[time-nuts] Measuring coax temperature coefficient with a TICC
Alan Melia
alan.melia at btinternet.com
Wed Apr 19 19:11:45 EDT 2017
MMmm interesting but what about skindepth ?? surely the "R" is not DC R so
would it matter? RF currents travelling in the copper anyway. I suspect
that a steel inner might increase the L/unit length?, maybe this is more
significant or not as is sceened by copper??
Alan
G3NYK
----- Original Message -----
From: "jimlux" <jimlux at earthlink.net>
To: <time-nuts at febo.com>
Sent: Wednesday, April 19, 2017 11:17 PM
Subject: Re: [time-nuts] Measuring coax temperature coefficient with a TICC
> 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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