Had swr increase with power on time 3 times. These all occurred with 1.5KW.
- BN-86 on a TH7 caused an increase in swr after a few minutes of key down.
- A section of hardline had taken a lightning hit. Couldn't find it for a
while. Finally found a slight bulge in the outer covering, but no holes. A
good portion of the shield was vaporized. But there was just enough shield
left for a dc ohm measurement. When I first keyed down it was fine. After a
minute or tow the swr increased.
- Last year my swr was changing on 80m. Turned out to be we have very acidic
soil here in NY. 20' of my feed lines were several inches in the ground to
get through a flowerbed. Over 8 years the shield on the hardline became
gooey. Actually it was decreasing the swr until I lifted the grounds from
the other feedlines. Then it went up.
Tom, share with us what you find is causing the problem.
[mailto:firstname.lastname@example.org]On Behalf Of Tom Branch
Sent: Tuesday, January 28, 2003 00:51
Subject: [TowerTalk] Rising VSWR
I'm trying to chase down a problem in my antenna system. On 80 and 160
meters, I see a rise in VSWR after calling CQ for a while or running RTTY.
This would lead me to balun saturation, but I have three baluns on the tower
for my sloper array it happens with any of them. They are 160 - 10 meter
baluns from the Radioworks and rated at 5 kW. I also have a line isolator
near the shack that's rated for 160 - 10 meters rated at 2 kw. There is
also a Alpha-Delta 2 kw Transitrap in the line. The antenna is resonant
with a 1.1:1 VSWR. on the test portions of 80 and 160 meters. All the
parts appear to be rated for the legal limit with the exception of the RG-8X
in the shack. I note the coax between the tuner and the single-point ground
does get a bit warm with high-power RTTY. I plan on replacing the run from
the tuner to the single-point ground (where it converts to RG-213) this
weekend with RG-213. Could the coax be causing the VSWR rise? I've run RTTY
on 20 meters at the legal limit--the coax gets warm but no rise in VSWR.
Thoughts or ideas?
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