ateijeiro0
15 HN mentions · mentioned in 14 months, 2017–2026
1:39 · 1.7M views · Dec 31, 2012
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.
HN commenters bring it out whenever AM radio, strong transmitters or accidental demodulation comes up, as the classic example of grass playing radio.
15 comments from Hacker News
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.
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
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
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
(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]