Ethernet cable (Was: Sun3 valuations?)
bill.gunshannon at hotmail.com
Tue Jan 23 13:09:53 CST 2018
"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. IEEE<https://en.wikipedia.org/wiki/IEEE>. p. 121."
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:
>> 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.
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
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