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.
Raspberry Pi Pico as AM Radio Transmitter
21–30 of 38 posts
Re: Raspberry Pi Pico as AM Radio Transmitter
#22Earlier quoted context omitted.
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.
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).
Transmitting on AM broadcast frequencies is generally prohibited unless it meets an extremely low-power exemption , even if you have amateur license(I have a Japanese amateur radio license). A practical way to reduce risk is to put a large resistor before the antenna so the radiated power stays within that exemption. You could start with 100 MΩ; if the receiver cannot pick it up, try 10 MΩ, and so on.
Re: Raspberry Pi Pico as AM Radio Transmitter
#23FM radio with an ATTiny: https://spritesmods.com/?art=avrfmtx
Something similar: https://www.youtube.com/watch?v=7t7_naYJnHo
Source code can be found here: https://github.com/spookysys/attiny-synth
Re: Raspberry Pi Pico as AM Radio Transmitter
#24If 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.
Re: Raspberry Pi Pico as AM Radio Transmitter
#25This 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 t…
GSMem (2015) 1-5.5m/30m with 3G from the RAM bus TEMLEST-LoRa (2025) 87.5m with LoRa over display cables LoPHY (2024) 700m with LoRA MAGNETO (2021) CPU-generated magnetic fields "Rowhammer for qubits" describes hypothetically using electron tunneling and magnetically biased bit flips in standard RAM to simulate quantum operators. I've heard stories of ham radio clubs teaching how to make a coaxial antenna out of coax…
>I've heard stories of ham radio clubs teaching how to make a coaxial antenna out of coaxial cable (cable TV copper cable)
That's Teleco 101, basically the first lessons from a Teleco trade/vocational degree. And OFC known at any electrician degree.
Re: Raspberry Pi Pico as AM Radio Transmitter
#26The 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-...
Re: Raspberry Pi Pico as AM Radio Transmitter
#27You think that's fun, rpitx will blow your mind: https://github.com/F5OEO/rpitx
The 101things radio stuff is super cool too!
Re: Raspberry Pi Pico as AM Radio Transmitter
#28[dead]
Re: Raspberry Pi Pico as AM Radio Transmitter
#29Earlier quoted context omitted.
On off keying at 1,000khz is AM transmitting though?
AM is short for Amplitude Modulation, and by definition needs a carrier wave. This is more like controlled interference, still impressive though.
But on-off keying is amplitude modulation… just with a 100% modulation index..
Re: Raspberry Pi Pico as AM Radio Transmitter
#30I 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,…
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.
If you're interested in this I definitely recommend you look into amateur radio licensing. I took mine a few years ago simply out of interest, and I learned so much from the advanced course.
VHF and UFH are so deeply embedded in technology we almost forget it's there. It's fun to sweep for other peoples environmental sensors in your neighbourhood, even more fun to track and listen to satellites as they pass overhead.