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KPA500 RFI problem

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Ron W3ZV

KPA500 RFI problem

At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and the KPA500 connected as recommended with Elecraft DB15HD cables. The antenna is a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of coax to the KAT500. I have a comment point ground to a ground rod six foot from the shack. I have operated the amp at 400+ watts from 80m to 6m. The only band that gives me a problem is 12m. When I am operating at 400 watts ssb, the amp will fault with a high swr indication within 5 to 20 seconds. Immediately prior to the fault the swr on the amp display was 1.2:1. Reducing power to below 300 watts seems to avoid the problem.

Assuming the consensus is that this is RFI, what would be the most likely suspect? Coax cables in/out? DB15HD cable? Power cable? What's the easiest way to diagnose and correct the problem? Thanks

Ron W3ZV

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k6dgw

Re: KPA500 RFI problem

It really sounds like something is breaking down when you transmit on
12m, not sure where RFI fits into this. The impedance at the balun-end
of your ladder line can be just about anything depending on frequency
[and length of the line]. The 4:1 balun will divide the magnitude of
that impedance by 4. "Anything" divided by 4 is pretty much still
"anything."

If the SWR went up slowly, it would suggest you're warming up something
in the system that doesn't really want to be that warm. You say it goes
up suddenly? This would suggest something has arced over. Your comment
about reducing the power "stops it" is really good evidence of this.

In the days of NTSC TV, saturating the ferrite in your balun would
generally get some aggravation from your neighbors, waveforms get very
square at saturation. It also would create SWR problems. Perhaps the Z
is very low on 12M, currents very high. I don't know what balun you have.

If you have or can borrow one, put an impedance bridge on the coax side
of your balun and see what the impedance is on all the ham bands. I
really doubt this has anything to do with an RFI problem.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org

On 1/8/2013 5:06 PM, Ron W3ZV wrote:

> At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and
> the KPA500 connected as recommended with Elecraft DB15HD cables. The
> antenna is a 120ft. doublet fed with ladder line to a 4:1 balun and
> 10ft of coax to the KAT500. I have a comment point ground to a ground
> rod six foot from the shack. I have operated the amp at 400+ watts
> from 80m to 6m. The only band that gives me a problem is 12m. When I
> am operating at 400 watts ssb, the amp will fault with a high swr
> indication within 5 to 20 seconds. Immediately prior to the fault the
> swr on the amp display was 1.2:1. Reducing power to below 300 watts
> seems to avoid the problem.
>
> Assuming the consensus is that this is RFI, what would be the most
> likely suspect? Coax cables in/out? DB15HD cable? Power cable? What's
> the easiest way to diagnose and correct the problem? Thanks
>
> Ron W3ZV
>
>
>
>
> ______________________________________________________________
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Rick WA6NHC

Re: KPA500 RFI problem

In reply to this post by Ron W3ZV

Try altering your feedline length (which means resetting the KAT500 memories
too). I had a similar issue on 80M.

However in my case, it made no difference when I added 30' more window line
but changing the coax length (+~30') allowed it to load. The doublet length
is 170' per side (all HOA stealthy too).

I use a 10 KW rated DX Engineering 1:1 common mode choke to convert window
line to coax AND keep RF outside the shack. Their website has a 'white
paper' comparing 1:1 and 4:1 which is worth reading too.

73,

Rick wa6nhc

-----Original Message-----
From: Ron W3ZV

At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and the
KPA500 connected as recommended with Elecraft DB15HD cables. The antenna is
a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of coax to the
KAT500. I have a comment point ground to a ground rod six foot from the
shack. I have operated the amp at 400+ watts from 80m to 6m. The only band
that gives me a problem is 12m. When I am operating at 400 watts ssb, the
amp will fault with a high swr indication within 5 to 20 seconds.
Immediately prior to the fault the swr on the amp display was 1.2:1.
Reducing power to below 300 watts seems to avoid the problem.

