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[K3-KPA500] SWR jumps up with 5 second key down

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mike

[K3-KPA500] SWR jumps up with 5 second key down

I have installed a new antenna and have strange changing swr. When testing with RigExperts meter I find good resonance at say 15m (21.200). With the K3 at 100 watts reading is 1 bar on K3 meter and 1.0 on KPA500 (STBY). When I bring the amp online and drive it at 200 watts, all is still good even with a 15 second key down period. Driving the KPA500 to 275 watts, still okay with key down, although the KPA500 meter now shows 1.1. BUT when I increase the drive a little more (300 watts) the swr jumps up to 2.5+ and the KPA500 shows REFL HI and drops into STBY.

And here is the kicker...NOT ALL THE TIME!

So I think it has to be in the coax. But the 75feet of RG213 is brand new premade from Cable Xperts with the connectors.

I will try a different coax. Any other suggestions?

..mike

Mark Stennett

Re: [K3-KPA500] SWR jumps up with 5 second key down

What happens when you run the KPA-500 into a dummy load? If all is well, I
would guess that something is changing under high power and affecting the
load.

-----Original Message-----
From: ai6ii <[hidden email]>
To: [hidden email]
Date: Mon, 4 Jun 2012 10:00:54 -0700 (PDT)
Subject: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down

I have installed a new antenna and have strange changing swr. When testing
with RigExperts meter I find good resonance at say 15m (21.200). With the
K3
at 100 watts reading is 1 bar on K3 meter and 1.0 on KPA500 (STBY). When I
bring the amp online and drive it at 200 watts, all is still good even with
a 15 second key down period. Driving the KPA500 to 275 watts, still okay
with key down, although the KPA500 meter now shows 1.1. BUT when I increase
the drive a little more (300 watts) the swr jumps up to 2.5+ and the KPA500
shows REFL HI and drops into STBY.

And here is the kicker...NOT ALL THE TIME!

So I think it has to be in the coax. But the 75feet of RG213 is brand new
premade from Cable Xperts with the connectors.

I will try a different coax. Any other suggestions?

..mike

--
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Don Wilhelm-4

Re: [K3-KPA500] SWR jumps up with 5 second key down

In reply to this post by mike

Mike,

My first guess is that it is not the coax, but attach a dummy load to
the antenna end of the coax to test it under full power just to be certain.

The most likely thing is that something in your antenna system is arcing
at the higher power. End insulators? Vegetation touching the antenna
wire? center insulator arcing? or balun failing at power?

73,
Don W3FPR

On 6/4/2012 1:00 PM, ai6ii wrote:

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Mike Furrey

Re: [K3-KPA500] SWR jumps up with 5 second key down

In reply to this post by Mark Stennett

My bet will be on a bad connection someplace after the amp. With power
something is shorting ... could be in coax connector, antenna, etc ... been
through that. Once had found an elevated radial on 160 inverted "L" had
dropped and touching a tree limb was the problem.

73, Mike

-----Original Message-----
From: Ron D'Eau Claire
Sent: Monday, June 04, 2012 12:33 PM
To: 'ai6ii' ; [hidden email]
Subject: Re: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down

Mark has an excellent point, especially if you have a ferrite core
transformer (balun, etc.) somewhere in the antenna system. One thing that
can cause that behavior is heating of the toroid core. At a certain
temperature, the core's magnetic properties change dramatically, changing
the inductance and so causing the SWR to change.

Ron AC7AC

-----Original Message-----

What happens when you run the KPA-500 into a dummy load? If all is well, I
would guess that something is changing under high power and affecting the
load.

