I'm running this on a Demo Board at 140MHz (Call Sign - KF7DHP), with a 2.7k ohm resistor from pin 7 to ground, and listening with a 2M receiver... and getting nothing. When I monitor the frequency, there's a slight increase of noise that continues for the duration of the .wav, but there's nothing decipherable.
I've tried being about four feet away from the demo board, and across a room. (about 25 feet), with the same results.
I don't believe that the PLL is broken; I can still get VGA and NTSC out of it. But not knowing for sure if the PLL is used on those, I can't say that I know it's still working for certain.
I guess it's also possible that my receiver is faulty, but I don't have another transmitter to test it with.
You should be able to receive it at 146.5 MHz (also on many other frequencies). The 140 MHz from CTRB is mixed with the 6.5 MHz CTRA. For narrow FM don't forget to decrease the deviation e.g.
FRQA := c6p500mhz + byte[p] << 10 'modulate carrier and amplify the sample
Thank you all for your help.
I got the Demo working on 146.50Mhz. I think that the propeller makes a pretty nice "Vader".
After that, I modified the demo to transmit my call sign (recorded by me in Audacity) every ten seconds. It works pretty well with an antenna about 4 inches long on my demo board.
Now, what would it take to push the propeller to decode FM on it's own? Is it fast enough to do that?
I apologize for the vagueness in my question, I had a long school day, and my brain wasn't processing very well.
I did mean "demodulating audio FM".
And don't worry, I only had it on for a few minutes. What would I have to do to make the propeller transmitter not bug the FCC?
I know that many people make their own transmitters for a "Treasure Hunt" game with directional antennas. Is it just the spectrum "splattering" or "jittering" that's the issue?
you really should not use the prop as a transmitter, unless you want a visit from the FCC.
I think if you want to do this sort of thing you are much safer operating under Part 15 (even if you aren't strictly complying with the antenna and power requirements) than in a Ham band. First of all, Part 15 has no requirements at all about the jitter sidebands. The Prop is an entirely legitimate transmitter under these low power below-the-radar rules. You do need to filter out the square wave harmonics because they'll be out of the allowed band, but the sidebands don't matter because the whole rule set is configured that your signal won't matter to the legitimate users no matter what a wreck it is. It's very unlikely, for example, that your 30 mW of prop-pin noise will annoy any of the legitimate users of, say, the FM broadcast band. By contrast, Hams are notoriously (and with good reason) jealous of the way their frequency allocations are used.
While the Part 15 limits are draconian the chances of getting caught if you stretch them a bit are actually very small, especially on the FM band where the whole point of FM modulation is that interference is rarely noticed. Not that I would *cough* advise such misbehavior, but if you're going to do it anyway I'd say do it on FM rather than Amateur 2M to avoid having a posse of DF antennas sniffing you out.
The Prop is an entirely legitimate transmitter under these low power below-the-radar rules. ...
No, it's not. Harmonics are only half the story. The problem with the Prop-as-transmitter is that PLL counter jitter splatters stuff all over the desired band and well outside of it. You can't produce a signal in the FM broadcast band without also affecting amateur radio, aviation, and marine radio, some of it being emergency frequencies. And which typical Prop users are adept enough with RF filters to limit out-of-band interference? It's not easy to do, especially at VHF frequencies and with the tools at a typical computer hobbyist's disposal.
In your 100 MHz example, the strongest birdies 1 MHz out are down 20 dB from the carrier, and all the rest are down > 40 dB. The odds of anybody more than a few feet from your setup ever detecting those signals is within the noise margin of zero. I would feel no remorse whatsoever about running that signal through a simple LC filter into a part 15 compliant antenna ... but then, it's not modulated.
You can't produce a signal in the FM broadcast band without also affecting amateur radio, aviation, and marine radio, some of it being emergency frequencies.
Well, you can if it's CW, but then you can't use cheap common receivers to detect it.
Comments
I've tried being about four feet away from the demo board, and across a room. (about 25 feet), with the same results.
I don't believe that the PLL is broken; I can still get VGA and NTSC out of it. But not knowing for sure if the PLL is used on those, I can't say that I know it's still working for certain.
I guess it's also possible that my receiver is faulty, but I don't have another transmitter to test it with.
I got the Demo working on 146.50Mhz. I think that the propeller makes a pretty nice "Vader".
After that, I modified the demo to transmit my call sign (recorded by me in Audacity) every ten seconds. It works pretty well with an antenna about 4 inches long on my demo board.
Now, what would it take to push the propeller to decode FM on it's own? Is it fast enough to do that?
BTW, you really should not use the prop as a transmitter, unless you want a visit from the FCC.
-Phil
I did mean "demodulating audio FM".
And don't worry, I only had it on for a few minutes. What would I have to do to make the propeller transmitter not bug the FCC?
I know that many people make their own transmitters for a "Treasure Hunt" game with directional antennas. Is it just the spectrum "splattering" or "jittering" that's the issue?
I think if you want to do this sort of thing you are much safer operating under Part 15 (even if you aren't strictly complying with the antenna and power requirements) than in a Ham band. First of all, Part 15 has no requirements at all about the jitter sidebands. The Prop is an entirely legitimate transmitter under these low power below-the-radar rules. You do need to filter out the square wave harmonics because they'll be out of the allowed band, but the sidebands don't matter because the whole rule set is configured that your signal won't matter to the legitimate users no matter what a wreck it is. It's very unlikely, for example, that your 30 mW of prop-pin noise will annoy any of the legitimate users of, say, the FM broadcast band. By contrast, Hams are notoriously (and with good reason) jealous of the way their frequency allocations are used.
While the Part 15 limits are draconian the chances of getting caught if you stretch them a bit are actually very small, especially on the FM band where the whole point of FM modulation is that interference is rarely noticed. Not that I would *cough* advise such misbehavior, but if you're going to do it anyway I'd say do it on FM rather than Amateur 2M to avoid having a posse of DF antennas sniffing you out.
-Phil
http://forums.parallax.com/showthread.php?141538-Fm-transmitter-can-you-make-it-with-prop-chip&p=1114675&viewfull=1#post1114675
In your 100 MHz example, the strongest birdies 1 MHz out are down 20 dB from the carrier, and all the rest are down > 40 dB. The odds of anybody more than a few feet from your setup ever detecting those signals is within the noise margin of zero. I would feel no remorse whatsoever about running that signal through a simple LC filter into a part 15 compliant antenna ... but then, it's not modulated.
You can't produce a signal in the FM broadcast band without also affecting amateur radio, aviation, and marine radio, some of it being emergency frequencies.
Well, you can if it's CW, but then you can't use cheap common receivers to detect it.