first thought I'm not so sure you'll be able to input the I/Q output from your 9951 to the propeller and have it work as a local oscillator in Phil's technique, the pins have to be sampled and I think this may introduce phase noise (jitter). However, there's nothing to prevent you from using the 9951 to mix externally using a Quadrature Synchronous Detector (QSD), or "Tayloe Mixer" as it's often called. The resultant baseband I/Q would be applied to the propeller via A/D converters, then the propeller can perform the DSP and output demodulated audio data to a D/A, etc.

There's a board and a kit of parts available for your 9951, it even has a quadrature synchronous detector and generator on-board already (good to about 70 MHz), look here:

www.wb6dhw.com (http://www.wb6dhw.com)

At the same site is a new 9912 controller board. There's a group dealing with these DDS controllers (and more) here:

groups.yahoo.com/group/dds_controller/ (http://groups.yahoo.com/group/dds_controller/)

You might want to consider Silicon Labs' [www.silabs.com (http://www.silabs.com)] Si570 or Si571 programmable VXO/VCXO instead of the 9951. It is simple to deal with, programs over I2C, has superb phase noise performance and no significant spurious products (unlike the 9951 DDS). However there is no direct I/Q output from the Si570/571, but you can use a simple circuit using two flip-flops to generate I/Q clock output at Fout/4; see the attached drawing.

There is a board and a link for a group buy for the Si570/Si571 at the WB6DHW site mentioned above as well. For best performance, I recommend you use the LVDS version of the Si570 and then convert to CMOS with a Fairchild FIN2002 LVDS/CMOS translator. This is not to say the CMOS version of the Si570 is poor, the LVDS version is only slightly better, and most CMOS versions available to buy have +/-50ppm stability over full temperature range while the LVDS version is +/-20ppm.

There's more information available on the Si570 (including an alternative controller board) at the following group. You may also buy Si570's, controller boards etc. at this group:

groups.yahoo.com/group/softrock40/ (http://groups.yahoo.com/group/softrock40/)

Good Luck, David

Rayman
08-14-2008, 05:03 PM
Nice! Assuming one can generate AM frequencies, can't you have Prop-Prop wireless with this?

Leslie (HA4WV)
08-14-2008, 05:52 PM
David,

I say thank you for the hint!
My first idea was a radio receiver (with I/Q demodulator) with the internal synthesiser of the Propeller. The inner synthesiser a lot imply additional noise. Anyway distinguished, but not radio onto an aim it was planned.
My second idea: an AD9951 generates the stable sinus oscillator signal. This signal is going onto a phase-shifter, in the output the quarter of the frequency and 90 degre phase shift. A mixer would get here, and the IQ sign onto the A/D converter. The digital output of the mixer (and A/D converter) circuit gets into the Propeller.
Effectively the propeller only a I/Q demodulator with FFT. Beside this controls the AD9951 DDS chip.

I think, it would be possible to achieve very clear radio reception with this solution in USB/LSB/CW/FM and other modes.

Leslie

Whit
08-14-2008, 06:36 PM
Thanks Phil! Who wouldn't want to give this a try? Neat project and a great educational project too.

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Whit+


"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

Jonathan
08-14-2008, 08:06 PM
Phil,

Very cool! I too live in a fringe area, but I have a decent antenna set up, along with a tapped coil/cap rig for tuning. I'll give this a shot later.

Jonathan

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www.madlabs.info (http://www.madlabs.info) - Home of the Hydrogen Fuel Cell Robot

Cluso99
08-14-2008, 08:06 PM
Fantastic - who cares much about the quality. It is the simplicity of the design (few parts) and the theory to make something work like this.

Your article is to be commended - great block diagram, schematic and theory of operation. This is a great educational project!

I remember building crystal sets in primary school - some fitted in matchboxes and some in shoe boxes. They were all great fun and learning experiences - this will be too - and keep kids out of trouble to boot! http://forums.parallax.com/images/smilies/jumpin.gif

Drone
08-14-2008, 08:15 PM
Hi Leslie,

Yes, your diagram is close, I think you get the idea. The QSD is external to the propeller as are the A/D and D/A. You will likely need a low pass filter after the D/A. You have four inputs to the QSD from your four-phase shifter. For a digital QSD, you can use only two 90 degree quadrature square wave inputs at the receive frequency. The dual flip-flop I/Q clock generator circuit in my last post does this from a source that's four times the receive frequency.

Study the Fairchild FST3253 data sheet for-example keeping in-mind that you are putting quadrature waveforms into the clock pins as per a schematic like the one attached to this message, make a timing diagram and follow how the switch commutes. The schematic attached is for an actual direct-conversion SDR kit you can buy for around $45 USD (see the softrock URL in my previous post in this thread). The schematic uses the Fairchild FST3253 with the flip-flop clock generator and Si570 for the local oscillator (CMOS version included in kit).

I don't want to hijack Phil's thread with a general discussion on SDR hardware. I sent you a Personal Message (PM) on this forum with my email address should you wish to discuss this further.

Best Regards, David in Jakarta

Beau Schwabe (Parallax)
08-15-2008, 01:03 PM
Phil,

Neat project!! ... and thanks for the comment "He Who Understands Inductors and Knows What to Do with Them"

It's funny, that while I was on vacation on the coast of Lake Michigan, I was working in Parallel apparently with what you were doing, but you beat me to it. lol
I knew what needed to be done, but did not get my head around a solution in code... Nice work!

Without going into a huge amount of detail... since the 330uH is by itself and not in parallel with an external capacitor to form an LC tank circuit (excluding the inductors self-capacitance) we will look at the impedance based on the frequency.

For the frequency range of 550kHz to 1600kHz the impedance of the 330uH inductor varies from 1.14K to 3.32K

reference:
http://www.cvs1.uklinux.net/cgi-bin/calculators/ind_imp.cgi


The Length of the Antenna also makes a difference and contributes an LC component to the impedance value above to form an RLC tank.

You can get much better results and use a much smaller antenna if you use an RF transformer (two closely coupled coils or a single tapped coil) with a Capacitor to match the resonant frequency to something like 1100kHz (<-- approximate middle of the AM dial) and use that in place of your 330uH coil. The impedance of the antenna should also be matched to the RF transformer.

Edit: Actually a 63pF capacitor in parallel with the 330uF inductor would be "tuned" to about 1100kHz but there wouldn't be a good way to couple your antenna to it unless you could wind a few (2-5) turns of wire around the outside of the inductor... one end tied to ground, and the other tied to your antenna.· At first I would try a variable capacitor that is within·63pF +/- 10 pF at least, but you may find a fixed value that works well also.· In this case we would not necessarily want a high 'Q' value for the coil, and or the cap, so a·5 to 10·Ohm resistor in series with the capacitor might also benefit.· What happens with a high 'Q' is that it becomes·a narrow band tuner, and you may loose other stations.· To be able to tune the other channels digitally, we want a little bit of padding here, so a wider band·tuner is more desirable.



I built your circuit, and used a 500uH coil instead of a 330uH (1.73K to 5.03K impedance) ... I also used a 10Meg resistor for the ADC instead of the 470K resistor. This helps
to provide less loading on the antenna from the feedback I/O pin, allowing weaker signals to be picked up.

With 22 gage solid wire, I used a 6-foot piece of it for my antenna. The attached wav file is the result from a radio station a little more than 9 miles from my home.



Other useful references:
http://www.consultrsr.com/resources/eis/induct5.htm
http://www.powerstream.com/Wire_Size.htm
http://www.daycounter.com/Calculators/Whip-Antenna-Design-Calculator.phtml

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 8/15/2008 5:02:55 PM GMT

Phil Pilgrim (PhiPi)
08-15-2008, 02:59 PM
Thank you, Beau! And thanks for the detailed analysis of, and improvements to, the RF circuitry. I'm rather envious of your near proximity to an AM radio station, the closest strong station here being some 40 miles away. Between that and your RF improvements, the S/N of your recording is many decibels above what I was able to obtain!

One thing I'd like to come up with is an easy-to-fabricate coil (or transformer) with your recommended values, made solely from hardware store and/or Radio Shack materials. I have a real aversion to winding coils that likely harkens back to childhood fumblings with fine enameled wire and empty toilet paper spools. I'm sure I'm not alone in this, so making this part easier will make the project more approachable for those who are more comfortable with digital design and programming.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Graham Stabler
08-15-2008, 03:11 PM
Nice one Phil and great quality from Beau's version. I wish my dad was still around, he was a keen radio ham (G0HLH) and would have loved this.

Complain about coil winding when you have some 2mm ID, bobbinless coils wound from 0.02mm (~1/1000") wire under your belt (and under the desk and behind the sofa) :)

Graham

heater
08-15-2008, 03:17 PM
This is very impressive.

About the only electronic components I have with me at the moment are a home made prop board and an LC tank (Ferrite rod, coil, capacitor) ripped out of a dead DCF77 radio controlled clock. So, will it be possible to tune this thing down to 77.5KHz and create a propeller time standard receiver ?

Sadly I have no means of building this at my current location.

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For me, the past is not over yet.

VIRAND
08-15-2008, 03:20 PM
Where's the noise? http://forums.parallax.com/images/smilies/shocked.gif It sounds too good to be AM.

Phil Pilgrim (PhiPi)
08-15-2008, 03:26 PM
Graham Stabler said...
Complain about coil winding when you have some 2mm ID, bobbinless coils wound from 0.02mm (~1/1000") wire under your belt...

I can't imagine! Let me guess: an MRI scanner for gnats? http://forums.parallax.com/images/smilies/smile.gif

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Graham Stabler
08-15-2008, 04:06 PM
Funnily enough I have considered such things :)

Magnetic actuator for a 2.4g IR controlled model aircraft.

Graham

Loopy Byteloose
08-15-2008, 05:29 PM
This quite wonderful as it really is a great learning exercise.

One can spend a lifetime running 'hello world' routines and blinking lights, but that has never been what Parallax wanted to facillitate.

The message here is that with a few simple tools, anyone can do far more than what a text book or tutorial teaches you.

The Propeller really allows you to explore outside the box of conventional digital wisdom. And it certainly·is all about exploring new uncharted territories. Thanks.

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It's sunny and warm here. It is always sunny and warm here.... (unless a typhoon blows through).

Tropically, G. Herzog [ 黃鶴 ] in Taiwan

Post Edited (Kramer) : 8/15/2008 10:38:05 AM GMT

Drone
08-15-2008, 07:20 PM
Hi Phil,


Phil said...
One thing I'd like to come up with is an easy-to-fabricate coil (or transformer) with your recommended values, made solely from hardware store and/or Radio Shack materials. I have a real aversion to winding coils that likely harkens back to childhood fumblings with fine enameled wire and empty toilet paper spools.


Salvage an AM transistor radio that has a speaker or try opening up an AM/FM clock-radio and I bet you'll find a ferrite rod or bar transformer/coil in there. Problem is you don't know what the relative permeability of the ferrite material is. No problem, just wind a bunch of turns on the thing and measure the inductance. The relative permeability is found using the attached equation which I scraped from this good page on ferrite antennas:

www.c-maxgroup.com/tech/antenna.php#01d (http://www.c-maxgroup.com/tech/antenna.php#01d)

Air wound (paper tube) coils still have their place. All materials are at-hand usually. A toilet paper roll or some-such plus scavenge some wire from a dead wall-wart power supply transformer or an audio transformer from a dead dial-up modem. Radio Shack sells assorted magnet wire, Catalog #: 278-1345. Or just use the nice thin wire on a salvaged ferrite antenna and wind it on a paper tube, now you don't need to measure the ferrite relative permeability.

A nice tool for calculating air-wound as well as toroidal inductors is miniRing Core-Calculator. Download it here, it is completely free:

www.dl5swb.de (http://www.dl5swb.de)

The link below has some good info on the ferrite transformer/coils you find in radios and how to modify them:

www.hard-core-dx.com/nordicdx/antenna/loop/amloop.html (http://www.hard-core-dx.com/nordicdx/antenna/loop/amloop.html)

You can buy ferrite rods with windings on them at the link below. But there's no technical information. In-fact I found these rods in other places as well but again, no technical information. Perhaps a deep search will turn else something up.

www.scitoyscatalog.com (http://www.scitoyscatalog.com)

I couldn't find a ferrite rod antenna on the Radio Shack site.

Regards, David

parsko
08-15-2008, 08:16 PM
Not much to add, but a great project! That sounded perfect, Beau! I think this is right up the alley for a young hobbiest. I recall, way back when, my father and I putting together one of those Radio Shack style kits (it was a platic, open topped boat) that had you wind your own motor. Seemed daunting, but I spent a ton of time with it in the bathtub!!! I bet you could make a small little kit for this, and put it in the education section. You have most of what you would need to put in it (document wise) in the posts above. Any more, and you'll lose people.

-Parsko

ps- Great project for a young baseball fan that's into electronics (a combination we need more of in this world of grotesquely publicized Olympics!)

Oldbitcollector (Jeff)
08-15-2008, 08:22 PM
I'm in the "almost lost" group already.. Awesome project!
I've already started looking through my shop for parts...

Question: what would it take to adjust to different frequencies?
Say aircraft (IIUC, it's close to AM) or even better police frequency.
Wouldn't this just be a matter of code?

OBC

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New to the Propeller?

Getting started with a Propeller Protoboard?
Check out: Introduction to the Proboard (http://jeffledger.googlepages.com/Protoboard_Introduction.pdf) & Propeller Cookbook 1.4 (http://ucontroller.com/Propeller%20Protoboard%20Designs%20for%20the%20Beg inner.pdf)
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us (http://propeller.warrantyvoid.us)
Got an SD card connected? - PropDOS (http://www.orrtech.net/propdos/)

Beau Schwabe (Parallax)
08-16-2008, 12:04 AM
Phil,

"One thing I'd like to come up with is an easy-to-fabricate coil (or transformer) with your recommended values, made solely from hardware store and/or Radio Shack materials."

See the·"Edit" to my original post.

If you are using a different value inductor, then use this ... http://www.deephaven.co.uk/lc.html·... to determine what parallel capacitor to use to approximate 1100kHz.


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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Phil Pilgrim (PhiPi)
08-16-2008, 12:22 AM
Thanks, Beau. It occurred to me that it wouldn't be so hard to drive a variac varactor with one of the Propeller's DUTY outputs and a suitable LP filter. This would help keep a narrow-band LC filter "in the loop", so to speak, so it wouldn't have to be fiddled with manually.

Also, you apparently have an inductance meter at your disposal. I suspect such an item is rare among most Propeller users — myself included. But this is something I'll bet could easily be fabricated using a Propeller and a few passive components. 'Any ideas along these lines?

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Post Edited (Phil Pilgrim (PhiPi)) : 8/15/2008 8:29:54 PM GMT

APStech-Attila
08-16-2008, 03:57 AM
Hi!

Nice work and a very smart idea. Thank you for sharing with the community.

I am feeling something like a Propeller based DC77 receiver behind the lines :) :)


Regards,
Attila

Phil Pilgrim (PhiPi)
08-16-2008, 04:51 AM
'Haven't heard anything around 77.5KHz yet. I need a much bigger inductance for that, methinks.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Beau Schwabe (Parallax)
08-17-2008, 03:01 AM
Phil,

"...Also, you apparently have an inductance meter at your disposal. I suspect such an item is rare among most Propeller users — myself included..."

What I have in the way of an inductance meter are a few·precision value inductors that are less than 1% tolerance that I can apply against an unknown inductor value using a method similar to what is described below...

Determine an unknown inductor based on results from a known inductor:

1) Determine the resonate frequency of your known LC values.
2) Substitute the known inductor with the unknown inductor, and measure the frequency.
3) The unknown inductance value can be determined by the following equation:

F1 = measured frequency from step 1
uH = known inductor value
F2 = measured frequency from step 2
uH! = unknown inductor value

uH! = uH * F1^2 / F2^2

"...But this is something I'll bet could easily be fabricated using a Propeller and a few passive components. 'Any ideas along these lines?..."

An attempt at this with the Propeller was the Bode plotter, but because it was not technically a "Bode Plot" and there was a bit of grief over the reference, the topic was buried.· Here is a link... http://forums.parallax.com/showthread.php?p=579380

A true "Bode Plot" would show the ratio between the input and the output in a logarithmic format... What I did·only shows the ratio between Vdd and the output after a voltage divider.










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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

heater
08-17-2008, 03:49 AM
Well DCF77 on 77.5KHz is in Frankfurt and only usable up to 2000Km from there. In the USA you have WWVB on 60KHz.
Not sure if any of these has any audio modulation that you might actually hear. Just a pulse in the carrier level every second.

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For me, the past is not over yet.

