Hello Bob.

11 Jul 04 11:24, you wrote to me:

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

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

 BL>  Actually, half. Now you\re startign to think like an engineer,
 BL> rather than a tech who only sees black and white. The next thing you
 BL> have ot ask youself is *what difference would it make?"

 BL>  Hint: two words: first word starts with "F", second word
"all."

it made a difference when I tried it.

 BL>  Imagine... you'\re an engineer designign a system, where one
 BL> computer might be right alongside, or 50-metres away, where the
 BL> level drops 20dB (10-times). What tolerance would you allow in levels?

20 db is 10 times? - ah 10 times the voltage 100 times the power  i'd forgotten that.

The loss in that cable is less than that at 100Mhz... at 10Mhz it must be
much better.

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

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

 BL>  Ahh, Grasshopper... have you ever heard of resistance besides
 BL> dialectric losses? Both of which increase, btw, with thin cable.
 BL> Dialectric loss hardly matters below 200 MHz.

I actually dug out a calculator ant tried to figure out the resistance of
this cable, and it's stuff all (about 5.5 ohms round trip on a 100 m
segment)

I called that 0.23 db loss, but in power terms it's twice that, but still
less than half a dB

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

 BL>  It'd still work,

Not in this corner of splong..

Jasen

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