Hal Roney wrote in a message to Mike Bilow:
MB> JC>     Is there a minimum length for 10base2?  (I'm curious if
MB> JC> there is such for 10baseT as well, but I'm not useing that
MB> JC> just yet...)
MB>Yes: 0.5m in both cases.
 HR> Actually its,
 HR> 0.5m to 185m  for 10base2   and
 HR> 0.6m to 100m  for 10baseT
 HR> but hey, whats 4 inches?
Actually, the minimum distance is a wavelength fraction.  Since the 
wavelength is, by definition, the phase velocity divided by the frequency, 
the faster phase velocity in UTP (about 0.95c) compared to coax (as low as 
0.66c) does cause the minimum distance to be slightly greater.  However, the 
minimum distance is a sort of fudge factor anyway, and the 0.5m specified is 
computed assuming a phase velocity of 1.0c to be conservative: at 5 MHz, the 
wavelength is 60m, so 1/100 wavelength is 0.6m.
The minimum distance is only relevant in case impedance discontinuities 
produce standing waves.  This particular failure mode is almost impossible 
with UTP because there are always exactly two nodes on each physical segment, 
so it is not really worth worrying about.
 HR> (just don't ask your wife that question or your
 HR> cable will be far to short) 
Fortunately, I'm not married.
 
-- Mike
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