DECServer 90L+ startup help

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Sun Dec 28 19:04:09 2003

> What I'm *not* doing is terminating - I didn't figure I'd have to
> with each connector on the servers joined by a single run of coax.

Yes, you need to terminate. Otherwise you get all sorts of signal
reflections when the impedance changes at the end of the coax, and the
error rate goes through the ceiling in consequence.

> I have the BNC Ts - should each end also need 50 Ohms...? Mongo not
> Grok LAN voodoo...

I don't really _understand_ transmission-line effects. But I know they
exist and I know that you don't play fast and loose with them unless
you know _exactly_ what you're doing (or you don't care about whether
it works or not).

>> If you've got a DS90 on its own it must have a t-piece with 2
>> terminators on its thinwire port,
> 2 50 Ohm terms per port?

Only if the port is not connected to anyone else.

Two 50-ohm terminators per thinwire segment. A box on its own is just
a very very small thinwire segment...and it wants those two
terminators. (Instead of a T with two 50-ohm terminators, you probably
could get by with a single 25-ohm "terminator" directly on the
connector, since all the distances are very much less than the carrier
wavelength. But that would mean finding such a thing.)

/~\ The ASCII der Mouse
\ / Ribbon Campaign
 X Against HTML mouse_at_rodents.montreal.qc.ca
/ \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
Received on Sun Dec 28 2003 - 19:04:09 GMT