[HN Gopher] Raspberry Pi Pico as AM Radio Transmitter
___________________________________________________________________
Raspberry Pi Pico as AM Radio Transmitter
Author : pesfandiar
Score : 53 points
Date : 2026-03-01 00:26 UTC (3 days ago)
(HTM) web link (www.pesfandiar.com)
(TXT) w3m dump (www.pesfandiar.com)
| hulitu wrote:
| > 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.
| tejtm wrote:
| "A rose by any other name would smell as sweet" -- Bill
| mikeyouse wrote:
| On off keying at 1,000khz is AM transmitting though?
| crims0n wrote:
| AM is short for Amplitude Modulation, and by definition needs
| a carrier wave. This is more like controlled interference,
| still impressive though.
| bitwize wrote:
| 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.
| westurner wrote:
| 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 coaxial cable (cable TV copper cable)
|
| "Can you hotwire this computer to transmit a tone through the
| radio?" -- Transformers (2007)
| mschuster91 wrote:
| > GSMem (2015) 1-5.5m/30m with 3G from the RAM bus
|
| What the fuck, that's crazy. For those similarly bewildered,
| look here [1].
|
| [1] https://www.usenix.org/conference/usenixsecurity15/techni
| cal...
| anfractuosity wrote:
| Based on a repo I found that twiddled the memory bus, I
| transmitted audio from a wav file via Pulse Density
| Modulation - https://github.com/anfractuosity/musicplayer
| anthk wrote:
| >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.
| juancn wrote:
| 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 wrote:
| https://vanhunteradams.com/Pico/AM_Radio/AM.html
| pesfandiar wrote:
| 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.
| anfractuosity wrote:
| If you PWM a signal, I presume you could add a filter to
| convert to amplitude changes?
| lormayna wrote:
| Please use an appropriate filter for the band that you are
| transmitting, otherwise you will pollute all the near frequencies
| with spurious.
| mk_stjames wrote:
| 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 wrote:
| 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.
| cadr wrote:
| 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).
| tl2do wrote:
| 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
| MO; if the receiver cannot pick it up, try 10 MO, and so
| on.
| alnwlsn wrote:
| At least you _are_ supposed to be allowed to transmit on AM
| (and FM) bands at very low power, at least under FCC rules.
| That 's how they can sell those adapters for car radios. Some
| other ones you definitely are not supposed to use as far as I
| know, like the old analog TV signals - I've seen a couple of
| those sorts of projects recently. On the other hand, you can go
| and buy an illegal TV transmitter on Amazon right now.
|
| Also a reasonably even bet that you already own a low-quality
| wall power supply that will produce more interference than
| anything you're going to be doing with a Pico and a 4" jumper
| wire (I've found a couple of offending devices in my house),
| but I'm certainly in no position to tell you if you should or
| shouldn't do something.
| fainpul wrote:
| FM radio with an ATTiny:
|
| https://spritesmods.com/?art=avrfmtx
| gsliepen wrote:
| Something similar: https://www.youtube.com/watch?v=7t7_naYJnHo
| Source code can be found here:
| https://github.com/spookysys/attiny-synth
| peterbmarks wrote:
| You think that's fun, rpitx will blow your mind:
| https://github.com/F5OEO/rpitx
| tl2do wrote:
| 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.
| anthk wrote:
| 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.
| genxy wrote:
| 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-...
___________________________________________________________________
(page generated 2026-03-04 23:00 UTC)