[Milsurplus] overheard telephone conversations

[AKLDGUY .]

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
>