Construction of radio equipment in a Japanese PoW camp | Hacker News Reader

Construction of radio equipment in a Japanese PoW camp

histru.bournemouth.ac.uk

157 pointsmarcodiego21 comments

Prisoners in the stalag camps in germany/poland did a trick with a rusty iron surface and a razorblade making a point contact junction diode of some kind, maybe morally closer to a crystal radio coherer. The "foxhole" radio is how its described.

The camps in Asia had amazing handicrafts, they made artificial limbs out of bamboo, surgeons tools made out of kitchen implements, colostomies were done and people used mess tins in place of a colostomy sack, "the war diaries of 'weary dunlop'" are well worth reading (Edward Dunlop was a surgeon in changi pow camp)

Ronald Searle (a British cartoonist) was also in the camps and drew some truly amazing portraits and scenes.

This one in italy: https://www.bbc.co.uk/history/ww2peopleswar/stories/70/a4127...

Colditz I think they repurposed a car alternator as a static-bicycle generator. They had a lot of space inside a stone structure to hide things.

I'm unable to look it up right now, but there is an excellent video of a man touching a long grass stalk to (what I presume) is an AM radio tower. The grass burns, and in the sizzling you can hear the radio station.

In principle, I think it's approximately the same theory of operation as the razor blade diode -- which is also similar to a "Cat's Whisker".

This: https://www.dailymail.co.uk/sciencetech/article-3276974/Incr...

Beware: RF burns take unusually long to heal. Also, the leaves are not working as the detector, they're an extremely inefficient speaker.

No, I think they actually are working as a detector, just a mechanical one!

The movement of the grass (relative to the surface of the tower) is not sinusoidal, it's clipped just like a diode rectifier -- and the grass' springiness acts like a mechanical capacitor, smoothing the motion out.

Interesting theory, but I'm still unconvinced.

AFAIK, the electric potential of the tower is a product of the signal that is being sent multiplied by the carrier wave. When the potential on the tower is high, it will burn the weed stronger; when the potential of the tower is close to 0, the rate of burn of the weed will not change. The burning weed will reproduce the potential of the tower: signal times carrier. Since the carrier is too high a frequency for our ears or the weed too, we only listen signal that is inside human hearing interval.

I think not only is the carrier too high for our ears to hear, but also too high for the grass to vibrate at. (500-800 kHz is pretty fast, Hence, the mechanical damping!)

I think I'm pretty close, but I need Smarter Every Day on this one!

the radio in that italy story didnt work

You have to read the second part: https://www.bbc.co.uk/history/ww2peopleswar/stories/89/a4127...

Moving.

> crystal radio coherer

I'm not sure there was such a thing. Coherers predated crystal detectors and from what I recall worked quite differently.

These guys in a Japanese PoW camp set up a workshop and built themselves a screwcutting metal lathe in secret: http://www.lathes.co.uk/bradley-pow-lathe/

It you like this don’t miss this page which has a lot of info but doesn’t seem to be linked from the Contents page:

https://histru.bournemouth.ac.uk/CHiDE/Oral_History_of_Defen...

It is linked from inside the page called “The Raid” and yes, possibly other places, but I’m linking it here because it is so easy to overlook with the sequential link scheme in the contents skipping over it.

I built a foxhole radio some years ago. Fun project when you’re not locked up.

https://blog.jgc.org/2012/02/my-foxhole-radio.html

Sort of reminds me how we constructed ham radio during socialism in 1980ties. Access to integrated circuits was restricted, we had to solder thousands of discrete parts, salvaged from old TVs and radios.

There is a book behind this whole event called the Perfect Raid (iirc). And a movie

https://www.youtube.com/watch?v=N51IAYnlNK0

What is a "valve" in this context? A transistor?

There were no transistors during WWII. (The first one was demonstrated in late 1947 apparently.) A valve is a vacuum tube (https://en.wikipedia.org/wiki/Vacuum_tube).

Ah bless, tell me your under 60 without disclosing your age.

Valves are still produced.

See https://www.europeanaudioteam.com/en/e.a.t.-kt88-diamond-val..., https://brimaruk.com/about-us/faqs-2/, etc.

Locality is more like it. Valves are what UK people call tubes.

A valve can refer to a vacuum tube or it can refer to a diode, which can be made from all manner of stuff such as razor blades, crystals, rocks. It's called a valve because of its rectifying behavior allowing current through in only one direction, this is also the reason for the diode's electronic diagram icon ---|>|---

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