Assuming the consensus is that this is RFI, what would be the most likely
suspect? Coax cables in/out? DB15HD cable? Power cable? What's the easiest
way to diagnose and correct the problem? Thanks

Ron W3ZV

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David Gilbert

Re: KPA500 RFI problem

In reply to this post by Ron W3ZV

That doesn't sound like RFI. My guess would be that something is
arc'ing over between your amp and the antenna. That could be happening
at any one of several places (particularly at connections or inside the
balun). If it's close to the shack you could probably hear it ... if
it's in the feedline or at the antenna you might be able to see it at
night or discover a carbon track somewhere.

73,
Dave AB7E

On 1/8/2013 6:06 PM, Ron W3ZV wrote:

> At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and the KPA500 connected as recommended with Elecraft DB15HD cables. The antenna is a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of coax to the KAT500. I have a comment point ground to a ground rod six foot from the shack. I have operated the amp at 400+ watts from 80m to 6m. The only band that gives me a problem is 12m. When I am operating at 400 watts ssb, the amp will fault with a high swr indication within 5 to 20 seconds. Immediately prior to the fault the swr on the amp display was 1.2:1. Reducing power to below 300 watts seems to avoid the problem.
>
> Assuming the consensus is that this is RFI, what would be the most likely suspect? Coax cables in/out? DB15HD cable? Power cable? What's the easiest way to diagnose and correct the problem? Thanks
>
> Ron W3ZV
>
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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David Gilbert

Re: KPA500 RFI problem

In reply to this post by Rick WA6NHC

He said that his SWR on 12m was already low, so I don't see how that
helps a lot.

Dave AB7E

On 1/8/2013 6:40 PM, Rick Bates wrote:

> Try altering your feedline length (which means resetting the KAT500 memories
> too). I had a similar issue on 80M.
>
> However in my case, it made no difference when I added 30' more window line
> but changing the coax length (+~30') allowed it to load. The doublet length
> is 170' per side (all HOA stealthy too).
>
> I use a 10 KW rated DX Engineering 1:1 common mode choke to convert window
> line to coax AND keep RF outside the shack. Their website has a 'white
> paper' comparing 1:1 and 4:1 which is worth reading too.
>
> 73,
>
> Rick wa6nhc
>
> -----Original Message-----
> From: Ron W3ZV
>
> At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and the
> KPA500 connected as recommended with Elecraft DB15HD cables. The antenna is
> a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of coax to the
> KAT500. I have a comment point ground to a ground rod six foot from the
> shack. I have operated the amp at 400+ watts from 80m to 6m. The only band
> that gives me a problem is 12m. When I am operating at 400 watts ssb, the
> amp will fault with a high swr indication within 5 to 20 seconds.
> Immediately prior to the fault the swr on the amp display was 1.2:1.
> Reducing power to below 300 watts seems to avoid the problem.
>
> Assuming the consensus is that this is RFI, what would be the most likely
> suspect? Coax cables in/out? DB15HD cable? Power cable? What's the easiest
> way to diagnose and correct the problem? Thanks
>
> Ron W3ZV
>
> ______________________________________________________________
> 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
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>

Rick WA6NHC

Re: KPA500 RFI problem

I was stating what worked for me on 80m. It shifted the voltage peak to
another portion of the feed, though the SWR was the same.

It brought the apparent SWR without the KAT500 from 24:1 down to a range
that was more acceptable to the tuner.

With the collection of 'stuff' that most of us collect, adding a chunk of
coax or window line is simple enough to try.

Rick wa6nhc

-----Original Message-----
From: David Gilbert

He said that his SWR on 12m was already low, so I don't see how that
helps a lot.

Dave AB7E

On 1/8/2013 6:40 PM, Rick Bates wrote:
> Try altering your feedline length (which means resetting the KAT500
memories
> too). I had a similar issue on 80M.

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k6dgw

Re: KPA500 RFI problem

In reply to this post by k6dgw

On 1/8/2013 6:58 PM, Ron Kenwood wrote:
> Fred:
>
> Should have done that first, but I got tunnel vision on the RFI
> solution. I have an AIM4170B which should do the job. I will let you
> know how it goes.