Phil Pilgrim (PhiPi)
08-17-2008, 06:52 AM
Even without modulation, if you tune to the side of the carrier by a few hundred hertz, you should still be able to hear it. Even SSB reception should be possible, since the LOs are essentailly reinserting a carrier.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

heater
08-17-2008, 01:33 PM
Good point Phil.

Guess you might also need a ferrite rod antenna and a capacitor to resonate with to get these signals from any distance.

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For me, the past is not over yet.

Phil Pilgrim (PhiPi)
08-18-2008, 04:54 AM
Beau Schwabe recommends a 500uH inductor for the AM broadcast band, so I set out to find a way to make one from readily-available materials. The coil is wound on a plastic sewing machine bobbin (Singer #2135), illustrated below. The bobbin comes with a spring-loaded metal spindle, which you will need to remove. To do so, push on the metal cone-shaped piece until a flat tab protrudes from the other side. With a pair of pliers, grab this tab, pull on it, and give it a quarter turn. The whole assembly will fall out, and you can discard it.

The wire to use is 30ga. enameled magnet wire, which you can get from Radio Shack as part of a three-pack assortment (#278-1345B). (The 30ga. wire is red-colored.) You will be winding this wire onto the bobbin about half-full. (See photo below.) To start, force the wire into the bobbin's slot with a couple inches hanging outside. You can wind it by hand, or you can use a variable-speed electric drill to speed things up. In the latter case, get a #9 drill bit and force the shank end into the bobbin's hub. Chuck up the cutting end, and slowly wind the wire on. (I didn't count the turns. I first filled the spool and measured the inductance. It was about 2000uH. So then I began removing bits at a time until I hit 500. Well, actually, it was 475, but by then it was too late to put any back! So you may want to add a few turns more.)

Once the spool is filled to the capacity shown, cut the wire, and force the loose end into the slot. Twist the two ends together to keep the wire on the spool from unraveling. Next, with a knife blade, scrape some enamel off the tips of the wire. Once you've gotten the enamel loosened, you can clean the remainder off with a fingernail. Tin the ends with solder. I soldered a two-pin header onto mine. You can also use a couple pieces of resistor wire (from at least a 1/4-watt resistor).

Now you have a 500uH (approx.) inductor that you can use to tune in your local AM stations. I attached mine in the breadboard area of an early-model Propeller Demo Board. There's a photo below, along with detail of how the 10M feedback resistor was soldered into place. You will also want to check out my original post for corrected software and a revised schematic.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

parsko
08-18-2008, 08:21 PM
Phil Pilgrim (PhiPi) said...
You can wind it by hand, or you can use a variable-speed electric drill to speed things up.
-Phil




Or you could just use the sewing machine!!! http://forums.parallax.com/images/smilies/tongue.gif

But seriously, a good idea for a way to captivate the wire.

I've thought a ton about this post while travelling over the past weekend. I think I'm going to do this soon, myself. I've also thought that this would be perfect for using the Prop as an RFID card reader, which was something I was going to try to do. But, without seeing your actual code, but seeing the pseudocode behind it in this post, I realize that I may not have been able to figure it out (without you doing it for me). But, with your code, it should be pretty easy. Would you agree?

-Parsko

ps - I also find myself more and more fascinated with inductance. Not sure what it is about it, but it consumes me every time I thing about using it for something.

Beau Schwabe (Parallax)
08-18-2008, 11:09 PM
parsko (http://forums.parallax.com/member.php?u=45771),

Yes, I agree, there is a certain caliber of·fascination about inductors that·sets them apart from other passive components.
·
As once explained to me...· an inductor and capacitor combination is like an electromagnetic laser, the values you use determine·how far apart the "mirrors" are placed.· Energy at the same wavelength that the "mirrors" are placed will be reflected back and forth and amplified significantly, while energy that does not match the wavelength will be attenuated.·



Phil,
Assuming that your bobbin is about 1/4 inch diameter, and the length is also about 1/4 inch, a 500uH coil would require about 280 turns using #30 wire and cause the overall diameter to grow outward to about 1/2 an inch.
If you use a standard coke can (2.6 inch diameter), you would only need about 58 turns of #30 wire for an equivalent coil.
Attached is a "Work in Progress" Air-Core coil calculator that I use that will give you a good ball-park value within 5%...
·

BTW) The coil shown next to the coke can would fall under the category "special case" that I have placed in the coil calculator where the 'l' and 'b' values are the same.

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 8/18/2008 4:21:38 PM GMT

Phil Pilgrim (PhiPi)
08-18-2008, 11:32 PM
Beau,

Now you've got me wondering if I really have 280 turns on that coil. (I doubt it.) I could wind another one by hand and count them, but I have a feeling that this will now entail a turns counter for my electric drill. BTW, I arrived at the inductance measurement using a 74HC00 in an LC oscillator configuration and using the formula:

····L = 1 / (4 * pi2 f2 C)

There's a chance, of course, that C (nominally 220pF) was a little off, but I got results with the 330uH coil that were within its tolerances.

I like the Coke can coil, BTW. It looks very easy to reproduce. Are there any performance advantages to be gained from a larger-diameter coil?

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Beau Schwabe (Parallax)
08-18-2008, 11:47 PM
Phil,

From my previous post, that's why I like to use the differential method ... uH! = uH * F1^2 / F2^2

This way, as long as your Capacitor is the same in both tests, any variations, even temperature, get canceled out.
All you need is a known coil value... the 74HC00 will work fine.· Just measure the frequencies between a known and an unknown.


The larger coil,· will have a higher 'Q' only because of less metal (the wire itself) in the core region... If the 'Q' is too high in this case it may not work as well without external tuning.· By introducing metal to the coil, you increase the inductance (in some cases by more than 50%) and decrease the 'Q'.· The 'Q' is the quality factor of the coil, for radio applications where a specific frequency is used, it is desirable to have a high Q.· In applications where we want broad band tuning and we don't have a specific frequency in mind, we want the 'Q' to be lower.



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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

parsko
08-19-2008, 12:04 AM
Beau,


What affect does the "wrapping" have on the inductance value ? I'm assuming that the wrapped wire is part of the actual magnet wire used in the coil. My guess is that it has a somewhat negligible effect. That is a good example of something that everyone in the world has (a can) to use to make coils!

-Luke

Oldbitcollector (Jeff)
08-19-2008, 12:08 AM
Beau,

Thanks for those universal calculations, however being a Pepsi drinker, I expect slightly better
performance from my coil... <smirk>

Now to round up some #30 wire..

OBC

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New to the Propeller?

Getting started with a Propeller Protoboard?
Check out: Introduction to the Proboard (http://jeffledger.googlepages.com/Protoboard_Introduction.pdf) & Propeller Cookbook 1.4 (http://ucontroller.com/Propeller%20Protoboard%20Designs%20for%20the%20Beg inner.pdf)
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us (http://propeller.warrantyvoid.us)
Got an SD card connected? - PropDOS (http://www.orrtech.net/propdos/)

parsko
08-19-2008, 12:09 AM
Phil,

If you have the patience, you could go through the attached document where I lay out all the calculations. I did this for my RFID project. The same conepts should be applicable to this directly. I can send the original (MathCAD) file, should you have that program.

http://forums.parallax.com/attachment.php?attachmentid=48259

-Luke

Beau Schwabe (Parallax)
08-19-2008, 12:17 AM
parsko (http://forums.parallax.com/member.php?u=45771),
·
I don't use wrapping techniques myself, but I think it's a two fold....· by wrapping you insure that the windings below are tight and compact (increase inductance).... Also, by wrapping you create a separation between other layers which decreases the·inductance.

Depending on the material used, wrapping·can also add capacitance by altering the·dielectric properties.· For high voltage applications, wrapping
might be desirable to minimize or prevent coil arching.


Edit:

Sorry, I misread your question.... the "wrapping" that I did to secure the coil was done with a scrap piece of wire, and is negligible as far as what it contributes to the inductance.· The only thing to make sure of is that the ends of the wrapped piece of wire do not touch, or you create a transformer with a shorted coil winding.· You can always use string.
·
·
···

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 8/18/2008 5:45:22 PM GMT

bmentink
08-19-2008, 07:54 AM
Hi Phil,

Great software.

I have been trying to understand it, and have done ok until I get to the cog that does the audio out.
In that cog you take the audio output from the mixers "a_audio" and shift it left by 20 then load up freqa with that value.
Can you please let me know what you are trying to achieve with that bit of code? ... especially the shift left part ... thanks.

(i.e are you trying to creat an audio modulated carrier with the cog counter which gets de-modulated by the filter on the audio out pin?)

Phil Pilgrim (PhiPi)
08-19-2008, 09:17 AM
bmentink,

The audio output counter is set up for DUTY mode. In this mode the carry out of PHSx is written to the pin every 12.5nsec. What results is a sequence of ones and zeroes, wherein the relative preponderance of ones is proportional to the value in FRQx. I have to shift the mixer value left by 20, before writing it to FRQx, because it's so faint. This essentailly multiplies it by 220. If I didn' t do that, you wouldn't hear anything.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Rayman
08-19-2008, 09:46 PM
Here's some options if you hate winding cores:

1.· Just a few turns around a Digikey torroid ferrite gives 500 uH.

2.· Inductance gyrator to simulate an inductor with an OPA340 opamp.

I just tried them both and they work (although I think I need to bias the opamp more towards Vdd/2)

Rayman
08-19-2008, 09:48 PM
PS: Is Phil's board older or newer than mine? It looks very different!

Beau Schwabe (Parallax)
08-19-2008, 10:16 PM
Rayman (http://forums.parallax.com/member.php?u=50210),
·
Good job!...· I don't have any formulas for coils with a core other than Air, only because the permeability of the core using other materials can vary greatly.··Based on your 500uH coil you have in the picture, there is about a 200% inductance increase if you compare·it to an equivalent air core.
·
"Inductance gyrator to simulate an inductor with an OPA340 opamp"·- can you provide a schematic for this?
·
"Is Phil's board older or newer than mine? It looks very different" - Some of the earlier boards used an inductor for each audio channel, this was later changed to an amplifier IC mainly to provide consistent audio strength over·wider frequency ranges.· Some other features have been added as well, such as a USB connection, and a second PS/2 connector.


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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Rayman
08-19-2008, 10:45 PM
Beau:· I'm not terribly pleased with my current circuit, so I didn't document it...· But, it's basically this one here:

http://sound.westhost.com/dwopa.htm#inductor

but with R1=10, C1=10nF, R2=variable 20k, set at 5K

I think it's operating right at the lower rail though because I'm using V+=Vdd and V-=Vss...· I think this causes some distortion, so I'll have to think of a way of shifting the bias...

There's also a diagram here:

http://en.wikipedia.org/wiki/Operational_amplifier_applications#Inductance_gyra tor

Oldbitcollector (Jeff)
08-19-2008, 10:49 PM
My current Propeller project (UPENE) has me too busy to get this built.
Any chance anyone coming to the expo is bringing this project with them?

There's a small kitchen nearby we can tie to the cold water pipe for the earth ground.

OBC

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New to the Propeller?

Getting started with a Propeller Protoboard?
Check out: Introduction to the Proboard (http://jeffledger.googlepages.com/Protoboard_Introduction.pdf) & Propeller Cookbook 1.4 (http://ucontroller.com/Propeller%20Protoboard%20Designs%20for%20the%20Beg inner.pdf)
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us (http://propeller.warrantyvoid.us)
Got an SD card connected? - PropDOS (http://www.orrtech.net/propdos/)

Rayman
08-19-2008, 11:15 PM
Beau Schwabe (Parallax) said...
·Based on your 500uH coil you have in the picture, there is about a 200% inductance increase if you compare·it to an equivalent air core.

I'd be surprised if it were only 200%...· I did build a similar sized air core one yesterday and it was only 6 uH.

Phil Pilgrim (PhiPi)
08-19-2008, 11:18 PM
Rayman,

That gyrator is great news! (Yes, I do hate winding coils!) I suspect a pullup (R3) from R2/C1 to Vdd is all you would need to bias it off the negative rail. Then you'd substitute R2||R3 for R2 in the formula for L. What's doubly neat about it is that R2 could theoretically be replaced by an nMOSFET, whose gate is driven by a DUTY-mode counter, to tune it for maximum output strength from the radio. I'm not terribly familiar with gyrators, but I assume one could also connect a cap from the input to ground to form a tuned circuit, right?

BTW, yes, my Demo Board is the early "Mark I" version.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Beau Schwabe (Parallax)
08-19-2008, 11:24 PM
Rayman (http://forums.parallax.com/member.php?u=50210),

You right, I don't know what I was thinking, or where I came up with that number now.... I calculated about 4uH for an Air-Core of similar size.

With 6uH that you measured it would be nearly an 8000% increase... Sorry


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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Phil Pilgrim (PhiPi)
08-19-2008, 11:24 PM
Rayman,

Addendum to my previous post: I suspect a pullup (R3) from R2/C1 to Vdd is all you would need to bias it off the negative rail. Then you'd substitute R2||R3 for R2 in the formula for L.

-Phil

The forum software wouldn't let me edit my previous post and gave me a weird error message about it being on a non-existent page.

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Rayman
08-19-2008, 11:31 PM
Oops. My gyrator may not be working at all... The radio sounds the same even with Vdd removed from the OpAmp...

Actually, the radio still works the same without the 500 uH inductor too...· I suppose it's because I'm using a very large antenna (metal gutter drain).· I'll have to try this later at home where AM is stronger and I can use a short antenna...

Post Edited (Rayman) : 8/20/2008 1:11:30 AM GMT

Rayman
08-20-2008, 08:12 AM
Well, now I'm confused because I tried it at home and just barely got something with the ferrite 500 uH inductor. Maybe it's my massive 2W 10-Meg resistor for the feedback resistor? I'll hook up a signal generator at work, if I get serious about it...

Phil Pilgrim (PhiPi)
08-20-2008, 09:31 AM
Rayman,

I didn't have much luck with a 10M in the breadboard area. That's why I picked A3 and A4: so an SMD resistor could be soldered "around the corner" on the Propeller chip itself.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Post Edited (Phil Pilgrim (PhiPi)) : 8/20/2008 4:53:33 AM GMT

rjo_
08-20-2008, 10:27 AM
Phil,

I just love threads like this... and right after OBC's meeting I'm going to dig into this.

Thanks a bunch.

Rich

Oldbitcollector (Jeff)
08-20-2008, 10:33 AM
Rayman said...


1. Just a few turns around a Digikey torroid ferrite gives 500 uH.




Ah! That I have.. Can you be more specific about the number of turns and the wire
you used, or should I count and guess? :)

OBC

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New to the Propeller?

Getting started with a Propeller Protoboard?
Check out: Introduction to the Proboard (http://jeffledger.googlepages.com/Protoboard_Introduction.pdf) & Propeller Cookbook 1.4 (http://ucontroller.com/Propeller%20Protoboard%20Designs%20for%20the%20Beg inner.pdf)
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us (http://propeller.warrantyvoid.us)
Got an SD card connected? - PropDOS (http://www.orrtech.net/propdos/)

Rayman
08-20-2008, 04:52 PM
OBC: Sorry, I didn't count, just took the photo...

Phil: Guess I'll have to try this on a Proto board. No way I'm messing with my demo board! 10MEG is a pretty big value for a feedback resistor. I think I'm going to have to try smaller values...

Phil Pilgrim (PhiPi)
08-20-2008, 10:01 PM
Rayman,

I originally used a 470K feedback resistor but, upon Beau's recommendation, saw an improvement in performance with 10M. One nice thing about using a resistance that large is that you can solder it onto the Propeller chip and just leave it there. Causing less than a microamp of "leakage current", it's not going to interfere with normal functioning of the affected pins one iota.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Rayman
08-21-2008, 06:59 AM
Ok, I got it going on a protoboard with just my torroidal 500-uH indunctor, 47-nF capacitor, and 1-MEG feedback resistor. Got 3 stations pretty good and others with a lot of static.

Using jumpers to make a ~2 meter antenna.

No earth ground, the whole thing is floating under laptop power.

No audio amp either, just basic RC filter to in-ear headphones (although the sound is a bit weak...).

Now, I can see if my gyrator works or not!

VIRAND
08-21-2008, 07:33 AM
I think laptops make an awful lot of AM static, especially from their screens.

In fact I used to use an AM radio as a diagnostic tool with computers,
since the receiver would make different sounds depending on what programs were running or not.

Then there's also that MP3 player program that transmits the music to a radio through the computer screen!
www.hackaday.com/2005/12/25/tempest-for-eliza/ (http://www.hackaday.com/2005/12/25/tempest-for-eliza/)

Post Edited (VIRAND) : 8/21/2008 12:39:49 AM GMT

Phil Pilgrim (PhiPi)
08-21-2008, 08:44 AM
I've always got two PCs, an LCD screen, at least one Stamp, numerous other digital devices — not to mention the Propeller itself, running at 80MHz — on when I'm testing the AM radio program. But the biggest source of hash by far has been the fluorescent lights in my shop. They all use solid state ballasts, and they are noisy, electrically speaking — one in particular, which I leave off.

