I did a lot of testing with a tuner followed by a high-quality DX
Engineering balun in a system with high, reactive SWR. I did not push it
far enough to destroy the balun, but I did note a gradual increase in
SWR. And yes, the rate of increase sped up as it got hotter. So I
suggest testing just long enough to see the process start!
In your data, the SWR decreases and then increases. I started with the
tuner set to provide an SWR to the transmitter of 1:1 so it could only
increase.
Incidentally, I found that the balun ran much cooler if the reactive
component of the line's impedance was canceled out by a balanced pair of
(in this case) capacitors.
73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 07/08/2019 16:40, Andy Durbin wrote:
"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
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