[Elecraft] Antenna or KAT500/KPA500 Problem

[Andy Durbin]

"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