[GreenKeys] [External] How were teletypes connected across long distances?

[Nick England]

For the gory details, see chapters 11-14 of the AT&T "Green Book"
https://long-lines.net/sources/att_principles_ocr.pdf

Nick England K4NYW
www.navy-radio.com


On Fri, Nov 24, 2023 at 11:34 AM Jones, Douglas W <douglas-w-jones at uiowa.edu>
wrote:

> From: Chuck Robertson [hootsk at gmail.com] -- Friday, November 24, 2023
> 8:58 AM
>
> > If they didn’t have modems or routers, and the machines send and receive
> only by 110v current, does that mean there were dedicated wires across long
> distances between cities,
>
> You need to remember that Teletypes were developed in an era when there
> was a developed telegraph network.  Teletype signalling was designed to be
> compatible with the existing Telegraph network.
>
> Now, go back an extra 75 years or so to what Samuel Morse actually
> invented.  Morse and Joseph Henry traveled back from Europe on the same
> boat, and fell into discussions of the whole idea of telegraphy.  Henry
> knew more about electromagnets than just about anyone, and Morse was
> inspired by the relay stations of the French optical telegraph, where a man
> with a telescope would read the signals sent from a distant hilltop and
> work the levers to relay that signal to the next hilltop.  Read the Count
> of Monte Cristo for a cute story about hacking that communications system.
>
> Anyway, out of that sea voyage came the electromagnetic relay, the key to
> the success of Morse's new telegraph network.  Every five miles or so, the
> telegraph line came to a relay station with a battery of crows-foot cells
> providing power for the loop to the next relay station.  At the heart of
> each relay station was one of Henry's newly invented relays, sending the
> signal onward to the next station.  That system was essential to Morse's
> first long distance telegraph line from Baltimore to Washington DC.
>
> Had he tried to do it with just one battery of cells somewhere along the
> line, getting the signal through would have required thousands of volts and
> risked the lives of the telegraphers.  With relays, the local battery at
> each relay station could be modest, only a few tens of volts.
>
> Properly adjusted relays can easily send data at 50 or 100 bits per
> second.  The telegraph network relied on patch panels for switching, to the
> extent that switched signals were used.  That continued to be the case with
> early teletype networks.  Most telegraph lines were unswitched, with
> signals taken down by a telegrapher on paper and handed to the telegrapher
> on the outgoing line.  When teletypes began replacing telegraphers, paper
> tape could be torn from a receiving teletype and carried to an outgoing
> teletype for transmission.  No change in the wiring was required.
>
>                Doug Jones
>                jones at cs.uiowa.edu
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