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Sudden jump in SWR when power above 80 watts

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KEN-3

Sudden jump in SWR when power above 80 watts

I am having trouble with my K3 tuner, the SWR jumps high when I turn it above 80 watts on 80m.

At first I thought it was something outside but after replacing open wire feedline, balun, coax, I have come to the conclusion that the problem must be internal to the K3.

The antenna is a 130' center fed dipole, fed with 45' of open wire to a 4:1 balun and then to the K3. It tunes easily and works okay on all the bands but on 80m, when I up the power above about 80 watts, the SWR jumps up and the K3 shuts down with "HI SWR.

The problem does not happen with my old TS-440, nor does it happen when I bypass the internal K3 tuner and use an external Palstar AT2K tuner.

I don't believe I had this problem when I bought the K3 last December but then I might not have run the power up all the way either.

Thoughts? Am I missing something? Has anyone else had this same problem?

Another thing I noticed (is it related?) is that when I tune the Palstar to 1:1 SWR, the K3 shows a 2+:1 SWR. If I use the K3 meter to tune the Palstar tuner, then the Palstar meter indicates a 2:1 SWR.

Thanks,

Ken WA8JXM
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Rick Prather-2

Re: Sudden jump in SWR when power above 80 watts

Ken,

Yes, I have the same problem.

Using a 102' doublet, open wire to a 4:1 outside the shack.

Works great everywhere above 160M but on 80 the SWR goes nuts over about 75 Watts.

My workaround has been to not run over 75 Watts :-)

Rick
K6LE

On 2/18/2012, at 1:40 , Ken <[hidden email]> wrote:

> I am having trouble with my K3 tuner, the SWR jumps high when I turn it above 80 watts on 80m.
>
> At first I thought it was something outside but after replacing open wire feedline, balun, coax, I have come to the conclusion that the problem must be internal to the K3.
>
> The antenna is a 130' center fed dipole, fed with 45' of open wire to a 4:1 balun and then to the K3. It tunes easily and works okay on all the bands but on 80m, when I up the power above about 80 watts, the SWR jumps up and the K3 shuts down with "HI SWR.
>
> The problem does not happen with my old TS-440, nor does it happen when I bypass the internal K3 tuner and use an external Palstar AT2K tuner.
>
> I don't believe I had this problem when I bought the K3 last December but then I might not have run the power up all the way either.
>
> Thoughts? Am I missing something? Has anyone else had this same problem?
>
> Another thing I noticed (is it related?) is that when I tune the Palstar to 1:1 SWR, the K3 shows a 2+:1 SWR. If I use the K3 meter to tune the Palstar tuner, then the Palstar meter indicates a 2:1 SWR.
>
> Thanks,
>
> Ken WA8JXM

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Don Wilhelm-4

Re: Sudden jump in SWR when power above 80 watts

In reply to this post by KEN-3

Ken,

A typical question when something like this arises is: "What does it do
if you drive a dummy load?".

While another transceiver handling your antenna situation may also be
good to know, it does not satisfy the question of "What does the K3 do
when driving a 50 ohm resistive load."

The question of the difference in SWR readings between your Palstar
tuner and the K3 cannot be answered without additional measurements
driving a "dummy load" that produces a known SWR.

One thing you could do if you have an antenna analyzer is to tune the
antenna tuner so the K3 indicates a 1:1 SWR - then remove the coax from
the K3 and read the impedance on the analyzer. Is it 50 + j0 or
somewhat close? If so, the K3 reading is correct, but if the SWR
reading is 2:1. then your Palstar reading is correct. If you have a
substantial length of feedline between the K3 and the Palstar tuner,
that might explain the difference in readings.

73,
Don W3FPR

On 2/18/2012 4:40 PM, Ken wrote:

Don Wilhelm-4

Re: Sudden jump in SWR when power above 80 watts

In reply to this post by Rick Prather-2

Rick and all,

Look for something in the antenna system that is arcing over above the
80 watt level (or whatever level the problem starts). Check every
junction in your antenna system. Your workaround may be OK, but the
real fix may increase your antenna efficiency.

