[Milsurplus] overheard telephone conversations

[Hubert Miller]

I wonder how much if anything of those FDM systems survives. Not very
practical for demonstration, i suppose. Compared to telco switching
equipment.
( A former co-worker has his own 1000 line telephone step-by-step (SXS)
'central office' on his property - calls it "Turnerville" ) 
-Hue 

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
AKLDGUY .
Sent: Tuesday, May 31, 2016 3:50 PM
To: milsurplus <milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] overheard telephone conversations

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