23 Jan
2018
23 Jan
'18
11:09 a.m.
From Wiki:
"Transceivers should be installed
only at precise 2.5-metre intervals. This distance
was chosen to not correspond to the wavelength of the signal; this ensures that the
reflections from multiple taps are not in phase. These suitable points are marked
on the cable with black bands."
It cites "IEEE Standard 802.3<https://en.wikipedia.org/wiki/802.3>-1985;-1985.
IEEE<https://en.wikipedia.org/wiki/IEEE>EE>. p. 121."
bill
________________________________
From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Pete Turnbull via
cctalk <cctalk at classiccmp.org>
Sent: Tuesday, January 23, 2018 1:54 PM
To: cctalk at classiccmp.org
Subject: Re: Ethernet cable (Was: Sun3 valuations?)
On 23/01/2018 16:48, Grant Taylor via cctalk wrote:
On 01/23/2018 09:10 AM, Bill Gunshannon via cctalk
wrote:
No, that's quite wrong. The marks are every 2.5m (8.2 feet) wich IIRC
is 1/19th of a wavelength apart, the point being to try to minimise the
likelihood of connections being made where they'd suffer constructive
(additive) interference and to prevent transceivers being too close
together.
--
Pete
Pete Turnbull
If you didn't locate the transceivers on
those black marks you would
have had terrible performance as that affects collisions. Timing
(among other things like grounding) was very important with that
version of ethernet hardware.
It's my understanding that the marks (black bands or other markings on
the sheath) were exactly one wavelength apart. Which from what I
remember ~> understand from my ham radio days is quite important.