[Milsurplus] Was: Foxhole Radio - re: Receiver LO radiation

[Hue Miller]

An interesting item, I think: while the USA went to great lengths to specify
limits to receiver reradiation, the FCC even publishing a list of "safe" and
"unsafe" receivers, this did not seem to be a concern for other countries.
I have 2 regenerative ship's receivers from the U.K., WW2, one by Marconi
and one by International Marine Radio. Both have RF stages, of course, but
otherwise nothing special. I recall reading in some introductory book,
something like "Electronics for Everyone", that "when WW2 started, some
English ships still had simple regenerative receivers, with no isolation
stage, and those had to be replaced".  (Fairly accurate paraphrase.)  That
makes sense, the old WW1 era equipment could potentially be a liability
for that reason. But as you see, these older equipments were not replaced
by anything where extreme efforts had been made to totally extirpate
receiver reradiation. You can even see a video of a U-boat radio room,
where a R2 entertainment radio is playing, and this is just basically a
broadcast receiver, with one RF stage, no special measures.
Now back to crystal receivers. Any resonant antenna will reradiate power,
so yes, if you apply modulation to an antenna, like via a carbon microphone,
you can passively reradiate a signal, but now with your modulation added,
albeit at a very low level of power. This is the basic principle for the 
Soviet
Union's bugging of the "Great Seal" of the U.S. at the U.S. Embassy in
Moscow, circa 1956. In that case, the bug was some kind  of cylinder
resonant at a microwave frequency, and audio impinging on it altered
the cavity's response so as to modulate the reradiated RF.
-Hue