Chris,
The power should be measured by the wattmeter in the KPA100 in both
cases. Note that you must use the KPA100 SO-239 jack (not the base K2
BNC antenna jack) anytime the KPA100 is installed.
The KPA100 contains a scaling circuit for the wattmeter (Q10 and Q11
with resistors R24 and R25) to change the wattmeter range between low
power and high power.
Other than the range scaling, there is no difference in the power
measurement.
To do that correctly, the wattmeter must be balanced (nulled) and then
calibrated with pot R26 for forward power and R27 for reverse power
(SWR). Use a good dummy load for that calibration and an external
wattmeter that you can trust for accuracy.
The ALC and the power level are not directly related, but the ALC does
depend on the RF Gain through the transmit stages, and the KPA100 adds
additional gain.
You might want to check the KPA100 bias adjustment before proceeding
with anything else. It sounds to me like your KPA100 may have too much
bias on the PA transistors which can drive them into distortion and
increase the gain of the KPA100.
The instructions for setting the bias as well as balancing and
calibrating the wattmeter can be found in the manual. When setting the
wattmeter balance, it is important to use a non-metallic screwdriver
because both ends of that capacitor are above ground and have some small
bit of RF on the cap. Using a metallic screwdriver will give you an
erroneous indication.
To make those adjustments, lay the KPA100 'on its back' to the right of
the K2 - place it on a book or other support about half the height of
the K2. You will have to remove the shield - remove only the zinc
screws, not the black ones that hold the shield clips.
73,
Don W3FPR
On 12/4/2013 3:54 PM, Chris Kimball wrote:
Critical question: When I adjust the power level of the K2/KPA combination
between low (10W) and high (100W) power is the power measurement taken at
the same point for both levels?
Clearly, the RF level scale changes between the two settings. 10W is full
scale below 10W, 100W is full scale above 10W. When operating below 10W is
the power level measurement taken from the K2 or from the KPA?
Assuming the ALC level depends on the power level measurement, a difference
in the point at which the power level is measured would explain the ALC
changes around the 10W level. My K2 and KPA were built and aligned by
different builders and there's no reason to believe they were set exactly
the same.
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