[Milsurplus] is that an oscillator I hear whining?!

[Richard Brunner]

This is an interesting subject I have been following for some time.  It ha=
s been 
believed in our electronic community that the Germans did df'ing on receiv=
er 
radiation, but I have been hard put to confirm it.  I have corresponded wi=
th 
Germans, and there is no evidence that it was done on a routine basis, tho=
ugh it 
could have been done on individual initiative.  They certainly knew about =
it, but 
believed one would have to be in the close vicinity of the ship to hear an=
ything.  
There was a magazine article in the late 1920's reporting that ship operat=
ors could 
hear receiver radiation up to 30 miles at sea, so that is a reasonable ran=
ge for 
regenerative receivers.  Using underwater listening ger=E4te/apparatus, su=
bs could 
hear ship's screws from 20 to perhaps 50 miles, (50 miles is debated) so t=
here 
would be no advantage in listening for receiver radiation.   Some German C=
O's 
were paranoid with fear that we were df'ing on their receiver radiation, a=
nd made the 
RO's shut down, and we weren't listening either.

Our navy did indeed insist on very low receiver radiation levels, but I th=
ink it was 
mostly for electromagnetic compatibility.  With many receivers running on =
a ship, 
you can't have them listening to each other's local oscillators.  Peter Wr=
ight's book 
was also very close range detection, perhaps a few hundred feet.

Tsch=FC=DF/Cheers
Richard Brunner, AA1P

European countries did indeed have radio vans to detect unlicensed receive=
rs, and 
would cruise up and down streets looking for it.  This implies very close =
range 
detection, because they would have to match taxed addresses with receiver 
radiation.  




> 
> Peter Wright's book _Spycatcher_ talks in some detail about 
> finding spy rigs in WW II by listening for the receiver LO.
> And, of course, this is just TEMPEST at work. 
> 
> -- 
> Mike Andrews
> mikea@mikea.ath.cx
> Tired old sysadmin since 1964
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