Index Home About Blog
Newsgroups: alt.dcom.telecom
From: (Floyd Davidson)
Subject: Re: Wiring diagram for Telco transformer needed
Date: Sat, 12 Jul 1997 10:18:35 GMT

Chris Williams <> wrote:
>In article <5q4mr1$>, wrote:
>>Chris Williams <> writes:
>>>    My air conditioner is causing my modem to disconnect every
>>> time it's compressor switches on. I've tried putting the
>>> computer and external modem on a UPS with no change. I've
>>> tried re-routing the phone line so that it no longer
>>> ran parallel to the AC with no change.
>>Better you should fix the compressor - if it's pulling that
>>much starting current something is surely wrong inside it.
>   This would seem like a possibility, but it's a new
>White-Westinghouse unit and doesn't seem broken. It's
>not like all the lights dim, just that the modem connection
>gets terminated.
>   Anyone familiar with the transformer?

From the sound of it the problem is an unbalance on your
telephone line.  If the line is properly balanced, and twisted
pair cable is used in your home between the telco demarc point
and your telephone sets and/or modems, then things like large
motors switching on and off or florescent lights and other
"noisy" devices, should not bother the modem at all.  But if the
line is not well balanced, or if any appreciable amount of
non-twisted pair is used, then everything that makes noise will
be heard on the telephone line.  Things like extention lines
with one of the two wires disconnected, or using 25-50 foot flat
non-twisted wire for an extention, or a staple through the wire,
or a wire that is kinked or worn or is contacting something like
a water pipe or metal of any kind are all things that can
unbalance a phone line.

Try using a separate cable from the demarc point to your modem
and disconnect everything else from that line.  Also be sure
that the cable you use is either very short (6 feet max) or is
twisted pair wire intended for telephone lines.  If that
connection still drops when the AC kicks in then either the
phone line itself is bad, or your modem is bad.

Can you hear a click on the line when AC switches if you are
making a voice call?  To be severe enough to actually knock the
modem off line requires a very audible burst of noise.  If you
are not hearing that, then it is very likely that your modem has
a problem which is causing the imbalance.  At that point you
might want to borrow another modem from a friend and see if it
also has the same problem.

As a last resort, call the telco!

Floyd L. Davidson          Salcha, Alaska

Index Home About Blog