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Comment by archo | Hacker News Reader

Hence the Crystal Set was born.

It's remarkable to see how crystal rectifiers played a crucial role in early radio sets--without external power.

> without external power.

The radio transmitter is the external power. The crystal set is a way to grab a tiny amount of the electrical power being paid for by whatever entity is running the transmitter. You can play around with the inverse square law and figure out how little power the set is grabbing, but it's working on the basis of what it does grab.

Reminds me a little of "The Thing"[1] — remarkable WWII-era passive listening device.

[1] https://en.wikipedia.org/wiki/The_Thing_(listening_device)

There is an excellent youtube series where "the thing" is recreated. There is a lot of subtle design involved.

https://www.youtube.com/watch?v=NLDpWrwijE8

A Crystal Radio Receiver, also called a Crystal Set : https://en.wikipedia.org/wiki/Crystal_radio

I made one in one of those electronic kits in the 80s that had springs you poked wires into. Pretty cool to pick up “the station” on am (there was no tuning I think loudest won)

I had one as well, but I recall a variable capacitor used for tuning.

Yep, the old Radio Shack 100-in-1 kits. Great fun (early to mid 70s for me).

I think mine was called "MyKit 100", no Radio shack branding.

There was a small booklet with circuits and connection lists, like 1-12-14 meaning that you where supposed to put wires between those connections.

Absolutely no explenation about how the circuits worked.

I'm not sure you can really do that now. There are far more non-voice things transmitted on AM frequencies, so there is a good chance that your not-very-selective home-made radio is picking up someones garage door opener as the strongest signal.

The FCC is rather prickly about electrical noise in the licensed bands, to the point companies have had to modify designs to not become impromptu transmitters on those frequencies. This is one reason power cords grow those little black cylinders called ferrite beads:

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

So, in theory, a crystal set should still be a good way to pick up conservative talk radio and sports talk and you kinda get the idea it wouldn't be a popular project for kids these days given the current media landscape.

Crystal sets are remarkably sensitive, though early radios were not very selective, which describes most of the issues with the first 20 years of radio.

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