One of the best ways to check if you have a bad coax is to terminate the
coax with a dummy load that gives you for instance 3:1 in SWR, i.e. 150
ohms.
If you have a better SWR, e.g. 2:1 you know you have a bad/lossy coax.
Terminating the coax with a 50 ohm dummy load doesn't give you any info
about the coax as the SWR can't get any better than 1:1. Just my 2 cents.
73 Bert, VE3NR
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Chuck
Sent: Wednesday, December 21, 2011 9:11 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] SWR Problem Balun or lightning protection?
If you have moisture in the coax, it can act like this. There will be a
high resistance path to ground which will heat up on transmit and reduce in
resistance, causing the SWR to rise. Test the coax with a digital meter and
you will probably find a meg-ohm or two from the center conductor to ground.
(Disconnect the antenna unless it is a gamma match or other, non-shorted at
DC feed and the balun, depending upon the type of balun.) If so, replace
the coax. Good luck!
Chuck W5PR
----- Original Message -----
From: "Joseph or Ruth Patrick" <hdmc38@bellsouth.net>
To: "Tony" <dxdx@optonline.net>
Cc: <towertalk@contesting.com>
Sent: Wednesday, December 21, 2011 7:48 AM
Subject: Re: [TowerTalk] SWR Problem Balun or lightning protection?
Good Morning Tony
It seems as if you have eliminated the lightning protection. I would ask if
you
can easily reach the balun? You may have to. Put a known good 100 watt dummy
load at the connection from the coax to the balun. If you come up good here
chances are it's the balun or further down the line. If you still get high
swr
with this check then it's the coax or connections. I had a 75' run of coax
go
bad and this was the best way I know of to check it. Others may have better
suggestions. Good Luck let us know how you make out. Merry Christmas to all.
73 DE K4XZ Joe Patrick
God Made Man
Sam Colt Made Them Equal
________________________________
All,
I bypassed the lghtning protection and the SWR problem is still there. I
installed a new coax connector on the shack side of the coax as well.
I still have to check the balun, balun leads and the coax-to-balun
connector. There's nothing else inline. The coax (Bury Flex) and balun
(3KW M2) were installed a few years ago.
I just checked the system again with two different 100 watt rigs and
found that:
- I can transmit for 2 or 3 minutes from a cold start before the SWR
starts to rise
- the SRW returns to normal 30 seconds after I stop transmitting
- it takes a lot less time for the SWR to rise after the 30 second rest
period
I did replace the ground wires with copper strap a few months ago, but I
haven't made any other changes to the tower and antenna system.
Why do these things always happen during the winter ; )
Tony, K2MO
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