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Antenna or KAT500/KPA500 Problem

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Antenna or KAT500/KPA500 Problem

Every so often at random after I have been on SSB for a while ( 80m with about 450w and a 1.1 to 1 SWR) my tuner jumps to retune or the amp faults and switches to standby. I am using a Van Gorden full size (102’) G5RV as
an inverted vee. The 31’ matching section is 300 ohm twin lead and, even though it has been up for 10yrs, is still flexible. Van Gordon is now out of business. The twin lead goes into a 3/4” pvc pipe and coax comes out the other end.
I am thinking that the 12” long pipe section has ferrite beads to cut common mode currents. I don’t know what wattage the ferrites are rated for.
Someone suggested that the ferrites might be heating up and causing my problem since the problem occurs after being on the air a while and could be thermal.
My questions are:
I have some new 450 ohm ladder line. Should I replace the 300 ohm with it? I know that most G5RV’s on the market today use 450 ohm not twinlead. If so what kind of line isolator is needed or what balun? Should I just replace the ferrite beads — and if so with what no. and mix. Can I just use an ugly balun (coiled coax). All thoughts are appreciated. The antenna itself has worked fine for me on all bands (80 thru 10) and I have worked all continents except Antarctica. Thank you in advance and 73 Mike KF6KXG

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Jim Brown-10

Re: Antenna or KAT500/KPA500 Problem

On 8/6/2019 7:00 PM, Mike Lichtman via Elecraft wrote:
> All thoughts are appreciated. The antenna itself has worked fine for me on all bands (80 thru 10)

You should buy yourself a copy of the ARRL Antenna Book and learn about
how to build your own antennas.

That tube contains a lot of little ferrite beads that act as a common
mode choke. This form of choke was developed many years ago by W2DU (now
SK). If you haven't already fried it by running 500W you probably will
eventually.

If your QTH allows more than one antenna, I strongly recommend the use
of resonant fan dipoles fed with coax. They are very easy to build. If
you do that, you can build your own common mode choke that is far
superior to the one you bought with the antenna. 80 and 40 M makes a
good combination for a fan, and the 40M element will work on 15M. If
you're limited to 100 ft or so, consider one of the loaded 2-band
dipoles built by Hypower Antenna Company (a ham in his basement), or buy
the loading coils and build your own. I used one of his 80/40 loaded
dipoles in Chicago. It also worked on 30 and 17. A 20M dipole is only 33
ft long, so it's pretty easy to rig almost anywhere. I wouldn't worry
about 15, 12, or 10M for the next 4-5 years, because they're nearly dead
as we approach the bottom of the current solar cycle.

There are several "how to" tutorials on my website, k9yc.com/publish.htm
, including one that describes how to build fan dipoles from inexpensive
and readily available parts. My guidelines for chokes is at
http://k9yc.com/2018Cookbook.pdf

73, Jim K9YC

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Vic Rosenthal

Re: Antenna or KAT500/KPA500 Problem

In reply to this post by Elecraft mailing list

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.
Twin lead will change characteristics significantly when it gets wet. So will ladder line, although not as much. So if this happens when it rains, that’s the issue.
There is also the possibility that there is a badly corroded connection inside the balun which opens when something expands due to heat. I once had this problem with what seemed to me to be a very well-constructed bead balun. The connection to the coax connector was the culprit. It was hard to find because it was intermittent.
If you replace the twinlead with ladder line, it will need to be slightly longer because the ladder line has a greater velocity factor than the twinlead. The Vf of twinlead is about 78% and of ladder line 91% so it will be longer by a factor of 1.17.

Victor 4X6GP

> On 7 Aug 2019, at 5:00, Mike Lichtman via Elecraft <[hidden email]> wrote:
>
> Every so often at random after I have been on SSB for a while ( 80m with about 450w and a 1.1 to 1 SWR) my tuner jumps to retune or the amp faults and switches to standby. I am using a Van Gorden full size (102’) G5RV as
> an inverted vee. The 31’ matching section is 300 ohm twin lead and, even though it has been up for 10yrs, is still flexible. Van Gordon is now out of business. The twin lead goes into a 3/4” pvc pipe and coax comes out the other end.
> I am thinking that the 12” long pipe section has ferrite beads to cut common mode currents. I don’t know what wattage the ferrites are rated for.
> Someone suggested that the ferrites might be heating up and causing my problem since the problem occurs after being on the air a while and could be thermal.
> My questions are:
> I have some new 450 ohm ladder line. Should I replace the 300 ohm with it? I know that most G5RV’s on the market today use 450 ohm not twinlead. If so what kind of line isolator is needed or what balun? Should I just replace the ferrite beads — and if so with what no. and mix. Can I just use an ugly balun (coiled coax). All thoughts are appreciated. The antenna itself has worked fine for me on all bands (80 thru 10) and I have worked all continents except Antarctica. Thank you in advance and 73 Mike KF6KXG
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Please help support this email list: http://www.qsl.net/donate.html
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ANDY DURBIN

Antenna or KAT500/KPA500 Problem

In reply to this post by Elecraft mailing list

"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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Vic Rosenthal

Re: Antenna or KAT500/KPA500 Problem

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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