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.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
For me, the past is not over yet.
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.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Leon Heller
Amateur radio callsign: G1HSM
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.
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.
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:
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 ??
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. 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.
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! )
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.
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.
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.
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 )
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.
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.
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.
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.
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 ..... )
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!
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:
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.
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. ...
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.
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!
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.
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.
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.
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.
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.
Comments
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.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
For me, the past is not over yet.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Leon Heller
Amateur radio callsign: G1HSM
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
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
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,·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
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.
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. 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
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! )
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.
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.
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.
Thank you, brilliant, I've never heard of Tayloe detectors before. What a fascinating read.
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
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.
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
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 ..... )
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
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.
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::
Thanks,
-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.
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
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.
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.
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
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.
V/R
Mike