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From: pat@hprnd.HP.COM (Pat Thaler)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Thin or Thick
Message-ID: <2480005@hprnd.HP.COM>
Date: 16 Oct 89 17:10:24 GMT
References: <624204828.0.AVL@MATH.AMS.COM>
Organization: HP Roseville Networks Division
Lines: 28

> / hprnd:comp.protocols.tcp-ip / BEAME@McMaster.CA / 10:18 am  Oct 15, 1989 /
> 
> > RG58 is based on a nominal impedence of 50 ohms and can range from 50 to 53
> > ohms.  To use it for thinnet applications you need to ensure the type you
> > buy is rated at 50 ohms.
> 
> We had someone who shall remain nameless (he dosen't work at here anymore),
> wire several areas with 53 ohm RG58. Does anyone know what the ramifications
> of this are ? We are mostly running 3C501 :-( cards in PCs.
> 
>         - Carl
>         Beame@McMaster.CA
> ----------
The 802.3 10BASE2 specification for the average coax characteristic impedance
is 50 +- 2 ohms and impedance variations of +- 3 ohms sinusoidal centered
around that value are allowed.  (50 ohms +- 1% is the spec for the 
terminator.)  If your actual impedance is 53 ohms, you are slightly out
of spec.  If your impedance is 53 ohms nominal with variation a few
ohms to either side you are a little further out of spec.  

If your wire is all 53 ohm, you probably won't see problems (but if
you see problems, it may be hard to say whether it is the wire or the
other networking products.)  If you have a mix of 53 and 50 ohm wire
(perhaps 53 ohm wired in the walls and 50 ohm cables from the wall
to the station), there will be extra reflections which could cause
high bit error rates (CRC and alignment errors).

Pat Thaler