[Antennaware] Hy-Gain TH-3 Mk4 Tribander problem

[RLVZ at aol.com]

Hi Guys,
 
I've had several Hy-Gain TH-3's over the past 30 years and never had a  
problem with one.  But I've now got a problem with the latest model:  TH3-Mk4:
 
Running it on 15-meters with the amplifier on, the SWR starts out at  1.2 to 
1 but as I transmit over a period of a few minutes the SWR gradually  climbs 
to over 2:1.
 
I've checked the traps and they are clean, I've checked the screws  inside 
the traps and they are tight and clean, I've tried replacing the balun  with the 
same problem, I've replaced the coax... same problem.  All  connections 
appear tight.
 
I even ran the antenna on saw horses until the SWR rose to over 2:1 and  then 
ran outside to check for hot spots!  Nothing was hot.
 
I've tried different SWR meters too.
 
Any idears?
 
Thanks!  73 & Merry Christmas!
 
Dick- K9OM



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