Hello Bob.

30 Jun 04 12:32, you wrote to Rod Gasson:

 BL>  You have to terminate it at *one* end, or the system will be running
 BL> into an open-circuit generating 20V! But that's got nothing to do with
 BL> the cable.

if you used a standard terminator on one end wouldn't you get only half the
expected impedance,  how many volts would you get then? 13.3 ?  and what's
it supposed to be? 10v ?

 BL>  The delay along a 10-metre 50-ohm cable would be something like 5
 BL> nanoseconds, but so what, when there are only two computers, one at
 BL> each end? The delay is goign to exist anyway, and when it reaches
 BL> the 50-ohm termination at either end it will be absorbed anyway.

but before it is absorbed it bounces back and reinforces the signal seen on
the cable.

 BL>  A
 BL> short cable will have negligible delay.

 BL>  The other thing I mentioned was the length. A long lossy cable (thin
 BL> cable) ends up looking like 50-ohms anyway. There are reflections, but
 BL> they are lost on the way back. For that thin cable, 10-metres will
 BL> be as good as infinity.

at 10Mhz I don't think there'd be be much loss over 10m

 RG>> It took me much experimenting before I discovered I needed the
 RG>> "T" at BOTH ends, and that both ends needed to be terminated
 RG>> before it would work.

 BL>  Rubbish. On a one-metre cable, it wouldn't matter a rat's arse
 BL> *where* you terminated it, all the way up to a gigahertz.

yeah, but I get the feeling that the ethernet cards refuse to work unless they
see a 25 ohm load.

as you say I seen no reason why it wouldn't work with a single terminator
but I feel it'd need to be a 25 ohm resistor. 22 ohms would probably be
close enough...  Hmm I'll have to score some T connectors and liberate one
of my BNC cables from the video lash-up and try it myself.

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