Tom Duckworth wrote:
Jim,
We use a benchmark 1 ns per foot of coax (RG-59).
This sounds fast. The normal taxiometer is at 66% of speed of ligth in
vaccum, which for 1 ns is about 3 dm so for the RG-59 that would be
about 2 dm.
Some cables reach 78%, but RG-58 and RG-59 is down at normal 66%.
You could measure the delay by using a resistive splitter (50 ohms) and
two cables (say a 2 foot and a three foot, each terminated at the far
end with a 50 ohm pass through terminator). Drive the splitter with your
10 MHz signal and measure, at the far end, using an appropriate
2-channel scope or counter with the necessary resolution, the difference
in time delay between the two, which will give you a pretty accurate
delay per foot. Both cables should be the same coax type.
Being a time-nut, using time-interval counters or TDR would be my
choice, but these tools/toys outnumbers the scopes...
Cheers,
Magnus
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