KPA-1500 power reading?

[Elecraft mailing list]

When I received my KPA-1500, I noticed I had to drive the LEDS into the
"red" zone to indicate 1500 Watts into my Bird 43 wattmeter with a 2500W
slug, and Palstar DL2K dummy load.

There also was a comprehensive part of the KPA-1500 manual that details how
to readjust the power indicating LED's, so I was wondering - what gives?

The Bird 43 specs have a tolerance of 5% of full scale, which for a 2500
watt slug is 125 watts.

I asked Wayne (or was it Eric?) at a show as to what was used by Elecraft to
calibrate the amp's power meter and was told they used the LP-100A.

So, that is the standard that was used in the Calibration of the KPA-1500's.

'73 de JIM N2ZZ



-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Mark Goldberg
Sent: Sunday, February 07, 2021 12:38 PM
To: Jim McCook
Cc: Elecraft Reflector
Subject: Re: [Elecraft] KPA-1500 power reading?

The meter itself can be off too. Using more slugs does help things,
but to be really sure, test equipment needs to be periodically
calibrated, which Hams never do. Dummy loads should be measured with a
VNA. So, what you did is a big help, but still can't provide 100%
assurance that it is accurate. I understand that is the best most Hams
can do and probably better than most.

An LP-100A does come with a NIST traceable calibration from the
factory and it can be recalibrated, again something Hams never do. I
have one fancy scope / spectrum analyzer that I do get calibrated
yearly and I use that for a reference. I have a VNA with a set of
calibration standards and use that to measure attenuators / taps that
I put between my transmitter and the analyzer. I admit I do not
calibrate anything else, but I use the calibrated stuff as transfer
standards. I also have a couple GPSDOs as frequency standards to
compare to.

73,

Mark
W7MLG

On Sat, Feb 6, 2021 at 4:55 PM Jim McCook <[hidden email]> wrote:

>
> Good points, Ray and Jim,  I should have been more detailed with what I
> posted. I checked The Bird 43 with two other Bird 2500w slugs from
> friends and they were all reading the same with a dummy load at 1500w.
> I did the KPA1500 calibration using the Bird with a high power dummy
> load, then checked again with my antennas in band segments where they
> present no significant reflected power and near 1:1 SWR.  At those
> points they were in sync.  Most of my antennas are flat on CW segments
> at specific spots without using the tuner in the KPA1500.  I operate 99%
> CW and realize that when the load changes from 50 ohms the Bird reads
> wildly high and cannot be trusted.  - Jim W6YA
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