[TowerTalk] measuring old coax, return loss ?

[Jim W7RY]

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.

We (Motorola System Technologists) did both, but the DTF RL was much 
more useful. You could see where the ground kits were installed along 
the Heliax, and you could also see where the Heliax had banged against 
the tower when it was being raised up, and being unrolled from the reel, 
or where the cable was bent to sharply.

There is a specification for Return Loss along the entire length of the 
cable. If it did not meet spec, the cable was usually replaced at the 
tower crews expense.

https://dl.cdn-anritsu.com/en-us/test-measurement/files/Technical-Notes/White-Paper/11410-00899C.pdf

*AVA5-50A Return Loss spec:*






AVA5-50A was MUCH EASIER to damage than LDF-4.

And yes, I have swept a 200' piece of used LDF4, and removed a dent in 
the cable, and you could watch the Return Loss get better.

73, Jim W7RY




On 5/8/2024 8:05 PM, Wes Stewart via TowerTalk wrote:
>     On Wednesday, May 8, 2024 at 04:32:19 PM MST, Ken WA8JXM<wa8jxm at gmail.com>  wrote:
>   
>   "IDK, is "return loss" measurement necessary?"
>
> Of course not.
>
> "I checked some old coax a few years ago, connected a dummy load to the far
> end and used the power meter on my Palstasr tuner to measure the input
> power, then moved it to the far end for a measurement. Very little
> difference in readings so I assume it was still good.  Am I missing
> something?"
>
> Only accuracy.  Otherwise, you are more or less using my "best" method described earlier.
> So, it depends.  If the cable is going to be used for a 160-meter dipole you're probably good enough.  On the other hand, if you're going to feed a two-meter EME array, that's a different story.  I've done both.
> Wes  N7WS
>
>
> On Wed, May 8, 2024 at 2:14 PM Wes Stewart via TowerTalk <
> towertalk at contesting.com> wrote:
>
>>    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.
>    
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-- 
Thanks and 73, Jim W7RY