-----Original Message-----
From: ai6ii <[hidden email]>
To: [hidden email]
Date: Mon, 4 Jun 2012 10:00:54 -0700 (PDT)
Subject: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down

I have installed a new antenna and have strange changing swr. When testing
with RigExperts meter I find good resonance at say 15m (21.200). With the
K3
at 100 watts reading is 1 bar on K3 meter and 1.0 on KPA500 (STBY). When I
bring the amp online and drive it at 200 watts, all is still good even with
a 15 second key down period. Driving the KPA500 to 275 watts, still okay
with key down, although the KPA500 meter now shows 1.1. BUT when I increase
the drive a little more (300 watts) the swr jumps up to 2.5+ and the KPA500
shows REFL HI and drops into STBY.

And here is the kicker...NOT ALL THE TIME!

So I think it has to be in the coax. But the 75feet of RG213 is brand new
premade from Cable Xperts with the connectors.

I will try a different coax. Any other suggestions?

..mike

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Rick Johnson-2

Re: [K3-KPA500] SWR jumps up with 5 second key down

Jump back down to Ron's input.
I had that exact same scenario with my OCFD. As soon as I transmitted
any length of time on CW above 250W the SWR would jump up and the
KPA500 would fault.
The problem was a too small torroid 4:1 balun. I bought a 5KW balun
from Hy Power Antennas and the problem went away.
Just because the balun is rated to 5KW doesn't mean you have to use
that much power.

73,
Rick W3BI

-----Original Message-----
From: [hidden email]
Sent: Monday, June 04, 2012 1:47 PM
To: [hidden email]
Subject: Re: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down

My bet will be on a bad connection someplace after the amp. With power
something is shorting ... could be in coax connector, antenna, etc ... been
through that. Once had found an elevated radial on 160 inverted "L" had
dropped and touching a tree limb was the problem.

73, Mike

-----Original Message-----
From: Ron D'Eau Claire
Sent: Monday, June 04, 2012 12:33 PM
To: 'ai6ii' ; [hidden email]
Subject: Re: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down

Mark has an excellent point, especially if you have a ferrite core
transformer (balun, etc.) somewhere in the antenna system. One thing that
can cause that behavior is heating of the toroid core. At a certain
temperature, the core's magnetic properties change dramatically, changing
the inductance and so causing the SWR to change.

Ron AC7AC

-----Original Message-----

What happens when you run the KPA-500 into a dummy load? If all is well, I
would guess that something is changing under high power and affecting the
load.

-----Original Message-----
From: ai6ii <[hidden email]>
To: [hidden email]
Date: Mon, 4 Jun 2012 10:00:54 -0700 (PDT)
Subject: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down

I have installed a new antenna and have strange changing swr. When testing
with RigExperts meter I find good resonance at say 15m (21.200). With the
K3
at 100 watts reading is 1 bar on K3 meter and 1.0 on KPA500 (STBY). When I
bring the amp online and drive it at 200 watts, all is still good even with
a 15 second key down period. Driving the KPA500 to 275 watts, still okay
with key down, although the KPA500 meter now shows 1.1. BUT when I increase
the drive a little more (300 watts) the swr jumps up to 2.5+ and the KPA500
shows REFL HI and drops into STBY.

And here is the kicker...NOT ALL THE TIME!

So I think it has to be in the coax. But the 75feet of RG213 is brand new
premade from Cable Xperts with the connectors.

I will try a different coax. Any other suggestions?

..mike

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Greg - AB7R

Re: [K3-KPA500] SWR jumps up with 5 second key down

I hate to say this but cable experts does not have a stellar record with
their installed connectors. I would cut them off and install new ones.

