Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!apple!bionet!hayes.ims.alaska.edu!floyd
From: floyd@ims.alaska.edu (Floyd Davidson)
Newsgroups: comp.dcom.modems
Subject: Re: Line Noise Redux
Keywords: Line Noise
Message-ID: <1991Jan7.023340.4433@ims.alaska.edu>
Date: 7 Jan 91 02:33:40 GMT
References: <59403@aurs01.UUCP> <19239@hydra.gatech.EDU>
Organization: University of Alaska, Institute of Marine Science
Lines: 35

In article <19239@hydra.gatech.EDU> gt5302b@prism.gatech.EDU (R. Steve Walker) writes:
>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. 
>>
>Try BallCo Inc. at (404) 979-5900.  They sell line noise eliminators for
>modems.  It works.


Except that he does NOT have line noise, so it won't be filtered out.

Notice he always has a "clean line" in the direction of the BBS, and
"line noise garbage" toward the caller.  That isn't caused by noise
on the line.  The line is a two wire device which has two way
transmission.  Noise on the line will garble traffic on both ends,
although it may be more significant on the receiving end of the line
that actually is causing the noise (lower signal to noise ration
for the recieved signal).

What he is experiencing is one way interference.  That is a character
trait of "4-wire" circuits where each direction has a separate 
transmission path all to itself.

It is probably a bad analog-to-digital converter in the line card
at the switch.

Line filters just won't do much for it.

Floyd
-- 
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.