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@gmail.com>
Date: 5/8/24 6:31 PM (GMT-06:00)
To:
Cc: towertalk@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@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@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
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