73
Greg
On Jun 4, 2012 10:55 AM, "Rick Johnson" <[hidden email]> wrote:

> Jump back down to Ron's input.
> I had that exact same scenario with my OCFD. As soon as I transmitted
> any length of time on CW above 250W the SWR would jump up and the
> KPA500 would fault.
> The problem was a too small torroid 4:1 balun. I bought a 5KW balun
> from Hy Power Antennas and the problem went away.
> Just because the balun is rated to 5KW doesn't mean you have to use
> that much power.
>
> 73,
> Rick W3BI
>
> -----Original Message-----
> From: [hidden email]
> Sent: Monday, June 04, 2012 1:47 PM
> To: [hidden email]
> Subject: Re: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down
>
> My bet will be on a bad connection someplace after the amp. With power
> something is shorting ... could be in coax connector, antenna, etc ... been
> through that. Once had found an elevated radial on 160 inverted "L" had
> dropped and touching a tree limb was the problem.
>
> 73, Mike
>
> -----Original Message-----
> From: Ron D'Eau Claire
> Sent: Monday, June 04, 2012 12:33 PM
> To: 'ai6ii' ; [hidden email]
> Subject: Re: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down
>
> Mark has an excellent point, especially if you have a ferrite core
> transformer (balun, etc.) somewhere in the antenna system. One thing that
> can cause that behavior is heating of the toroid core. At a certain
> temperature, the core's magnetic properties change dramatically, changing
> the inductance and so causing the SWR to change.
>
> Ron AC7AC
>
> -----Original Message-----
>
> What happens when you run the KPA-500 into a dummy load? If all is well, I
> would guess that something is changing under high power and affecting the
> load.
>
> -----Original Message-----
> From: ai6ii <[hidden email]>
> To: [hidden email]
> Date: Mon, 4 Jun 2012 10:00:54 -0700 (PDT)
> Subject: [Elecraft] [K3-KPA500] SWR jumps up with 5 second key down
>
>
> I have installed a new antenna and have strange changing swr. When testing
> with RigExperts meter I find good resonance at say 15m (21.200). With the
> K3
> at 100 watts reading is 1 bar on K3 meter and 1.0 on KPA500 (STBY). When I
> bring the amp online and drive it at 200 watts, all is still good even with
> a 15 second key down period. Driving the KPA500 to 275 watts, still okay
> with key down, although the KPA500 meter now shows 1.1. BUT when I increase
> the drive a little more (300 watts) the swr jumps up to 2.5+ and the KPA500
> shows REFL HI and drops into STBY.
>
> And here is the kicker...NOT ALL THE TIME!
>
> So I think it has to be in the coax. But the 75feet of RG213 is brand new
> premade from Cable Xperts with the connectors.
>
> I will try a different coax. Any other suggestions?
>
> ..mike
>
> ______________________________________________________________
> 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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>
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>

mike

Re: [K3-KPA500] SWR jumps up with 5 second key down

In reply to this post by Rick Johnson-2

Okay, some more info. The KPA500 does not have a problem with the inverted vee for 40 meters, but I will set it up with a dummy load to check just in case. And I will try the dummy load at the antenna end of the coax as a test tomorrow.

The antenna is the new Q-52 2 element yagi five band from N6BT. It uses relays on both the driven element and the reflector to cover 20m (high and low) 17, 15, 12 and 10. I have contacted Tom Schiller who says he has tested the antenna with 600-700 watts on CW so power should not be a problem. I also thought the high power might somehow be keying the relays as the eight-wire control cable parallels the coax 4 feet across the boom, down the 30 foot mast in through the garage in a pvc conduit then into the shack. I tried moving the control box away from the amp and experimented with running the coax a different route into the shack, although the coax and control cable still came down the mast next to each other. None of these had any affect.

..mike AI6II

Re: [K3-KPA500] SWR jumps up with 5 second key down

In reply to this post by mike

What Antenna are you using? Not only the balun needs to be rated for your power but the coils and wire does too. Many mfgrs overrated their equipment. For 500 watts use kw rated antennas. RG 213 is good but wire and loading need to be #14.

