[Elecraft] K3 Autotuner malfunction

[Don Wilhelm]

Rob,

I would suggest that on 40 meters and 80 meters, your loop is presenting 
a very low impedance to the shack end of the feedline.
Tuners of all types do not work well into very low impedance loads.
Add or subtract somewhere between 1/8 and 1/4 wavelength of feedline at 
the problem frequencies and see if that helps your problem.  Of course, 
that solution possibly could introduce problems on other bands, but it 
is worth a try.

73,
Don W3FPR

On 7/3/2015 2:29 PM, Rob KK4R wrote:
> I have been having problems with my K3 auto tuner using an antenna that has
> worked well and been tuning easily for nearly all bands.  My first reaction
> was to assume the antenna, an 80m horizontal loop, was the problem, but I am
> now convinced otherwise.  To prove that, I did the following:
>   - took the antenna down, refurbished it, and replaced the feed line (not
> wasted energy);
>   - tried other baluns;
>   - confirmed that my LDG tuner has no problem tuning; and
>   - tuned it manually with the K3 tuner.
>
> The problem behavior is this.  On 40m and 80m, the K3 will not find a decent
> SWR (<1.7:1) when auto-tuning.  On 80m it has done fine tuning one direction
> across the band and failed going the other direction over a significant
> portion of the band.  This is repeatable.  On 40m, the SWR for the antenna
> system at the rig end is only about 1.7:1 at the low end and 1.4 at the high
> end.  At the low end, the K3 tuner will not find a match under when the ATU
> TUNE button is used, except in particular circumstances.  Using the menu
> system to check tuner values, it ends up with the capacitor connected at the
> antenna side at a low value and with a low value of series inductance.
> Effectively this is near the bypass mode.  Hitting the ATU TUNE button to
> cause a long tune cycle makes no difference.  Manually, the capacitor can be
> switched to the transmitter side, and a match near 1:1 is easily set by
> adjusting L and C.
>
>