OK, don't jump to conclusions though. If the impedance you measure on
the coax side of the balun is really high, it is 4 times that on the
"balanced" side, which at that point may not be all that "balanced."

If the impedance you find is very high, look carefully at your balun.
If it's been arcing from over-voltage, you might find it. One way to
fix this is to change the length of your feedline, but of course, that
screws up all the other bands. Maybe your 120' dipole just won't work
on 12m for you.

Looking forward to your results, antennas are one of the last bastions
of ham DIY.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org

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David Gilbert

Re: KPA500 RFI problem

In reply to this post by Rick WA6NHC

True. That is a possibility, of course ... that on 12m the voltage
maximum just happens to hit a weak spot in his feed system. In that
situation, adding some feedline could shift the maxima to a location
better able to handle the high voltages. I think I'd still want to find
that weak spot before I did anything else, though.

73,
Dave AB7E

On 1/8/2013 8:09 PM, Rick Bates wrote:

> I was stating what worked for me on 80m. It shifted the voltage peak to
> another portion of the feed, though the SWR was the same.
>
> It brought the apparent SWR without the KAT500 from 24:1 down to a range
> that was more acceptable to the tuner.
>
> With the collection of 'stuff' that most of us collect, adding a chunk of
> coax or window line is simple enough to try.
>
> Rick wa6nhc
>
> -----Original Message-----
> From: David Gilbert
>
> He said that his SWR on 12m was already low, so I don't see how that
> helps a lot.
>
> Dave AB7E
>
>
> On 1/8/2013 6:40 PM, Rick Bates wrote:
>> Try altering your feedline length (which means resetting the KAT500
> memories
>> too). I had a similar issue on 80M.
>

Jim AB3CV

Re: KPA500 RFI problem

In reply to this post by Ron W3ZV

I strongly suspect you have a common mode problem. These can be very
frequency dependent.

Read: http://audiosystemsgroup.com/RFI-Ham.pdf especially the section on
common mode chokes. There is a cookbook near the end for band specific
chokes.

For more details on the math read:
http://fermi.la.asu.edu/w9cf/articles/balun.pdf

I'd also recommend you take out the 4:1 transformer.

Good luck

jim ab3cv

On Tue, Jan 8, 2013 at 8:06 PM, Ron W3ZV <[hidden email]> wrote:

> At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and the
> KPA500 connected as recommended with Elecraft DB15HD cables. The antenna is
> a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of coax to
> the KAT500. I have a comment point ground to a ground rod six foot from the
> shack. I have operated the amp at 400+ watts from 80m to 6m. The only band
> that gives me a problem is 12m. When I am operating at 400 watts ssb, the
> amp will fault with a high swr indication within 5 to 20 seconds.
> Immediately prior to the fault the swr on the amp display was 1.2:1.
> Reducing power to below 300 watts seems to avoid the problem.
>
> Assuming the consensus is that this is RFI, what would be the most likely
> suspect? Coax cables in/out? DB15HD cable? Power cable? What's the easiest
> way to diagnose and correct the problem? Thanks
>
> Ron W3ZV
>
>
>
>
> ______________________________________________________________
> 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
>
>

alsopb

Re: KPA500 RFI problem

Sounds like the 4:1 balun may be overheating on 12M. Chances are if
you've been doing this for a bit, it's ruined. Heat anneals the core
and changes it's electrical properties for the worse. Heat may have
cracked it.

Now whether a 4:1 balun is the thing to use is another issue.
You don't say how long your open wire line is so it is impossible to
estimate the impedance seen by the balun.

Here are the approximate antenna feedpoint impedances for a 120' double
50' up.

