K2 Linear Amp Driving Power

[Roy Morris-6]

This is a followup...
I put the linear output into a dummy load and tuned the amp to 1500 watts.  The K2/100 was reading approx 50 watts on the LCD screen and the K2 LEDs would indicate 4 to 5 bars in the RF mode.  This is good.  If I dropped the power to 1000 watts the LCD screen would indicate anywhere from 16 to 25 watts and the LEDs would indicate 1 to 2 bars.  I switched the tuner from the dummy load to the antenna position and it did not make any difference (it worked the same).  This was done on 75 and 20 meters.  I believe the DAC converter is affected by the strong RF field; however, the Bird 43 did indicate the same power out of the K2/100 as the K2s LCD screen indicated.  The K2 power knob becomes somewhat touchy at the 1000 watt level, and the K2 LCD power indication seems to get more realistic as the power goes on up to the 1500 watt level.  The K2VCOSHLDKT has been installed.  I have moved the K2 approx 3 feet away from the linear amp, but it is on the same side as the amps power transformer.  The K2 is also about 3 feet from the Astron VS35M.  (The foldback current limiting setting on the power supply is set fully clockwise)  Maybe magnetic fields can cause funny things to happen.  Roy Morris  W4WFB
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[Don Wilhelm-3]

Roy,

Your follow-up brings more questions than it answers.

It could just be the knee of the diode curve for the diodes in the wattmeter
of the KPA100 - or since the Bird agrees with the K2 display, it may be that
your amp is not really linear or the wattage indication on the output side
is incorrect.

Try the same thing with another transceiver driving the linear (with the
Bird in-line as with the K2) and see how the amp responds with the same
power inputs as indicated on the Bird - that will at least give you a basis
for comparison (but not really yield valid measurements - see below).

BTW, for the output to go from 1500 watts to 1000, if 1500 watts takes 50
watts, then the output with 25 watts should be 750 watts unless the amp is
not working in its linear range.  1000 watts out should require 33.3 watts
input.

How accurate is your Bird?  When was it calibrated last?  How did you
calibrate the KPA100 wattmeter?  Do you know how much you can trust the
output indication from your other transceivers?  The difference between 25
watts and 33 watts is about 33% and could be easily attributed to an
accumulation of tolerances.  If accuracy counts, everything in the system
must be properly calibrated and characterized to before drawing any
conclusions.

73,
Don W3FPR

> -----Original Message-----
>
> This is a followup...
> I put the linear output into a dummy load and tuned the amp to
> 1500 watts.  The K2/100 was reading approx 50 watts on the LCD
> screen and the K2 LEDs would indicate 4 to 5 bars in the RF mode.
>  This is good.  If I dropped the power to 1000 watts the LCD
> screen would indicate anywhere from 16 to 25 watts and the LEDs
> would indicate 1 to 2 bars.  I switched the tuner from the dummy
> load to the antenna position and it did not make any difference
> (it worked the same).  This was done on 75 and 20 meters.  I
> believe the DAC converter is affected by the strong RF field;
> however, the Bird 43 did indicate the same power out of the
> K2/100 as the K2s LCD screen indicated.  The K2 power knob
> becomes somewhat touchy at the 1000 watt level, and the K2 LCD
> power indication seems to get more realistic as the power goes on
> up to the 1500 watt level.  The K2VCOSHLDKT has been installed.
> I have moved the K2 approx 3 feet away from the linear amp, but
> it is on the same side as the amps power transformer.  The K2 is
> also about 3 feet from the Astron VS35M.  (The foldback current
> limiting setting on the power supply is set fully clockwise)
> Maybe magnetic fields can cause funny things to happen.  Roy
> Morris  W4WFB

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