[Milsurplus] overheard telephone conversations

[Nick England]

Info on the Bell A-3 frequency band scrambling voice secrecy system is
here. (The site is mostly about Germany breaking the system during WW2)
http://chris-intel-corner.blogspot.com/2012/02/intercepted-conversations-bell-labs-3.html

It isn't clear from what I have read whether this was in regular use for
trans-oceanic telephone calls or just for military/government channels.
More info is likely in
Bell Labs report ‘History of speech privacy systems-1970’,

Nick England K4NYW
www.navy-radio.com

On Mon, May 30, 2016 at 9:21 AM, AKLDGUY . <neilb0627 at gmail.com> wrote:

> How were they encoded?
>
> Be careful how you answer. You're addressing a former
> telecommunications technician, 1968-1984.
>
> When I was transferred into the long distance transmission
> division in 1975, there was a very old Western Electric
> system that had been in use back in the 1930s and was still
> being kept running as a standby in case of emergency.
> It was junked not long after, because by that stage we had
> enough diversity with multiple routes such as coaxial cable
> and microwave links out of Auckland.
>
> It was an industry-standard 60-108 KHz carrier system of
> 12 channels at 4 KHz spacing designed for open wire 600
> ohm line.
>
> Essentially it was an upper sideband broadband system,
> with crystal filters for each direction of speech, 24 filters
> in all. Each filter was in a sealed (soldered) copper case
> about a foot long, 4" wide, 5" high. I can't remember what
> tubes it used, but they were big glass ones like in radios
> of the early 30s.
>
> That was probably the state of telecommunications
> technology in the 1930s. I don't know whether SSB was
> used for those 1937 radio telephone links, but if it was,
> an enthusiast may have figured out that a BFO would
> allow reception.
>
> So I'm interested to hear what kind of encoding you
> think was used.
>
> 73 de Neil ZL1ANM
>
> On 5/30/16, Rob Flory <farmer.rob.flory at gmail.com> wrote:
> >  "Radio telephone communications opened in 1927 on a 24 hour
> >  basis, US-UK. By 1949, there were 70 radio telephone circuits for
> >  all 5 continents."
> >
> > They were encoded, so an enthusiast would not have been able to overhear
> > them.
> >
> > RF
> > <http://www.qsl.net/donate.html>
>
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