Hello Bob.

18 Jul 04 09:59, you wrote to me:

 JB>> This week I happened by a garrage sale and grabbed a BNC cable
 JB>> (approx 10m) some Tees and terminators, I tried it - nothing
 JB>> like real-world experience. With a terminator at each end it
 JB>> works, any other setup including, no terminators, one
 JB>> terminator at one end and both terminators (and both Tees) at
 JB>> one end doesn't work.

 BL>  I can't argue with a measurement, but I don't understand.

 BL>  There must be something about the pulse timing (or amplitude) that
 BL> is *very* critical. 10-metres is a quarter-wave for 120MHz, even
 BL> higher in thin coax, and a 10MHz pulse is only going to shift 10
 BL> degrees or so...

???

Signal speed in the cable is 2/3 c  so near 200 000 000 m/s  so a full wave
at 10Mhz is  20m (or from one end of the 10m cable (which I didn't
actuually measure) to the other and back again)

 BL>  The pulse will ring, with overshoot in the negative direction...
 BL> perhaps it's that.

 BL>  Oh, well... I'm wrong. Well done. A measurement is worth a hundred
 BL> opinions. Now all you have to do is explain why...

I say it's the impedance the card sees... wether it sees the higher
impedance because of the reflected signal or because there's just less
load...

probably an over simplification, but I'm not the engineer. :)

Jasen

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