The other situation that will cause "bad behavior" above a certain power
level (and on a particular band) is common mode RF coming in from the
antenna and its feedline. The SWR sensing circuits may "go crazy" in
the presence of too much RF voltage. In this case, the use of common
mode chokes at the antenna, and possibly at other points along the
feedline may be what it takes to "tame the beast".

73,
Don W3FPR

On 2/18/2012 5:14 PM, Rick Prather wrote:

> Ken,
>
> Yes, I have the same problem.
>
> Using a 102' doublet, open wire to a 4:1 outside the shack.
>
> Works great everywhere above 160M but on 80 the SWR goes nuts over about 75 Watts.
>
> My workaround has been to not run over 75 Watts :-)
>
> Rick
> K6LE
>
> On 2/18/2012, at 1:40 , Ken<[hidden email]> wrote:
>
>> I am having trouble with my K3 tuner, the SWR jumps high when I turn it above 80 watts on 80m.
>>
>> At first I thought it was something outside but after replacing open wire feedline, balun, coax, I have come to the conclusion that the problem must be internal to the K3.
>>
>> The antenna is a 130' center fed dipole, fed with 45' of open wire to a 4:1 balun and then to the K3. It tunes easily and works okay on all the bands but on 80m, when I up the power above about 80 watts, the SWR jumps up and the K3 shuts down with "HI SWR.
>>
>> The problem does not happen with my old TS-440, nor does it happen when I bypass the internal K3 tuner and use an external Palstar AT2K tuner.
>>
>> I don't believe I had this problem when I bought the K3 last December but then I might not have run the power up all the way either.
>>
>> Thoughts? Am I missing something? Has anyone else had this same problem?
>>
>> Another thing I noticed (is it related?) is that when I tune the Palstar to 1:1 SWR, the K3 shows a 2+:1 SWR. If I use the K3 meter to tune the Palstar tuner, then the Palstar meter indicates a 2:1 SWR.
>>
>> Thanks,
>>
>>

KEN-3

Re: Sudden jump in SWR when power above 80 watts

In reply to this post by Don Wilhelm-4

On Feb 18, 2012, at 5:35 PM, Don Wilhelm wrote:

> A typical question when something like this arises is: "What does it do if you drive a dummy load?".

Well, I don't have a true dummy load. However, since the problem doesn't occur when letting the Palstar do the tuning (at either setting), I assume that's close enough to answer the question that it doesn't happen with a pure 50 ohm load.

Ken WA8JXM
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KEN-3

Re: Sudden jump in SWR when power above 80 watts

In reply to this post by KEN-3

No. When I moved the balun inside, it went from a 30' length of coax to a 4' length. No change in the SWR jump.

Likewise no difference in the jump when changing from a 4:1 to a 1:1 balun.

It's difficult to change the open wire feedline length: If I shorten it, it won't reach the antenna, if I lengthen it, it performs poorly laying on the ground ;-)

I doubt that the 3' length of coax from the K3 to the Palstar makes a 2:1 SWR difference between the two tuners on 80m.

Ken WA8JXM

On Feb 18, 2012, at 5:47 PM, Rick Bates wrote:

> I'll wager that if you change the length of the feedline or the coax from
> the balun, that you'll see different loads. Which is pretty much what
> you're doing with the Palstar being external (adding more coax).

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KEN-3

Re: Sudden jump in SWR when power above 80 watts

In reply to this post by Don Wilhelm-4

On Feb 18, 2012, at 5:43 PM, Don Wilhelm wrote:

> Rick and all,
>
> Look for something in the antenna system that is arcing over above the
> 80 watt level (or whatever level the problem starts). Check every
> junction in your antenna system. Your workaround may be OK, but the
> real fix may increase your antenna efficiency.

