[Elecraft] K3/KPA500/KAT500 SWR problem

[Bill Johnson]

Good points, Don.  As a KAT500 FT'er, I used an extensive external grounding
system.  I also use a large loop, a 75 dipole and multi band shortened
dipole as well.  Generally I have little to no issues.  One can "get by"
while on QRP, with significant losses on improperly installed antenna
systems, but once the power goes, esp., QRO, the problems are "amplified"
(pun intended)!  I am also very careful when making a large frequency
excursion to start a lowered power tune, despite memory tuning, just to give
a lower power tune rather than full power.  

73,
Bill
K9YEQ

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Don Wilhelm
Sent: Monday, December 30, 2013 4:26 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] K3/KPA500/KAT500 SWR problem

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

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