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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet noise problem?
Message-ID: <7858@utzoo.UUCP>
Date: Thu, 2-Apr-87 12:19:47 EST
Article-I.D.: utzoo.7858
Posted: Thu Apr  2 12:19:47 1987
Date-Received: Thu, 2-Apr-87 12:19:47 EST
References: <7823@utzoo.UUCP>, <7834@utzoo.UUCP>
Organization: U of Toronto Zoology
Lines: 32

> ... About every 36
> microseconds, regular as clockwork, the transceiver put out a 400-ns pulse
> at about -2V (i.e., Ethernet transmit voltage).  Not a carrier sequence,
> not a noise burst, but a fairly clean more-or-less rectangular pulse.  No
> wonder the controller was complaining of collisions when it tried to send...

It occurs to me that I didn't make one aspect of this clear enough:  these
pulses were on the *coax*, not on the transceiver cable.  I.e., this
transceiver is actually crudding up the Ethernet itself, not just making
trouble for its own controller.

A few people have assumed that I have gotten confused about transceiver
heartbeat.  Unless I am *seriously* mistaken about what heartbeat is, this
isn't it -- wrong cable, wrong signal characteristics (square pulse instead
of 10-MHz wave), wrong timing (continual rather than a short burst at the
tail end of each transmission).

For compatibility fans, by the way, the NI1010A controller claims to be
Ethernet 1, but one of its test commands claims to listen for heartbeat!

> Finally, just for the hell of it, I tried exchanging the NT100 for a Sun
> transceiver (3Com 3C101 ...  Problem vanished...

Just to keep people up to date on the fun...  This substitution has indeed
cured the problem completely.  The Ethernet cable is electrically clean
according to my scope, and the NI1010A is communicating successfully with
a Sun via the Ethernet.  There may possibly be a noise problem on the
transceiver cable -- I don't have an easy way to get a scope probe into
it -- but on the surface everything's quiet.
-- 
"We must choose: the stars or	Henry Spencer @ U of Toronto Zoology
the dust.  Which shall it be?"	{allegra,ihnp4,decvax,pyramid}!utzoo!henry