[TowerTalk] measuring old coax, return loss ?

[Jim Brown]

On 5/8/2024 6:23 PM, Jim W7RY wrote:
> In my opinion, DTF (distance to fault) measuring the return loss is a 
> much more informative measurement.
> You can see the bad spots in the coax, were they dont make specs. You 
> cant do that with just a return loss measurement.

Yes. And in general, TDR sweeps to find discontinuities in the cable can 
be performed with antenna loads connected. Because the coax will be 
matched only at the operating frequency of the antenna, both 99.99% of 
the sweep will produce reflections. This is true whether the excitation 
is an impulse or a sweep for which an inverse FFT is then performed to 
get the time response.

DG8SAQ's software for his VNWA does the latter, and the user has a 
choice of multiple windowing functions to provide the most useful view 
of the data. Depending on the frequency range being swept, a stepped 
rather than an impulse excitation can be used, which can display Zo of 
the cable(s) that are being swept (for example, a line that includes 
cables of differing Zo).

73, Jim K9YC