Modem to Modem without a line simulator?

Tom Watson tsw-cc at
Mon Dec 31 14:13:53 CST 2007

>From a digest article I must comment on...

> Is it possible to connect two modems (eg: Hayes 2400 to Hayes 2400)
> using a 'dead' or isolated pair of copper wire and have them be able
> to communicate?

As said before, just get one modem in Originate mode, and the other in Answer
mode and go from there.  Most "modern" modems (that have some Part 68
certification) can do this quite easily as long as you have access to the
command stream on each side.  The more difficult is when you don't (usually on
one side).  Then you attempt to get the "answering" modem in answer mode
sending its carrier before he "originating" modem asks for it, and will sense
it when it wants to.  The part that is touchy is making the timeout on the
"answer" side long enough.

Ob ClassicComp:  I should really try this with my Bell 103A modem (I got one,
don't ask!) to see if I can get it to "connect".  It might need some DC voltage
from tip to ring (green wire to red wire) to trip some relay (it was before
optical couplers!).  What an experiment to do!

If you want to make two "500" sets talk to each other, a nice 6 Volt battery
works quite well placed in series with the two sets.  It won't make them ring,
but you CAN talk.  Use a lantern battery (or 4 D cells) and unless you are
making DTMF (touch-tone) on a polarity sensitive set (older 2500 sets) polarity
makes little difference.

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