> Scott,
>
> Did you try testing with a 50 ohm dummy load instead of an antenna?
> How goes it react?
>
>
> /Ken /
> /WA2LBI /
> /LG G6 /
> /
> /
>
> ------ Original message------
> *From: *K9MA
> *Date: *Wed, Feb 6, 2019 10:50
> *To: *
[hidden email] <mailto:
[hidden email]>;
> *Cc: *
> *Subject:*[Elecraft] KPA1500 ATU
>
> Ever since I received my KPA1500 (SN 00178), I've observed that the ATU
> sometimes won't achieve a match better than about 1.4:1, even though the
> antenna SWR is well within range. (ATU STOP TUN SWR = 1.0:1, tune power
> 40 W) Now, 1.4:1 doesn't sound that high, but the amplifier will often
> not operate at full output at that SWR, either due to excessive current
> or drive power. This is particularly troublesome when tuning across a
> band. Clearly, the KPA1500 is designed to deliver 1500 W to a 50 Ohm
> load, with little margin for a mismatch. More margin would have
> increased cost, size, and weight, of course.
>
> Just to be sure there isn't something unique wrong with my KPA1500, have
> others observed similar behavior?
>
> A little ice on the antenna this morning provided an opportunity for a
> test. On 40 meters, the antenna SWR was 2.2:1. The best match the
> KPA1500 ATU could attain automatically was 1.4:1, in multiple attempts.
> I was able to manually get it down to 1.1:1. (SWR as indicated by the
> KPA1500 display.) It was a little tricky, requiring one value to be
> increased beyond the SWR minimum before the other was adjusted, as often
> happens with manual tuners. With the KPA1500 ATU bypassed, the K3 ATU
> automatically got it down to 1:1 on the first try.
>
> My conclusion is that there's something about the KPA1500 ATU algorithm
> that prevents it from achieving a better match, in some cases. (I'm
> assuming that, aside from their power ratings, the components in the
> KPA1500 ATU and the K3 ATU are similar.) I'm wondering if the KPA1500
> ATU algorithm could be improved to perform more like that of the K3 ATU.
> That would allow operating the KPA1500 closer to full power across a
> band without having to ride the power control.
>
> Further details of ATU component values, etc. are available.
>
> 73,
>
> Scott K9MA
>
> --
> Scott K9MA
>
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>
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>
> _____________________