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...
alnwlsn 60 minutes ago [-]
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.
pesfandiar 2 hours ago [-]
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 51 minutes ago [-]
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 44 seconds ago [-]
Transmitting on AM broadcast frequencies is generally prohibited unless it meets an extremely low-power exemption (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.
tl2do 12 minutes ago [-]
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.
lormayna 2 hours ago [-]
Please use an appropriate filter for the band that you are transmitting, otherwise you will pollute all the near frequencies with spurious.
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 2 hours ago [-]
If you PWM a signal, I presume you could add a filter to convert to amplitude changes?
bitwize 4 hours ago [-]
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 2 hours ago [-]
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)
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...
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.
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.
https://spritesmods.com/?art=avrfmtx
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?
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.
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)
What the fuck, that's crazy. For those similarly bewildered, look here [1].
[1] https://www.usenix.org/conference/usenixsecurity15/technical...
The fact that you are receiving it with an AM radio, doesn't mean that you are transmitting AM.