Chris, I have been monitoring this thread, since I have had some similar problems with my K2. My recent experience may help you.
In the K2, amplifier gain is in the ALC loop. When you switch from low power to high (go from less than 10W to greater than 10W), the KPA100 gain changes the ALC behavior and may be the source of many of the differences you see between low and high power operation. If the KPA100 needs some adjustment, that could also be a factor. In my case both calibration/alignment and gain were causing problems. I recalibrated the KPA100 first and noticed some improvements immediately in output power on the high bands and in the agreement between set power and output power. Note that I did this even though I believed that I had taken care in the original calibration. Maybe things change over time, or perhaps I did a better job this time, but the effort was rewarded. Once the recalibration was done, I followed Don's suggestion and adjusted R98 to reduce the ALC loop gain. Prior to adjusting R98, my K2 would hunt endlessly at some power levels, jumping up and down by significant amounts and never converging to the set power level. At other power levels, it might settle down at a value that wasn't as close to the set value as you might like. After adjusting R98, the K2 always converges to the set value with a relatively small error, because the ALC steps are smaller. You mentioned that you don't have a power meter to use for adjustments to the KPA100. I have two, but after a comparison, decided instead to use a voltage measurement across a good dummy load to calculate power. This method seemed to give me the most reliable result across the range of interest. If you have a good dummy load, you can use a scope to measure peak-to-peak voltage or use a diode detector to get a DC voltage off the dummy load. The Elecraft 20W load is very good and has a built in provision to take a DC voltage measurement for conversion to power. With that taken care of, you can adjust your amp with little trouble. Rob -- View this message in context: http://elecraft.365791.n2.nabble.com/K2-KPA-ALC-problem-tp7581353p7581458.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
