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
damage
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