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Comment by varispeed | Hacker News Reader

Remember schematics for radios powered just by radio waves. No need for battery or hand-crank. That was in some old books, but never managed to build one.

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I could be wrong but I think that only works for AM, not for FM.

supposedly you can demodulate FM with "slope detection", off tuning slightly so as the signal varies in and out of the resonance of the tuned circuit you can get an audio signal. Its gonna be mono lol. The "Q" of the tuned circuit needs to be pretty good and its interesting to see that they use copper tubing as the coil wire or more technically in the linked page, a resonator.

https://electronbunker.ca/eb/FMCrystalSet.html

That's AM crystal radio but there aren't that many AM stations left these days, most have been torn down because (thanks to AM) they need insane amounts of power to be receivable across larger distances.

Not in the USA. We still have 50,000 watt clear channel stations. On a clear winter night, local lore has it that WJR-760AM Detroit could be heard in Mexico. Crystal radios still work...well, not fine, but as good as they ever did. AM frequencies are low enough they skip off the ionosphere.

I remember a family road trip from Chicago to South Carolina in our '77 Impala wagon, when my whole family was listening to a DePaul basketball game on WBBM Chicago. My dad was a big fan. It was late at night, and the game came down to the last shot in the last second or so. The station was barely coming in, so we pulled over and heard DePaul win on a buzzer-beater... then the station blinked out. It was perfect.

I always think about this when I see another story about AM's demise.

> We still have 50,000 watt clear channel stations

On shortwave, we even have 250,000 W transmitters just blasting RF everywhere.

We call them flame throwers for a reason.

Mmm, I think you may have AM and FM reversed there. If I remember correctly, FM only goes 65 miles or so, but AM can go thousands of miles under the right conditions (at night, mostly).

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