From: floyd@hayes.ims.alaska.edu (Floyd Davidson) Subject: Re: Modem and noise problems - Please help Date: Tue, 10 Aug 1993 04:14:35 GMT
In article <4g2w8B1w165w@techsys.mcws.fidonet.org> berk@techsys.mcws.fidonet.org (Berk Walker) writes:
>> >
>> >Otherwise, hook up an oscilloscope on the phone line and look for
>> >disturbances. Or call your local phone company.
>>
>> O-scopes are nice things... but they are almost ALL made with an
>> unbalanced input. If you connect that to the phone line, which
>> is really a balanced transmission line, you will *cause* it to
>> have all of the symtoms the original article described!
>>
>> Floyd
>>
>>
>> --
>Most 'scopes have two inputs. If you use A+B (inverted) yu will have a
>balanced, isolated input. <include "o"> ^.
And if you know how to terminate it properly and can figure out
what you are looking at... you probably have access to proper
test equipment and wouldn't bother with a scope.
O scopes are almost totally useless for testing telephone lines.
I've only seen one person actually hook a scope to a cable pair,
and when us old testboard techs sit around and tell jokes about
the biggest bozo's we ever saw, thats the story I tell. Guys with
a year or two of experience might get it, but guys with 25 or 30
years ALL find it quite funny.
Want to tell me about how you can test cables with an O'scope? :-)
Floyd
-- floyd@ims.alaska.edu A guest on the Institute of Marine Science computer Salcha, Alaska system at the University of Alaska at Fairbanks.