I'm glad some folks are getting decent reception with this project. Being in a fringe area surrounded by noise, I'm rather envious!

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

PJ Allen
08-21-2008, 09:54 AM
I've made lots of crystal, regenerative, and TRF radios.· Wrapping an air-core coil is easy.··For a coil-form you can use a cardboard tube, a plastic pill bottle, a wood dowel; diameters of 1 inch or more make for·good handling.

The inductance of an air-core coil --

L = (R2 x N2) / (9R + 10L)

L = µH, R = coil radius (inches), N = number of turns, L = length of the windings

------

µH per inch = R2 x (1 / wire diameter)2 / (9R + 10)

turns per inch = 1 / wire diameter

length of wire req'd = N * 2R * π

Beau Schwabe (Parallax)
08-21-2008, 10:28 AM
PJ Allen,

Yeah, those are the same formulas that I have used and placed in a spreadsheet with a couple of other coil geometries. I have found them to be reasonably accurate to better than 5% in many cases.

Coil Calculator Spreadsheet:
http://forums.parallax.com/attachment.php?attachmentid=55202

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Jonathan
08-23-2008, 12:37 AM
Finally got around to trying this, it's been a busy week.

Anyway, I can't seem to pick anything up. There are two major diffs between my setup and the one shown. I am using a much longer antenna, and the Prop I am using has a 10 mHz xtal instead of 5. Of course I changed the _xinfreq and PLL. Any reason these diffs would make it not work? I don't think so but I thought I'd check. I live WAAAY out in the sticks, which is why I have an outdoor antenna set up. I'm guessing it's just low signal strength, but I thought I'd check here and see if anyone has any other ideas.

Oh, one other small thing, my air coil measured 600uH instead of 500, but that may just be my meter, it is built according to calculations.

Jonathan



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www.madlabs.info (http://www.madlabs.info) - Home of the Hydrogen Fuel Cell Robot

Rayman
08-23-2008, 12:50 AM
Well, I think the feedback resistor has to very close to the Prop chip for low inductance. It didn't work for me on the Demo board proto area, but worked on the Proto boards through-holes.

Beau Schwabe (Parallax)
08-23-2008, 01:04 AM
Rayman (http://forums.parallax.com/member.php?u=50210),

My experience is that the inductance needs to be balanced and the proto boards parasitic capacitance should be observed.
·
If I space the 10Meg resistor out by 4 holes on the proto-board and make sure that it is equidistant from the proto boards through-holes that are being used, it works ok.· Also I use the same length of jumper wire from the proto boards through-holes to the Demo board proto area. (Even the 3 inch piece of wire has·enough inductance to throw things off... so you use two of them to balance or cancel each others effects out).· The positioning of the jumper wire should be symmetric as well in relation to the 10Meg resistor and the I/O's being used.
·

·

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 8/22/2008 6:11:20 PM GMT

Phil Pilgrim (PhiPi)
08-23-2008, 01:05 AM
Jonathan,

Your inductor is probably close enough, and the 10MHz crystal with PLL8X should not be a problem. A good earth ground will help, if you don't already have one. Also, soldering the feedback resistor directly onto the Prop's pins is essential. Surface mount resistors are best for this. One thing that helped me, since I also live in a fringe area, was having another radio at hand to find the strongest station to set my program on and to verify any faint signals I thought I heard through the static while I was tweaking things. Eliiminating as many sources of noise as possible also helps.

Beau might be able to weigh in on the consequences of using a longwire antenna vs. the shorter whips we've been experimenting with. I do know that AM broadcast waves are vertically-polarized, so a horizontal longwire antenna may not be optimal.

In any event, don't expect to hear anything nearly as clean and strong as Beau's .wav file if you're out in the boonies!

-Phil

Addendum: Beau beat me to it! I would defer to his advice where it contradicts mine! http://forums.parallax.com/images/smilies/smile.gif

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Post Edited (Phil Pilgrim (PhiPi)) : 8/22/2008 6:12:36 PM GMT

Jonathan
08-23-2008, 01:08 AM
Aha. I am trying on a DIP prop on a breadboard. Alas, I don't have an alive demo board (I killed mine, dunno how, sniff) or a protobaord handy. Any way to work around this? I'm a long time crystal set maker and love this sort of thing.

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www.madlabs.info (http://www.madlabs.info) - Home of the Hydrogen Fuel Cell Robot

Jonathan
08-23-2008, 01:18 AM
I have a good ground, 3 six foot copper clad ground rods one foot apart and bonded together, and it is only used as a RF ground (not tied to my mains power ground). I'll try soldering a resistor directly to the DIP prop I have. I'll also try Beau's layout tips. I don't expect great sound, it would just be fun to hear anything.

Also, what about an adjustable air cap across the 500uH inductor?

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www.madlabs.info (http://www.madlabs.info) - Home of the Hydrogen Fuel Cell Robot

Phil Pilgrim (PhiPi)
08-23-2008, 01:59 PM
If you're in a fringe area, like I am, you may find this RF preamp useful for pulling in those weak stations:

http://forums.parallax.com/attachment.php?attachmentid=55288

The circuit comes from a set of lab notes (http://www.seas.upenn.edu/~ese206/labs/MOSFET/MOSFETLab2.pdf) prepared for the "Electrical Circuits and Systems II (ESE206)" course at the University of Pennsylvania. (Published university lab notes are a great way to pick up electronics info, BTW.) The amplifier uses three transistors from a CD4007 (http://www.ti.com/lit/gpn/cd4007ub) (MC14007) "dual complementary pair plus inverter" CMOS IC and runs on 5V. The CD4007 is nominally a digital IC which finds many uses in analog circuits, such as this one. It's configured as a common-source amplifier (the nMOSFET) with an active load (the two pMOSFETs hooked up as a current source). The wiring seems to be uncritical. I just used the breadboard area of my Propeller Demo Board, and got much better results than with the original circuit. Your results may vary...

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Jonathan
08-23-2008, 09:25 PM
Phil,

Dang, I was sure I had some CD4007's laying around, but an hour of digging yields none. Before I start digging through dead equipment looking for one to salvage, any alternates?

Thanks a ton for the circuit and info though! Worst comes to worse, I'll have to order some and *shudder* wait for them to arrive. On the other hand, maybe I'll get done what I'm suppopsed to do today. :)

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www.madlabs.info (http://www.madlabs.info) - Home of the Hydrogen Fuel Cell Robot

Phil Pilgrim (PhiPi)
08-23-2008, 10:30 PM
Jonathan,

Beau suggested (via email) a CD4049 inverter. You could try that in lieu of the CD4007 and the 5.1K resistor. Just connect the 10M resistor from output to input to bias it into linearity. Be sure to ground any unused inputs. I didn't have any 4049s to try this, although I could've used the inverter section in my 4007. What I did try was a 74HC00 NAND gate connected as an inverter (one input tied high), but with mixed results.

One thing to note: this is a broadband amplifier, so it amplifies noise, too. I'm considering adding another stage, but without some added selectivity to go with it, the sound quality probably won't improve.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Leon
08-24-2008, 02:01 AM
A single JFET such as a BF244 with a resistor load should work just as well.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Phil Pilgrim (PhiPi)
08-24-2008, 03:34 AM
Leon,

That's a good point. Here (http://www.elecfree.com/electronic/amfmsw-active-antenna-by-mpf102/) is a circuit that uses an MPF102 (available at Radio Shack). I haven't tried it, and now my 60KHz WWVB ferrite antenna has arrived from DigiKey, so I'm gonna be busy!

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Timmoore
08-24-2008, 06:27 AM
Phil, thanks for this code, it works really well as a mixer for a Theremin sensor as well.

I have some sensors based on the front end sensors of this http://thereminvision.com/version-2/TV-II-index.html·but I have connected the sensors directly to a prop running a modified version of your code. The quadrature code is pretty much the same but its a fixed frequency encoder, the mixer cog cycles round each outputs a value per sensor. I dont use your audio cog at all.

Oldbitcollector (Jeff)
09-09-2008, 08:29 AM
Here's a challenge for you EE's.

I'd like to include this project in my 101 projects book, but we need a description of
how this works in a manner that someone new could understand. It's been suggested
that this might not be possible. Nah... Let's see if someone can pull it off. :)

OBC

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New to the Propeller?

Getting started with a Propeller Protoboard?
Check out: Introduction to the Proboard (http://jeffledger.googlepages.com/Protoboard_Introduction.pdf) & Propeller Cookbook 1.4 (http://ucontroller.com/Propeller%20Protoboard%20Designs%20for%20the%20Beg inner.pdf)
Updates to the Cookbook are now posted to: Propeller.warrantyvoid.us (http://propeller.warrantyvoid.us)
Got an SD card connected? - PropDOS (http://www.orrtech.net/propdos/)

Timmoore
09-09-2008, 08:53 AM
If you want a 2nd related project, how about a theremin synthesizer. The sensor is a lm555 with a couple of resistors/caps. A modified version of phils code can decode a hand moving near the antenna and generate tones from it. 2 sensors one feeding the tone value and the other the volume and you have a synthesizer.

Drone
09-09-2008, 04:09 PM
Hi OBC,

At the moment I can't expand on Phil's software description, but I do happen to have a simulation of how the quadrature amplitude demodulation Phil mentioned works. Note the pictures attached. I've also attached the LTSpice/SwitcherCADIII simulation files in the .zip if you want to try them yourself. (You can get the excellent LTSpice application free from www.linear.com (http://www.linear.com).)

Basically what happens is you take one amplitude modulated signal and by one of various means possible such as quadrature power division or quadrature down-conversion, you end up with two identical amplitude modulated signals that are 90 degrees out of phase. The two signals are commonly referred to as I for In-phase, and Q for quadrature.

Once you have the I and Q amplitude modulated signals, to demodulate them you simply take the root sum of squares [sqrt(I^2+Q^2)]. The simulation time-domain plots show this process.

The top two plots are the radio carriers in quadrature. The third plot from the top is the original modulating signal. The next two plots show the amplitude modulated carriers in quadrature. The bottom plot performs the mathematics on the two signals plotted above thereby recovering the modulating signal. Note the formula just above the bottom plot pane.

In-general, once you have signals in quadrature, you can do all sorts of things with them mathematically. I-Q signals are at the foundation of most of software-defined radio designs.

Hope this helps a bit... David

rjo_
09-10-2008, 05:45 AM
OldBit,

I'm a good subject... I know nothing about any of this and I haven't had a chance to go back and study the thread yet. I have heard of Spice but never used it.

I can follow Drone's explanation... I'm not worried about the math... as long as it works. The only thing I don't get is why you do the modulation/demodulation in the first place...

Rich

Bob Lawrence (VE1RLL)
09-10-2008, 06:22 AM
for: rjo_

en.wikipedia.org/wiki/Demodulation (http://en.wikipedia.org/wiki/Demodulation)

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Aka: CosmicBob

rjo_
09-10-2008, 06:54 AM
Bob,

Years ago, quad coils came for MRI and I thought that they were better because the biologic signal itself was circularly polarized...and you were basically catching the same signal twice:) Now I'm completely confused!!! Sometimes a misperception is more comfortable that realizing that you are completely wrong. There might be a grain of truth to what I thought, but I'll have to look for it again:)

Thanks,


Rich

Bob Lawrence (VE1RLL)
09-10-2008, 09:57 AM
rjo_,

I don't know anything about MRI beyond the basics. If you start a new thread over in the sandbox section and tell us about your experience, I'll follow it. http://forums.parallax.com/images/smilies/cool.gif

Maybe this is what you were referring to:
A recent development in MRI technology has been the development of sophisticated multi-element phased array coils which are capable of acquiring multiple channels of data in parallel. This 'parallel imaging' technique uses unique acquisition schemes that allow for accelerated imaging, by replacing some of the spatial coding originating from the magnetic gradients with the spatial sensitivity of the different coil elements.

en.wikipedia.org/wiki/MRI#Radio_frequency_system (http://en.wikipedia.org/wiki/MRI#Radio_frequency_system)


I'm really interested in trying Phil's AM radio project but have too many things on the go right now. I did start on an ant system for the proto board a few months back but never got around to getting it finished yet.

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Aka: CosmicBob

Bob Lawrence (VE1RLL)
09-10-2008, 10:01 AM
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Aka: CosmicBob

Bob Lawrence (VE1RLL)
09-10-2008, 10:05 AM
I'll try to make it an active antenna at some point. It's not pretty but it's a start http://forums.parallax.com/images/smilies/burger.gif

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Aka: CosmicBob

Beau Schwabe (Parallax)
09-10-2008, 12:01 PM
To Modulate is to move or deviate your signal (or Data) away from your carrier.
To De-Modulate is to detect how far the signal (or Data) has been moved.

The Carrier is the base frequency you want to send your data on.

AM modulation varies the Amplitude proportionally to the analog signal being sent over a fixed carrier frequency.
FM modulation varies or shifts the frequency proportional to the analog signal being sent over a varying carrier frequency.

Quadrature demodulation is used, because it's an easy way to re-capture the carrier signal. All we need to know for quadrature demodulation is the frequency being used.
Thanks to the Pythagorean theorem, we do not need to know the phase relationship of the carrier between the transmitter and receiver.

C = √(A^2 + B^2)

See the attached WMV file showing the I-Q representation of a sinusoidal wave...

As the "I"n-Phase and "Q"uadrature-Phase move in relation to the sine wave, notice the "white" bar (the hypotenuse of I and Q). This represents the Carrier Signal strength.

Any deviation in signal either through AM or FM modulation will cause small fluctuations in the hypotenuse (Signal Strength) that can easily be converted into Audio with a LOW-PASS filter.


http://forums.parallax.com/attachment.php?attachmentid=55710

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 9/10/2008 3:06:48 PM GMT

rjo_
09-10-2008, 08:26 PM
Beau,

That is a beautiful explanation... does this mean that by definition the quadrature modulated signal is always over unity?


Rich

Beau Schwabe (Parallax)
09-10-2008, 10:02 PM
rjo_ (http://forums.parallax.com/member.php?u=48782),

"does this mean that by definition the quadrature modulated signal is always over unity?"

No, not really, the signal should have unity throughout....· It's just that any deviation in frequency, amplitude, or Phase in the
modulated signal will propagate into the de-modulated signal for easy recovery using this method.· This deviation will cause the
'strength' to increase or decrease but average Zero over time.


Suppose at 0 Deg...

I = cos(0) = 1
Q = sin(0) = 0

Strength = √(I^2+Q^2) = 1

...at 30 Deg

I = cos(30) = 0.866
Q = sin(30) = 0.5

Strength = √(I^2+Q^2) = 1

...at 45 Deg

I = cos(45) = 0.707
Q = sin(45) = 0.707

Strength = √(I^2+Q^2) = 1


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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

rjo_
09-11-2008, 12:15 AM
This is going to take me a while... but it is definitely stuff I want to know.

Thanks

Rich

Ken Peterson
09-11-2008, 02:20 AM
I've been thinking about coming up with a way to do wireless propeller to propeller communication with minimal components. This looks like a promising approach. I've already successfully transmitted tones to an FM radio with nothing more than a piece of wire on a pin. I think using ASK it would be easy to transmit data.

I wonder if there's an easy way to detect FM with this approach? Perhaps with a couple more counters! http://forums.parallax.com/images/smilies/smile.gif

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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

- Bjarne Stroustrup

Ken Peterson
09-11-2008, 02:27 AM
Come to think of it, if you duplicate the design where you are tuning to just above and just below the carrier (call them A and B), then perhaps you can FSK the transmitted signal and detect the bit value by taking the difference between the two outputs on the receiving end. If A > B then it's 0, if A < B then it's 1.

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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

- Bjarne Stroustrup

Sapieha
09-11-2008, 02:29 AM
Hi Ken Peterson.

It is one of My idea to have fast fully programable IN/OUT to PIN UPP/DOWN multi function counters in PROP II



Post Edited (Sapieha) : 9/10/2008 7:35:10 PM GMT

Phil Pilgrim (PhiPi)
09-11-2008, 02:50 AM
Ken,

One approach to demodulating FSK would be to adjust the tuning frequency above or below both FSK frequencies, essentially creating a BFO. The output will consists of FSK in the audio range, which can be bandpass-filtered in code to retrieve the 1s and 0s.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Phil Pilgrim (PhiPi)
09-11-2008, 11:18 AM
Attached is a set of traces that may help to explain what's going on in the receiver. (BTW, I'm the one who suggested to OBC that, despite the simplicity of the hardware, the underlying theory might not be a suitable beginner's topic. Also, beginner's projects need to have a high probability of success; otherwise, a neophyte is likely to become discouraged. This project, in particular, has sketchy prospects for a satisfying outcome, depending on where one lives. I nearly threw in the towel myself, when I was initially unable to pick up anything in my fringe reception area. It was only my confidence in the underlying theory that kept me going. But, all that notwithstanding, I've decided to try for a simpler explanation at least. Maybe the illustration will help.)