80M 47 -j188 SWR=17:1 4:1 balun at antenna feedpoint makes situation
worse
40M 1724 +j1869 SWR =75:1 4:1 balun at antenna helps
20M 415 + j880 SWR =45:1 4:1 balun at antenna helps
15M 186+281j SWR =13:1 4:1 balun at antenna helps
12M 1293-155j SWR =63:1 4:1 balun at antenna helps
10M 122.4-j100 SWR =4:1 4:1 balun at antenna helps

It is clear that 12M may be close to the worst of the lot

If one knew the electrical properties and length of the ladder line, one
can do the impedance transformations and determine just what impedances
the balun sees. One may end up with entirely different conclusions from
above. The G5RV is an example of a "doublet" antenna where the ladder
line length is pruned to find an acceptable match on several bands.

73 de Brian/K3KO

On 1/9/2013 13:41, Jim Miller wrote:

> I strongly suspect you have a common mode problem. These can be very
> frequency dependent.
>
> Read: http://audiosystemsgroup.com/RFI-Ham.pdf especially the section on
> common mode chokes. There is a cookbook near the end for band specific
> chokes.
>
> For more details on the math read:
> http://fermi.la.asu.edu/w9cf/articles/balun.pdf
>
> I'd also recommend you take out the 4:1 transformer.
>
> Good luck
>
> jim ab3cv
>
> On Tue, Jan 8, 2013 at 8:06 PM, Ron W3ZV <[hidden email]> wrote:
>
>> At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and the
>> KPA500 connected as recommended with Elecraft DB15HD cables. The antenna is
>> a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of coax to
>> the KAT500. I have a comment point ground to a ground rod six foot from the
>> shack. I have operated the amp at 400+ watts from 80m to 6m. The only band
>> that gives me a problem is 12m. When I am operating at 400 watts ssb, the
>> amp will fault with a high swr indication within 5 to 20 seconds.
>> Immediately prior to the fault the swr on the amp display was 1.2:1.
>> Reducing power to below 300 watts seems to avoid the problem.
>>
>> Assuming the consensus is that this is RFI, what would be the most likely
>> suspect? Coax cables in/out? DB15HD cable? Power cable? What's the easiest
>> way to diagnose and correct the problem? Thanks
>>
>> Ron W3ZV
>>
>>
>>
>>
>> ______________________________________________________________
>> 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
>>
>>
> ______________________________________________________________
> 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
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2012.0.2221 / Virus Database: 2637/5519 - Release Date: 01/08/13
>
>

-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2221 / Virus Database: 2637/5519 - Release Date: 01/08/13

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David Gilbert

Re: KPA500 RFI problem

If that balun had overheated and become ruined on 12m it almost
certainly would have affected other bands as well. A ruined balun is a
changed balun.

Dave AB7E

On 1/9/2013 7:26 AM, Brian Alsop wrote:

