K2: KAT2 Calibration Results, typical?

[Michael Linden]

Hi folks,

  I've finally had time to recalibrate my K2's KAT2 automatic antenna
tuner module using 25 and 100 Ohm loads on 40m. Please take a look at
my results and let me know if this is typical or if you think I have a
problem.

              25 Ω (2.0:1) 50 Ω (1.0:1) 100 Ω (2.0:1)
1900 kHz 2.1:1 1.0:1 1.9:1
3700 kHz 2.1:1 1.0:1 1.9:1
7150 kHz 2.0:1 1.0:1 2.0:1
10125 kHz 1.9:1 1.0:1 2.0:1
14172 kHz 1.8:1 1.0:1 2.2:1
18110 kHz 1.6:1 1.0:1 2.3:1
21200 kHz 1.5:1 1.0:1 2.4:1
24900 kHz 1.4:1 1.1:1 2.5:1
28500 kHz 1.4:1 1.2:1 2.6:1

        KAT2 - CALP (Watts) OHR WM-2 (Watts)
1900 kHz 5.5 6.0
3700 kHz 6.0 6.0
7150 kHz 3.9 4.0
10125 kHz 5.2 5.0
14172 kHz 5.2 4.9
18110 kHz 5.5 5.0
21200 kHz 5.5 4.9
24900 kHz 5.0 4.3
28500 kHz 5.0 4.1

  Given the VSWR numbers, I thought that performing the 25/100 Ohm
calibration on 20m or 30m might give me better overall results. To the
contrary, the overall results were much worse than performing the
calibration on 40m -- 40m seems to be the sweet spot for CALS.

  Likewise, attempts to improve on the overall forward power
calibration (make 10m a bit better and 160m a bit worse) only yielded
results that were worse overall. As with CALS, 40m also seems to be the
sweet spot for CALP.

  Note that my OHR WM-2 Wattmeter was calibrated with lab equipment at
40m. Also, my 25 Ohm and 100 Ohm loads were checked with my MFJ SWR
Analyzer.

  Any comments would be appreciated!

Michael N9BDF, K2 #4137
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[Don Wilhelm-4]

Michael,

I don't believe your results are a lot out of line, but neither can I
say that they are normal.
The diodes used in the wattmeter can have a frequency dependency - that
will be true for both the KAT2 and the OHR WM-2. If the frequency
dependency of the KAT2 is opposite that if the OHR WM-2, that will make
a greater difference between the two and will make the discrepancies
look larger than they actually are. So the bottom line is that you have
several variables that could be investigated if you wish. I do not
believe you have anything really wrong, just that the wattmeter readings
for both the KAT2 and the WM-2 are not up to the level of laboratory
measurements - or at least I would not trust them for exact measurements.

If I need a measurement that I can really trust, I use known good
terminating resistors (dummy loads) and measure the RF Voltage across
the resistors with a calibrated oscilloscope and 10X probe - and if the
power level is higher, I use a 20 (or 30) dB coupler like the Elecraft
CP1 to reduce the RF voltage to a point where I can measure it
accurately. Keeping the setup to the basics reduces the number of
variables, but it does require more computation - it is often easier
just to read a meter, or adjust a tuner for minimum SWR without regard
for the precise value of that lowest point, and that is the difference
between operating conditions and lab measurements.

Your measurements indicate that either the KAT2 or the WM-2 are adequate
for operating and should do the job nicely, but they are not adequate
for lab measurements unless they are first calibrated at the frequency
of interest.

73,
Don W3FPR

M. Linden wrote:

> Hi folks,
>
>   I've finally had time to recalibrate my K2's KAT2 automatic antenna
> tuner module using 25 and 100 Ohm loads on 40m. Please take a look at
> my results and let me know if this is typical or if you think I have a
> problem.
>
>     25 Ω (2.0:1) 50 Ω (1.0:1) 100 Ω (2.0:1)
> 1900 kHz 2.1:1 1.0:1 1.9:1
> 3700 kHz 2.1:1 1.0:1 1.9:1
> 7150 kHz 2.0:1 1.0:1 2.0:1
> 10125 kHz 1.9:1 1.0:1 2.0:1
> 14172 kHz 1.8:1 1.0:1 2.2:1
> 18110 kHz 1.6:1 1.0:1 2.3:1
> 21200 kHz 1.5:1 1.0:1 2.4:1
> 24900 kHz 1.4:1 1.1:1 2.5:1
> 28500 kHz 1.4:1 1.2:1 2.6:1
>
> KAT2 - CALP (Watts) OHR WM-2 (Watts)
> 1900 kHz 5.5 6.0
> 3700 kHz 6.0 6.0
> 7150 kHz 3.9 4.0
> 10125 kHz 5.2 5.0
> 14172 kHz 5.2 4.9
> 18110 kHz 5.5 5.0
> 21200 kHz 5.5 4.9
> 24900 kHz 5.0 4.3
> 28500 kHz 5.0 4.1
>
>   Given the VSWR numbers, I thought that performing the 25/100 Ohm
> calibration on 20m or 30m might give me better overall results. To the
> contrary, the overall results were much worse than performing the
> calibration on 40m -- 40m seems to be the sweet spot for CALS.
>
>   Likewise, attempts to improve on the overall forward power
> calibration (make 10m a bit better and 160m a bit worse) only yielded
> results that were worse overall. As with CALS, 40m also seems to be the
> sweet spot for CALP.
>
>   Note that my OHR WM-2 Wattmeter was calibrated with lab equipment at
> 40m. Also, my 25 Ohm and 100 Ohm loads were checked with my MFJ SWR
> Analyzer.
>
>   Any comments would be appreciated!
>
> Michael N9BDF, K2 #4137
>  
>

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