[GreenKeys] "Long Lines" sign

[Sheldon Daitch]

David,

Nice description of the undersea cable configuration.

FDM was also used on radio systems, although at not
nearly the channel capacity capable on a coaxial cable
system.

One interesting comment was the reference to the
SSB makeup of an FDM system, and the "complaints"
that are sometimes heard in other forums regarding how
AM and SSB have poor frequency response and have
high distortion factors.  In working with program grade
FDM channels, for broadcast use, any limitations for
AM and SSB transmit/receive systems is really a
function of the equipment itself, not that the
mode is SSB.

One small note, tho, is that the AT&T Long Lines
did not necessarily mean really long distances.  IIRC,
AT&T Long Lines was the radio and multiplex side
of the company.  The Bell Operating Companies
were wholly owned by AT&T, to operate the
central office equipment and the subscriber circuits,
while AT&T Long Lines was the carrier between
the toll offices.  In reality, it was really one large
organization, but legally, they were different
organizations.

Good write-up,

73
Sheldon





David Ross wrote:

> greenkeys folks -
>
>   Re the "Long Lines Department" sign -  I believe that "Long Lines" was
> a division of Bell Telephone that had to do with long-haul telephone
> multiplex transmission.  A friend of mine used to work for Long Lines -
> he worked with the transpacific telephone cable which terminated near
> Los Osos, CA.
>   Back in 1979 I got a tour through that cable's terminus in Los Osos
> Valley, CA -  really fascinating.  It was a "Frequency Division
> Multiplex" system, a totally analog scheme which stacked up multiple
> single-sideband conversations and piped them in/out over a coaxial
> cable.
>   Bear in mind that this was a very looooong cable -  ran from
> California's central coast direct to Guam & then on to Japan (if memory
> serves).  Built into the cable were many many vacuum tube repeaters,
> necessary to boost that wideband analog signal over that distance.  The
> repeater's power circuits were arranged in series and were powered by a
> current source & current sink at opposite ends of the cable -  the
> current source was of pretty low amperage, but one end had a voltage
> compliance of like +3000 Volts and the other end had a voltage
> compliance of like -3000 Volts -  necessary to run all those repeaters
> in series in that undersea cable.
>
> 73
> Dave Ross    N7EPI    ross@hypertools.com
>
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