In the top set of traces, there are two sinewaves: one in red, which is the audio signal, and one in gray, which is the RF carrier. When the audio signal is used to multiply the carrier, the product we end up with is an amplitude-modulated (AM) radio signal. This is shown in magenta. This is the waveform what leaves the antenna at the radio station and makes its way into our little radio via its own antenna. By that time, the peak amplitude can be measured in microvolts — millivolts, if we're lucky.

This tiny signal is presented to pin A3 of the Propeller via a capacitor. Also connected to A3 is a 10 megohm resistor from A4. A counter is configured in feedback mode (normally used for sigma-delta ADC), which reads pin A3 and, at the next clock interval (12.5ns later) outputs the opposite signal (i.e. 0 -> 1 and 1 -> 0) to A4. This "negative feedback" will tend to keep the signal on A3 centered on Vdd/2, which is the Propeller's digital input threshold. But, becasue the feedback resistor is so large, and because there's residual capacitance between the Propeller's pins and ground, the effect of the A4 output on A3 won't be instantaneous. So if the signal coming in on A3 goes very high, it may take several clock periods for a low on A4 to bring it back down. So, the higher the signal on A3, the more 0s we'll see on A4; and the lower the signal on A3, the more 1s we'll see on A4.

If we were using this counter as an ADC, we could set its FRQx to 1 and let it count the number of 1s it sees on A3 in a given interval. This count would be proportional to the average signal strength on A3 during that interval. But we're not going to do that. Instead, all we need is that string of 0s and 1s on pin A4. This is shown as signal "ADC" in the middle of the attached image, in magenta. If you squint your eyes, you can almost make out the sinusoids (inverted) from the modulated signal, even though, at each instant, A4 is either high or low.

Two additional counters are used to form the square wave signals I and Q, shown in blue and green. These signals have the same frequency as the carrier, which is how we tune the radio. They are 90° out of phase from each other, though, and have an unknown phase relationship with the incoming carrier. Now, here's where the magic happens. We can take the ADC bitstream from A4 and /XOR (/XOR is the same as the equality function) it at every step with I & Q to produce two resultant bitstreams (shown above I and below Q on the graph). If the carrier happens to line up with I (i.e. if it's in phase with I), more high points than low of ADC will coincide with high points of I, resulting in an abundance of highs after the /XOR; and more low points than high of ADC will coincide with low points of I, again resulting in an abundance of highs after the /XOR. The opposite happens when the carrier and I are 180° out of phase. But in both cases, the number of highs and lows will be at an extreme from the norm, which is a 50% duty cycle.

On the other hand, if I is 90° out of phase with the carrier, in either direction, the highs and lows will balance out, and their number will be about equal after the /XOR. The reason for having two "local oscillator" signals, I and Q, is so we don't have to rely on just one being in the right phase with the carrier. If one is nearly in phase or 180° out of phase, the other will be closer to 90° out of phase. Moreover, we can combine the outputs of the two /XORs in such a way that the result is completely independent of the carrier's phase.

As a side note, in an analog direct-conversion receiver, the I and Q oscillators would be producing sine waves, not square waves. And these two signals would be multiplied by the incoming signal, not /XORed, to produce the instaneous Fourier sine and cosine components of the amplitude. Our use of square waves is a little shaky, since each is composed of a sine wave and its odd harmonics (see Wikipedia article (http://en.wikipedia.org/wiki/Square_wave)) in diminishing amplitudes. For this reason, if we tuned our receiver to 550 KHz and there was a strong station at 1650 KHz (550 x 3), we might pick that up as well. A tuned antenna circuit, rather than just an inductor, would help to alleviate that possibility.

The Propeller's counters have a logic look-up table mode, that allow them to count the ones from any two-input (i.e. from two pins) Boolean function. And that includes /XOR. So we don't need any external logic to perform this function. We just tell the counters to do it for us. Then all we have to do is sample the "ones" count in a given time interval, which the counters track for us, and record the result. The green and blue traces at the bottom of the illustration show these counts, obtained over the intervals between their changes in value.

Once we have the sample counts from the /XORed I and Q, we subtract the average count (i.e. half the sampling interval) from each and square the result. Then, we add the squared values and take the square root of the sum to get the "root mean square" (RMS) amplitude of the incoming radio wave at the chosen frequency. This amplitude is a discrete sample (shown in red at the bottom of the illustration) of the original audio signal (shown in red at the top).

I hope this helps. If not, let me know where things get fuzzy, and I'll try again. (By the way, these graphs were not contrived in any way for illustration purposes but, rather, represent the output from an actual computer simulation of the radio. The data were then imported to Excel to create the graphs.)

-Phil

Addendum: Changed the notation in the text and graph from "XOR" (^) to "/XOR" (=) to reflect the results shown in the graph. The program uses XOR, but both XOR and /XOR work equally well. /XOR actually makes a better example, since it more closely follows the multiplication used in analog direct conversion receivers.

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Post Edited (Phil Pilgrim (PhiPi)) : 9/11/2008 5:56:22 PM GMT

parsko
09-11-2008, 08:26 PM
Phil,

EXCELLENT explanation. Of all these RF/RFID discussions and explanations, this one has been the easiest (and most laymen) for me to follow.

One thing, please. Could you provide a snapshot of the picture that has a differenct timescale? I'm curious to see it "stretched" out so I can see the detail of the the bitstreams, and how their timing lines up with the carrier wave. I'm taking this from where you say: "We can take the ADC bitstream from A4 and XOR it at every step with I & Q to produce two resultant bitstreams (shown above I and below Q on the graph)."

Also, as a side. It seems that your resultant discrete sample lags wrt the original audio signal (the two red lines). This MUST happen, in all demodulating setups, right? You can't read the signal unless you have time to read the signal. How much is the lag? Is it only 12.5ns? I've often thought about this "lag". You can see it, sometimes, when talking to a friend on the phone, who is watching the same program on TV. His TV sounds a bit behind yours, yet you are both conversing seemlessly.

Thanks for the great explanation. This gem should be bookmarked (has been for me!).

-Parsko

Ken Peterson
09-12-2008, 12:17 AM
Parsko: The lag from the TV's that you mention could be due to the speed of sound. Perhaps their TV is further away from the phone than yours is. In Phil's example, we're talking about a lag of just a few cycles at about 1 MHz so probably a couple of microseconds. I'm not sure the human ear can detect such a small lag.

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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

- Bjarne Stroustrup

Rayman
09-12-2008, 12:22 AM
Thanks Phil for that picture!

That really does explain it best, I think...

PS:· Any chance the Prop2 could do FM this way?

Phil Pilgrim (PhiPi)
09-12-2008, 12:23 AM
parsko,

Attached is the blowup you requested.

The discrete sample lags the original because of the sample interval. The longer the sample interval, the more the lag and, also, the lower the audio frequency response. In the software I posted, the sample rate is 16 KHz. So the lag could be as much as 62.5 µsec.

-Phil

Addendum: I just noticed that the function reflected in the graphs is not XOR, but NOTXOR, in otherwords, equality. It doesn't really affect the outcome, though: both work equally well. I'll have to change the notation on the original graph...

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Post Edited (Phil Pilgrim (PhiPi)) : 9/11/2008 5:33:36 PM GMT

Ken Peterson
09-12-2008, 12:30 AM
When I have time (I hope soon) I'm going to try to get one prop to talk to another wirelessly. Even if can get a few Kbaud that would be cool.

Phil: I'm thinking if I use a carrier (Say 27 MHz) FSK modulated with a bit stream, and I tune just above and just below the carrier with two pairs of I&Q frequencies, and take the RMS value of each, then I can compare those RMS values. Or I can take the difference between each RMS value and a running average of each RMS value and compare the differences. Then I would determine the input to be a 1 or 0 based on which difference is higher.

I'm just thinking that detecting a digital signal should be easier than an analog signal. I also think that FSK will be more resistant to noise than ASK.

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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

- Bjarne Stroustrup

Phil Pilgrim (PhiPi)
09-12-2008, 12:35 AM
Comparing the RMS values should work. I don't know how much luck you'll have at 27 MHz, though. Generating clean I and Q signals with an accurate phase relationship may prove difficult. You'll probably get the cleanest signals using the counters' PLL capability, but adjusting the relative phases will be tricky.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

parsko
09-12-2008, 01:53 AM
Phil,

Sweet graph. That is exactly what I was askin for. It was kinda clear before what was going on, but being able to see that detail in the bitstream really helps me understand.

I think I got it right with my guess on the lag. Enough lag and we could be hearing the news from yesterday, right? Luckily the prop is wicked fast.

-Luke

Ken Peterson
09-12-2008, 02:16 AM
Phil Pilgrim (PhiPi) said...
Comparing the RMS values should work. I don't know how much luck you'll have at 27 MHz, though. Generating clean I and Q signals with an accurate phase relationship may prove difficult. You'll probably get the cleanest signals using the counters' PLL capability, but adjusting the relative phases will be tricky.

-Phil


True:· Perhaps I can heterodyne it down to a lower IF and go from there.

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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

- Bjarne Stroustrup

Phil Pilgrim (PhiPi)
09-12-2008, 02:32 AM
Ken,

One additional note: For the sake of comparison, you can skip the square root. Comparing the sums of squares will yield the same result.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Ken Peterson
09-12-2008, 02:35 AM
Phil: Yes, I was thinking that myself.

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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

- Bjarne Stroustrup

rjo_
09-12-2008, 10:06 AM
Phil et al,

My problem is that when I'm fresh enough to read, I'm in a place that I can't get at my computer. So, I decided to just print this thread out so that I can carry it with me... without associated graphics, it comes to about 14 pages of printed material per thread page.... you've got yourself a good chapter in someone's book.


This thread is a classic... not a sticky... a classic. We don't have a category for classic threads, but when we do, this one belongs in it.

Thanks to Phil and everyone that spent good time doing some serious thinking about how to make the inscrutable scrutable, to make the opaque clear... and to make the salty ... well... more salty:)

U no wat I meen.


Rich

ILMP

Nick McClick
09-13-2008, 03:00 AM
Truly. The whole point is to learn by doing, and I've learned a lot more about radio from this thread (& my new prop radio) than from studying for my amateur radio license.

Good stuff, thanks for the knowledge share. I'd love to publish articles like this on my site once I'm done with all the launch stuff. Another great article is the RFID thread (http://forums.parallax.com/showthread.php?p=744800).

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Concentrate on understanding the problem, not applying the tool

Post Edited (Nick McClick) : 9/12/2008 8:09:34 PM GMT

Christof Eb.
01-16-2009, 02:36 AM
Hi Phil,
ok, I am a little bit late. I just experimented with your program these days. This is very impressive!
I did not want to solder on my board and to the propeller pins. Do not want to risk to kill the prop.....
So I just built up the adc on the breadboard. - There was nothing to hear than some "am radio sound."
Now I have included a transistor -see the circuit- and I am able to clearly hear and understand a radio station.
The station is roundabout 50km from my home and broadcasts with 100kW Power.

Many thanks!

One question to the specialists: There is some ugly noise with 50 or 100Hz. There are some counters left. Can't they be used for filtering?

Christof

Phil Pilgrim (PhiPi)
01-16-2009, 02:46 AM
Christof,

Nicely done! Your transistor preamp is a valuable contribution to this thread, and I appreciate your taking the time to publish it here.

As to the 50/100Hz noise, it sounds like you're getting some powerline interference. It should be easy enough to program a notch filter to eliminate it. Try Googling IIR notch filter or FIR notch filter for some ideas.

-Phil

Clock Loop
09-02-2009, 12:46 PM
I MUST post here to get this thread bumped up to the top. This is an example of an AMAZING use of the propeller.
Phil, you should REALLY consider putting a thread in the completed projects forum about this.

Also, I was wondering if a transmitter could be made for the same band.

Obviously transmission requires permission, but consider this...

In worst case scenario, if our methods of communication were to fail, I often think about how people might communicate when they have no other way. Am radio seems to be a good method, and having a cheap, easy, low power method to get the word out to the masses would be ideal. Even more ideal is to make a USB receiver that gets AM data. Or even a USB transmitter. Obviously the amount of data is limited, but its better than nothing. Consider the BBS network before the internet. Messages came from around the world through a network of BBS systems.

Anyone wanna touch on this? Something as simple as serial over AM?

Post Edited (Clock Loop) : 9/2/2009 9:26:40 AM GMT

Mike Green
09-02-2009, 01:07 PM
You really need a lot of quality analog circuitry around Phil's circuit to do a decent job of reception of something that didn't come from the tens to hundreds of thousands of Watts of power fed into a very large antenna over a good ground plane typical for a commercial AM broadcasting station.

You also need some high quality analog filtering to take the output of a Propeller counter and make a clean QRP (low power) signal out of it for transmission. You won't get much range with the amount of power (maybe 100mW) available except under very good conditions. You probably would need at least a couple of Watts of output power for any meaningful transmission range and that's with a very good antenna and fairly good conditions.

There is an Amateur Radio band (160M - 1.8MHz to 2.0MHz) adjacent to the AM broadcast band that could be used for experimentation if you have a license.

HollyMinkowski
09-02-2009, 02:09 PM
@Beau Schwabe

Could this same scheme be used to let the propeller listen in to
and use the WWV signal at 2.5 MHz???????

That would sure let a prop keep accurate time!


Q: Are you in Oklahoma City, that station says it's in Ok City?
I get up to Ok City about 6x/yr

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Post Edited (HollyMinkowski) : 9/2/2009 7:15:07 AM GMT

heater
09-02-2009, 04:21 PM
You might have more luck with the huge amount of power pumped into WWVB time signals at 60KHz. tf.nist.gov/stations/wwvb.htm (http://tf.nist.gov/stations/wwvb.htm)

I've been pondering the German time signal DCF77 on 77.5Khz but it's a bit or a reach to my location (Helsinki).

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For me, the past is not over yet.

Ken Peterson
09-02-2009, 06:18 PM
Seems to me I remember reading about picking up WWVB on a Propeller or some other microcontroller. Now...where was that???? http://forums.parallax.com/images/smilies/eyes.gif

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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."

- Bjarne Stroustrup

Toby Seckshund
09-02-2009, 06:31 PM
Heater

One of the reasons that the power levels appear to be so high is that the aerial @ 60KHz is so wavelenth·short and therefore so inefficient, it has to be thumped hard to get something out.

Efficiency goes down at the square of the reduction

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Ken Peterson
09-02-2009, 06:57 PM
I think a WWVB receiver also has to have a fairly large antenna, so it's not something you can make really compact. You'd need a large inductive antenna with a ferrite bar.

heater
09-02-2009, 06:58 PM
Quite so. Actually I was just reading the DCF77 page. They mention 50KW. Which is not so huge given there are 1MW am transmitters around.

DCF77 claims to deliver a useful signal over a radius of 2000Km which puts me just on the edge.

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For me, the past is not over yet.

he1957
09-02-2009, 07:32 PM
Very impressive Phil - very creative, many thanks.

Alas, its a shame such wonderful projects become "lost" in the sheer size and high levels of activity in such Forums. At least I am happy and glad that someone (thanks Clock Loop) has "revived" this and made it noticable. I was thinking about SDRs and how a Propeller might be useful - excellent work - thanks again!


Cheers,

Harry E.

dMajo
09-02-2009, 10:42 PM
Ken Peterson said...
Seems to me I remember reading about picking up WWVB on a Propeller or some other microcontroller. Now...where was that???? http://forums.parallax.com/images/smilies/eyes.gif


http://forums.parallax.com/showthread.php?p=778790

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· Propeller Object Exchange (last Publications (http://obex.parallax.com/objects/?o=0&ot=dsc&n=20)/ Updates (http://obex.parallax.com/objects/?o=8&ot=dsc&n=50))

Toby Seckshund
09-02-2009, 11:46 PM
Heater

I seem to remember that the DCF77 signal is not far from the 4th harmonic of 15.625 line freq and so you have to filter very carefully (or not let anybody close, use glass monitors)

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HollyMinkowski
09-03-2009, 04:00 AM
Toby said...
One of the reasons that the power levels appear to be so high is that the aerial @ 60KHz is so wavelenth short and therefore so inefficient, it has to be thumped hard to get something out.


