QRO - KPA500 Failure
Posted by
ANDY DURBIN on
Feb 10, 2020; 6:04pm
URL: http://elecraft.85.s1.nabble.com/QRO-KPA500-Failure-tp7658244p7658350.html
"This is probably what folks are thinking of when they assume maximum dissipation occurs at less than full output."
A possible source of error in my data is that the dummy load is cool at the start of the power ramp and hot by the time peak power is reached. I recorded LP-100A data during each test run and can see some change in the load characteristics. I did not attempt to compensate for this when plotting the data. I simply reported values of R and X that were about average for each test run.
One way to find out if the change in load is significant would be to start the power ramp at maximum power rather than minimum power.
Some time after I ran those tests I expanded the capability of my Arduino station controller to add a page that displays PA voltage, PA current, PA DC input, PA dissipation, RF Output, and efficiency. A snapshot of the displayed data can be sent to the controller's logger output.
I just ran a test which had a brief transmission close to full power and another brief transmission at half power. This test was performed at 14.01 MHz using a dummy load. Here are the data:
26:36:36.672 KPA Mon frozen
PA voltage=60.6
PA current=14.1
PA input=854
RF out=495
PA diss=359
PA effic=57
26:37:32.437 KPA Mon frozen
PA voltage=64.6
PA current=10.0
PA input=646
RF out=250
PA diss=396
PA effic=38
Dummy load heating would not have been significant factor in this test but the results still show higher PA dissipation at 250 W out than at 495 W out.
It's really simple to produce a similar data set and there are lots of KPA500 owners here. If you think my data are invalid please share your test data. I don't mind being wrong as long as I learn something new.
73,
Andy, k3wyc
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