Discussion

Raspberry Pi Pico as AM Radio Transmitter

juancn: I don't get why PWM wouldn't work? Would the harmonics make the tuner ignore the signal?Because the speaker is still slow, so if it got to it, there should be audio, but maybe the circuit filters out the PWM signal outright?

nom: https://vanhunteradams.com/Pico/AM_Radio/AM.html

pesfandiar: Highly recommend his Pico-based microcontroller course: https://www.youtube.com/playlist?list=PLDqMkB5cbBA4GisLzRSqw...The PWM-based modulation is interesting, but as an amateur, I couldn't fully understand it or trust that the radio receiver reliably picks up the duty cycle as amplitude.

lormayna: Please use an appropriate filter for the band that you are transmitting, otherwise you will pollute all the near frequencies with spurious.

hulitu: > Raspberry Pi Pico as AM Radio TransmitterThe fact that you are receiving it with an AM radio, doesn't mean that you are transmitting AM.

tejtm: "A rose by any other name would smell as sweet" -- Bill

mk_stjames: I want to point out that what keeps this 'OK' is that the little wire is so 'electrically short' compared to the actual wavelength at 1000khz (a real quarter wave antenna at that freq is like 75 meters)... and thus this limits the power of this 'transmitter' to probably nanowatts.If the PIO pin could drive a fair amount of current at 3.3v into a long enough wire at that frequency you'd start to get into milliwatts, and AM radio is NOT a band that even amateur license operators can broadcast over a a certain power on. FCC part 15 dictates no more than a 3 meter antenna for personal devices at AM frequencies which is what does the power limiting essentially.The harmonics fall off quick enough on such a setup that it wouldn't really be a problem - but the only way to really KNOW that is to have a real solid understanding of how this 'radio' you've just made is working, meaning how that square carrier wave is really being driven off the PIO pin, and thus you need the requisite EE knowledge and/or ham radio test equipment and experience.I've seen more and more of these 'ChatGPT coded up a radio transmitter' posts and it kinda rubs me the wrong way. I'd like to see more calculations and disclaimers for people showing some responsibility with radio, and if it drives people to studying and taking an amateur radio license test that would be for the better...

pesfandiar: Mea culpa.Without the proper knowledge or measurement equipment, I observed that the audio would fade out after a 30 cm distance. Combined with running it for mere seconds to test and record a demo, I assumed to be in the clear with the spirit of the regulations. Appreciate the reminder to be responsible with RF.

mikeyouse: On off keying at 1,000khz is AM transmitting though?

crims0n: AM is short for Amplitude Modulation, and by definition needs a carrier wave. This is more like controlled interference, still impressive though.

anfractuosity: If you PWM a signal, I presume you could add a filter to convert to amplitude changes?

peterbmarks: You think that's fun, rpitx will blow your mind: https://github.com/F5OEO/rpitx

cadr: I don’t know what the regulations are in your country (looks like you are maybe in Canada?), but in many countries it is straightforward to get an amateur radio license, and then you can have all sorts of fun (under the rules).