50kw is not that much at that low frequency since the antennas are always too close to the ground for much signal to
go out toward the horizon...the signal goes straight up and must bounce multiple times to reach anyone far away...each bounce weakens the
signal. I have 1kw on 160 meters to a full size dipole at only 40' ... it's a very LONG antenna! Most of my signal goes straight up but that does
have the advantage that there is no skip zone at all. Contacts are easy from 0 miles away to about 800 miles....much farther on CW. My antenna is
strung up between 2 small crank-up towers my dad erected and the soil beneath is very dry sand.

I mentioned the WWV signal at 2.5mhz because the prop would need a pretty large antenna to pick up that signal at 60khz...it seemed that such
an elaborate antenna was impractical, but then my atomic clock picks that signal up well... no idea what the antenna inside looks like...maybe
I will pop it open and see. If I do I will post the image of the antenna in this thread. I think those clocks only listen for WWVB for a few minutes
during the night as they would have little luck on 60khz during the day.

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Phil Pilgrim (PhiPi)
09-03-2009, 04:26 AM
For 60KHz, the usual "antenna" is a ferrite "loopstick", and they can be quite small. DigiKey sells them for their time receiver modules. I could never get one to work though, since I'm outside the prime reception zone.

-Phil

HollyMinkowski
09-03-2009, 04:38 AM
@Phil Pilgrim

You would think they would run at least 1,000,000 watts at 60khz to get better range.
That would be more than +12db from what they run now and would make a big difference.
They waste money on everything else so why not make the time signals more usable.

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heater
09-03-2009, 04:50 AM
You can by alarm clocks, for about $10, around here that sync to DCF77.
I bought one last year, it only worked for two days so I exchanged it. The next one worked for a week. At that point a got tired of running back to the shop so I cracked it open.

The antenna is only an old trany radio style coil on ferrite rod about 4cm long. To tune it up there is cheapo capacitor soldered across it.

Amazing it received anything.

So there's the antenna for my Prop DCF77 receiver.

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For me, the past is not over yet.

HollyMinkowski
09-03-2009, 06:20 AM
@Phil Pilgrim

Maybe you could wind a few hundred feet of wire onto a 10' piece of PVC pipe
and then mount it outside for an antenna.

Reception would be great and your wife would love it.


LoL

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Toby Seckshund
09-03-2009, 02:52 PM
The most power I put into an aerial was 500KW (real Watts). This used two 250KW sets paralleled up and stuck up an experimental multi-band array (500 ft masts). The array took it ok, but the old farm house right in front of it suffered "internal lightning". Good old days.

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HollyMinkowski
09-03-2009, 03:07 PM
The WWVB antenna.
I see wires from tower top to tower top.
http://upload.wikimedia.org/wikipedia/commons/3/3c/WWVB_Antenna.jpg

That antenna looks awfully close to the ground for 60khz.
Maybe about like supporting a 10 meter dipole from
pencils stuck in the ground. Then again, if there were
any frackin sunspots you could probably work China
on a 10 meter dipole that close to the ground http://forums.parallax.com/images/smilies/smile.gif

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Post Edited (HollyMinkowski) : 9/3/2009 8:14:24 AM GMT

heater
09-03-2009, 04:18 PM
According their web site DCF77 has main and standby antennas of 150m and 200m height respectively.
The tallest antenna mast in the world is KVLY-TV at 629m so they are not doing so badly.

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Toby Seckshund
09-03-2009, 06:06 PM
Back in the 70's there were articals in WW about 10KHz aerials, slung across Swiss mountain tops. Submarine comms probably. There is an escarpment to high masts setup in Shropshire, UK (not on the map).

Holly·· The fact that the land under your topband aerial is sandy will help it. The effective ground will be lower than the real gound level, which is the same as the aerial being·higher up (assuming that the sand isn't full of salt water)

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Retrobits
09-03-2009, 11:46 PM
Slightly off-topic note - I used to have an Icom R-70A HF receiver.· It literally tunes all the way down to zero Hz, but I was convinced anything below 150 KHz was probably unusable due to analog circuit constraints.· That is, until I successfully received WWVB at 60 KHz.· This was in Los Angeles, and with an indoor wire antenna and poor ground. http://forums.parallax.com/images/smilies/smile.gif

WWVB·uses a weird modulation - it's not meant to hear by ear.· To do so, you need to tune slightly off frequency and use either the CW or USB mode.· But it was there all right.· I listened to the signal a long time (I was quite happy at that "catch"), and it followed the pattern documented by NIST.

There is no voice signal of course - it carries a binary signal pattern.· WWV/WWVH, while carrying voice signals, also have a binary·signal as well.· On those stations, listen sometime for the low-frequency pulses - you can make them out by ear, and decode them using the pattern guide from NIST.

- Earl

HollyMinkowski
09-04-2009, 12:44 AM
@Toby

I always wondered if that was so about the sandy soil.

Since dirt is somewhat conductive I wonder how far
you could communicate by sending current pulses
through the ground?

If you drove 2 copper ground rods into the soil
and separated them by say 1000' and sent strong
DC pulses through that circuit just how far away
could you be with a detector of some sort and still detect
that current flow?

If you sent really massive pulses it might be a long
way. Like if you charged up high v capacitors and
discharged them through the earth between the rods.

Wouldn't it be somewhat like rf as far as propagation goes? I mean
the signal would drop off dramatically but no matter how
weak they became wouldn't they still exist many miles away?
Wouldn't every possible path between the 2 rods be
a resistor that would always carry at least some tiny fraction
of the electron flow? Even if that path traveled from one pole
to a point a hundred miles away and then back, there would
have to be some small number of electrons following that
path...it seems so?

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Mike Green
09-04-2009, 12:54 AM
It would be like any other sheet resistance. Take a square of carbon impregnated cloth and plunk down two electrodes at opposite ends of the square, in a little bit from the edges, and run pulses of electricity between the electrodes and measure the voltages between points on the cloth. You can simulate this pretty easily on a computer with a nice graph of the voltage detected. If you used an AC waveform to excite it, you'd even get radiated RF. Most of the energy would go into heating up the sheet resistance (or ground), but some of it would radiate.

HollyMinkowski
09-04-2009, 01:37 AM
@Mike

I just love thinking about how far signals can propagate.

Like how you can calculate the size dish you would need
to detect a .01 watt microwave signal sent from Alpha Centari using a simple
1/4 wave whip antenna. The dish would be huge but if you
built it you would be able to copy the signal after it had
made the 4 year trip to earth http://forums.parallax.com/images/smilies/smile.gif

Doubling the size of a dish gives you a 3db boost in signal.
A dish the size of a Direct TV dish has about 26db of gain.
The huge Robert C. Byrd dish at Green Bank has a bit over 80db
and one that could pick up that weak signal from 4 light years out
would probably need something approaching 100db (I have not
done the calcs) and the dish would really be something to look at,
it would be so big you would have to construct it in a gravity free
location because gravity stresses would tear it apart...I guess the
only place would be the spot between earth and moon where the
gravity balances to zero value. Some day such projects will
be carried out by robots, humans could never see such jobs through.


The light frequency radiation from a single LED travels easily
all the way to a distant place like mars. It seems unbelievable
but if you just think about it a little. Like if the earth was in darkness
you could not see it with an instrument from mars but if you then
covered the whole earth with glowing LEDs it is obvious you
could see that from mars, so that means that the light from every
LED makes it there, albeit only a few photons from each one.

Thought experiments, I just love em http://forums.parallax.com/images/smilies/smile.gif

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HollyMinkowski
09-04-2009, 01:44 AM
The Byrd dish at Green Bank, note that
it is an offset feed dish same as the little dishes
you see on homes everywhere, except grown very large.

http://t1.gstatic.com/images?q=tbn:ulPN1RL2vWvZGM:http://ecolloq.gsfc.nasa.gov/archive/2008-Fall/images/GBT.JPG

EDIT: The reason the feed is at the top of the dish and not
at the easier to engineer bottom location like a home satellite
dish is because that allows the dish to point at the horizon. If the feed
was at the bottom then to see the horizon the dish would have to be elevated
on a pedestal so you could tilt it down far enough...and it would look
pretty silly http://forums.parallax.com/images/smilies/smile.gif

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Post Edited (HollyMinkowski) : 9/3/2009 7:04:45 PM GMT

Toby Seckshund
09-04-2009, 01:46 AM
A friend and me used to talk though the ground back, when we were at school. We were about half a mile away from each other and put about 30Volts p/p into each end. My parents garden was end on to his direction but his was completely side on and so he could get about 150 ft separation to my 30 ft. It was never solid and full of all sorts of interference. One pole and the mains earth was much better.

Kept us off the streets, I suppose.

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HollyMinkowski
09-04-2009, 01:58 AM
@Toby

That is just amazing!!

The fact that you were able to do that has to mean that
data could be passed between distant points without
wires and without rf or light.

Now how could we do this with 2 props???
The cheapest possible way of course, I'm very frugal http://forums.parallax.com/images/smilies/smile.gif

I'm guessing that the data rate would have to be low and
that a lot of error correction might be needed and involve
quite a bit of re-transmission, maybe 56kbps at a few miles
would be a possibility?

It would be fun to make 2 simple prop devices that
could deliver phone modem speed internet to someone
a few miles away! I know it's a simple thing to send
wifi from a cheap router that far but this would involve no
telltale antennas http://forums.parallax.com/images/smilies/smile.gif

What a fun idea.

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Toby Seckshund
09-04-2009, 02:10 AM
Holly

I don't think your "low" speed of 56K would be posible. We were only messing about with audio so I bet 300/1200 Baud would be nearer the mark.

There is a 1200 Baud objet already.

As for your upside down dish. I turned my fathers dish that way so that it didnt get such a bashing from the gales. Where he lives on the south coast, there is a strait line to South America for the wind to work up some enthusiasm.

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Post Edited (Toby Seckshund) : 9/3/2009 7:16:48 PM GMT

Fxc2hh
09-04-2009, 02:13 AM
What is the possibility of increasing the range using fractal antennas which is what a lot of cell phones use?

I was watching a program on PBS and some·man got the idea to make fractal antennas out of learning about Mandelbrots because he was getting in trouble with his landlord who didn't allow antennas on·his balcony and·fractal antennas·helped make some cell phones possible.

"Although the first validation of the technology was published as early as 1995 (see ref.1) recent independent studies continue to show the superiority of the fractal element technology in real-life applications, such as RFID.[4] (http://en.wikipedia.org/wiki/Fractal_antenna#cite_note-3)"

http://en.wikipedia.org/wiki/Fractal_antenna

Toby Seckshund
09-04-2009, 02:27 AM
Chuckz

Fractal type aerials were around before 95 but they probably didn't get around to grabbing the name rights. Early (UK) Sat ae's were flat and small but that company got swamped by the evil one and the bright white dishes sprouted.

To try and get around the ravages of the wind my father and me made a "Blind aerial" from concenteric foil rings on a window roller blind (scaled fron the SETI site). LMB in the right place and pull down the blind an there was the signal. Working out the elipses for 30 degree ele and 18 deg E/W offset was a bit mind blowing. In the end it was done with a wall, tracing paper and an overhead projector.

We made 'us own entertainment.

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Style and grace : Nil point

HollyMinkowski
09-04-2009, 02:44 AM
@Toby

I turned the small dish I rigged up for wifi upside down
like that as I could not aim at the horizon with it on the bottom.
The pole did not allow it to be positioned low enough...

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- Some mornings I wake up cranky.....but usually I just let him sleep -

Leon
09-04-2009, 02:49 AM
Toby Seckshund said...
Back in the 70's there were articals in WW about 10KHz aerials, slung across Swiss mountain tops. Submarine comms probably.



Does Switzerland have a navy, let alone submarines? http://forums.parallax.com/images/smilies/lol.gif

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

HollyMinkowski
09-04-2009, 03:47 AM
The Swiss might have been contracted to provide secret
communications to submarine fleets.

The Swiss are so trustworthy with secrets...NOT!
(google UBS accounts tax)

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- Some mornings I wake up cranky.....but usually I just let him sleep -

VIRAND
09-04-2009, 12:21 PM
[quote] I don't think your "low" speed of 56K would be posible. We were only messing about with audio so I bet 300/1200 Baud would be nearer the mark.

There is a 1200 Baud objet already.
-----------------------------------------
EDIT: (quote, malfunctioned ^^^)

The frequencies that 56K telephone modems used are actually in the range of 300-3000 Hz.
It took me awhile to find someone who could tell me how that worked at the time because
you can't modulate 56000 pulses on a channel that only allows 3000 pulses, but it uses
phase modulation, either Quadrature AM (sine+cosine dual carrier on same frequency)
or Quadrature Phase Shift Modulation (quickly selecting different pieces of the sine and cosine
maybe 4 times AT LEAST within one cycle of the carrier frequency). It's simpler to use 300 or 1200,
or DTMF, or Teletype, or Kansas City Standard/ BYTE Standard or even high speed morse code.

FCC in Region 2 does not regulate that telephone audio "Voice Frequency" band, so turn on your loud hi-fi
with the BASS up and the TREBLE down, and the volume up to ELEVEN (haha), and then
connect it to two different grounds for simplex (not simultaneous) transmitting and receiving.
If you get the buzz from power line radiation then use a delay or notch filter to cancel it out.

If you receive very high pitched data noises that way, it means the sky is falling! 8O

Post Edited (VIRAND) : 9/4/2009 5:26:36 AM GMT

Phil Pilgrim (PhiPi)
09-04-2009, 12:33 PM
The 56K modem spec also relies on the fact that beyond the (short) local loop, everything is digital, and it only works at that speed if it's digital all the rest of the way to the server (e.g. via a T1 line or better). If communicating phone to phone (i.e. analog loop -> digital -> analog loop), you will not get 56Kbaud.

-Phil

heater
09-04-2009, 01:43 PM
Phil, please clarify. I could see that maybe communicating data at 56K in an audio analog line may only work for short distances. But I don't see if my short analog connection to a digital network works at 56K at my end why it can'y work just the same at, say your, end.

Anyway doesn't 56K rely on compression? I always though that was cheating.

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For me, the past is not over yet.

Phil Pilgrim (PhiPi)
09-04-2009, 02:29 PM
heater,

Everything I know I learned from Wikipedia: en.wikipedia.org/wiki/56_kbit/s_modem (http://en.wikipedia.org/wiki/56_kbit/s_modem). http://forums.parallax.com/images/smilies/smile.gif

-Phil

dMajo
09-04-2009, 02:42 PM
Heater, your so called 56K modem is asymmetrical device when working in that mode (RX@56K, TX@33K). When you are connected to your ISP you have 1 A/D conversion from your line to the telephone company equipment. From here the data are routed/exchanged digitally to/with your ISP. When connecting to a friend your data have 1 A/D conversion from line to telephone central equipment, than they are routed digitally to the destination and converted again (D/A) before entering into your friend's line. So you have double conversion which introduce to much errors in the communication. This is one point, the second is that your modem is asymmetrical so your RX@56K is coming from your friend's TX@33K and vice-versa.

The telephone copper line bandwitdth should not be a problem, if you think on ADSL speeds, but again here you have only one A/D conversion between your ADSL modem and ISP's DSLAM.

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heater
09-04-2009, 03:19 PM
dMajo. I forgot about the asymmetry. That's another "cheat" to make the spec look good in my mind.

Also what I forgot is that the analog signal from my modem gets converted to a digital voice stream for transport over the telephone network. At that point it must be severely bandwidth limited. Even if the short twisted pair copper out of my house to the exchange can handle the speed that digital voice channel from then on probably does not.

In my last job my company had designed its own DSL routers 3 ports per box working at 2MB/sec over 3Km or more. so the copper should not be the problem.

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For me, the past is not over yet.

Toby Seckshund
09-04-2009, 06:50 PM
Copper to copper took all those years of·improvements and "cheats". When you are sticking a couple of copper pipes into the ground... It would be interesting to see·what the·group delay characteristics of an open field (with and without a cow) would·give.

As Holly is a Lady, She may not be willing to water them in properly.

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Style and grace : Nil point

Fxc2hh
10-01-2009, 11:03 AM
Holly,

I know you are frugal but I found this new product which has a 40 mile range on Sparkfun and it isn't cheap but you have to be able to do at least 9600 or 115,200 bps.· Here is the link:

XTend 900 1W RPSMA - 40 Mile Range
sku: WRL-09411 (http://www.sparkfun.com/commerce/product_info.php?products_id=9411)

·

Cluso99
10-02-2009, 01:55 AM
Heater: Modems over the switched network (PSTN) are limited to 4KHz bandwidth at the telephone exchange as they are then packed up into blocks. The 56Kbps is the actual speed although this is often not achieved due to line conditions between the house and telephone exchange. Compression is on top of this. However, there is redundency within the 56Kbps. I am not sure of the actual method in 56K but in lower speeds, QAM (Quadrature ??? Modulation) was used where 4 bits (probably more later) were sent simultaneously depicting a quadrant where the signal was. Phase shifting and other methods were used.

