Path: utzoo!attcan!uunet!cs.utexas.edu!ut-emx!!spurgeon
From: spurgeon@.uucp (Charles E. Spurgeon)
Newsgroups: comp.dcom.lans
Subject: Re: ethernet transceiver needed?
Message-ID: <37837@ut-emx.uucp>
Date: 2 Oct 90 17:51:30 GMT
References: <482@lawday.Dayton.NCR.COM> <1990Oct2.053859.15305@grian.cps.altadena.ca.us> <1990Oct2.080310.1@rogue.llnl.gov>
Sender: news@ut-emx.uucp
Reply-To: spurgeon@atget.cc.utexas.edu.UUCP (Charles E. Spurgeon)
Organization: UTexas Computation Center, Austin, Texas
Lines: 45

In article <1990Oct2.080310.1@rogue.llnl.gov> oberman@rogue.llnl.gov writes:
>In article <1990Oct2.053859.15305@grian.cps.altadena.ca.us>, steve@grian.cps.altadena.ca.us (Steve Mitchell) writes:
>> $200.  The tranceiver runs off the db-15, so it's a tidy installation.
>> The coax is ThinNet, cable type RG-58A/U.  Just make sure you're
>> terminated at both ends!  I saw a review of a couple of brands of
>
>One minor correction: The cable should be RG-58C/U. A/U is not quite withing
>the 10base2 spec. I believe it's off by about 2 ohms. A/U is also usually hard
>to find.
>
>While the A/U cable would almost certainly work, I suggest that you start with
>the correct cable since it's just as easy.
>

The 802.3a specs for the Type 10BASE2 thin Ethernet system note that
the coaxial cable parameters listed in the specs "... are met by cable
types RG58A/U or RG58 C/U."  (section 10.5.1.6 on page 36 in my old
green book supplement to the 802.3 standard.)

The Belden Wire and Cable Co. catalog (1-800-BELDEN-1 to request a
copy) shows that the RG-58A/U and RG-58C/U cables that Belden lists
are all 50 ohm impedance.

There are some RG-58/U cables shown on the same page, and the RG-58/U
type cables are 53.5 ohm impedance.  They would not make acceptable
thin Ethernet cables.  Ethernet relies on the detection of precise DC
voltages for operation, and the use of incorrect impedance cables can
cause problems.

For 10BASE2 networks Belden recommends their Belden 9907 and 89907
(plenum version) cables.  These cables have better propagation times
than the older RG-58A/U and C/U cables.  However, they appear to have
a smaller outside diameter, so if you use their cable you'd need to
make sure than any BNC connectors you buy will fit on the smaller OD.

Charles E. Spurgeon                                                     
Network Grenade Juggling Dept.       | spurgeon@emx.utexas.edu          |
University of Texas at Austin        | ...!cs.utexas.edu!ut-emx!spurgeon|
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Charles E. Spurgeon                                                     
Network Grenade Juggling Dept.       | spurgeon@emx.utexas.edu          |
University of Texas at Austin        | ...!cs.utexas.edu!ut-emx!spurgeon|
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