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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet noise problem?
Message-ID: <7834@utzoo.UUCP>
Date: Fri, 27-Mar-87 14:31:16 EST
Article-I.D.: utzoo.7834
Posted: Fri Mar 27 14:31:16 1987
Date-Received: Fri, 27-Mar-87 14:31:16 EST
References: <7823@utzoo.UUCP>
Organization: U of Toronto Zoology
Lines: 35

Well, the plot sickens.  First, to sum up the two replies I got:

One said that the NT100 is Ethernet 2 while the NI1010A is Ethernet 1.
I had wondered about compatibility problems a bit myself, but the two
were bought as a package, claimed to be compatible, and the transceiver
explicitly claims to be E1 compatible.  Read on...

The other reply cited past experience with marginal rejection of power-
supply noise in the NI1010A's receiver.  The fix that worked for them was
to add a couple of capacitors to the board.  Their account had certain
features that resembled our situation, but read on...

I did some more experimenting.  In particular, I took a look at what was
going on on the cable with a scope.  Most interesting.  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...
Anyone ever seen anything like this?

Finally, just for the hell of it, I tried exchanging the NT100 for a Sun
transceiver (3Com 3C101, almost certain to have compatibility problems
since it's definitely E2/802.3).  Problem vanished.  No more pulses on
the Ethernet, no more trash-on-the-line LEDs on the controller, no more
complaints about collisions from the controller.  I won't be absolutely
sure that this is functioning 100% correctly until I put something else
on that Ethernet and get them talking, but it looks okay.

My conclusion is that either (a) I've got a defective NT100, or (b) there
is something else wrong, and the difference between the 3Com and Interlan
transceivers is enough to make the difference between smooth functioning
and trouble (3Com draws less power, or has cleaner signals?).  Thoughts?
-- 
"We must choose: the stars or	Henry Spencer @ U of Toronto Zoology
the dust.  Which shall it be?"	{allegra,ihnp4,decvax,pyramid}!utzoo!henry