Re: KPA-1500 issues

Posted by Paul Baldock on Nov 27, 2018; 7:39pm
URL: http://elecraft.85.s1.nabble.com/KPA-1500-issues-tp7646571p7646575.html

There is definitely room for improvements in the
tuning algorithm. Because of this I have tuned
all my segments manually. I find if the SWR is
not adjusted to be close to 1:1 in all segments
of a band then the drive requirements vary across
that band, which would be very annoying.

In addition the tuner may not always be in the
segment you think it is. This is due to the 8KHz
resolution of the internal counter, that wins
over you sending it a more accurate frequency,
and also the hysteresis algorithm that can
require a 2 segment frequency change before the
tuner changes. Gary from Elecraft says "if you
are off by one bin segment then it should not matter too much"

I also note that when into a perfect 50 Ohms, and
the tuner bypassed, on 6 meters, my KPA1500 says
the SWR is 1.4:1. On 10 meters it reads 1.2:1.
Rene from Elecraft says "this is the best they can do".

Other than the issues above I am very happy with the KPA1500.

- Paul


  At 09:59 AM 11/27/2018, Dick via Elecraft wrote:

>I've experienced some of these same issues with
>my KPA-1500.  In addition, sometimes the amp
>will switch to stand-by for no apparent reason,
>on 6 meters the AT won't tune a 1.7 to 1 SWR
>under 1.5 to 1, and one of the exhaust fans got
>a good deal noisier after about 25 hours of
>operation.  My amp is back at Elecraft for
>service as I write. Â  73, Dick- K9OMÂ  Â  On
>Mon, Nov 26, 2018 at 5:15 PM K9MA
><[hidden email]> wrote: > This was my first
>serious contest effort with the new amplifier.
>It is > paired with a K3. It survived about 24
>hours of operation, though it > faulted a few
>times, as described below. Clearly, the
>protection > circuitry did its job. Firmware is
>1.87. > > A couple glitches: > > The power gain
>drifts downward as the transistors heat up. If I
>start > out at 1500 W, it will drift down to
>about 1100, without changing > frequency or SWR.
>Conversely, if I turn the drive up after the amp
>is > warm, and forget to turn it back down, the
>amp will fault when cold. > Since the amp is
>talking to the K3, couldn't some clever software
>fix this? > > Despite setting tune power to 40
>W, the ATU sometimes just won't get the > SWR
>below 1.4:1 or so. This is with antennas below
>2:1, and the ATU stop > set to 1.0. This happens
>on 40 meters, so it's probably not an ATU L/C >
>resolution limit. This 1.4:1 SWR is sometimes
>high enough to limit > output to well below 1500
>W due to high drive power or high current. I >
>have not yet tried manually tuning the ATU to
>see if I can get the SWR > lower. > > Finally,
>after "training" the ATU across the band, I
>sometimes find that > the SWR has gone up
>significantly at some frequencies. I don't
>believe > this is due to changing antenna SWR.
>It seems more like the ATU has > "forgotten" the
>settings, or tried to retune itself without
>permission. > (HiSWR RETUNE OFF) > > Has anyone
>else seen similar issues? > > 73, > > Scott
>K9MA > > -- > Scott K9MA > > [hidden email]
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