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

[Eric Smith <eric@brouhaha.com>]

et472@FreeNet.Carleton.CA (Michael Black) writes:
> I don't think any modem ever got power from the phone line.

I've seen designs for 103J type modems (up to 300 bps) that were
entirely line powered, but it would be difficult if not impossible
to get enough power from the line for a modern high-speed modem
(V.92, V.90, or even V.34).

However, many older modems did depend on having DC line current for
their line-side circuitry to work.  They just didn't power anything
on the computer-side of the galvanic isolation (transformer) from
the line.

But as I pointed out in another posting, most modern modems don't
care about DC line current at all.