There was a modem called TrailBlazer which used a totally different technique which used multiple sections of the 4KHz bandwith. I think they split it into 7Hz channels and sent each channel slowly (300baud?). It provided about 500 channels and they selected the best group from this. From memory, it used a TMS320 DSP to do this. It was a half duplex system with a tiny back channel.

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· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index (http://forums.parallax.com/showthread.php?p=778427)) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)
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Cluso99
10-02-2009, 04:37 AM
Holly,

Aerial farms like that were the norm in the 60's for overseas telecommunications before undersea cables and satellites.

Then came the huge satellite dishes with cryogenic cooling on the back of the dish for the LNA's (low noise receivers) which is when they discovered microwaves cooked the birds flying in front of them. A few years later they had improved the receivers enough that the receivers could be in a building and refrigeration was no longer required. I saw both at OTC (the phone company) at Ceduna, South Australia in 1971 on one of my training trips. Absolutely fascinating.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=838091), RetroBlade (http://forums.parallax.com/showthread.php?p=838053),·TwinBlade (http://forums.parallax.com/showthread.php?p=806697),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index (http://forums.parallax.com/showthread.php?p=778427)) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)
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Post Edited (Cluso99) : 10/1/2009 9:44:38 PM GMT

HollyMinkowski
10-02-2009, 05:39 AM
@Cluso99

Sat communications is really interesting to me... we work
with microwave communications a lot here and set up a lot
of terrestrial and satellite links. It's amazing what you can do
with cheap 24db gain dishes on 2.4ghz. Using one of these
pointed at the Clarke belt you could put a usable signal into a
dish on a sat 24,000 miles up using a Linksys router. To bad we
don't have a nice hobby sat up there to play with http://forums.parallax.com/images/smilies/smile.gif

There are huge 350' dish antennas in geosynchronous orbit.
Can you imagine what those can do!?

Small sm chips on a board could send data to those
systems.

www.globalsecurity.org/space/systems/trumpet.htm (http://www.globalsecurity.org/space/systems/trumpet.htm)
http://www.globalsecurity.org/space/systems/images/sigintadvancedoriontrumpet-s.jpg

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"Where am I? Where am I going? Why am I in a handbasket?"

Cluso99
10-02-2009, 05:53 AM
Holly: HAM's have satellites up there. Look for AMSAT under ARRL. Some were launched as long ago as the mid 70's IIRC. The amateurs discovered microwaves and were using them for moonbounce comms.

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· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index (http://forums.parallax.com/showthread.php?p=778427)) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)
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HollyMinkowski
10-02-2009, 06:04 AM
@Cluso99

Yes, the ham sats are cool but I was wishing for a stationary
hobby sat in the Clarke belt that you could use by hooking a
Linksys router to a fifty dollar 24db gain dish pointing at a fixed
target....hack the Linux router a bit and all sorts of cool things
could be done http://forums.parallax.com/images/smilies/smile.gif

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Cluso99
10-02-2009, 06:46 AM
Holly, they had packet repeaters years ago, so would not be surprised if they don't have anything similar to what you want. Only issue is it must not carry anything commercial. I started lobbying for 2m frequencies for microcomputer traffic in 76 but became inactive before it happened - minicomputers and microcomputers (programming and design) got me totally hooked and amateur radio went by the wayside. Still have my license VK2ZTZ.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=838091), RetroBlade (http://forums.parallax.com/showthread.php?p=838053),·TwinBlade (http://forums.parallax.com/showthread.php?p=806697),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index (http://forums.parallax.com/showthread.php?p=778427)) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)
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localroger
10-02-2009, 07:12 AM
Cluso99, I am pretty sure there has never been a geosynchronous OSCAR satellite; as it is OSCARs have generally hitched rides to orbit with other payloads, but you can't get to GEO that way. Also GEO sats have to have onboard propulsion or they drift out of place, and the belt is rather crowded and slots are not assigned lightly.

Cluso99
10-02-2009, 11:06 AM
localroger: I don't know - never used one, but given the number of astronauts that are hams and do contacts from space, nothing would suprise me.

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· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=838091), RetroBlade (http://forums.parallax.com/showthread.php?p=838053),·TwinBlade (http://forums.parallax.com/showthread.php?p=806697),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index (http://forums.parallax.com/showthread.php?p=778427)) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)
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Cluso99
10-02-2009, 11:44 AM
I am interested in receiving the Marine AIS which is around 100MHz IIRC. It is a VHF signal transmitted by vessels to indicate their position, ID, etc.

Does anyone have any ideas how much of this could be done in the prop and what else would be required?

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=838091), RetroBlade (http://forums.parallax.com/showthread.php?p=838053),·TwinBlade (http://forums.parallax.com/showthread.php?p=806697),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index (http://forums.parallax.com/showthread.php?p=778427)) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)
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BradC
10-02-2009, 12:19 PM
Cluso99 said...
I am interested in receiving the Marine AIS which is around 100MHz IIRC. It is a VHF signal transmitted by vessels to indicate their position, ID, etc.

Does anyone have any ideas how much of this could be done in the prop and what else would be required?


Check out Silicon Chip, August 2009

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lt's not particularly silly, is it?

Cluso99
10-03-2009, 09:32 AM
Thanks Brad. I can buy an AIS fairly cheap. In fact, for a long voyage (not just up and down the coast) I would use a Class B AIS transciever for safety.

BTW: For others, up and down the coast of Australia (Sydney to Cairns) is about 1500NM (3,000km) - We have done that - see www.bluemagic.biz and most of the trip with mobile internet and phone coverage. We were 10-20NM out to sea and my wife was chatting to my son in Canada and daughter in Sydney on msn. Somehow, we don't leave our technology behind anymore http://forums.parallax.com/images/smilies/smile.gif

Just thought it could be a nice project to use as much as I can within the prop. Since others have done radio receivers, though this could be an interesting and useful (to a small number) project.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=838091), RetroBlade (http://forums.parallax.com/showthread.php?p=838053),·TwinBlade (http://forums.parallax.com/showthread.php?p=806697),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index (http://forums.parallax.com/showthread.php?p=778427)) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)
· Search the Propeller forums (http://search.parallax.com/search?site=parallax&client=parallax&output=xml_no_dtd&proxystylesheet=parallax&proxycustom=<HOME/>&ie=&oe=&lr=)·(uses advanced Google search)
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Dr_Acula
10-30-2009, 05:39 PM
I've just finished reading through this entire thread. Thanks ++ to PhiPi for the great tutorials and math. There were a few posts about getting prop to prop communications going and I'm wondering if anyone managed to do this?

The DSP capabilities of the prop at high frequencies opens up a lot of possibilities, especially when the frequencies are up in the AM band so standard AM radio parts can be used.

Just brainstorming here, but let's say we pick a frequency (1Mhz) and use AM ferrite antennas and keep the Tx power to tens of milliwatts. How far could this transmit?

Ballpark, I'd be guessing not very far, maybe as far away as you can hear a computer on an AM radio. Did anyone ever test this?

But perhaps the range can be extended to tens of metres with a bit of amplification on the Rx (ie the first stage of an AM radio). Ok, assuming there is the range, then you could combine the maths of the bell modem. But I wonder, is it theoretically possible to get faster baud rates using the DSP power of the prop?

For example, take a 1Mhz signal. Feed this into a tank circuit that resonates (I did some fun experiments with this when I first got my CRO). Feed in 10 pulses from a square wave and let the tank come up to full resonance over 10 pulses. Then let it fade away over another 10 pulses. Now, you could call that a '1' and a lack of a signal a '0', but I don't think it would be very good with noise rejection. But say you sacrifice a little more speed and use a Manchester type coding with 01 equal to 1, and 10 equal to 0. Synch it up with some 010101 pulses (each 1 consisting of 20x1usec pulses), and then it ought to stay in synch for long enough to send a byte, probably a lot longer since both props are xtal driven.

That ought to get the baud rate up to ?10 - 20kbaud. The code might end up simpler too. And it ought to be able to cope with noise from clocks like in a computer (and the prop xtal itself) as these are always on. Ok, it is more components than the little radio receiver, but these are cheap components.

Thoughts would be most appreciated.

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www.smarthome.viviti.com/build (http://www.smarthome.viviti.com/build)

Cluso99
10-30-2009, 06:50 PM
James:

Using a 1MHz carrier will not allow you to modulate at those frequencies (1uS pulse = 1KMHz). I am not sure at what the maximum ratio would be but I would suspect max would be < 1:100 so thats 10KHz max.

Modems use a maximum of about 3KHz bandwidth because the phone companies have a 4KHz total cutoff and rolloff starts before this. The Bell 202 modem is 300 baud. Bell 212 and V.21 are 1200 baud and use a more complex method (QAM) method requiring DSP computations.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=849265),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) (http://forums.parallax.com/showthread.php?p=778427) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)·
· Prop OS: SphinxOS (http://forums.parallax.com/showthread.php?p=819353)·, PropDos (http://www.orrtech.us/propdos/) , PropCmd (http://obex.parallax.com/objects/440/)··· Search the Propeller forums (http://www.google.com/advanced_search?q=+site:forums.parallax.com&num=20&hl=en&lr=)·(uses advanced Google search)
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Post Edited (Cluso99) : 6/13/2010 11:04:24 AM GMT

Dr_Acula
10-30-2009, 08:12 PM
Hi Cluso,

There must be a cunning way to make this work given the marvellous powers of PASM and sampling and processing at high speeds. I am just not sure what it is...

But, re (1uS pulse = 1KHz) (http://(1uS pulse = 1KHz)), is not 1uS =1Mhz, and 1ms equal to 1Khz?

Assume a wired connection for a moment rather than wireless, with imperfect coupling of two tank circuits say via a perfect resistor (no L). Start oscillating the first circuit, and the second will start to oscillate in parallel, but not instantly. I doubt you can send just one sinewave at 1Mhz (maybe you can??) and detect it at the other end. But surely if one oscillator starts oscillating then the other will follow. The question is how many cycles it takes for it to follow? With a sine wave of, say, 1Mhz, modulated at, say, 1Khz, then you will have 1000 cycles per 'data' bit. But will it work at 100, or 10?

I'm thinking that because it is possible to do direct DSP, one is not limited to traditional limitations of 'audio' frequencies.

I suppose one could also consider the upper frequency limit. 5Mhz xtal. How many instructions is that per second? Are we getting up to frequencies where we don't need wound ferrite antennas and it is possible to do this with long wire antennas tuned to the right frequency? Hmm - 433Mhz is 17.3cm. 43Mhz is 173cm for a 1/4 wave. What are the overclockers up to?

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Phil Pilgrim (PhiPi)
01-27-2010, 02:04 AM
FM broadcast signals range in frequency from 88 MHz to 108 MHz, which is too high to detect with counter-driven I/Q mixers, due to the PLL jitter at such frequencies. You would be better off using a digitally tunable FM receiver chip and detecting its audio output.

-Phil

Phil Pilgrim (PhiPi)
06-12-2010, 06:07 AM
I've recently gotten enthused about ham radio (again) and built a proper antenna for the amateur HF bands to go with a new transceiver. So I thought I'd give the Prop radio a try on shortwave, using the antenna. The antenna consists of a 6-foot vertical section atop a tapped loading coil (pictured below). This is mounted on the eaves of my garage. The ground side of the coax feed is connected to an insulated wire "counterpoise" about 15 feet long (for reception on 20 meters) which angles toward an endpoint about three feed above ground. The tap on the loading coil is adjusted for maximum audio "noise" volume.

http://forums.parallax.com/attachment.php?attachmentid=71101

At the other end of the antenna cable (RG58A/U), I built the JFET preamp circuit posted in this thread several pages back and reiterated here:

http://forums.parallax.com/attachment.php?attachmentid=71102

This feeds the antenna input to the original AM receiver circuit on page one. I modified the quadrature generation software to use the counters' PLL mode automatically when the receive frequency is high enough. The new program is attached below.

Listening on the lower end of the 20-meter ham band, I was able to detect CW signals. Granted, they weren't as loud as they were in my new transceiver, but they were loud enough to copy. I suspect that I have a severe impedance mismatch between the 50-ohm antenna feed and the RF amplifier input. Perhaps, if I can figure out how to correct it, I'll get better reception.

-Phil

ElectricAye
06-12-2010, 08:57 AM
WTF OMG LOL

Just today my kid asked me if we could hook up a long wire somehow and listen to people all over the world. Of course I immediately thought about the Prop, but had no idea where to even begin looking.

I had totally forgotten about this thread. Thanks for tuning in to our thoughts over here! http://forums.parallax.com/images/smilies/shocked.gif

Cluso99
06-12-2010, 10:20 AM
Nice work Phil. Perhaps ARRL may have a circuit of a preamp suitable for what you require.

That would be way cool on my boat. I have an antenna in the side stay of about 12m (ceramic isolators in one side stay) ready for an HF radio (Icom 802) which I have not bought yet. These HF radios use tuners and perhaps the prop could be used to automatically tune the aerial too.

You should bump this thread occasionally as I had forgotten it too! It doesn't sort of fit anywhere easily where we can remember it.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=849265),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) (http://forums.parallax.com/showthread.php?p=778427) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)·
· Prop OS: SphinxOS (http://forums.parallax.com/showthread.php?p=819353)·, PropDos (http://www.orrtech.us/propdos/) , PropCmd (http://obex.parallax.com/objects/440/)··· Search the Propeller forums (http://www.google.com/advanced_search?q=+site:forums.parallax.com&num=20&hl=en&lr=)·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz (http://www.bluemagic.biz)·· MultiBlade Props: www.cluso.bluemagic.biz (http://www.cluso.bluemagic.biz)

Beau Schwabe (Parallax)
06-12-2010, 12:01 PM
Phil Pilgrim,

I wonder if that MPF102 circuit couldn't be made a little more regenerative to give the signal a little more boost.


Can you measure the current off of the 9V? It may be ok, since I have seen similar circuits, but since the MPF102 is a J-Fet it tends to be 'ON' when the signal at the gate is not present. J-fets are also very resistive and this may be just fine. To add a little regeneration, you'd want to take a little bit of signal from the 'drain' of the MPF102 (side connected to the inductor) and feed that back to the gate of the MPF102. ...And I mean a little bit... like through a 10Meg resistor or greater. Even if you placed a second inductor between the 220pF and the gate of the MPF102 (in series) and placed the inductor (already in the circuit) in close proximity, that might even be enough to add a little regeneration.

Anyway, just a thought

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Phil Pilgrim (PhiPi)
06-12-2010, 12:48 PM
Beau,

I tried the 10M feedback resistor, but with no noticeable improvement.

The 20m band opened up quite a bit this evening and I was able to copy a strong SSB station. It was completely intelligible, too. But this is one of the advantages of direct conversion: no need for a separate LO and BFO. They're both the same thing! AM, SSB, and CW demodulate with equal facility.

-Phil

Cluso99
06-12-2010, 02:52 PM
Phil, here is a similar circuit using 470pF caps. http://www.ee.washington.edu/circuit_archive/circuits/activeant.html

I also saw some circuits using the NE602/NE612 which were interesing.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=849265),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) (http://forums.parallax.com/showthread.php?p=778427) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)·
· Prop OS: SphinxOS (http://forums.parallax.com/showthread.php?p=819353)·, PropDos (http://www.orrtech.us/propdos/) , PropCmd (http://obex.parallax.com/objects/440/)··· Search the Propeller forums (http://www.google.com/advanced_search?q=+site:forums.parallax.com&num=20&hl=en&lr=)·(uses advanced Google search)
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Phil Pilgrim (PhiPi)
06-12-2010, 10:04 PM
Thanks. That's the first instance of the circuit I've seen that suggested values for the inductor. But the commentary sort of nails down the fact that I'm misapplying it. It's designed to be an active antenna, not a receiver front end. Despite the fact that it works in my app, I know it could be better. I need to find a circuit that will match the 50-ohm antenna feed.

-Phil

Beau Schwabe (Parallax)
06-13-2010, 12:12 AM
Phil Pilgrim,

The only real difference between an active antenna and a receiver is that with an active antenna you are not placing an LC tank filter on the front end to block out your unwanted signals. The Active antenna IS a regenerative circuit in the sense that there is a small amount of parasitic capacitance between the gate and the drain that couples 'some' of the signal back to the gate. Since the MPF102 is a J-Fet, it works opposite of a MOSFET. When there is no signal at the gate, the J-FET conducts therefore making the Drain closer to GND. When there is a signal at the gate it tends to 'pinch' the conduction between the Source and the Drain making it less conductive. As a result the Drain becomes more positive through the inductor. The inductor here is not critical, but it works better than simply using a resistor because it promotes more of a sinusoidal response which is what you want and it can also act like a noise filter. This small amount of 'more positive' voltage at the Drain is coupled to the gate through capacitance within the MPF102 itself and is enough to slightly re-enforce the signal arriving at the gate from the antenna. The capacitor on the output simply acts as a DC block only allowing the small AC fluctuations to pass to the remainder of your circuit.

