Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site watcgl.UUCP
Path: utzoo!watmath!watcgl!dmmartindale
From: dmmartindale@watcgl.UUCP (Dave Martindale)
Newsgroups: net.lan
Subject: Re: Ethernet cable length query - (nf)
Message-ID: <2309@watcgl.UUCP>
Date: Mon, 26-Mar-84 00:22:25 EST
Article-I.D.: watcgl.2309
Posted: Mon Mar 26 00:22:25 1984
Date-Received: Mon, 26-Mar-84 20:43:51 EST
References: <1151@cbosgd.UUCP>
Organization: U of Waterloo, Ontario
Lines: 39

You can always turn a "vampire" tap into the other type by taking a few
feet of Ethernet cable, putting appropriate connectors on each end, and
attaching the "vampire" tap to it.  But I would expect that the vampire
tap causes the least impedance disturbance in the cable, since it doesn't
involve adding two connectors and a non-homogeneous piece of cable every
time a transceiver is added to the network.

When DEC installed our transceivers, they had problems with the drilled
holes shorting out the cables.  I note that the catalog says that the
installation kit includes "braid terminators".  I don't remember DEC
installing anything that would fit that description.  Does anyone know what
they are?

Anyway, to check your transceiver's connection:  If you have transceiver
housings made by AMP, at least, the transceiver board connects to the cable
by 3 pins in the housing and receptacles for these pins on the circuit
board.  Take the cover off the transceiver housing, pull the circuit board
straight out of the housing, and the three pins will be obvious.  The outer
two should be connected to the cable ground; check with an ohmmeter between
them and the ground of the nearest cable end.  The centre pin is the centre
conductor of the cable, and an ohmmeter reading between there and the
centre pin of the cable end connector should show only a couple of ohms.
Finally, the resistance from the centre to either outer pin should be
either infinity, 50, or 25 ohms, depending on whether 0, 1, or 2 terminators
are installed on the cable segment in question.  If any of these measurements
is incorrect, that should tell you that there is a short or open somewhere.
An open is easy, a short between the signal and ground conductors in
the cable means that there is a short somewhere along the cable.  It's
probably at one of the transceivers, but don't overlook the terminators
either.  We had intermittent shorts caused by metal chips in the terminator,
caused by someone using a wrench or pliers to tighten the cable connector.
(They should be hand-tight only)

The clamp bolts on the transceiver are just there to hold the clamp together.
"Snug" is probably the best way to describe the proper torque.  The
screw in the centre of the clamp cover is a pin which pushes the
centre conductor of the cable into firm contact with a pin in the transceiver
housing.  It should be tightened firmly enough to make good electrical
contact.