Build a radio wave detector with balls of aluminum foil | Hacker News Reader

Build a radio wave detector with balls of aluminum foil

wired.com

71 pointsBrajeshwar21 comments

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Wait, so you're telling me that my hat instead of stopping mind control attempts is actually AN ANTENNA?

Truth was bound to get leaked at some point. CIA had a good run.

MIT researchers discovered the truth years ago: tin foil hats may actually increase exposure to RF in some bands.

https://web.archive.org/web/20100708230258/http://people.csa...

do you find it funny?

Mehdi from electroboom did video on this, the range is few meters. If I remember correctly the spark breaks oxide layers and makes contact.

https://www.youtube.com/watch?v=VMkdnj698-0

Delightful! Thank you!

So much more fun than the article.

Mehdi from Electroboom and Michael from Vsauce are my two favorite bat shit crazy unhinged people of the internet.

Mehdi is such a wonderful educator! I wish I’d had him as a professor for whatever topic he’d be interested in teaching.

https://archive.ph/ea6TC

That voltage from the crystal creates an electric field, which exerts a force on free charges in the air. (There's always some free charges floating around, like electrons and ions.) These charges accelerate and collide with air molecules, kicking loose more free electrons that also accelerate and collide, and so on, in an exponential chain reaction. We call this an electron avalanche. And guess what happens? Accelerating charges create a changing electric field—which, yup, creates a changing magnetic field, etc., and that disturbance radiates outward as an electromagnetic wave.

Huh? It has nothing to do with "free charges in the air." That's... kind of the whole idea behind EM theory.

That said, I've never heard of anyone building a detector out of balls of aluminum foil, so that's pretty cool. I'd classify it as a rectifying detector rather than a coherer, though, because nothing is physically moving. A real coherer had to be physically bumped or tapped between received signals.

That is how air becomes conductive.

Electromagnetic waves can exist in vacuum. No (conductive) air is required.

This coherer also must be bumped between received sigs.

I suppose what he is saying is that the crystal creates an electric current in some conductor. That conductor then has an electric field around it. If you had some charged particle nearby there could be a force exerted on it. That author then says "charges accelerate and collide with air molecules". Strictly speaking this is true.

But this description sounds more like a particle accelerator and less like anything to do with radio waves. All of this stuff is irrelevant. As you've pointed out, you could just as easily put the crystal in a vacuum and get RF emissions from it.

Yeah, this write-up seems to be confusing a townsend avalanche (what it describes) with far field electromagnetic wave propagation (an entirely different thing).

Jagadish Bose's Mercury coherer , which had the additional property of being self restoring, was "adopted" by Marconi for his radio receiver. Jagadish Bose had no interest in commercialising or patenting his design. It's history is somewhat of a sore point. Most Bengali's believe J.C. Bose was ripped off and not given due credit.

"Sir J C Bose's Diode Detector Received Marconi's First Transatlantic Wireless Signal of December 1901 (The “Italian Navy Coherer” Scandal Revisited)" https://www.tandfonline.com/doi/abs/10.1080/02564602.1998.11...

Non paywalled link https://www.cse.iitm.ac.in/~murthy/sirjcbose.pdf

https://en.wikipedia.org/wiki/Jagadish_Chandra_Bose

Anyhow, rather than grains and gravels of metal that had to be physically separated by tapping, the oil-film-over-mercury would reset on its own due to surface tension when the EM stimulation ceased. This allowed for higher "Baud".

I don't think a radio wave detector would ever stop detecting these days, unless you put it inside a faraday cage

Remember kids: radio antennas are detecting and using free energy from radio waves :)

Its literally 120 years old invention

Is circuit from picture suppose to be open? Or close one end of plug to the negative?

With this tiny setup what is the distance? Or need to have light very close to cup.

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