Sent from my iPhone

On Jun 4, 2012, at 12:00, ai6ii <[hidden email]> wrote:

> I have installed a new antenna and have strange changing swr. When testing
> with RigExperts meter I find good resonance at say 15m (21.200). With the K3
> at 100 watts reading is 1 bar on K3 meter and 1.0 on KPA500 (STBY). When I
> bring the amp online and drive it at 200 watts, all is still good even with
> a 15 second key down period. Driving the KPA500 to 275 watts, still okay
> with key down, although the KPA500 meter now shows 1.1. BUT when I increase
> the drive a little more (300 watts) the swr jumps up to 2.5+ and the KPA500
> shows REFL HI and drops into STBY.
>
> And here is the kicker...NOT ALL THE TIME!
>
> So I think it has to be in the coax. But the 75feet of RG213 is brand new
> premade from Cable Xperts with the connectors.
>
> I will try a different coax. Any other suggestions?
>
> ..mike
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K3-KPA500-SWR-jumps-up-with-5-second-key-down-tp7557071.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html

Hank Garretson

Re: [K3-KPA500] SWR jumps up with 5 second key down

On Mon, Jun 4, 2012 at 11:30 AM, Willis <[hidden email]> wrote:

For 500 watts use kw rated antennas. RG 213 is good but wire and loading
> need to be #14.
>

Not my experience. For over five decades, I have used #18 wire for many
antennas. Current antenna has segments of #18 with no ill effects at 1.5kW
output.

73,

Hank, W6SX
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k6dgw

Re: [K3-KPA500] SWR jumps up with 5 second key down

In reply to this post by mike

On 6/4/2012 10:00 AM, ai6ii wrote:

I strongly doubt that. Loose connector maybe, but you've probably
already checked that. Some suggestions:

1. Does it do it with dummy load on output of KPA500?

2. Does it do it with dummy load on far end of coax in place of antenna
[not always easy to do]?

3. Does it do it with another antenna [if you have one for 15]?

4. Does it do it on any other bands?

5. You said it is one of Tom's multiband yagi's. Did you tighten
everything down when you assembled it? If I were to bet on it, I'd bet
this is your problem.

6. Is there a balun? If so, what happens to your TV when this high SWR
occurs? All transformer cores will saturate at some power level, the
flux in them just cannot increase anymore, all the little magnet-lets
are already aligned. The power at which this happens is sensitive to
the temperature, and when it does, the balun become non-linear and you
radiate all sorts of trash. However, if I were to bet, I'd bet this is
*not* your problem.

I haven't read the rest of the email list yet and I'll bet there are a
lot of suggestions for you there by this time. I'd have typically taken
mine off-list to you and let you publish the resolution once, however
apparently, that is poor list etiquette. I'd like to know what the
resolution is, I occasionally have a sort of similar problem on an old
antenna that's been up for maybe 15 years.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

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mike

Re: [K3-KPA500] SWR jumps up with 5 second key down

Unfortunately when lowering the aluminum mast this morning it snapped off at the half way mark and bent some of the antenna element tubing. But I did place a dummy load on the coax and as expected it was fine. I also checked the connections everywhere and they were all tight. I heard from another Q-52 user who said he found he had to redo the element mounting because the small PVC used to isolate the elements doesn't stop arcing at power over 250 watts. That would describe my symptoms exactly.

Before I can continue to get this antenna setup I will have to find another way to put it in the sky. Bummer.

..mike AI6II

VK1OO, Mike Walkington

Re: [K3-KPA500] SWR jumps up with 5 second key down

Hi Mike,

I have the same Q-52 and am beginning to experience the same issue on 20m. Did you get the issue resolved? Where exactly was the problem? Any help would be appeciated.

Mike
VK1OO

Cheers
Mike
VK1OO (ex AC7MZ, VK1KCK)
K2: 2599

VK1OO, Mike Walkington

Re: [K3-KPA500] SWR jumps up with 5 second key down

All,

I think I've finally found the cause of my problem. The PVC spacer that goes around the driven element where it is attached to the boom plate has a cut down one side to to allow it to compress when tightened with a u-bolt. What I could not notice until I totally dismantled the element was that the split was full of carbon as was the mounting plate along the length of the split. I am assuming that the split which was facing up filled up with water and helped create an arc between the driven element and mounting plate.

Mike
VK1OO

Cheers
Mike
VK1OO (ex AC7MZ, VK1KCK)
K2: 2599