AUI cables in UK?

From: Pete Turnbull <>
Date: Mon Mar 8 12:56:56 2004

On Mar 8, 16:10, Johnny Billquist wrote:

> I'm pretty sure that the stripes are at 2.5 m.

They are. I'm looking at a length of etherhose right now.

> I'm also pretty sure that the standard says you should have 5 meters
> between transcievers.

That's what I thought, but I don't actually have a copy of the
standard, just my well-thumbed copy of Charles Spurgeon's "Ethernet"
book. It says the stripes are 2.5m apart but transceivers can be
placed at 5m or 7.5m or any multiple of 2.5. Well, 2.5 is a multiple
(in the mathematician's sense of 1 x 2.5) so maybe 2.5 is OK.

> But I have actually never really understood why. Maybe just to not
> the cable to much with vampire taps? There cannot be an electrical or
> signal reason for this, as far as I can tell.

I can't think of one either. The reason for the 2.5m spacing is that
it's an odd fraction (about 1/19th) of a wavelength, so when you put
taps on the cable, the small reflections caused by the discontinuities
are out of phase and don't tend to be additive.

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Mon Mar 08 2004 - 12:56:56 GMT

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