[time-nuts] Measuring coax temperature coefficient with a TICC
jimlux
jimlux at earthlink.net
Wed Apr 19 18:17:05 EDT 2017
On 4/19/17 11:57 AM, Hal Murray wrote:
>
> kb8tq at n1k.org said:
>> Iâ€™d want to be pretty sure what the center conductor was made out of. Iâ€™ve
>> seen some stuff in coax that â€œone would thinkâ€ should not be there (copper
>> over steel â€¦).
>
> 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?
This being timenuts, I think you might do it with just timing measurements.
Let's see - the different candidate materials all have different thermal
resistance coefficients. So you can make some DC measurements. If you
knew it was some combination of copper and steel, for instance, you
could probably determine the ratio from that alone (or, for that matter,
doing it at a single temperature, if you can *measure* the diameter of
the conductor).
There is some variation in material properties (not all copper is the
same, and, in particular, steel varies widely depending on alloy and
manufacturing).
The propagation equation has a dependence on both R and G as well as L
and C
Is the change in prop speed due to the change in R bigger or smaller
than the change due to L and C (from dimensional changes)?
The L and C terms both have a frequency dependent (linear in frequency)
term. The R term has a fairly complex dependency on frequency, in terms
of skin depth relative to the diameter of the conductor. The G term
also has a frequency dependence.
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