Crystal set without crystal ?

[60 oldjohn]

Is it possible to make a receiver without crystal, ie just a razor blade on a wire for the detector. I think I may remember seeing it in the Colditz. fact or film makers stretching the truth?

John.

[paulsherwin]

It's possible to make a detector like this, though it's very tricky to get right and it won't be very efficient. If they were shown using it to listen to the BBC in Colditz Castle then I'd say dramatic licence was definitely being used.

[G6Tanuki]

There are loads of non-traditional things you can use as detectors in crystal-sets.

A search for "foxhole radio" will turn up plenty of references/examples/circuits.

[60 oldjohn]

Thank you, I may have been able to answer my own question, During the war my father lived 1 mile from a high power propaganda transmitter, he heard "voices" coming out of a bucket that was touching a wire fence.

John.

[paulsherwin]

There are stories of people living near to Droitwich hearing sound coming from their gas cookers.

[ms660]

And their teeth fillings.

Lawrence.

[Boater Sam]

And their bike frames when they rode between the masts!

[Peter.N.]

Same thing from Fort Halstead, one of our customers was picking up sounds on her bed springs.

Peter

[David G4EBT]

There's an interesting and instructive paper on razor blade detectors and POW radios here:

http://rageuniversity.com/PRISONESCA...l%20Radios.pdf

There are YouTube videos of razor blade detectors in action too, some more successful than others.

I think a lot of the claims about 'foxhole radios' are urban myths which don't stand close examination.

They infer that soldiers pinned down in foxholes in battlefields had the time and inclination to fiddle around with razor blades, pencils, safety pins, cardboard tubes, silver paper, copper wire, drawing pins, bits of wood and the like, and just happened to have these items to hand, along with high resistance headphones or a crystal earpiece, to construct a working radio to enable them to keep up with news broadcasts. Battlefields did rather tend to be a tad noisy too, and guys tend not to linger around too long in one place.

A tour of any of the many battlefields of Europe would soon dispel the myth of the 'foxhole radio'. POW radios? Possibly. I've visited Colditz Castle Museum and they do have one on display there. (Well they would have, wouldn't they?).

Neverthless, a 'crystal' set using a blued razor blade as an alternative to a crystal is an interesting project and there's doubtless much fun to be had from experimenting to prove that such a radio can indeed be made - least ways, on the kitchen table in the safety of one's home - if not in a 'muddy foxhole' in a WW2 battlefield under a hail of enemy gunfire!

[G6Tanuki]

If I was building such a radio my biggest issue would be getting hold of a good earpiece. In WWII-times you might have difficulty finding a telephone.

Crystal detectors are no big issue - I remember as a kid making a crystal-set and looking through the pile of coal delivered to my parents house in the hope of spotting that metallic glint of Iron Pyrites - "Fool's Gold" - which was what we all aspired to.

Galvanised Iron, heated, also provided Zinc-oxides which can work well as a detector.

http://sparkbangbuzz.com/zinc-oxide-...xide-diode.htm

Indeed, zinc-oxide devices can - with a 1.5v cell - provide enough 'gain' to oscillate!

http://www.sparkbangbuzz.com/els/iposc-el.htm

http://www.sparkbangbuzz.com/els/zincosc-el.htm

[ms660]

We live on a pile of iron pyrites and probably several other metallic crystals, I reckon if I stuffed a headphone jack through the grass I'd hear some program or other.

Lawrence.

[60 oldjohn]

This question arose after a friend asked me the question, and I was not sure of the answer. I had not intended to make one but after reading the replies I may have a go.

John.

[Sideband]

I used a safety pin, a piece of lead from a pencil and a razor blade that had been heated in a flame. The pencil lead was bound to the safety pin with cotton (after cutting off the 'head') and the sharp end was pushed into one end of a piece of balsa wood about 4" x 4" x 1/2" The razor blade was mounted on the balsa wood with drawing pins so that the piece of lead on the safety pin could touch the razor blade and be 'adjusted' across the surface. This very crude detector actually worked when connected to a crude coil and a pair of high impedance headphones. The pencil lead was scratched across the surface of the razor blade for best reception a bit like the old original cats whisker type. The difficult part was getting a reliable connection to the safety pin.

That was my very first foray into radio when I was about 9 and I picked the idea up after reading a wartime story book....kids did things like that in the early 60's......!

[Biggles]

When I was first starting out in the hobby, and very young, I remember reading all about the coherer detector and decided to try building one, using iron filings in a tube, but needless to say I had no luck with it, totally failing to understand the mechanism of how it should work. Shortly after that I happened upon an old telly and discovered the delights of the yellow sleeved glass GEX34 diode. I had much more success with crystal sets after that. Living about 5 miles from Stagshaw 50Kw AM transmitter this was hardly surprising, even our telephone used to pick that up. Unfortunately at the time it used to broadcast BBC Radio 4, not a lot of interest to a 10 year old kid.

[short wave]

I have heard of using coke (not coal) and springy wire (not sure if copper or iron)

[Biggles]

I suspect quite a lot of different materials could be pressed into action for a detector. At the end of the day all you are looking for is some kind of non-linearity. Obviously some materials are better than others. I experimented a bit with different materials and have used original galena which was mined many years ago in the hills at Nenthead not far from me. There is an interesting mineral mining visitor centre too. Also plenty galena to be found "wild" on spoil heaps in the area if you have sharp eyes and a bit of patience.
Alan.