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 6/12/2010 5:17:54 PM GMT

Phil Pilgrim (PhiPi)
06-13-2010, 12:31 AM
Beau,

The input impedance of the JFET is very high. But the antenna cable impedance is only 50 ohms. This would seem to imply that an RF transformer or tapped inductor on the input might improve the response. Or should I consider an amplifier with a low input impedance, such as a common base bipolar transistor?

-Phil

Beau Schwabe (Parallax)
06-13-2010, 12:51 AM
"This would seem to imply that an RF transformer or tapped inductor on the input might improve the response."

I've seen this sort of thing before, and it amazes me every time before I look at it a bit and it makes a ton of sense.

Many times on an antenna input you will see 1 or 2 turns ... one side going to GND and the other side going directly to the antenna ... that couple to a larger coil driving the detection circuitry. The reason this is done is EXACTLY to match the impedance and provide a little bit of galvanic protection to the input gate.

I don't think it would hurt to try it, in fact it may surprise you!! http://forums.parallax.com/images/smilies/smile.gif

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Leon
06-13-2010, 01:34 AM
The input resistance of a JFET is very high, but the input impedance at RF will be a lot lower.

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Leon Heller
Amateur radio callsign: G1HSM

Beau Schwabe (Parallax)
06-13-2010, 10:22 AM
Phil Pilgrim,

Any significant difference if you cascode two MPF102's together?

Similar to this arrangement, but both gates would be tied together and connected as the input.

en.wikipedia.org/wiki/Cascode (http://en.wikipedia.org/wiki/Cascode)

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Cluso99
06-13-2010, 03:14 PM
Phil: Here is a circuit that does a similar thing http://www.wb5rvz.com/sdr/sr_lite_ii/·using a PC and sound card.
This circuit and others are·known as an SDR (Software Defined Radio). There is quite a bit of info on the web. http://wwwhome.cs.utwente.nl/~ptdeboer/ham/sdr/

The FST3253 spec is here·http://www.fairchildsemi.com/ds/FS%2FFST3253.pdf
Texas Instruments version 74CBT3253 is available from DigiKey http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-6434-1-ND
The OpAmp LT6231 is expensive and is also available from DigiKey http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LT6231CS8%23PBF-ND

The 74LVC2G66 Dual BiLateral Switch may work (6-10ohm) instead of 74CBT3253 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-13271-1-ND
The 74LVC4066 may also work (6ohm) but is only in stock as QFN http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=568-3019-1-ND

This is a simple circuit and your code (I am presuming this is what you are doing) could demodulate the audio.

The prop may be able to generate the clocks removing the requirement for the LO & Dividers. I am usure whether the OpAmp LT6231 would still be required. This could make a truly simple circuit.

Any thoughts????

Here is another set of circuits using the FST3253 http://home.pages.at/chirt/Projects/HDR2005/sch/QSD_sch.jpg·and the home page for the rest of the circuits http://home.pages.at/chirt/Projects/HDR2005/sch/sch.htm

Here is a good article and references for an SDR. Also is a simple Antenna Tuner. http://www.nonstopsystems.com/radio/frank_radio_sdr.htm

POSTEDIT: I just re-read the whole thread and how the Receiver works. So I have missed this. So, Phil, you have been able to get the LO running up to 30MHz? Even with a little bit of the circuitry in some of the above examples, the Prop may function even better.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=849265),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) (http://forums.parallax.com/showthread.php?p=778427) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)·
· Prop OS: SphinxOS (http://forums.parallax.com/showthread.php?p=819353)·, PropDos (http://www.orrtech.us/propdos/) , PropCmd (http://obex.parallax.com/objects/440/)··· Search the Propeller forums (http://www.google.com/advanced_search?q=+site:forums.parallax.com&num=20&hl=en&lr=)·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz (http://www.bluemagic.biz)·· MultiBlade Props: www.cluso.bluemagic.biz (http://www.cluso.bluemagic.biz)

Post Edited (Cluso99) : 6/13/2010 11:07:28 AM GMT

Phil Pilgrim (PhiPi)
06-14-2010, 02:06 AM
Cluso99,

I'm torn about moving the mixer off-Prop, since the Prop handles that task so neatly. The idea here (for me, anyway) is for the Prop to do as much internally as possible. The SDR technique seems to be one of mix first; amplify later. But I can't do that: I have to amplify first then mix because, once the signal reaches the Prop, there's no more analog amplification possible. So I guess the question is how much noise the Prop adds in the mixing process and whether I can overcome it with enough pre-amplification, and at what cost.

-Phil

Cluso99
06-14-2010, 01:37 PM
Phil,

Yes. I like to make the prop do as much as possible and use minimal circuitry outside too.

I·understand a little more as I have been reading about the various SDR solutions, thanks to your article. I would never had believed the prop could do this.

Let's think a little more about this. The best way to get some amplification is to amplify after the mixer because the bandwidth is smaller and the frequency is lower. The nicest way to do this seems to be using the 74CBT3253, 74LVC4066 or 74LVC2G66 as the mixer. The prop can do the LO producing I & Q outputs to drive the mixer (analog switches). That would output an IF stage which we could amplify simply and feed to the prop for the next stage mixing and drive the audio output. Thus, we have·a Superheterodyne SDR receiver. Probably there is a simple and cheap IC that will do the filtering and amplification at an IF of 455KHz. This method of course is a more complex solution than yours, and alos requires more propeller resources.

Now, could we use this method to extend the tuning range of the radio? Probably the answer is yes. Could we get to say 150MHz? Of course, we need to be able to switch the aerial tuning, so we need to look at this. Can we perhaps use more 4066's to switch in taps in the LO coil??? Do we have to increase the IF to do this? For say 144MHz, we need to generate a LO frequency of ~143.5MHz or ~145.5MHz for a 455KHz IF. How does the prop do the Quadrature Frequency generation - does it require 4x Frequency first???

Next, can the prop demodulate an FM signal?

What I am getting at is can we build a Propeller based wideband 800Khz-150MHz SDR (receiver) cheaply??

Another other possibility is to use the NE612A (NE602) (mixer and LO) and a 455KHz ceramic filter sfg455a3 feeding the prop.

While looking further I came across this solution. It uses a Wideband amplifier (frontend) such as the video amp NE592. This is a really simple circuit and can do up to 90-120MHz. Much better gain is achieved at <30MHz. Maybe this could then feed the prop directly (i.e. replace your FET circuit) using your current code. The chip is available in a nice DIP8 package NE592D8 $0.46·from Future Electronics··http://www.futureelectronics.com/en/Search.aspx?dsNav=Ntk:PartNumberSearch%7cNE592D8G% 7c1%7c,Ny:True,Nea:True·· Maybe this should be tried first as it may solve your noise problems. It could be an elegant solution if it works.

I also found this wideband amp·using a 2N3563 Gain ~19dB, BW ~200KHz-50MHz, Input ~50 ohm, Output ~75 ohm http://www.arising.com.au/people/Holland/Ralph/buffer/highimpedanceprobe.htm· (see halfway down the page) There is also an MPF102 circuit here.



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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=849265),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) (http://forums.parallax.com/showthread.php?p=778427) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)·
· Prop OS: SphinxOS (http://forums.parallax.com/showthread.php?p=819353)·, PropDos (http://www.orrtech.us/propdos/) , PropCmd (http://obex.parallax.com/objects/440/)··· Search the Propeller forums (http://www.google.com/advanced_search?q=+site:forums.parallax.com&num=20&hl=en&lr=)·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz (http://www.bluemagic.biz)·· MultiBlade Props: www.cluso.bluemagic.biz (http://www.cluso.bluemagic.biz)

Phil Pilgrim (PhiPi)
06-14-2010, 02:30 PM
A single conversion from high-band SW or VHF to 455KHz is probably inadvisable, due to image rejection issues. I've seen several QRP superhet designs that use a 4MHz IF, along with crystal lattice filters for selectivity. Combined with a simple front-end bandpass filter, this would handle out-of-band rejection adequately. The Propeller could easily supply jitter-free I and Q 4MHz LO signals for the final, internal conversion to baseband.

The initial LO might best be done as a VCO sinewave (e.g. Colpitts) oscillator, with feedback to the Prop, which could then control the frequency by a filtered DUTY mode output to a varactor. The VCO approach has an additional advantage that it could also be used to source a sinewave carrier for transmit purposes, which would require less filtering than a squarewave source would. Of course a DDS chip could well serve the same purpose, but at a somewhat greater cost.

It may boil down to a proof of principle vs. performance issue, with the former favoring a more Propeller-centric architecture and the latter using proven analog circuitry. A lot of this RF stuff is terra ingognita to me. I look at schematics for radios and just scratch my head over why things are done the way they are. Then there are the inductors. Inductors are magic ju-ju. There must be chants one has to intone as enameled wires get pushed through little ferrite donuts to make just the right coils. If a comparison could be made to hardware store items, inductors are like plumbing parts, while the components familiar to digital designers are more like standardized fasteners. That's one reason my knee-jerk inclination is to get everything into the digital domain as soon as possible. In the digital world, we have it easy by comparison to RF analog. That's why RF design engineers have my utmost admiration, wonder, and respect. I just hope it's not a dying art.

-Phil

Cluso99
06-14-2010, 04:06 PM
I echo your comments re RF (and inductors). I have not used any of what I learnt in RF 40 years ago excepting the first couple when I did some limited 2m & 6m designs. I went into digital and computers pretty quickly and haven't done much analog since. Even the modem designs I did in the 80's & 90's were almost totally digital (except for the DAA).

Next time I order from Future Electronics I might get the NE592D8 to try.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=849265),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) (http://forums.parallax.com/showthread.php?p=778427) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)·
· Prop OS: SphinxOS (http://forums.parallax.com/showthread.php?p=819353)·, PropDos (http://www.orrtech.us/propdos/) , PropCmd (http://obex.parallax.com/objects/440/)··· Search the Propeller forums (http://www.google.com/advanced_search?q=+site:forums.parallax.com&num=20&hl=en&lr=)·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz (http://www.bluemagic.biz)·· MultiBlade Props: www.cluso.bluemagic.biz (http://www.cluso.bluemagic.biz)

heater
06-14-2010, 04:32 PM
Any chance of getting this to work down at 77.5KHz?

I'd like to receive the time and standard frequency station DCF77 (Germany). I even have a LC tank out of an broken radio controlled clock waiting for it.

Prop as a frequency standard would be great.

It might have to work rather well here in Helsinki regarded as being on the edge of the reception area.

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For me, the past is not over yet.

Leon
06-14-2010, 04:42 PM
I built a very simple frequency standard many years ago with a Signetics PLL chip that locked the VCO to the old 200 kHz BBC long wave transmitter. It's now on 198 kHz, which isn't so convenient.

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Leon Heller
Amateur radio callsign: G1HSM

Don M
06-14-2010, 07:57 PM
Last week I was at the Embedded Systems & Sensor Conference in Chicago. At the Digi booth they were selling their M10 satellite communication evaluation kit for $99. I picked one up. You get free 90 days worth of time communicating via the Orbcomm fleet of LEO satellites. Operates on 150-160 Mhz. Thought it might be fun to play with. They tell me it will cost somewhere around $5-10 per month depending on the amount of data you transmit. Haven't confirmed that yet with Orbcomm.

Here is a link to the kit: http://www.digi.com/products/model.jsp?lid=EN&pgid=100&pfid=74&mtid=3311&amtid=3311&pm=Y

Phil Pilgrim (PhiPi)
06-14-2010, 10:30 PM
heater,

It should work fine at 77.5KHz. I bought a loopstick antenna from DigiKey to pick up the 60KHz WWVB signal from Fort Collins, Colorado. I could not get it to work with the Prop circuit. So I tried it with the time receiver chip that I also got from DigiKey. That didn't work either. Checking the WWVB range map, I discovered that I was outside the reception area. But, if you're close enough to a station, there's no reason the Prop shouldn't be able to pick it up. You'll have to write some additional code to demodulate the data, however.

-Phil

Cluso99
06-16-2010, 05:05 PM
Phil: I have just been looking at the AIS (an identifier for ships similar to what planes have). It uses the Marine VHF band and channels 87B (161.975·MHz) and 88B (162.025·MHz).·http://en.wikipedia.org/wiki/Automatic_Identification_System

It uses 9600 baud GMSK (Gaussian minimum shift keying) and SDLC protocol. I would expect we could decode this with the prop. I wrote SDLC on a micro back in 1983, but alas, I through out the backups 10 years ago :-(

So, I expect with a front-end mixer & LO we could bring 160MHz down to a usable IF frequency where we could demodulate within the prop. This sounds like an interesting extension to your work with this and your modem code. Now to find the time amongst my other work and prop projects.

The prop could then be an HF Receiver and a VHF AIS Receiver all in one.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade (http://forums.parallax.com/showthread.php?p=786418),·RamBlade (http://forums.parallax.com/showthread.php?p=849265),·SixBlade (http://forums.parallax.com/showthread.php?p=780033), website (http://bluemagic.biz/cluso.htm)
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator) (http://forums.parallax.com/showthread.php?p=790917)
· Prop Tools under Development or Completed (Index) (http://forums.parallax.com/showthread.php?p=753439)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) (http://forums.parallax.com/showthread.php?p=778427) ZiCog (Z80) (http://forums.parallax.com/showthread.php?p=788511) , MoCog (6809) (http://forums.parallax.com/showthread.php?p=811043)·
· Prop OS: SphinxOS (http://forums.parallax.com/showthread.php?p=819353)·, PropDos (http://www.orrtech.us/propdos/) , PropCmd (http://obex.parallax.com/objects/440/)··· Search the Propeller forums (http://www.google.com/advanced_search?q=+site:forums.parallax.com&num=20&hl=en&lr=)·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz (http://www.bluemagic.biz)·· MultiBlade Props: www.cluso.bluemagic.biz (http://www.cluso.bluemagic.biz)

Toby Seckshund
08-14-2010, 08:31 AM
Just a general question.


To make up some front end filters I am wondering if the use of toroid cores would be slightly "more modern" than a whole bunch of copper wound around a drill, as I did as a kid.

I have a few cores that have mostly a pale green body, with one flat edge being a dark torquoise. They are 0.45 inch diameter (11mm) and 0.17" thick (4mm).

Do these markings form a code to state stuff like frequency capabilities etc ??


As always, all clues gratefully received.

Cluso99
08-14-2010, 11:38 AM
No idea Toby. This is not my specialty. Maybe you can find something on one of the ham forums, not that I know of any.

Phil Pilgrim (PhiPi)
08-14-2010, 05:32 PM
Toby,

What you have is a T44 toroid with a powdered iron core. (The "44" is the size, and the fact that it's colored, says "powdered iron".) There is also a dash number that goes with it, given by the color code, which specifies the magnetic properties (e.g. T44-2). Unfortunately, each manufacturer has its own color code, so you would need to know who the manufacturer is to look up this info. Once you have this, you will know how many uH per turn and what frequency range the core is good for.

You could also just wind a few turns on it and measure it with an inductance meter or, lacking one of those, add a precsion (or accurately measured) cap and see where it resonates. A series resistor, a Propeller, and a scope are all you need for the latter measurement. Connect the scope leads across the LC "tank" and stimulate it through the resistor with a range of frequencies from the Prop. At resonance, you will see a sharp increase in amplitude on the scope.

Powdered iron toroids like yours are normally used in tuned circuits, while ferrite toroids (flat gray colored) are used for transformers and chokes.

I recently purchased a toroid assortment from Hendricks QRP kits (http://www.qrpkits.com/toroidkit.html). It includes the most common powdered iron and ferrite cores used in receivers and low power (QRP) transmitters, along with some magnet wire. The price for the kit is very fair, working out to about $.50 per toroid. I've already used one of them to make a common mode choke in a Propeller-based antenna analyzer I hope to post about soon.

-Phil

Toby Seckshund
08-14-2010, 07:26 PM
Thanks for that info. The reason I was unsure about them is that mostly they came off of old PCBs, having 10, or so, tirns of heavy enamaled wire. The obviously are power suppressor chokes and wouldn't require stunning HF performance.

I wound a trial coil, for about 7MHz (40M) but without a heafty 200pF+ it ended up being about one and a quarter inches long due to the space winding (TCW only available). I had a Heathkit RF-1U in the garage, which worked to my supprise after 10+ years and I have seen a dip on its output, via a 'scope, whilst tuning it. Years ago I had all sorts of generators and dipabsorbtion meters but gave then to a local club when I moved.

