TELECOM Digest OnLine - Sorted: Re: History of Hayes Modem

Re: History of Hayes Modem

Al Gillis (
Sat, 14 Jan 2006 05:25:51 -0800

(Snipped much excellent discussion of the early years of our crazy hobby.)

> [TELECOM Digest Editor's Note: My question would be, _who_ was the
> inventor of the MO(dulate)DEM(modulate) in that case? If Hayes only
> 'refined' it somewhat, with 'smart stuff' in it such as 'AT' and '+++'
> then whose idea was it to ship data over the phone wire originally? PAT]

Let's not forget about the "Acoustic Coupler" which was sort of an
accessory to a modem. I don't remember exactly, but I suspect the
heyday of the acoustic coupler was before Tom Carter won the right to
connect privately owned equipment to the telephone network in
CarterPhone -vs- AT&T.

Anyway, in the days when many computers connected to the telephone
network through fixed facilities (also remember the DAA - "Data Access
Arrangement" which allowed privately owned modems to be connected to
the telephone network) there was sometimes a need for portability.
You could get a hand truck and move your terminal equipment from place
to place. Maybe you had a Teletype machine or, if you were really
modern you had a "glass Teletype" which was a CRT based terminal. But
when you got where you were going you needed to make a connection to
the service you used. If there were no DAA available ( it needed to
be previously ordered from and installed by the telephone company) you
were S.O.L. as it were. This is where the Acoustic Coupler entered
the picture.

The meat of the acoustic coupler was a pair of "cups" into which you
placed the handset of a telephone. One cup had a speaker in it; the
other cup had a microphone. The microphone and speaker were connected
to the modem portion of the thing (which had an RS-232 connection for
your terminal or computer). When a telephone handset was placed in
the cups properly the coupler's microphone "heard" the signal coming
from the handset's receiver and the coupler's speaker "talked" to the
handset's transmitter. So the modem was coupled acoustically to the
telephone line. This got around the issue of needing a DAA to make an
electrical connection to the telephone network and nearly any
telephone would work. So with the modem connected to the Teletype and
the acoustic coupler "connected" to the telephone you established a
connection and got your work done or browsed through the latest
messages on your favotire BBS.

Acoustic Couplers pretty much topped out at 300 bits per second. The
first one I used was part of a Teletype network and was a 110bps
device (that was slow!). Later I got one of those Texas Instruments
thermal printer terminals with an acoustic coupler built in; it would
go 300 bps and I could carry it with one hand! I thought nothing
would be able to stop me then!

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