Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!cbmvax!adam
From: adam@cbmvax.UUCP (Adam Levin CATS)
Newsgroups: sci.electronics
Subject: Conferencing two phone lines
Message-ID: <6612@cbmvax.UUCP>
Date: 18 Apr 89 15:16:14 GMT
Reply-To: adam@cbmvax.UUCP (Adam Levin CATS)
Distribution: usa
Organization: Commodore Technology, West Chester, PA
Lines: 31

This topic was pretty well hashed out on the net about half
a year ago, but the exact method wasn't covered.

I have two phone lines that I want to be able to "conference"
from time to time.  We learned that you shouldn't just connect
tip-to-tip and ring-to-ring because of voltage differences between
your location and the phone company (not to mention if a call
should come in on one line while a call is in progress on the other).

It was advised that one needed to use an isolation transformer
between the two lines.  As I recall, this was a 600 Ohm 1:1
transformer.  I bought such a beast at Radio Shack, but connecting it
to the phone lines seems to load them too much; there is an
obvious degradation of the signal.  I made the connection like so:

  Tip 1___  ___Tip 2
         |  |
         \  \
         /  /
         \  \  600 Ohm 1:1 transformer
         /  /
Ring 1___|  |___Ring 2


Has anyone successfully built a device like this?
I'd really appreciate hearing about it!  Adam

-- 
     Adam Keith Levin  --  CATS   Commodore-Amiga Technical Support
     1200 Wilson Drive / West Chester, PA  19380     (215) 431-9180
     BIX: aklevin        UUCP: ...{amiga|rutgers|uunet}!cbmvax!adam