TELECOM Digest OnLine - Sorted: Re: Very Early Modems

Re: Very Early Modems

Joe Morris (
Wed, 1 Jun 2005 22:07:26 UTC writes:

> Anyway, the phone system as of 1960 was similar. It was fine for us
> to talk over and an occassional click or pop or slight crosstalk was
> ignored by humans.

> But sending data at 2400 is another story. One little click disrupts
> a whole stream and requires a re-transmission. The older switches
> could be 'noisy'.

You don't have to get up to the "fast" speeds like 2400 bps to have
problems with some switches.

My PPOE (an Enormous State University) installed a new SxS exchange in
the mid-1960s. Just as the new switch went into service the Computer
Center (where I worked) took delivery of some IBM 2740 terminals and
obtained WECo DataPhone 103A2 boxes to connect them to the switched

The noise, presumably from the new, unburnished wipers, was so bad
that we couldn't get reliable communications between a pair of the
2740s linked back-to-back through the switch. The speed was that of
just about all of the Selectric-based termials: 134.5 baud.

After a few months of service the noise subsided, but I suspect that
we put more duty time on the error light than the IBM designers had
planned for. (And just as the noise levels dropped, we had to send
all of the time-sharing equipment back to IBM because the computer
center's budget was chopped to free up money for the football team's
new artificial grass ... but that's another story)

Joe Morris

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