[Elecraft] 80m KPA1500 High reflected power problems

[Don Wilhelm]

Peter,

Isolate the problem to the amplifier.  Get a high power dummy load if 
you do not already have one.  Run the amp at 1000 watts or more into the 
dummy load.  If the amp behaves the same as it does with the antenna, 
then the problem is in the amplifier.
But if the amp behaves into the dummy load, look for marginal 
connections to your antenna, PL-259 connectors not sufficiently 
tightened, balun overload, arcing at either the center insulator or at 
the end insulators.
There is very high RF voltage at the antenna ends, and it may be arcing 
over the end insulators - don't overlook that possibility.

73,
Don W3FPR

On 3/9/2019 1:50 PM, Peter Dougherty wrote:
> HI guys,
> I'm still having a serious problem on 80m with my KPA1500.
> 
> With the amp inline I'm getting high reflected power fault everywhere below
> about 3675. My antenna (an inverted vee) is resonant at 3550, and the SWR is
> below 2:1 from 3500 to 3630.
> 
>   
> 
> This was happening in the past as well, and prompted me to completely
> rebuild the antenna last summer. The antenna is fed with 100' of brand new
> Davis BuryFlex feedline, a brand-new 5kW-rated Balun Designs 1:1 current
> balun, new 12 AWG copper-clad steel wire, even new heavy ceramic insulators!
> 
> 
> Without the amp everything's fine. I can push 100W through to the antenna
> all day; the SWR LEDs on the amp (bypassed) show two green and that's it.
> It's fine on every other band, including 80/75 phone.
> 
>   
> 
> With the amp in, If I drop the drive to 10W or less, the amp is happy and I
> get about 450 Watts out. But the instant I drive it with ~15 Watts (when the
> K3s kicks the high power module in, and I hear the internal relay click, I
> get the HI SWR warning and the amp faults. 100% repeatable. Doesn't matter
> if the tuner is in or out..there's NO way to get high power out of the KPA
> on 80 CW.