[TowerTalk] measuring old coax, return loss ?

[Jim W7RY]

Look at the link  just sent.
I should cover that.

Jim W7RY


On 5/8/2024 8:23 PM, Dave . wrote:
> I have a aligent 8920a..it has been calibrated...I have the Aligent return loss adapter...two 6db attenuators
> And a Huber Shuner power divider...and a 50ohm dummy load........I also have the RF Tools software for the Aligent..
>
> So..is it better to measure with the 50ohm dummy termination.....OR a Short?  And what is the difference in the readings shown?
>
> I'm sure this is easy peasy for you..however we are eager to learn and can't wait to learn more
>
> The videos on how to do this procedure are lacking ...very lacking......I was hoping that there would be some from Aligent..but none..
>
> Thank you in advance.
>
> Dave
>
>
>
>
> -------- Original message --------
> From: Ken WA8JXM <wa8jxm at gmail.com>
> Date: 5/8/24 6:31 PM (GMT-06:00)
> To:
> Cc: towertalk at contesting.com
> Subject: Re: [TowerTalk] measuring old coax, return loss ?
>
> IDK, is "return loss" measurement necessary?
>
> 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?
>
> Ken WA8JXM
>
> 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.
>> 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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-- 
Thanks and 73, Jim W7RY