[TowerTalk] Rising VSWR

[Tom Branch]

Greetings,

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?

Tom

tom at k4nr.org
http://www.k4nr.org