[GreenKeys] Economist on Telex

[Jim Haynes]

On Sat, 2 Feb 2008, Larry Tighe wrote:

> Question por favour,
>
> Was/is Telex DC all the way from one machine to the other? AFSK maybe in 
> between?  My RCA machines run at 66 WPM...Telex speed??
>
> Was Telex always dial-up?  Who were the Telex owners...RCA, W.U., Bell System 
> ??
>
> I'm firing up my two Model 15 RCA machines now and running some tape into 
> them from past W1AW transmissions....all this discussion has motivated me to 
> turn them on and "listen" :>)
>
> Lar
A good reference on Telex, if you can find it, is "Teleprinter Switching"
by Rossberg & Korta, published about 1960.  This discusses a number of
Telex systems of the world.  As for owners, remember that in Europe most
of the time the state-run post office operations also ran the telephone
and telegraph business.

Transmission was originally DC between the customer premises and the
switching office.  Transmission between switching offices could be
anything; probably lots of carrier systems operating on voice-grade
circuits.  Later there was no doubt AFSK transmission between customer
premises and switching offices, where voice-grade local loops were
available and there was objection to running high-voltage high-current
DC telegraph loops in the same cable with voice traffic for reasons
of crosstalk.  There was also some low-level DC operation in late days.

I have a late Telex machine which seems to have something like an RS-232
interface (but only the send and receive data leads, no others)  So it
could be used with a modem or with a low-level DC transmission system.

Western Union, after repeatedly being rebuffed in attempting to get the
government to force AT&T out of the TWX business, introduced Telex to
the U.S. as a competing service about 1958.  They seem to have used
mostly Siemens switching equipment; and originally bought some European
Telex teleprinters, but later used Model 32s and Model 15s geared for
50 baud.  W.U. was almost the only customer for the Model 32.

One thing Telex offered that TWX did not was international communication.
However W.U. was not allowed by the government to handle international
traffic, so it had to be handed off to the international carriers such
as RCA and Western Union International.

Standard Telex speed is 50 baud, 7.5 unit code, which gives about 66 wpm.
But so does the Western Union 45 baud, 7.0 unit code, so WPM numbers
can be ambiguous.