[Elecraft] K3/KPA500/KAT500 SWR problem

[Don Wilhelm]

Things like that will show up at medium to higher power levels even 
though all looks well at lower power.
Common mode RF voltage getting into the shack will also cause similar 
behavior.
Ninety percent of those type problems are solved in the antenna field - 
tight good quality connections, good coax and adequate common mode 
chokes installed at the right places will usually fix it.

Note also that a good ground system in the shack is usually *not* a good 
RF Ground and thinking it to be an RF ground will lead to a lot of 
confusion and false moves.  For instance, an RF Ground (point of zero RF 
voltage crossing) is found at the center of a dipole's center insulator 
or between the base of a vertical and a ground plane.  The job of a 
current choke (or balun) is to constrain the feedline to equal and 
opposite currents between the conductors so the RF ground point as well 
as RF voltage sources stay where they belong.  I digress, but a ground 
rod does not make an RF Ground no matter how it is connected.  It may 
actually be a high impedance for RF - consider a wire to that ground rod 
of 8 feet - that will have a high impedance on 10 meters just because it 
is a 1/4 wavelength connected to earth (a low impedance point).

73,
Don W3FPR

On 12/30/2013 3:48 PM, Buck - k4ia wrote:
> I had a similar issue.  Drove me crazy.  Then one day I put my hand on 
> the PL259 on my antenna switch and noticed it was warm.  Swapped out 
> the 90 degree connector on the coax and problem solved.  The high 
> power from the amp must have been causing a fault in the connector.
>
> Lesson 1.  Check all your connections.
> Lesson 2.  Stop buying cheap coax connectors
>
> Buck
> k4ia