Hook an antenna to your Propeller, and listen to the radio! (New shortwave prog

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  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2009-10-01 - 22:39:08
    @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 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
    sigintadvancedoriontrumpet-s.jpg

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  • Cluso99Cluso99 Posts: 15,815
    edited 2009-10-01 - 22:53:54
    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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  • HollyMinkowskiHollyMinkowski Posts: 1,398
    edited 2009-10-01 - 23:04:39
    @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 smile.gif

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  • Cluso99Cluso99 Posts: 15,815
    edited 2009-10-01 - 23:46:55
    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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  • localrogerlocalroger Posts: 3,339
    edited 2009-10-02 - 00:12:34
    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.
  • Cluso99Cluso99 Posts: 15,815
    edited 2009-10-02 - 04:06:10
    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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    Links to other interesting threads:

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  • Cluso99Cluso99 Posts: 15,815
    edited 2009-10-02 - 04:44:07
    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:

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    · Prop Tools under Development or Completed (Index)
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    · Search the Propeller forums·(uses advanced Google search)
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  • BradCBradC Posts: 2,601
    edited 2009-10-02 - 05:19:47
    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?
  • Cluso99Cluso99 Posts: 15,815
    edited 2009-10-03 - 02:32:35
    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 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:

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    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: Micros eg Altair, and Terminals eg VT100 (Index) ZiCog (Z80) , MoCog (6809)
    · Search the Propeller forums·(uses advanced Google search)
    My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2009-10-30 - 10:39:59
    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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  • Cluso99Cluso99 Posts: 15,815
    edited 2009-10-30 - 11:50:05
    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,·RamBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)·
    · Prop OS: SphinxOS·, PropDos , PropCmd··· Search the Propeller forums·(uses advanced Google search)
    My cruising website is: ·www.bluemagic.biz·· MultiBlade Props: www.cluso.bluemagic.biz

    Post Edited (Cluso99) : 6/13/2010 11:04:24 AM GMT
  • Dr_AculaDr_Acula Posts: 5,484
    edited 2009-10-30 - 13:12:14
    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 [url=http://(1uS pulse = 1KHz)](1uS pulse = 1KHz)[/url], 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)Phil Pilgrim (PhiPi) Posts: 22,565
    edited 2010-01-26 - 19:04:47
    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)Phil Pilgrim (PhiPi) Posts: 22,565
    edited 2010-06-11 - 23:07:56
    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.

    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:

    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
  • ElectricAyeElectricAye Posts: 4,561
    edited 2010-06-12 - 01:57:36
    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! shocked.gif
  • Cluso99Cluso99 Posts: 15,815
    edited 2010-06-12 - 03:20:13
    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,·RamBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)·
    · Prop OS: SphinxOS·, PropDos , PropCmd··· Search the Propeller forums·(uses advanced Google search)
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  • Beau SchwabeBeau Schwabe Posts: 6,420
    edited 2010-06-12 - 05:01:58
    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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    [url=mailto:bschwabe@parallax.com]Beau Schwabe[/url]

    IC Layout Engineer
    Parallax, Inc.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,565
    edited 2010-06-12 - 05:48:32
    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
  • Cluso99Cluso99 Posts: 15,815
    edited 2010-06-12 - 07:52:04
    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,·RamBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)·
    · Prop OS: SphinxOS·, PropDos , PropCmd··· Search the Propeller forums·(uses advanced Google search)
    My cruising website is: ·www.bluemagic.biz·· MultiBlade Props: www.cluso.bluemagic.biz
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,565
    edited 2010-06-12 - 15:04:19
    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 SchwabeBeau Schwabe Posts: 6,420
    edited 2010-06-12 - 17:12:57
    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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    [url=mailto:bschwabe@parallax.com]Beau Schwabe[/url]

    IC Layout Engineer
    Parallax, Inc.

    Post Edited (Beau Schwabe (Parallax)) : 6/12/2010 5:17:54 PM GMT
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,565
    edited 2010-06-12 - 17:31:07
    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 SchwabeBeau Schwabe Posts: 6,420
    edited 2010-06-12 - 17:51:56
    "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!! smile.gif

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    [url=mailto:bschwabe@parallax.com]Beau Schwabe[/url]

    IC Layout Engineer
    Parallax, Inc.
  • LeonLeon Posts: 7,620
    edited 2010-06-12 - 18:34:13
    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
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  • Beau SchwabeBeau Schwabe Posts: 6,420
    edited 2010-06-13 - 03:22:51
    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

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    [url=mailto:bschwabe@parallax.com]Beau Schwabe[/url]

    IC Layout Engineer
    Parallax, Inc.
  • Cluso99Cluso99 Posts: 15,815
    edited 2010-06-13 - 08:14:48
    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,·RamBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)·
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    Post Edited (Cluso99) : 6/13/2010 11:07:28 AM GMT
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,565
    edited 2010-06-13 - 19:06:37
    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
  • Cluso99Cluso99 Posts: 15,815
    edited 2010-06-14 - 06:37:29
    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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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,565
    edited 2010-06-14 - 07:30:19
    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
  • Cluso99Cluso99 Posts: 15,815
    edited 2010-06-14 - 09:06:25
    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,·RamBlade,·SixBlade, website
    · Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
    · Prop Tools under Development or Completed (Index)
    · Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)·
    · Prop OS: SphinxOS·, PropDos , PropCmd··· Search the Propeller forums·(uses advanced Google search)
    My cruising website is: ·www.bluemagic.biz·· MultiBlade Props: www.cluso.bluemagic.biz
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