Re: Extending the range of null modem to 100ft.

[Andy McFadden <fadden@fadden.com>]

Ed Eastman <noone@nowhere.net> wrote:
> No, you don't need a live phone line, in fact it is better to not have 
> one or else you'd need two phone lines so they could REALLY call each 
> other.
> 
> Run a phone cord from one modem strait to the other.  Tap ATD on one 
> telecom software then ATA on the other and your modems will initiate and 
> answer (squacks, etc).

Interesting.

If you take two standard phones and plug them together, nothing happens.
There's no power on the line, and you can't get enough out of a piezo-
electric microphone to drive a phone signal.

For this to work, one or both modems must be supplying current on the
phone line.  Some of the telco devices I've worked with have used an
optical component (can't think of the part name now) to electrically
isolate the analog and digital components.  As with common household
phones, these didn't supply power.

All of which makes me wonder what percentage of modems do supply power.
It would have to be on the "answering" side, since it needs to start
the negotiation.

You may also need to enable "blind dialing", since modems tend to want
to hear a dial tone before they start dialing.  A steady carrier tone
may be enough though -- I don't think it's picky about frequency.

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