[defrost]

In an extreme emergancy (eg: captured in a POW camp) you might just have to build your own:

Queensland Prisoners secret radio revealed

>> Two Queensland brothers, Ernest and Charles Hildebrandt, built a secret wireless radio receiver which they operated in the camp near Bandoeng in Java which was overran by Japanese soldiers in 1942.

>> Constructed of parts scrounged from the internment camp where they were held prisoner in Java during the war, the transmitter was built into a Dutch gas-mask container and hidden under a square of concrete measuring 12 by 7 inches.

[*] https://blog.qm.qld.gov.au/2019/11/12/on-this-day-queensland...

[grendelt]

Scanning that article I was blown away to see it said "the transmitter..." - then I realized the author is play fast and loose with the terms transmitter and receiver (surprise! They aren't interchangeable!). It looks like a tube-based regen receiver.

In Europe, Allied POWs would build "foxhole radios" which had no selectivity and you'd hear the strongest signals best - and during WW2, that was the BBC.

[user3939382]

> which had no selectivity

All of the foxhole radio designs I've seen actually do have an (albeit very crude) way to select a frequency. Maybe all the designs I've seen aren't faithful to the ww2 versions?

[grendelt]

I mean, if you could get your hands on a variable capacitor, you're in business. That was unlikely to be an item you could scrounge up though. The guys in the article managed to find a tube and other parts, so that's quite impressive, but you can still get more minimalist.

The most basic is a length of wire wound around a coil form (toilet paper tube, plastic bottle, etc), the "detector" was a blued steel surface (DE safety razor blade), a safety pin to act as a "cats whisker" (bonus if you can use graphite pencil lead attached to it), some high impedance headphones (WW2 tanker/air crew headsets usually fit the bill), a good ground and as much wire for an aerial/antenna as you could get away with.

Using the length of the coil, and where you connected the antenna, you could kinda-sorta tune for better efficiency at different parts of the band (be it SW or AM). (Longer coil = lower freq)

I made a few of them years ago, and posted the results on my now-defunct blog. The DB is still intact with my files and findings, but my code base is hosed (need to remake it).

[HillBates]

Coverage of earth by earth sensing satellites in visible spectrum is so high, that you can literally write different message into sand / earth every hour. No radio construction necessary XD

[junon]

Someone needs to be looking, though.

[mrslave]

And someone less desirable could also be looking.