Posted by
ANDY DURBIN on
May 26, 2018; 6:28pm
URL: http://elecraft.85.s1.nabble.com/PA-DISS-fault-and-relationship-to-SWR-tp7641241.html
Up until this weekend I had experienced 3 PA DISS faults with my new KPA500. I provided data to Elecraft and, after a fairly long and informative email exchange, I was told the fault is very rare and most likely caused by some problem at my station.
I developed a 10 frames per second data logger which polls and records data from the KPA500 serial interface as well as the ALARM signal available on the AUX port. The ALARM signal was also used as a trigger so that 'scope data could be time correlated with the logger data. CQ WPX CW contest seemed to be a good opportunity to gather data if the fault could be reproduced. After experiencing 5 PA DISS faults on 20 meters I abandoned the contest, looked at the recorded data, and ran some additional tests.
The data show that PA dissipation (DC input power - RF output power) is strongly dependent of load SWR. That in itself is probably not surprising. What was surprising was that my KPA500, when operating into an antenna load that the KPA500 reports as 1.4:1 SWR, has a PA DISS of 500 W when producing 400 W output. What was more surprising is that, although the PA DISS fault is designed to trip at 400 W ("The PA Diss uses non-averaged data to do a comparison between the calculated power from PA voltage and PA current and the measured output power. If it is more than about 400 watts on four consecutive checks (each 8 mSec apart) then we declare the fault.") it did not trip for a key down test lasting several seconds.
Sample data for different load condx shown below. None of these key down tests resulted in PA DISS fault.
SteppIR: LP-100A SWR 1.58:1 PA DC Input / RF Out / PA DISS
^OS1; ^WS390 014; ^VI592 151; ^BN05; ^TM047; 893.92 390 503.92
^OS1; ^WS390 014; ^VI590 151; ^BN05; ^FS00; 890.9 390 500.9
SteppIR: LP-100A SWR 1.38:1
^OS1; ^WS428 013; ^VI585 143; ^BN05; ^TM039; 836.55 428 408.55
^OS1; ^WS430 013; ^VI589 144; ^BN05; ^FS00; 848.16 430 418.16
Dummy load LP-100A SWR 1.08:1
^OS1; ^WS440 011; ^VI598 132; ^BN05; ^FS00; 789.36 440 349.36
^OS1; ^WS440 011; ^VI595 132; ^BN05; ^TM043; 785.4 440 345.4
Can someone at Elecraft please explain why PA DISS fault does not trip when key down PA DISS (calculated from WS and VI serial data) exceeds the 400 W threshold defined for this fault condition. When the PA DISS fault was seen in the contest it always happened during the first element of the CW transmission.
Raw logger data, Excel data, and scope traces have been saved. KPA500 firmware is 1.54.
73,
Andy k3wyc
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