Topband: RG-6 Delay cables

[Richard (Rick) Karlquist]

On 4/8/2020 10:37 AM, Lee STRAHAN wrote:
> Good morning from Oregon Top-Band people,
>
> Cable loss was -.61 dB at 59 Deg. F,  And -.58 dB at an averaged cable temperature of 23 Deg. F.
> 59 Deg. F                  23 Deg. F
> 1 - 74.59 DEG          -74.60  DEG.
> 2 - 74.59 DEG         -74.60  DEG.
> 3 - 74.59 DEG         -74.60  DEG.
> 4 - 74.59 DEG         -74.60  DEG.
> 5  -74.60  DEG         -74.60  DEG.
> 6 -74.60  DEG          -74.60  DEG.
> 7 -74.60  DEG          -74.60  DEG.
> 8 -74.60  DEG          -74.60  DEG.
> 9 -74.60  DEG          -74.60  DEG.
> 10 -74.60  DEG        -74.60  DEG.
> 
> My bottom line conclusion is that for our purposes on the top-bands I no longer wonder if the cable delay and attenuation remained constant with winter deployed arrays.
> Incidentally, T&B Snap and Seal have been the best connectors here for repeatability.
> 
> Lee Strahan
> K7TJR
> 

These numbers seem too good to be true.
The tempco works out to less than 7 PPM/°C.
Consider that the coefficient of thermal
expansion of copper is +17PPM/°C.

Refer to Figure 7 of this:

https://www.timesmicrowave.com/DataSheets/Literature/Current%20innovations%20in%20phase%20stable%20coaxial%20cable.pdf

The graph on the right shows non-linear tempco curves.
When you have non linearity like this,
it is possible to pick two points on the curve
such that a line drawn through them has a slope of zero.
Maybe you ran into that.

The numbers you reported for the loss seem roughly
consistent with what the thermal coefficient of
resistance of copper predicts.

Rick N6RK