[GreenKeys] re Question regarding TWX and Dial TWX...

[Don Robert House]

Thanks Russ,
"For filling in the blanks."

While Answer-back mechanisms may not have been required for TWX to  
operate but every one of the machines had the assembly. I coded the  
drum for every customer.
The early DTWX Directories even showed what the answer message was,  
but later the codes were not published.  The customer made the  
decision of what the answer printed out.

I installed a 28ASR TWX at Hallicrafters in Rolling Meadows, IL.  Had  
to have two government security guys with me.  Go on, try to work that  
way!!!
The machine was special in that the cables that went to the 101B  
Dataset went thru a stainless steel box with 35 screws on it so that  
they could hook up a KW-7 crypto box.
HALLICRAFTERS would not fit on the drum, too many letters.  So I made  
up HALICFTERS but I was called back to change it to HALICRAFTR.

I kept having to go back to the installation because their technicians  
claimed the TD would not send.  The problem was that they were not  
providing a ground from the KW-7.
They would not believe me, so after one of them looked closely, I used  
a screwdriver to provide the ground and off went the tape.... after  
drawing an arc close to the man's nose.
I never got called back after that!

Memories, memories...

Don
K9TTY


On 23 Apr 2010, at 11:46 AM, wa3frp at aol.com wrote:



Let me try to fill in some of the blanks.

AT&T was in the TWX business and Western Union was in the Telex  
business.  TWX was used in North America only and at the end was  
composed of both baudot (3 row) and ASCII (4 row) machines. Telex was  
a worldwide network that was built to CCITT standards.

Since these two networks, TWX and Telex, started differently, there  
were integration issues. TWX did not require answerback mechanisms.  
Telex required that each machine have a unique answerback message.  At  
the beginning of the message, the sender would transmit a WRU (Who aRe  
yoU) code usually FIGS D, and the recipient machine would  
automatically initiate a response which was encoded in a rotating drum  
with pegs. The position of the pegs sent an unambiguous identifying  
code to the sender, so the sender could verify connection to the  
correct recipient. The WRU code would also be sent at the end of the  
message, so a correct response would confirm that the connection had  
remained unbroken during the message transmission.

In addition, the baudot versions used a slightly different speed.  TWX  
used 60 WPM (45.45 baud) just like Amateur Radio RTTY uses today.  
Telex was just a little faster at 66 WPM (50 baud).

TWX used the public switched telephone network. In addition to having  
separate Area Codes (510, 610, 710 and 810) for the TWX service, the  
TWX lines were also set up with a special Class of Service to prevent  
connections to and from POTS to TWX and vice versa.

By the time that I became involved in TWX, all of the loops were  
analog versus the 120 /240  VDC loops that Western Union had in place  
until the mid 1970s.

Telex used a network and switches that were built and dedicated  
specifically for Telex.  This statement is true for the Western Union  
and CNCP portions of the network in the States and Canada but it is  
probably true for the rest of the world.

The Western Union Telex loops came in two flavors: The first option,  
sometimes called local or loop service, provided a 60 milliampere loop  
circuit from the exchange to the customer teleprinter. The second  
option, sometimes called long distance or polar was used when a 60  
milliampere connection could not be achieved, provided a ground return  
polar circuit using 35 milliamperes on separate send and receive  
wires. By the mid 1970s, and under pressure from the Bell operating  
companies wanting to modernize their cable plant and lower the  
adjacent circuit noise that these Telex circuits sometimes caused,  
Western Union migrated customers to a third option called F1F2. This  
F1F2 option replaced the DC voltage of the local and long distance  
options with modems at the exchange and subscriber ends of the Telex  
circuit.

Western Union started offering connections from Telex to the AT&T  
Teletypewriter eXchange (TWX) system in May 1966 via its New York  
Information Services Computer Center. These connections were limited  
to those TWX machines that were equipped with automatic answerback  
capability per CCITT standard.

Western Union purchased the TWX system from AT&T in January 1969. See  
Western Union News Volume II, No. 4, January 15, 1969. The TWX system  
and the special area codes (510, 610, 710 and 810) continued right up  
to 1981 when Western Union completed the conversion to the Western  
Union Telex II system. Any remaining "3-row" baudot customers were  
converted to Western Union Telex service during the period 1979 to 1981.

Telex was very profitable for Western Union as it was making a margin  
of over 40% on revenues of 450M USD during the 1970s.  This was a  
higher profit margin than private wire which was basically break even  
and the telegram service which made some profit but nothing like 40%.

Deskfax was already on its way out by the mid to late 1960s when Telex  
was introduced. It also had limited use.  This was not typically a  
subscriber to subscriber service but a Western Union to subscriber  
service and a way for Western Union to get a printed telegram to a  
subscriber without manual physical delivery.

The Western Union involvement in Telex and Telex II service ended in  
July 1990 when WU reached agreement to sell its Business Services  
(Telex and EasyLink) unit to AT&T for $180 million cash.

Western Union had a virtual monopoly on Telex service in the USA but  
it did not have direct lines to other countries based on a 1939  
agreement. Companies such as RCA Global Communications (Globecom), ITT  
World Communications (Worldcomm), Tropical Radio Telecommunications  
(TRT) and others provided gateway services for Telex traffic to and  
from other parts of the world. In addition, these International Record  
Carriers (IRCs) had the right to offer Telex service in the cities  
where they operated.  This was basically in New York City for  
Globecom, Worldcom and Miami for TRT.

As Manager of Circuit Switching Systems, I was a part of the team that  
converted Delaware, New Jersey and Pennsylvania from TWX to Telex II  
in addition to my responsibilities for designing, implementing and  
operating the Telex network in those states. It was great to walk  
through a Telex exchange as it sounded like thousands of crickets and  
you knew that all of the "doorbell circuits" were working correctly  
just by the sounds of the exchange in operation. Bell System employees  
who worked in Number Five Crossbar know that I'm talking about.

73 de Russ WA3FRP


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