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From: floyd@ims.alaska.edu (Floyd Davidson)
Newsgroups: comp.dcom.modems
Subject: Re: Line Noise Redux
Keywords: Line Noise
Message-ID: <1991Jan3.043303.23660@ims.alaska.edu>
Date: 3 Jan 91 04:33:03 GMT
References: <59403@aurs01.UUCP>
Organization: University of Alaska, Institute of Marine Science
Lines: 60

In article <59403@aurs01.UUCP> luce@aurw46.UUCP (J. Luce) writes:
>I run a BBS using a 2400 baud modem (I have tried 2 flavors of modem
>with the same thing occurring). The Caller gets line noise garbage and 
>the BBS sees nothing but a clean line. I have called my own BBS on a
>voice line in the house and have seen it myself. 

The fact that it is in one direction only indicates one of two things.
It is either a relatively narrow frequency range that is interefering
or it is occuring someplace where you circuit is a four wire circuit.

Cable noise is almost never a restricted frequency range source.  
Sometimes crosstalk with another modem might give you that, but
on a residential line it is unlikely.

Your local house wiring is all part of a two wire circuit.  Any
wide band noise burst or crosstalk with a voice circuit will affect
both the transmit and receive.

Since you have tried more than one modem and still have the problem
it is fairly clear that the phone company has a problem.

If you are on copper cable all the way to the switch it is most
likely the line card in the switch.  However if you are some
distance from the switch it may be on some form of cable carrier
between you and the switch, and the cable carrier is 4-wire
(a separate channel for transmit and a separate channel for
receive).

If you are getting garbage that is totally random it likely is
a line card or a channel card (switch or carrier).  If you get
repeating characters (like:  {{{{{{{{) it is a T-carrier system
that is not syncronized (clock slips).

Since you get the noise when you call from your other line,
and you more or less indicate that almost every call is noisy,
I think you can eliminate everything past the line card in the
switch.  But if some calls are clear and others are noisy,
then you do need to note where the noisy ones come from and
where the clear ones come from and look for a pattern.  If
noise is only when it is a call local to your line switcher,
but clears up if the call comes from another line switcher,
then the problem is past your line card.  In that case it
would be in the "network" or whatever they call the 
switching matrix on that particular switch.

All of the above assumes a 4-wire switch (eg. digital). If
you are on an old mechanical switch then it has to be some
kind of carrier.

When you talk to the phone company get a tech on line or
at least ask the clerk on the trouble desk to have a tech
call you.

Floyd

Disclaimer:  I don't work on line switchers, only trunks.
-- 
Floyd L. Davidson                                  floyd@ims.alaska.edu
Salcha, AK 99714                    paycheck connection to Alascom, Inc.
 When I speak for them, one of us will be *out* of business in a hurry.