early modems / was Re: Telephony switches..

Brent Hilpert hilpert at cs.ubc.ca
Sun Jul 8 21:17:20 CDT 2007

Mo wrote:
> So to answer the first question, yes, some of us do collect modems -
> its just a more subdued kind of fascination with blinkenlights.
> I also have one of those (Anderson-Jacobsen?) teak box modems, which

Livermore Data Systems for the ones being discussed last week, although Doug
suggested AJ may also have produced wood box ones.
If you're taking that 'teak' attribution from my earlier statement, I have to
modify it: upon closer inspection (an unfinished area of wood) it looks like
mine may be a lighter shade of black walnut, finishing stain perhaps making it
look a little more like teak (I still think Doug's may be mahogany) (..for
what it all matters).

> still works, though the foam padding is disintegrating, and there isn't
> much to call at 110bps...

I pulled mine (actually identified as a Livermore Data Systems Model A) out in
the past week for closer inspection and to produce the schematic. All of 13
transistors - it's about as complex as a portable transistor radio from the
period but it probably cost 10-20 times as much (much higher component
quality, in part). Component date codes are 1969 to 1970.

Carrier frequencies are 1070/1270 (XMT) and 2025/2225 (RCV) so I think it
should be good for 300 baud (originate mode). I'm not completely familiar with
the relationship of the 103/113/... modem standards vs baud rates (was there
one bell standard (carrier frequencies) covering multiple baud rates (110/300)
or were there different standards for the different rates?

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