old modems & a packet switcher

From: Allison J Parent <allisonp_at_world.std.com>
Date: Mon Aug 3 17:39:23 1998

< Hmmm. Well, I wonder about this. I know such services exist in the US
< well, but they still at least have battery on the line. I would wonder
< what good a dry point-to-point connection through the telco would be ove
< several miles, where the resistance in that length of wire would absorb
< whatever voltage you put on it.

The service exists, I used to use it 25 years ago for remote base stations
(radio service). It was called a dry copper pair and went point to point
with NOTHING else. It had to be that way as you would put audio on it and
DC on it to either key the transmitter or disable to tone squelch. the
average circuit resistance ws about 1kohm/mile. So the remote end didn't
sense voltage but instead sensed current (~8-9ma) and polarity to do
switching. Audio was put on the pair the normal way (differential via
transformer).

Allison
Received on Mon Aug 03 1998 - 17:39:23 BST

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