[GreenKeys] Telex/TWX?

[WA3FRP at aol.com]

Hi!   I'm a retired  Western Union guy!  I was responsible for Telex in PA, 
NJ and DE from the late 1960's through  the 1970s.  What a dream job for a  
young ham radio operator loved RTTY.  
Telex was either Telegraph or Teleprinter Exchange, depending on whom you  
ask. TWX was as George said Teletypewriter Exchange. 
Western Union Telex started in the late 1950s in the  USA using  Siemens 
central office equipment and as a satellite network of the existing  Canadian 
Telex Network.  
Telex was 5 level 50 baud, using CCITT codes.  Hams today use 45.45 baud 5 
level for  RTTY which was derived from the TWX version of Telex's Baudot system. 
 In addition, TWX had an ASCII version  running at 110 baud.  So, there were  
actually two TWX networks.  One was  Baudot and the other was ASCII 
Western Union started out using  Siemens T100 teleprinters. These excellent 
machines were made of cast iron and  used a worm gear to advance the carriage. 
Then Western  Union changed sources. I remember that Siemens lost it's  US 
production  facility to a fire. That is either a good memory or a bad rumor.  
After that point, Western  Union used Teletype machines.  Most customers ordered 
Model 32 ASR and KSR machines but there were a  population of Model 28 KSR ASR 
and KSR machines for heavy duty applications.  Later on, during the 1980s, 
there were other choices including a design that  used an Okidata 82A as the 
printer. 
TWX machines were all sourced via Western Electric and Teletype (big  
surprise).  So, the TWX was a  collection of Model 33 and Model 35 equipment.  Like 
Telex, most customers opted for  lighter duty (Model 33) machines. 
The TWX network was an overlay on the  US telephone  network, using the same 
central office equipment and trunking.  The Baudot version of TWX, also known 
as  three row TWX, used area code 510.  The ASCII version of TWX, known as 
four row TWX,  used area codes --  610, 710, 810 and 910. There was a manual 
switchboard (10A/B switchboard) where  customers could call into that provided 
translation between the 5 and 8 level  codes and buffering (speed change) between 
the two TWX services. The 10A/B  switchboard also provided operator 
assistance services for TWX customers.  
As George noted, and since the TWX network ran on the POTS network, all  the 
loops used modem tones.  Telex  originally used two different loop 
technologies.  The first method was call "local" and  used a 60 MA loop circuit, which 
should be very familiar to everyone on  Greenkeys as that's the technology that 
most of us use today.  A Telex machine could be a few blocks  away and still 
run "local" back to the Telex Exchange with low bias and  distortion.  After 
that there was  "polar" or “long distance” (LD) which split the loop circuit 
into two separate  circuits, i.e., send and receive circuits. Looking at the 
polar circuits from  the Telex Exchange perspective, the send side was plus/minus 
120 volts DC  working to a ground at the customer location while the central 
office receive  side supplied a ground to the plus/minus 120 volts DC coming 
from the customer.  We were running "polar" circuits for 25-30 miles back in 
the day with very good  results. Not bad for a ground return  circuit! The loop 
had to be a dry loop, with the 88 mH loading coils  removed.  
The Telex loops were 'fun' to work with as you could easily get a nice  shock 
while running cross-connects on the distribution frames.  Bell notified 
Western  Union, sometime in the late 1970s, that the high voltage local and  polar 
circuits were being phased out and all Telex loop circuits were  subsequently 
converted to the "F1F2" system, using analog signaling  technology. 
73 
Russ WA3FRP