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

[jimlux]

On 4/19/17 3:34 AM, Bob kb8tq wrote:
> Hi
>
>
>> On Apr 18, 2017, at 8:33 PM, jimlux <jimlux at earthlink.net> wrote:
>>
>> On 4/18/17 3:55 PM, Bob kb8tq wrote:
>>> Hi
>>>
>>> On something like a 500’ spool of coax, the question will always be “what temperature is it where in the spool”. A single sensor will
>>> only give you precise information if the temperature ramp is *very* slow (as in days …).
>>>
>>
>> measure the DC resistance of the spool, and you'll be able to get a sort of "average" temperature.
>
> 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 …).
>

One would want to calibrate your "coax as temp sensor" just in case 
you've got some exotic stuff with silver plated over stainless steel 
(used in cryo applications).  But you could probably do that with a 
short length.

Copper is about 0.4% /degree
Iron is about 0.6%

So, over a -10 to 60 degree swing you'd see about significant (30-40%) 
change in the resistance, and it would be easy to tell if it's copper or 
iron or NiCr or something really exotic.

The Belden catalog says that RG58/U type coax is about 7-8 ohms/1000 ft. 
So a 10 foot length is 0.07 ohms - A bit tricky to measure that low, but 
not impossible, and certainly within the scope of a time-nut skilled in 
the electronics arts.