[Elecraft] Strange SWR change on 20 at

[Don Wilhelm]

Terry,

I would be suspicious of the voltage balun, or connections in the 
feedline/antenna that are breaking down with increased power.  Change 
the voltage balun to a good common mode choke.  A 1:1 choke may work as 
well or better than a 4:1.
You might also have a lot of common mode current on the 450 ohm 
feedline.  A common mode choke on each side of the feedline (at the 
antenna) will help if that is the case.

73,
Don W3FPR

On 5/13/2017 12:07 PM, Terry Brown wrote:
> I recently started using my horizontal loop that is about a full wavelength
> on 80, for 20 meters.  I took down my yagi as we are moving; drat!  My
> Horizontal Loop is at 40 ft.  height and fed with 450 window line into a 4:1
> voltage balun with about 15 ft. of coax to rig.
> 
>   
> 
> I am running 100 watts through my KXPA100.  I tune a frequency in the CW
> portion of 20 to about 1.2 :1 and start sending CQ.  After about 3 to 4  3x3
> CQ's,, the SWR goes off the charts and power drops to zero.   I can retune
> the antenna and the process repeats itself.  20 meters is the only band
> affected.
> 
>   
> 
> I am wondering if I am having RF problems in that part of the 20 meter bands
> This only occurs on 20 meters.  The Amp is grounded, but the KX3 is not
> bonded to the Amp.