Good afternoon, here in EN31do.

Please do not flame me. 

I have the top US Commercial 'Phone license (since 1954 - with radar
endorsement), extra ham radio license, and 40 years in broadcasting mostly
on the technical side. I am marginally conversant at best on digital
technology and modes - but still interested. I am not a CW fan because I
could never develop the coordination necessary; same reason that I could
never be a very good clarinet player. (I van not even make the "Vulcan"
sign!)

A question was asked and this is an insight.

A very long time ago I talked to an old ham that said he had done the razor
blade or equivalent receiving thing. I can no longer find my notes even
though I still have a crystal set diagram from a junior high teacher of
mine, a Mr. Harrison in the 1950 period of time.

The earphone, in his recounting, had come from a pilot that had been shot
down and somehow was not divested of that device before being incarcerated.

A corner of the blade was use against a dissimilar metal or even rust but
not corrosion. The usual filter capacitor was probably not present and in
effect is somewhat optional. My memory does not work for the aerial/antenna
but if the fence wasn't electrified that might be a possibility.

Selectivity was the strongest signal. Is this the "Luxemburg effect?"

There were many prison camps. No doubt there were different schemes for
reception when it could be done. Of course there is no "pat" answer but it
is interesting and not all things interesting are practical at all times.
Maybe this helps.

AND then there is the "stolen power" crystal set scheme which is one section
for the detection and another to provide a flimsy power supple for an FET or
some such.

73 - and happy New Year from Iowa, U.S.A.

Doc.