alt Hacker NewsRaspberry Pi Pico as AM Radio Transmitter
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The RP2350 can write at 175MB/s using the HSTX, https://github.com/steve-m/hsdaoh-rp2350 more than enough for SDR.
https://www.digikey.com/en/maker/tutorials/2025/what-is-the-...
You think that's fun, rpitx will blow your mind: https://github.com/F5OEO/rpitx
I don't mean to pick on the author... but there are some common LLM-isms in here which are really starting to annoy me:
return (int64_t)(now_us - deadline_us) >= 0;
return now_us >= deadline_us;
return now_us > deadline_us;
The weirdly pedantic use of stdint.h types with unnecessary casting is another LLM-ism I see more and more. Passing int8_t to a function by value is really weird... and the second half of this conditional:
if (midi_note < 0 || midi_note > 127) {
None of this is a huge problem on it's own. But the cognitive cost of a million odd little things like this adds up really quickly across a large codebase when you're trying to debug something.
Please use an appropriate filter for the band that you are transmitting, otherwise you will pollute all the near frequencies with spurious.
Given GPIO frequency limits, reproducing a beautiful sine wave for a 1000 kHz carrier is a real challenge. He should borrow an oscilloscope and measure the output waveform.
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?
If you use GNU+Linux/BSD or anything with an X server, by tweaking the modelines you can broadcast a song over AM by using harmonics from your screen.
Search for Tempest for Eliza.
This is the first use people cooked up for the MITS Altair computer, which at the time could only output to its blinkenlights without expansion. Before a tiny company called Micro-Soft released BASIC for the thing, some madlad at the Homebrew Computer Club found a way to spin the CPU in loops tight enough that the interference could be picked up as tones on an AM radio, allowing for music to be created. Good to see the old traditions are still alive.
> Raspberry Pi Pico as AM Radio Transmitter
The fact that you are receiving it with an AM radio, doesn't mean that you are transmitting AM.
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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...