Data communications over telegraph circuits 1935

Well I guess Alaska was special anyway since the telephone company was Alascom. Telex started out in life (in Germany, etc.) as a DC telegraph system; and that is what W.U. imported into the U.S. TWX even in manual switchboard days sometimes used modems between the customer and the serving office. In this case the modems were 43A1 carrier channel units packaged to be self-contained with power supply. I presume the reason is that they had a voice-grade loop to the customer and didn't want to put DC telegraph on it; or maybe the voice grade loop was itself carrier derived so they couldn't put DC telegraph on it.

Then Dial TWX used the 101 family of modems, a huge beast that sat in the bottom of the Teletype machine and had about 99 wires running between it and the Teletype. Some of the telephone operating companies saved money by buying simpler private-line sets from Teletype and using them with 103 modems. The 103 modems had strapping options to control which pair of frequencies was originate and which was answer, and on each pair which tone was mark and which was space. Thus by strapping the same modem could be used in eight different mutually-incompatible services. TWX was one, Data-Phone was another, WADS was another, and there was something to be called WADS-prime, and that only used up half the possibilities.

buttociated Press in its later years also went from DC telegraph lines to voice-grade lines with modems. --

jhhaynes at earthlink dot net