TELECOM Digest OnLine - Sorted: Re: Very Early Modems

Re: Very Early Modems
Mon, 16 May 2005 20:30:07 EDT

In a message dated 16 May 2005 13:14:42 -0700, writes:

> In the IBM history series by Pugh et al, they said IBM converted
> punched cards to paper tape for transmission in the 1940s. My guess
> is that that particular transmission used telegraph TTY lines (not
> voice) of either AT&T or Western Union. Recall that AT&T maintained
> telegraph long distance lines as part of carrier long distance
> circuits. Because of the low bandwidth, a telegraph channel could be
> carried on the low end of a carrier channel. Accordingly, no
> modulation was required and thus no modem needeed.

Telegraph circuits were widely used, both Morse and teletypewriter,
well into the 1950s and 1960s by news services, stock brokers,
railroads, pipeline companies and no doubt many other users. The use
of telegraphy pre-dated carrier systems and while many of the circuits
were later converted to carrier, many of them undoubtedly remained

There were also the TWX services (Bell) and Telex (Western Union)
which were similarly carried on telegraph circuits.

Incidentally, in later years Western Union was a big user of Bell
telegraph circuits, especially within a city but also many intercity
routes where they were either not able to finance their own circuits
to accomodate their growth or did not feel the rate of return would be

Wes Leatherock

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