[Elecraft] KXAT100 "Hunting"

[Don Wilhelm]

Ted,

You may need additional current mode chokes on the feedline in addition 
to the small ones provided by Buddipole.

I would suggest "training" the tuner on each band segment that you want 
to use and then put the tuner into MAN mode.
I realize that is more difficult with the Buddipole because after 
changing bands with its taps and element lengths, you might not end up 
with exactly the same thing each time.
So as an alternative, set the band on the Buddipole, then with the 
KXPA100 in AUTO, do a TUNE at low power - when that tune completes, 
switch to MAN mode and operate.  The KXPA100 should not automatically 
tune in MAN mode.

If you are operating SSB (and less often CW), there can be a false 
sensing of a high SWR condition that will cause retuning if in AUTO mode.
That is because of a combination of two things - first the syllabic 
nature of SSB speech and secondly because the KXAT100 (and other tuners) 
do not sample the forward and reverse voltage at the same instant.  So 
if the forward voltage is sampled at a time when the RF output (do to 
the variations in SSB speech) is low, and the subsequent sampling of the 
reverse voltage happens to be at a time when the RF output is high, a 
false computation of the SWR will result (it is all a matter of the math).

In other words, once the antenna is tuned, switch to MAN mode on the tuner.

73,
Don W3FPR

On 1/30/2016 12:54 PM, 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
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