[Elecraft] KXAT100 "Hunting"

[Vic Rosenthal 4X6GP/K2VCO]

My guess is the same as yours -- common-mode current on the outside of 
the coax upsetting the tuner circuitry. If you have a large ferrite 
toroid (ferrite #31 should work on all bands), try winding several turns 
of the coax around it. It might work better near the rig or near the 
antenna.

Also, changing the length of the feedline might help. Odd multiples of 
1/4 wavelength are bad.

73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/

On 30 Jan 2016 19:54, Dauer, Edward wrote:
> My KX-line tuner (the KXAT100 installed in the KXPA100 amp) recently
> started an odd behavior.  I wonder if anyone can help explain it.  When
> tuning into an indoor Buddipole set at resonance, the ATU finds a
> near-perfect solution when the power applied during tuning stays below
> about 40 watts.  With the ATU set in “auto” however, if the power out is
> higher than 40 watts the tuner hunts without stopping.  I have watched the
> SWR readings change, often going briefly to 1.0 or 1.1:1, but the tuner
> just keeps hunting, endlessly, even when the frequency is unchanged.  Yet
> when it is first tuned at a lower power, either in Auto or Manual-tune,
> and the ATU is set to Manual, it stays at the solution perfectly well no
> matter how high the power goes.  I can live with this, just by tuning at
> low power and then switching to Manual, but I wonder why the Auto function
> works well up to a certain point but goes berserk at any power higher than
> that?  Is the higher ERP sneaking back into the control circuitry somehow?
>
> Ted, KN1CBR