Re: Antenna or KAT500/KPA500 Problem

Posted by Vic Rosenthal on Aug 07, 2019; 2:19pm
URL: http://elecraft.85.s1.nabble.com/Antenna-or-KAT500-KPA500-Problem-tp7654300p7654305.html

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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