KPA1500 ATU

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KPA1500 ATU

K9MA
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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Re: KPA1500 ATU

wa2lbi@gmail.com
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: K9MADate: Wed, Feb 6, 2019 10:50To: [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

[hidden email]

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Re: KPA1500 ATU

K9MA
Hi Ken,

At the frequency of interest, the KPA1500 ATU goes right to bypass mode
with a dummy load.

73,
Scott K9MA



On 2/6/2019 10:06, [hidden email] wrote:

> 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
> [hidden email]  <mailto:
> [hidden email]>
>
> _____________________


--
Scott  K9MA

[hidden email]

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Re: KPA1500 ATU

N4ZR
In reply to this post by K9MA
I'm seeing a similar phenomenon, Scott, but figured I'm too much of a
newbie with the amp to question it.

73, Pete N4ZR
Check out the Reverse Beacon Network
at <http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.

On 2/6/2019 10:49 AM, K9MA wrote:

> 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
>
>
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KPA1500 ATU

ANDY DURBIN
In reply to this post by K9MA
"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."

What is the SWR stop threshold set to.  It's controlled by serial command (^STS) and I assume that, like the KAT500, the value(s) can be set with the utility.  

Andy, k3wyc
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