1.7M views · Dec 31, 2012 · 1:39 · 0 HN recommenders · 15 mentions · discussed 2017–2026
Two experimenters hold blades of grass near a radio transmitter antenna and hear the AM station through the arc between antenna and grass. It is a short, informal demonstration of unintentional AM demodulation.
Why Hacker News points people here: HN commenters bring it out whenever AM radio, strong transmitters or accidental demodulation comes up, as the classic example of grass playing radio.
“AM radio is such a simple modulation scheme that even a piece of grass can be used to demodulate it, with enough power.”HN comment, 2022
“if you go down the rabbit hole, you end up here”
Grass demodulating an AM radio signal near a tower.
Not exactly what you were asking for, but made me think of these: link and link and if you go down the rabbit hole, you end up here: this video
“Also reminds me of this old video”
Audio from grass near an AM radio tower.
I suspect it's accompanied by some speakers too, because otherwise the sound would be a lot "emptier" and less bassy. Similar device: link Also reminds me of this old video: this video
“radio burns are super nasty.”
Grass picks up AM radio near a transmitter.
Reminds me of this - this video Obviously don't do this. I would be concerned about standing this close as well, radio burns are super nasty.
“your comment reminded me of this video”
Grass receiving AM radio near a high-power transmitter.
Fair point. Call it 60w or even 1w if that feels better. It's still many orders of magnitude over what you would be receiving across space from another solar system. Also, for mild amusement, your comment reminded me of this video this video
“AM radio is such a simple modulation scheme that even a piece of grass can be used to demodulate it, with enough power.”
Grass demodulating AM radio with enough transmitter power.
AM radio is such a simple modulation scheme that even a piece of grass can be used to demodulate it, with enough power. this video
“you can listen to AM radio by just touching the mast with any random item”
Touching a radio mast with grass to hear AM.
Well, if you're mad enough and don't care about trivial things like life, you can listen to AM radio by just touching the mast with any random item: this video
Example of audible AM radio from unintended objects.
I grew up in a house that was next door to a radio rebroadcasting facility, and we could definitely hear the radio station coming from the walls of our house sometimes, e.g. even their station identification so there was no ambiguity. I assumed it was the house wiring (mostly knob and tube) acting as an antenna. I'm reasonably sure that was AM, though. Was the sound you heard like either of these? link this video
“Heres an example of a thistle being used to convert an AM signal into audio.”
Plant touching broadcast tower demodulates AM into audio.
Certainly a brass headboard doesn't have a semiconductor in it. But that doesn't mean the story is bullshit. Just that it's not working in the way they think it is. Heres an example of a thistle being used to convert an AM signal into audio. Granted, they are touching the plant directly to the broadcast tower, and it's outputting enough power that it starts burning and even burns the hand of the person holding the plant. this video
“If there's enough power, everything turns into a demodulator...”
Anything becomes a demodulator given enough power.
I had two videos on my mind before I clicked that link. It was one of them. (The other one: this video ) If there's enough power, everything turns into a demodulator...
“In this video they can apparently hear the transmission by holding a blade of grass against the transmitter”
Grass appears to play AM radio, though commenter doubts it.
In this video they can apparently hear the transmission by holding a blade of grass against the transmitter this video The video looks convincing but it could also be faked, and I don't think it's possible. The signal coming into the radio tower (which is basically just a big antenna) would already be modulated to a much higher frequency (702khz or whatever). I guess there could be some other effect that makes it audible when you hold a blade of grass or a hotdog to the transmitter, but I don't think it would be intuitive.
“this old classic video of some intrepid guys getting tufts of grass to play music with the help of a radio tower.”
Old classic of grass playing music via a radio tower.
Reminded me of this old classic video of some intrepid guys getting tufts of grass to play music with the help of a radio tower. this video
Example of antenna very close to a radio tower.
Well, I'm expecting an average case, not "playing AM radio with grass", because in the vast majority of the cases, antennas won't be situated within a few meters of the radio tower: this video
“touching vegetation against a (presumably AM) radio mast.”
Vegetation against an AM mast demonstrating unintentional amplitude modulation.
(too late to edit) I remembered this example of "unintentional amplitude modulation" of a strong AM RF signal: touching vegetation against a (presumably AM) radio mast. "Listening radio with grass" this video link
“If you put random vegetation directly on the radio mast (NOT recommended!), it makes sound directly-”
Vegetation on a radio mast produces sound directly.
With enough power anything is possible... If you put random vegetation directly on the radio mast (NOT recommended!), it makes sound directly- this video
“you can listen to AM radio with grass”
We probably shouldn't deprecate AM for emergency broadcasts given you can listen to AM radio with grass this video
