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@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@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
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