[TowerTalk] measuring old coax, return loss ?

[Wes Stewart]

 The "best" way depends on what equipment you have to make the measurements.  In my best case, I have a DG8SAQ Vector Network Analyzer (VNWA) that, with proper calibration will measure the through loss directly.
My second best is, besides using the VNWA in the reflection mode, is to use a DG5MK FA-VA5 one-port Vector Antenna Analyzer.  Take two sets of data, one with the far end shorted and one with the far end open.  The use AC6LA's ZPlots program to extract the lost and velocity factor, if you care.
The least accurate, but probably good enough in many cases is to use whatever device you have to measure return loss, but the line must be terminated in a very highly reflective load, i.e. short or open.  The coax loss is them 1/2 of the return loss in dB.  When measuring with a dummy load, you don't know what you're measuring, the load, the coax or the combination.  A short or open removes one variable.
In all cases remember that loss and velocity factor (Vp) vary with frequency.
Wes  N7WS

    On Wednesday, May 8, 2024 at 09:43:14 AM MST, Jamie WW3S <ww3s at zoominternet.net> wrote:  
 
 What is a good way to test older coax? return loss? I am seeing 12, 
almost 13 db return loss into a dummy load, with about 55 ft of coax, 
good, acceptable or ?!?!?!?!
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