Scott, Did you try testing with a 50 ohm dummy load instead of an antenna? How goes it react?
Ken WA2LBI LG G6 ------ Original message------From: K9MADate: Wed, Feb 6, 2019 10:50To: elecraft@mailman.qth.net;Cc: Subject:[Elecraft] KPA1500 ATU Ever since I received my KPA1500 (SN 00178), I've observed that the ATU sometimes won't achieve a match better than about 1.4:1, even though the antenna SWR is well within range. (ATU STOP TUN SWR = 1.0:1, tune power 40 W) Now, 1.4:1 doesn't sound that high, but the amplifier will often not operate at full output at that SWR, either due to excessive current or drive power. This is particularly troublesome when tuning across a band. Clearly, the KPA1500 is designed to deliver 1500 W to a 50 Ohm load, with little margin for a mismatch. More margin would have increased cost, size, and weight, of course. Just to be sure there isn't something unique wrong with my KPA1500, have others observed similar behavior? A little ice on the antenna this morning provided an opportunity for a test. On 40 meters, the antenna SWR was 2.2:1. The best match the KPA1500 ATU could attain automatically was 1.4:1, in multiple attempts. I was able to manually get it down to 1.1:1. (SWR as indicated by the KPA1500 display.) It was a little tricky, requiring one value to be increased beyond the SWR minimum before the other was adjusted, as often happens with manual tuners. With the KPA1500 ATU bypassed, the K3 ATU automatically got it down to 1:1 on the first try. My conclusion is that there's something about the KPA1500 ATU algorithm that prevents it from achieving a better match, in some cases. (I'm assuming that, aside from their power ratings, the components in the KPA1500 ATU and the K3 ATU are similar.) I'm wondering if the KPA1500 ATU algorithm could be improved to perform more like that of the K3 ATU. That would allow operating the KPA1500 closer to full power across a band without having to ride the power control. Further details of ATU component values, etc. are available. 73, Scott K9MA -- Scott K9MA k...@sdellington.us _____________________ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
