"It is possible that the ferrites are heating. If that is the case, you could test it by transmitting a steady carrier for a minute while watching the SWR. If it’s heating, there should be a gradual rise."
I have data for SWR runaway events that I believe were caused by heating of the ferrite cores in a common mode choke. The SWR change for these events was not gradual. It was closer to exponential. Once runaway starts SWR reaches the point that it trips something in just a few seconds. The ferrite choke was in easy reach (outside but only 5 feet above ground) and nearly burned my fingers. Made me think about oil immersion for cooling but have not tried that. Instead I set a lower max power for that antenna. KPA500 can be protected from these events by setting KAT500 key interrupt threshold to a value lower than the SWR that trips the KPA500. My series of runaway events, and my attempts to protect against them, exposed a defect in the KAT500 utility so installation of the latest version may be required. Data for one event: "SWR runaway and choke cores too hot to touch several minutes later. 470 W 160 m FT8 with multiple transmissions before onset. 2019-03-27 21:11:15 TX_freq=1839500 2019-03-27 21:11:15 split offset = -500 2019-03-27 21:11:31 New IF - IF00001839500 000000016121010000; << TX starts 2019-03-27 21:11:32 New VSWR - VSWR 1.34; 2019-03-27 21:11:32 split offset = -500 2019-03-27 21:11:32 New VSWR - VSWR 1.33; 2019-03-27 21:11:32 New VSWR - VSWR 1.31; 2019-03-27 21:11:32 New VSWR - VSWR 1.29; 2019-03-27 21:11:33 New VSWR - VSWR 1.27; 2019-03-27 21:11:33 New VSWR - VSWR 1.25; 2019-03-27 21:11:33 New VSWR - VSWR 1.24; 2019-03-27 21:11:34 New VSWR - VSWR 1.22; <<< SWR decreasing rapidly 2019-03-27 21:11:34 New VSWR - VSWR 1.20; 2019-03-27 21:11:34 New VSWR - VSWR 1.19; 2019-03-27 21:11:35 New VSWR - VSWR 1.18; 2019-03-27 21:11:35 New VSWR - VSWR 1.16; 2019-03-27 21:11:35 New VSWR - VSWR 1.15; 2019-03-27 21:11:35 New VSWR - VSWR 1.13; 2019-03-27 21:11:36 New VSWR - VSWR 1.11; 2019-03-27 21:11:36 New VSWR - VSWR 1.10; 2019-03-27 21:11:36 New VSWR - VSWR 1.09; <<< SWR passes through zero 2019-03-27 21:11:37 New VSWR - VSWR 1.10; 2019-03-27 21:11:37 New VSWR - VSWR 1.11; 2019-03-27 21:11:37 New VSWR - VSWR 1.13; 2019-03-27 21:11:38 New VSWR - VSWR 1.14; 2019-03-27 21:11:38 New VSWR - VSWR 1.19; <<< SWR increasing rapidly 2019-03-27 21:11:38 New VSWR - VSWR 1.22; 2019-03-27 21:11:38 New VSWR - VSWR 1.25; 2019-03-27 21:11:38 New VSWR - VSWR 1.29; 2019-03-27 21:11:38 New VSWR - VSWR 1.34; 2019-03-27 21:11:38 New VSWR - VSWR 1.39; 2019-03-27 21:11:39 New VSWR - VSWR 1.44; 2019-03-27 21:11:39 New VSWR - VSWR 1.50; 2019-03-27 21:11:39 New VSWR - VSWR 1.58; 2019-03-27 21:11:40 New VSWR - VSWR 1.65; 2019-03-27 21:11:40 New FLT - FLT4; <<<< KAT500 fault trip 2019-03-27 21:11:40 New AMPI - AMPI1; <<<< Key line opened 2019-03-27 21:11:40 New VSWR - VSWR 1.66; 2019-03-27 21:11:40 New VSWR - VSWR 1.67; 2019-03-27 21:11:40 New VSWR - VSWR 1.70; 2019-03-27 21:11:41 New VSWR - VSWR 1.72; 2019-03-27 21:11:42 New VSWR - VSWR 1.70; 2019-03-27 21:11:42 New VSWR - VSWR 1.72; 2019-03-27 21:11:42 New VSWR - VSWR 1.70; <<< SWR peaks 2019-03-27 21:11:43 New VSWR - VSWR 1.69; 2019-03-27 21:11:43 New VSWR - VSWR 1.67; 2019-03-27 21:11:44 New VSWR - VSWR 1.66; 2019-03-27 21:11:45 New IF - IF00001840000 000000016020010000; << TX ends" (When interpreting the data be sure to note that only parameter changes are recorded. This means the events are not at equal time intervals. Later data recordings are tagged with 1 millisecond time resolution which makes analysis a bit easier) 73, Andy, k3wyc ______________________________________________________________ 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 Message delivered to [email protected]
