Path: utzoo!attcan!uunet!cs.utexas.edu!ut-emx!bud
From: bud@ut-emx.UUCP (C. E. "Bud" Spurgeon)
Newsgroups: comp.dcom.lans
Subject: Re: RG58 C/U vs ThinWire Ethernet?
Message-ID: <13099@ut-emx.UUCP>
Date: 16 May 89 20:47:40 GMT
References: <1026@draken.nada.kth.se> <802@helios.toronto.edu>
Reply-To: bud@emx.UUCP (C. E. "Bud" Spurgeon)
Organization: UTexas Computation Center, Austin, Texas
Lines: 46

In article <802@helios.toronto.edu> sysruth@helios.physics.utoronto.ca (Ruth Milner) writes:
>In article <1026@draken.nada.kth.se> ragge@nada.kth.se (Ragnar Sundblad) writes:
>>
>>Now people that usually know something of what they are talking about,
>>although they are sellers (not of the cable), have told me that it is
>>not recommendable to build long (100<l<185m) networks with RG58, I
>>should use this ThinWire cable instead if I don't want to get problems
>>when there are many nodes connected.
>>
>>(I mentioned this to a cable seller. He told me that "it had something
>>to do with the timing" (RG58 = ~0.66c, ThinWire = ~0.80c).  As long
>>as I don't run at the timing margins, I don't give very much for
>>that (perhapse I could get 0.000001 times better performance :-).)
>
>We use RG58U for all our thinwire Ethernet segments, and have had no
>trouble with it (actually, I was under the impression that RG58 was the
>cable that ThinWire, i.e. 10BASE2, was actually spec'd around). There are 

The IEEE 10BASE2 spec for thin Ethernet notes that the coaxial cable
specifications are met by two cable types, RG58A/U and RG58C/U.

From Belden cable RG58A/U is P/N 8259.  It has a cellular polyethelyne
dialectric, a nominal impedance of 50 ohms, a stranded center
conductor, and a propagation rate of 78% of light.

Belden sells RG58C/U as P/N 8262.  It has a solid polyethelyne
dialectric, 50 ohms, stranded, and a prop rate of 66% of light.

Both cables can be strung to 185 meters and meet the Ethernet timing
specs.  The foam poly has better propagation, but beware of
environmental hazards.  In one building that had a lot of thin
Ethernet we noticed that the tray into the wiring closet had a sharp
edge on the end of it.  The bundle of RG58A/U cables had enough
weight that the cables were crimped going over this edge.  Foam poly
is easily deformed.  The solid poly holds up better to the sorts of
hazards these cables see.

I seem to recall that DEC sells a special thinwire variation that has
a smaller OD than either of these two cables and requires special BNCs
and crimping tools.  Make sure that whetever you buy fits the
connectors and tooling you get.  Most of the installation problems
with this technology will be with connectors that aren't installed
correctly.

Plain old RG58/U (Belden 8240) has an impedance of 53.5 ohms and does
NOT meet the 10BASE2 specs.