[time-nuts] Measuring coax temperature coefficient with a TICC

Bob kb8tq kb8tq at n1k.org
Wed Apr 19 19:23:04 EDT 2017


> On Apr 19, 2017, at 2:57 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> kb8tq at n1k.org said:
>> I’d want to be pretty sure what the center conductor was made out of. I’ve
>> seen some stuff in coax that “one would think” should not be there (copper
>> over steel …). 
> Does that effect the propagation time?
> If I gave you a good scope picture of a pulse after going through chunk of 
> coax, could you figure out the ratio of copper to steel?  Would you need to 
> know the length or could you figure that out too?

The issue is skin depth. On something like TV coax operated at the normal 
frequencies, a copper jacket is likely as good as full coper. The skin depth is such
that the signals never “see” the iron core to any real extent. 

With a pulse that has a fast edge things are quite so cut and dried. Most of the 
“signal” that you are measuring in that fast rising edge is at high frequencies. That
would suggest that the skin depth stuff would get you there as well. 

Best way to do it would be at low frequencies either DC or a LF sine wave.


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