From: John Tserkezis 
Reply-To: Fidonet AVtech Echo 

Jasen Betts wrote:

> maybe the impedance mismatch is a problem, the ethernet cards are designed to
> drive 25 ohm load when they're sending. (50 on each end of the run)

  As I understand it, it's still 50 ohm.  The terminators make the ends look 
like an infinite length cable so there are no reflections.

  Reflections garble the data enough to make it useless for everyone let alone 
the transmitter trying to detect a collision or not.

  In theory, cable length should not be an issue (aside perhaps from degraded 
signal strength by the time you get to the end of that 300 metre stretch), 
although I've seen some cards have a _minimum_ cable specification (about two 
metres if I recall).

  Again in theory, if you had a long enough cable length on one (or both) ends, 
the system should still work, because there are no reflections, thus no 
corruption of signal.
  What you would need is a cable length long enough at the ends that the 
inevitable reflections are degraded enough by the time they come back, that 
they offer little or no effect on the closer valid signals.
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