Is your dummy load absolutely a flat 1.0:1 from 1.0MHz to 30MHz?
73,
Tom
Amateur Radio Operator N5GE
ARRL Lifetime Member
QCWA Lifetime Member
"Only the white eyes would believe they could cut the top
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On Tue, 07 Feb 2012 13:35:47 +0000, Brian Alsop <als...@nc.rr.com> wrote:
>Guys,
>
>I'm also curious about this-- especially what's going on on 15M.
>My values at 500 W out into a dummy load are:
> (amp), [volts], {efficiency}
> 1.8MHz DC (11.5) [63.1] {70}
> 3.5MHz (11.2) [63.5] {71}
> 7MHz (12.2) [62.5] {67}
> 10.1MHz (not measured)
> 14MHz (13.4)[61.8] {60}
> 18.1MHz (12.9)[62.8] (63}
> 21MHz (15.8)[61.2] {52}
> 24.9MHz (14.6) [60.1] {56}
> 29.7MHz (14.7)[60.4] {56}
>
>These are in reasonable agreement with David's except for perhaps 10M.
>
>The problem with these measurements are the wattmeter accuracy (10%?)
>and the current measurement inaccuracy. Default wattmeter calibration
>factors were used above. Elecraft is using a Hall effect device to
>measure PA current. It would be nice to know just what accuracy to
>expect from it.
>
>The efficiencies appear to be in the right ballpark. They tend to fall
>on a straight line log plot vs frequency, decreasing at higher freq's.
>
>If nothing else, the above numbers serve as a benchmark for future
>comparisons down the road for my amp.
>
>Note: The current measurement can be significantly affected by RF on the
>outside shield of the coax. Until a choke was employed on the feedline,
>the 24.9 MHz current with a real antenna measured 3 amps too low. With
>the choke it agreed with the above dummy load value. I suspect lots of
>KPA-500 users do have this condition-- given the types of
>antennas/tuners et al described by uses on this reflector.
>
>73 de Brian/K3KO
>
>On 2/4/2012 20:27, david park wrote:
>> I have recently assembled KPA500 serial number 641. When testing into a
>> dummy load I find that I get a large variation in the DC power input when
>> driving for 500W CW when I go from band to band. My worst band is 21MHz,
>> where I get the highest current (lowest efficiency). The drive was adjusted
>> to give 500W as indicated by the LCD display. Here are my results:-
>>
>> 1.8MHz DC current 10.0A fan hardly ever comes on
>> 3.5MHz DC current 10.0A fan hardly ever comes on
>> 7MHz 12.0A
>> 10.1MHz 12.4A
>> 14MHz 14.3A
>> 18.1MHz 13.8A
>> 21MHz 16.4A temperature rises rapidly and fan
>> soon gets to full speed
>> 24.9MHz 13.5A
>> 29.7MHz 12.3A
>>
>> I have no results for 50MHz band as I have no transceiver covering that band.
>>
>> The readings drift as the heatsink (and the dummy load) warm up, and so I
>> took readings quickly and allowed time for the heatsink to cool down between
>> each band. I find that the KPA500 current sensor tends to give low readings.
>> I would be interested in knowing how other amplifiers perform.
>>
>> David Park G3PSV
>>
>
>
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