[time-nuts] Newbie questions

[Magnus Danielson]

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