> It is 50 ohm cable but the card is driving two stretches of cable
> in connected to it in parallel (by the Tee connector), so it sees
> a 25 ohm load.

JT> Ok, that sounds logical too. But they never taught us that in
JT> transmission line theory. The bastards only concentrate on
JT> ideal models, never real life examples.

 The usual case is a 50-ohm source drivign a 50-ohm load, in which
case it delivers half the open-load voltage. The network drives from a
constant current (hi-impedance) so you need two 50-ohms to match it
corectly and the *current* halves into the 25-ohm the transmitter
sees.

JT> It was an el-cheapo time domain reflectometer, one signal
JT> generator, one cro. Leave the other end underminated, (or
JT> shorted) and look at the reflections. We estimated distance
JT> going on the time of the reflection. Worked quite well. Saved
JT> us from reterminating the whole network.

 Waht did the pulses look like, unterminated by the break? Did they
ring like a bastard, or where they still reasonably clean?

JT> Naw, the longer the better. If you have t-pieces inbetween, you
JT> can experiment and progressivly remove each one and look at how
JT> it effects the reflections.

   To see the ringing, look at the end that is unterminate (or
broken).

Regards,
Bob



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