Re: Issue on connect 2 modems with a single phone line

From: Brad Campbell
Date: Sat Dec 18 2004 - 03:00:13 EST

Manu Abraham wrote:
On Sat December 18 2004 11:01 am, Brad Campbell wrote:

I have used analogue modems back to back for years and have *never* come
across a modem that sourced anything other than it's ringing signal (via an
opto) from the phone line. Every single modem I have here will talk to the
others over a straight telephone cable.

What about power ? The opto-coupler will not work without power.

If you read what I wrote you will note the opto-coupler is used for ring detection only and then only triggers when it sees an AC ring pulse. You don't need ring detection to run modems back to back and therefore it's not a problem.

As for the Capacitor and Transformer, you are correct. I merely mis-communicated my message.
Point is the same, you can connect 90% of Analogue modems back to back with only a bit of wire and they will talk. (I say 90% as I'm sure there is one out there somewhere that uses the phone line voltage for something but I have *never* seen one). Remember that off-hook phone voltages can get down to around 3v while on hook you may have 50v.

Don't theorize about it, try it.

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