>> 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 needed.
>> It was also said IBM limited development in this area to avoid
>> annoying AT&T who was IBM's best customer.
>> However, in the 1950s, IBM developed card-to-card directly without
>> paper tape and "over AT&T lines". Modems were developed to take good
>> advtg of the available bandwidth (about 1200 baud). Undoubtedly the
>> equipment and implementation was developed in close cooperation with >> AT&T.
>> I was wondering if the modems in that application were supplied by IBM
>> (who appears to have developed the technology) or by AT&T. My
>> understanding that AT&T's "Dataset" modem-telephones didn't come out
>> until the 1960s.
>> Comments by anyone familiar with pre-1960 data communications would be
>> greatly appreciated.
> Here is a picture of a 1958 AT&T modem (not sure if this is the first
> commercial modem, the Bell 103. If so it was 300 baud):
>
formatting link
So the carrier was on tape. How interesting.
I guess at that point it was hard to stabilize a tube based oscillator.