[Elecraft] KXAT100 "Hunting"

[Dauer, Edward]

Thanks, Don.  I will try adding feed line chokes (after rereading K9YC’s 
tutorials on the subject.)  Meanwhile, tuning at low power and then 
switching to manual does work, though it’s inconvenient with the Buddipole 
which in some configurations has a very sharp SWR null.  The Auto function 
is useful when prowling the entire band quickly from 7005 to 7055 or the 
like.  Tuning at low power then switching to manual with any significant 
frequency change adds a couple of steps . . . 

However, I have to confess that this is not one of life’s major issues.  I 
remember some years ago hearing someone complain that the driver’s side 
power window in his car did not have the function that allows the window 
to travel its full length with one flip of the switch, as most other cars 
do today.  His required that he actually hold the switch until the window 
was all the way up.  What an awful burden to bear, I thought.  My first 
car (a ’57 MGA) didn’t even have crank-up windows.  What MG then called 
windows were solid pieces of fabric and plastic in a steel frame that 
mounted into the doors on posts.  They could be in either of only two 
positions - on the door, or in the trunk.

Useful to remember when complaining about the limits of an auto-tune 
function.

Cheers,

Ted







On 1/30/16, 3:15 PM, "Don Wilhelm" <w3fpr at embarqmail.com> wrote:

>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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