Dave Marthouse wrote:
> Anyone who can shed light on this subject would be appreciated to
> help scratch my historical itch.
I pulled up the Bell System Eng & Science history and there is an
extensive chapter on radiotelephony and overseas calls. They go into
good detail on the technical challenges of high powered transmitters,
greatly varying originating voice signal strength, amplification, echo
control, 2-wire to 4-wire conversion, antenna design and construction,
signal propagation, etc. It is in the first volume of the series,
1875-1925. I strongly recommend it*. A large muncipal or college
library likely would have it.
As mentioned, they used both high and low frequency depending on
conditions. Channel capacity was very limited. It appears that
functions of radio transmission we take for granted today all had to
be worked out by them. It amazes me that a tiny little cell phone can
do everything (although at much lower power) they needed to do to send
and receive a telephone radio signal.
They DID use a basic encryption to provide some privacy by inverting
some frequency bands and "wobbling". As mentioned, a determined
listener could bypass that but a cascual listener would not hear
intelligable conversation. The book goes into detail on this process.
*I also recommend Vol 2 which covers 1925-1975. Lots of interesting
stuff on switching development. Vol 3 covers military applications
which I didn't find so interesting but there are chapters on military
radio development. At the beginning of WW II they experimented with
both AM and FM vehicle radios to see what was best. They also talk
about the challenges of dealing with sub-contractors meeting demanding
military specs. Equipment for the domestic market simply would
quickly break in the rough military environment.