[Milsurplus] overheard telephone conversations

AKLDGUY . neilb0627 at gmail.com
Tue May 31 18:50:13 EDT 2016


The consensus seems to be that WW2 necessitated encryption
and spurred on its development, but there's nothing to suggest
that 1937 radio telephone calls were made unintelligible to the
casual HF listener.

It doesn't even seem clear whether SSB was used. Terrestrial
telephone links certainly used upper sideband in broadband
Frequency Division Multiplex systems pre-war, as I pointed out
in an earlier post where I described the Western Electric crystal
filters. I just now recalled that those filters had the ring modulator
or demodulator (depending on speech direction) built-in, together
with impedance matching transformers.

73 de Neil ZL1ANM


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