Anyway, I have listned to the HF version and all I got was a convincing bunch of woops, whistles and splats that SW would give but no stations, or the Heathkit which whilst hopelessly off callibration is on the right freq acording to the freq counter. I will continue to play with it.

It has certainly raised an interest in radio once again, especially having now seen the SDR software that is free .


Moral of the story, hold on to all of your "junk" to you dying day ( try finding a variable capacitor nowerdays! )

Heater.
08-14-2010, 07:37 PM
Toby:

try finding a variable capacitor nowerdays!

Ha! I think I bought the last one in Finland a couple of years back.

Knocked up a simple MW radio with it and was disappointed that it did not work. Later I realized there is pretty much nothing on MW around here any more.

Heater.
08-14-2010, 08:41 PM
Then there are the inductors. Inductors are magic ju-ju. There must be chants one has to intone as enameled wires get pushed through little ferrite donuts to make just the right coils.

A few decades ago when I was still in school a couple of us used to visit a friend who's father was in the TV transmitter installation business. He got us all interested in electronics and we spend many happy Saturday afternoons at his place learning this and that. Ultimately he got us all building tube amateur band receivers. I was amazed how he fished some formers out of the junk box casually wrapped a few tuns of wire around them added a tuning capacitor and some beehive trimmers and bingo the thing was receiving and we were listening to guys yacking in South America. Not a calculation or measurement anywhere.

It was then that I realized the magic ju-ju would be forever out of reach to me.

Toby Seckshund
08-14-2010, 09:12 PM
That was what I got from my father. We just knew that on a 1/4" former 10 turns, along with a 30pF behive would give 30MHz, 6 turns for FM radio and 4-5 for 144MHz. It was a good cover for using the nail varnish too !

The old Heathkit worked, and that saved its life. Otherwise the duel gang cap would have been liberated. I an still thinking of building a RX in it (and telling my dad that it was banjaxed)

Tayloe detectors seem to be easily thrown together, and use the Prop as the controler.

Heater.
08-14-2010, 09:34 PM
Toby,

Thank you, brilliant, I've never heard of Tayloe detectors before. What a fascinating read.

Toby Seckshund
08-14-2010, 09:55 PM
The usual switching chips have 5 Ohms wheras the HC4066 sort have 50 Ohms. I think that they say that this will worsen the noise figures but I bet it would still be a good proof of concept (which is just a way a saying that the 3 pages of greek maths is too high to even graise my grays )

Toby Seckshund
08-18-2010, 08:45 AM
Has anybody tried this with a DIP40 Prop ?

I put the resistor and capacitor fairly close to the pins (a few mm) but I have yet to hear even my RF test genny stuffed up it's nose. I get the various whoops, whistles and splats that MF/SW would give but all the human generated stuff is absent.

Phil Pilgrim (PhiPi)
08-18-2010, 05:07 PM
If you use a DIP40, I would recommend soldering the 10 Meg (SMT) feedback resistor directly to the pin pair. Also, plugging the DIP40 into a solderless breadboard will compromise its performance, due to stray capacitance. This effect might be minimized by clipping the feedback pin short so it doesn't connect to the solderless breadboard.

-Phil

Toby Seckshund
08-18-2010, 06:05 PM
I had made up simple PCB for this test where the 1M res (no 10M) was from P3 (pin4) to P4 (pin5) within about 0.2" of track. To this must be added the lenth of the Props pin and that of the low profile socket. I used copper pour so that there are guard rings around the pads.

So I have, sort of, tried my best short of actually using a QFP. Hey-Ho.

I might try using the I and Q into a Tayloe and see what that gives.

Phil Pilgrim (PhiPi)
08-18-2010, 07:11 PM
Toby,

What frequency range are you trying to receive? What kind of inductor and antenna are you using? It's easiest to get the thing working on a strong broadcast station first, then work you way up to SW.

I'm thinking about doing a superhet with a 10 MHz IF. That would allow the Propeller's I/Q detector to work with jitter-free I and Q signals. It would also permit a lattice filter to be built from readily-available SMT 10 MHz crystals. I will probably use an SA612 LO/mixer, with the LO controlled VCO style from the Prop. Since the mixer has some conversion gain, the Prop will see a stronger signal at its detector input.

-Phil

Toby Seckshund
08-18-2010, 09:26 PM
At first I had tried the 14MHz that your second version used, then when that didn't seem to be too good I went down to the MW original. I have tried all sorts of inductors from 500mH ones to a hand wound one that works out at about 7MHz. The local MW station around here is 50KW on 1.58MHz and is 15 miles away. As I said I cannot get it to pick up my generator.

The 7MHz coil has been tapped off at the top and at about 25% up to prevent excessive loading.

I will have another crack at it over the next few days.


At least it has kicked an interest into building a LC meter, for the bench ( and an ESR meter for work ..... )

Rodo12
10-06-2010, 02:09 PM
Hi Phil,
I am playing with your AM radio object for the propeller. Very cool! If I wanted to disable the frequency scanning feature and tune to a particular frequency, what would I change?
I am a newbie with the propeller, and I think it has something to do with the line of code in the start PUB that reads,
repeat tune_freq from 550_000 to 1600_000 step 10_000
but I'm not sure.
Thanks!

Bob L.

Phil Pilgrim (PhiPi)
10-06-2010, 02:43 PM
Thanks Bob, I'm glad you're enjoying the radio project. You're right about what needs changing. Suppose you wanted to stay tuned to 1000 KHz. You can change the repeat statement thus:



repeat tune_freq from 1000_000 to 1000_000

-Phil

Perry
04-15-2011, 02:46 AM
I have enjoyed this radio project for a long time and thought it could use a better interface.

Thanks to my work on the "Poor Mans Digital Oscilloscope" I have a program that can add a useful interface to many projects.

This radio has 5 presets ...................................... F1,F2,F3,F4,F5
decrement/increment frequency by 1_000.......... F6,F7
decrement/increment frequency by 10_000........ F8,F9
decrement/increment frequency by 100_000...... F10,F11
dump picture to SD card ..................................... F12
increase frequency by 10_000 ever 5 seconds toggle "s" key
toggle oscilloscope display with space bar
type digits for desired frequency followed by enter key.

The picture included is of the output received from a cheap 49Mhz R/C transmitter.

Phil Pilgrim (PhiPi)
04-15-2011, 03:19 AM
Perry,

I'm glad you've had success with your project. Your scope output is awesome! Were you using the simple LCR receiver front-end or something more elaborate? Can you post a schematic, please, if it's something different?

BTW, I'm pleased that you've been able to make use of my core AM receiver code, and I'm very happy to share it. But when you publish it, as you've done here in AM_Receiver.spin, it needs to retain my copyright notice, along with your own notice for the parts you've modified or added, in accordance with the MIT License, viz::


... The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. ...

Thanks,
-Phil

Beau Schwabe (Parallax)
04-15-2011, 04:19 AM
Phil,

Is this the current circuit you are using?
http://forums.parallax.com/attachment.php?attachmentid=71102&d=1276321096

I might have an add-on that could improve sensitivity... The idea is to keep the I/O pin of the Propeller as close to the threshold voltage of the I/O as possible. This is where the I/O istelf is the most sensitive to external 'noise'. In principle this is similar to the Sigma delta ADC but it only uses one I/O pin. IOW, the output pin becomes the feedback pin. It requires a 'cog' but basically provides a voltage reference equal to the I/O threshold. You simply couple this reference voltage to the input pin of your existing circuit via a high value resistor (10M) and your sensitivity should increase. As it is the capacitor just forms a DC block, and the reference is maintained by a signal average that may not be optimal for the input.

Phil Pilgrim (PhiPi)
04-15-2011, 04:42 AM
Beau,

To be honest, I've lost track. IIRC, the one I had the best success with was the CD4007 cascode front-end. I'd love to see your approach in more detail!

-Phil

Perry
04-15-2011, 05:15 AM
Phil,

Is this the current circuit you are using?
.

No I am really getting too old for this stuf, my eyesight seems to be getting worse so I rarely try to make any small circuit of consequence.

The circuit used was the one outlined on the first post only with a capacitor labled 151 and a toroid with about 23 turns. but amazingly when I removed the capacitor to get it's value for this post it still worked but at 1/4 the volume.

And testing again at 1AM EST, when the R/C controller is signaling there is some kind of heterodyning going on as I also heard voice and chimes from some SW source

As for my antenna, don't tell the telco about this. I don't have a land line anymore and live in an Aluminum Trailer. I use a high voltage capacitor ( labled 103) connected to the yellow wire connecting to the 'phone jack. I had wanted to get short wave and as Aluminum Trailer is almost like a huge "orgone box" I decided that if the telephone company had disconnected me properly I would get a huge outside long wire antenna this way.

I recall trying this with Phil's first version of his radio software there was obvious jitter problems, but the new version should be capable of receiving R/C signals of even 1200 baud modulation.

Beau Schwabe (Parallax)
04-20-2011, 03:06 AM
Phil,

I just realized I never posted anything... Fail :frown:

At the beginning of the year over the Christmas break I was playing around with this idea. I basically took what the sigma delta ADC does with two pins (Feedback and Drive) and combined the function into one pin and called it the "I/O threshold switching voltage reference".

It's not exact, but it's very close, and will be very close to the threshold voltage of any of the other I/O pins on that same chip die (even temperature tracking)

Anyway, the setup I was using involves a tuned LC tank between the reference and another I/O pin but for your application you could use something in the way of a 1 Meg or 10 Meg resistor in place of the LC tank. This way it becomes a broadband receiver.

The main idea is that now you have a reference that you can loosely couple with a high impedance resistor to the input. The closer your input I/O is to that reference, the more sensitive it will be to reception if there is a signal there.

Perry
04-20-2011, 01:58 PM
Phil,

I just realized I never posted anything... Fail :frown:

Anyway, the setup I was using involves a tuned LC tank between the reference and another I/O pin but for your application you could use something in the way of a 1 Meg or 10 Meg resistor in place of the LC tank. This way it becomes a broadband receiver.



Thanks Beau

I am away from home now but will try this in a few days.
I'd like to try something with a modern take on the older radio construction technique of using plugin tuner modules for different bands.

Perry

madrfskills
05-23-2011, 05:53 AM
Here is another idea. I can't take credit for this one, but I didn't include the original author's name in my notes. Rats.

At any rate, here's the idea: as anyone who has used a CMOS inverter knows, it absolutely, positively wants to oscillate. Why not let it? In the circuit below the inverter will break into oscillation at a frequency defined by the L-C tank formed by the varactor diode and its parallel inductor. The microcontroller periodically forces QUENCH low to bring the inverter out of oscillation - but it will break into oscillation again when QUENCH is deasserted. The key, though, is that the amount of time it takes for it to ring varies directly with the RF signal level at the antenna at the L-C tank frequency. The subcircuit to the right of the antenna is a rectifier which low-pass filters the envelope so we get a pulse width modulated signal (called, oddly enough, SIGNAL in the schematic) with PW proportional to RF power. This type of receiver is called a superheterodyne.

You can push this to about 10-20MHz. You tune it by providing a DC bias to the varactor through the blocking inductor. For the prop, you'll need to use a PWM channel feeding a low pass filter and voltage scaling network to get decent tuning range. Note that I haven't done this on a prop yet.

One advantage to a superhet is very high single-stage gain, since the gain of an oscillator approaches "infinity" at the center of its passband, as it transitions to oscillation. Infinity here can mean >80-90dB. On the other hand, linearity is crappy and it radiates a copious amount of noise.


81427
V/R
Mike

Toby Seckshund
05-23-2011, 06:53 PM
Using a quenched oscillator makes this a super regenerative receiver. A RF buffer amplifier between the oscilator and the aerial will cut down on the radiated bursts.

madrfskills
05-23-2011, 09:19 PM
Using a quenched oscillator makes this a super regenerative receiver. A RF buffer amplifier between the oscilator and the aerial will cut down on the radiated bursts.

Quite right, Toby - its a super-regenerative. Very, very silly of me to mistype like that!

Either -

1) Built a superhet with the daughter and my mind is clogged, or
2) I've been drinking too much, or
3) I've been drinking too little

Cheers!
Mike

Toby Seckshund
05-23-2011, 09:55 PM
Too much ? Too little ???

One should always maintain a balanced diet. Never eat on an empty stomach.

Cluso99
07-11-2013, 01:55 AM
Over on the P2 forum a question about SDR was asked. So just to bump this thread again.
BTW perhaps using a cheap DVB-T dongle (with the RTL2832U chip) and the prop could work together?

Toby Seckshund
07-11-2013, 08:49 AM
I was deep in the dreaming of a general coverage RX using a TV tuner head and Prop when I saw the SDR# project. For Ł12 I had a EZCAP RX head that nominally goes from 50MHz - 2GHz (with a hole around 1.1GHz). It is not that great on sensitivity but that gives me something to do with pre-amps / filters etc. There are a ton of birdies too, but hey, Ł12 (inc p&p Deal Extreme). I believe that it is only the ones that have the radio option as well as the TV that are of any use.

With all of the bandwidth over USB2 and 0.9 - 2MHz BW it wouldn't run on a P4 2.5GHz 400FSB board, the nice guys at SDR# even compiled a version that did 250KHz BW for me. On a 2.8GHz but 800MHz FSB the 2MHz system runs at 60 -70 CPU.

The waterfall and other bits could be dropped off of the workload but there is a lot of maths, and a USB2 interface.

tingo
07-12-2013, 12:32 PM
Which EZCAP dongle is that? Is it one of the RTL2832 dongles?

Toby Seckshund
07-12-2013, 02:31 PM
I have lost/thrown the box but I am sure that it was this one, which does use the RTL2832 -

Ezcap EZTV645 DVB-T Digital TV USB 2.0 Dongle with FM/DAB/Remote Controller at the bottom of http://dx.com/s/ezcap

I think that there are others that would run but it would be wise to check that they are on the approved lists.

Windoze will not report what it is as you have to use the ZADIG drivers, Windoze bleats about it not having a bulk endpoint ...

I must see what the latest versions of SDR# have on them, I am using one from about a year ago. I was so grateful for then making a version that could limp along on the 2.8G P4, that I was trying to get going for my father, that I stuck with the first one that ran properly (with too much BW the CPU went to 101% and froze up) .

Sod's law made it that just as I was getting somewhere, his eyesight gave up.

tingo
07-31-2013, 01:30 PM
Yeah, I already have another RTL2832 device. Thanks for telling which version you used.

Toby Seckshund
07-31-2013, 07:17 PM
I should warn people that I got hold of another (free) EZCAP dongle. That one is nowhere as good as the first one, it receives but is not as sensitive (not that good in the first place ) and gets blown off the face of the earth by anything local. I live 300m under a flight path and there a loads of pager base stations blasting away, somewhere about here too. So 100 - 150MHz region is a bit busy/hostile.

But hey, they are cheep.

Back on thread:- I did try the Prop RX stuff but only with 40DIP ones, I really must try it with the new one pin DAC.

LEE M
11-28-2013, 04:05 PM
Wow you guys are like geniuses. I have a prop and an ADC MCP3208 and I'm trying to MEASURE the amplitude of all the frequencies from 6 meg to 40 meg. I don't need accuracy but PRECISION. I can follow your code, somewhat, and the frequency cycling is EXACTLY what I am looking for... now I am just trying to figure out how to introduce the ADC into the mix and get some measurements from it all. I REALLY appreciate any assistance any of you could render as this has the potential to help my crew beyond imagination. Thank you.

Seairth
05-01-2014, 11:19 AM
I was looking through the code and came across the following block:



:mix waitcnt time,sample
mov i_samp,phsa
mov phsa,#0
mov q_samp,phsb
mov phsb,#0


I suggest the following code instead:



:mix waitcnt time,sample
mov i_samp,phsa ' capture both PHSx back-to-back
mov q_samp,phsb
sub phsa,i_samp ' Use SUB instead of MOV #0 to keep any
sub phsb,q_samp ' accumulation in the past 4-8 cycles


Unfortunately, I have not yet set up this project, so I can't tell if this makes any practical difference to the sampling/mixing.

kuroneko
05-01-2014, 11:31 AM
:mix waitcnt time,sample
mov i_samp,phsa ' capture both PHSx back-to-back
mov q_samp,phsb
sub phsa,i_samp ' Use SUB instead of MOV #0 to keep any
sub phsb,q_samp ' accumulation in the past 4-8 cycles

Accumulations are not reflected in shadow[phsx].

Seairth
05-02-2014, 01:56 AM
Accumulations are not reflected in shadow[phsx].

For d-field, the shadow register is read instead of the actual PHSx register? Huh. I did not know that.