This is called a "vampire tap" and isn't as useful as you might think. Back
in the old days there was a big yellow cable that had ethernet on it. You
attached this to the cable and clamped it on (there are markings to show
where taps go). There are some rules about taps, they had to be at least 5
meters (15') apart because that insured collision detection would work
correctly (15' == 15ns in light speed). This then connected to a cable,
(called an AUI cable) which connected to a "MUX box", if you want to be a
DEC purest you would use a DEC DELNI (which couldn't deal with back to back
packets going through it). Then, somewhere else on the cable would be
another tap connected to another mux and a machines connected to it. 

You could of course run a cable write from the DELQA (DEQNA) to the vampire
tap but then either your computers had to be 15' apart, or you ended up
with loops of heavy yellow cable lying about. Sun paid thousands of dollars
to "upgrade" the hanging ceiling supports to carry the weight of the
ethernet cable.

These days people use a CAT5 tranciever and go to a regular hub. 

--Chuck

P.S. Several people have sold (or tried to sell!) DEC DELNIs on Ebay. They
aren't very practical hence there low value.

P.P.S. If you have a BA213 (at one point I thought you were trying to wire
up a BA123 for DSSI) I've got a dead one with the wiring harness. You'll
have to describe what the top of the BA213 has in it to see if its a good fit.


At 04:32 PM 1/27/00 -0500, Douglas Meade wrote:
>I picked up a couple of HA4000's recently, having only seen them
>before in pictures.  I was interested in putting some real DEC
>equipment into my home network of Vaxes and Pmaxes.  However, 
>giving them a good look, I realize I don't have the foggiest
>idea how to hook them up.  In the middle of the device, there
>is a clamp, with a little sharp thingy that looks like it's supposed
>to dig into a wire of some kind, passing through there.  Would 
>that be a thinnet coaxial cable?
>
>Doug
>
>