[Elecraft] KXAT100 "Hunting"

[Dauer, Edward]

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