That's where I first started. I replaced the ancient twin lead with new open wire. No change. I replaced the 4:1 balun with a new 1:1 balun. No change.

I replaced the coax to the balun. No change. I inspected the center insulator, that's a block of quarter inch PVC with everything separated at least two inches. I checked the end insulators. They look fine and they are tied to Dacron line. The ONLY thing I didn't change is the antenna wire ;-)

The antenna is in free space with the closest object being the antenna mast a foot away.

What did stop the problem is changing rigs (to a TS-440) or changing the antenna tuner (to the Palstar). What's in common with the problem? The K3.

>
> The other situation that will cause "bad behavior" above a certain power
> level (and on a particular band) is common mode RF coming in from the
> antenna and its feedline. The SWR sensing circuits may "go crazy" in
> the presence of too much RF voltage. In this case, the use of common
> mode chokes at the antenna, and possibly at other points along the
> feedline may be what it takes to "tame the beast".

Now that sounds like a possibility.

Ken WA8JXM
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KEN-3

Re: Sudden jump in SWR when power above 80 watts

In reply to this post by Rick Prather-2

Thanks to all of you who replied that you have also experienced the same issue. I guess I am not alone!

Maybe Wayne or someone from Elecraft will contribute some info.

73, Ken WA8JXM

On Feb 18, 2012, at 5:14 PM, Rick Prather wrote:

> Yes, I have the same problem.

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KD8NNU

Re: Sudden jump in SWR when power above 80 watts

In reply to this post by KEN-3

Sounds like my shack when I had RF problems. Strange SWR was one of my
problems also.

One thing I found is that I need to wind a big choke on the power leads
into the K3 to stop a lot of my problems. It was the last thing I did
to fix issues. I wish I would have know to start there :-)

~73
Don
KD8NNU

On Sat, Feb 18, 2012 at 6:09 PM, Ken wrote:

> On Feb 18, 2012, at 5:43 PM, Don Wilhelm wrote:
>
>> Rick and all,
>>
>> Look for something in the antenna system that is arcing over above
>> the 80 watt level (or whatever level the problem starts). Check
>> every junction in your antenna system. Your workaround may be OK,
>> but the real fix may increase your antenna efficiency.
>
>
> That's where I first started. I replaced the ancient twin lead with
> new open wire. No change. I replaced the 4:1 balun with a new 1:1
> balun. No change.
>
> I replaced the coax to the balun. No change. I inspected the center
> insulator, that's a block of quarter inch PVC with everything
> separated at least two inches. I checked the end insulators. They
> look fine and they are tied to Dacron line. The ONLY thing I didn't
> change is the antenna wire ;-)
> The antenna is in free space with the closest object being the antenna
> mast a foot away.
>
> What did stop the problem is changing rigs (to a TS-440) or changing
> the antenna tuner (to the Palstar). What's in common with the
> problem? The K3.
>
>
>>
>> The other situation that will cause "bad behavior" above a certain
>> power level (and on a particular band) is common mode RF coming in
>> from the antenna and its feedline. The SWR sensing circuits may "go
>> crazy" in the presence of too much RF voltage. In this case, the use
>> of common mode chokes at the antenna, and possibly at other points
>> along the feedline may be what it takes to "tame the beast".
>
>
> Now that sounds like a possibility.
> Ken WA8JXM
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Don Wilhelm-4

Re: Sudden jump in SWR when power above 80 watts

One great solution is to put a good balanced link coupled antenna tuner
between the transceiver and the parallel feedline. I emphasize "link
coupled" because that alone will stop common mode current.
You can homebrew one, or look for a Johnson Matchbox.

73,
Don W3FPR

On 2/18/2012 6:33 PM, [hidden email] wrote:

> Sounds like my shack when I had RF problems. Strange SWR was one of my
> problems also.
>
> One thing I found is that I need to wind a big choke on the power leads
> into the K3 to stop a lot of my problems. It was the last thing I did
> to fix issues. I wish I would have know to start there :-)
>
> ~73
> Don
>