> Sounds like the 4:1 balun may be overheating on 12M. Chances are if
> you've been doing this for a bit, it's ruined. Heat anneals the core
> and changes it's electrical properties for the worse. Heat may have
> cracked it.
>
> Now whether a 4:1 balun is the thing to use is another issue.
> You don't say how long your open wire line is so it is impossible to
> estimate the impedance seen by the balun.
>
> Here are the approximate antenna feedpoint impedances for a 120'
> double 50' up.
>
> 80M 47 -j188 SWR=17:1 4:1 balun at antenna feedpoint makes
> situation worse
> 40M 1724 +j1869 SWR =75:1 4:1 balun at antenna helps
> 20M 415 + j880 SWR =45:1 4:1 balun at antenna helps
> 15M 186+281j SWR =13:1 4:1 balun at antenna helps
> 12M 1293-155j SWR =63:1 4:1 balun at antenna helps
> 10M 122.4-j100 SWR =4:1 4:1 balun at antenna helps
>
> It is clear that 12M may be close to the worst of the lot
>
> If one knew the electrical properties and length of the ladder line,
> one can do the impedance transformations and determine just what
> impedances the balun sees. One may end up with entirely different
> conclusions from above. The G5RV is an example of a "doublet" antenna
> where the ladder line length is pruned to find an acceptable match on
> several bands.
>
> 73 de Brian/K3KO
>
>
>
>
>
> On 1/9/2013 13:41, Jim Miller wrote:
>> I strongly suspect you have a common mode problem. These can be very
>> frequency dependent.
>>
>> Read: http://audiosystemsgroup.com/RFI-Ham.pdf especially the section on
>> common mode chokes. There is a cookbook near the end for band specific
>> chokes.
>>
>> For more details on the math read:
>> http://fermi.la.asu.edu/w9cf/articles/balun.pdf
>>
>> I'd also recommend you take out the 4:1 transformer.
>>
>> Good luck
>>
>> jim ab3cv
>>
>> On Tue, Jan 8, 2013 at 8:06 PM, Ron W3ZV <[hidden email]> wrote:
>>
>>> At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and
>>> the
>>> KPA500 connected as recommended with Elecraft DB15HD cables. The
>>> antenna is
>>> a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of
>>> coax to
>>> the KAT500. I have a comment point ground to a ground rod six foot
>>> from the
>>> shack. I have operated the amp at 400+ watts from 80m to 6m. The
>>> only band
>>> that gives me a problem is 12m. When I am operating at 400 watts
>>> ssb, the
>>> amp will fault with a high swr indication within 5 to 20 seconds.
>>> Immediately prior to the fault the swr on the amp display was 1.2:1.
>>> Reducing power to below 300 watts seems to avoid the problem.
>>>
>>> Assuming the consensus is that this is RFI, what would be the most
>>> likely
>>> suspect? Coax cables in/out? DB15HD cable? Power cable? What's the
>>> easiest
>>> way to diagnose and correct the problem? Thanks
>>>
>>> Ron W3ZV
>>>
>>>
>>>
>>>
>>> ______________________________________________________________
>>> 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
>>>
>>>
>> ______________________________________________________________
>> 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
>>
>>
>> -----
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 2012.0.2221 / Virus Database: 2637/5519 - Release Date:
>> 01/08/13
>>
>>
>
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2012.0.2221 / Virus Database: 2637/5519 - Release Date: 01/08/13
>
> ______________________________________________________________
> 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
>

alsopb

Re: KPA500 RFI problem

Dave,

Most likely a tuner is being used.
If the balun failed one might not notice that since one generally tunes
to min SWR. Unless one recognizes something changed, one wouldn't know
it failed. This is especially true for auto tuners.

This "not knowing it failed" is wide spread for bead baluns-- although
this isn't the case here.

73 de Brian/K3KO

On 1/9/2013 17:26, David Gilbert wrote:

>
> If that balun had overheated and become ruined on 12m it almost
> certainly would have affected other bands as well. A ruined balun is a
> changed balun.
>
> Dave AB7E
>
>
>
> On 1/9/2013 7:26 AM, Brian Alsop wrote:
>> Sounds like the 4:1 balun may be overheating on 12M. Chances are if
>> you've been doing this for a bit, it's ruined. Heat anneals the core
>> and changes it's electrical properties for the worse. Heat may have
>> cracked it.
>>
>> Now whether a 4:1 balun is the thing to use is another issue.
>> You don't say how long your open wire line is so it is impossible to
>> estimate the impedance seen by the balun.
>>
>> Here are the approximate antenna feedpoint impedances for a 120'
>> double 50' up.
>>
>> 80M 47 -j188 SWR=17:1 4:1 balun at antenna feedpoint makes
>> situation worse
>> 40M 1724 +j1869 SWR =75:1 4:1 balun at antenna helps
>> 20M 415 + j880 SWR =45:1 4:1 balun at antenna helps
>> 15M 186+281j SWR =13:1 4:1 balun at antenna helps
>> 12M 1293-155j SWR =63:1 4:1 balun at antenna helps
>> 10M 122.4-j100 SWR =4:1 4:1 balun at antenna helps
>>
>> It is clear that 12M may be close to the worst of the lot
>>
>> If one knew the electrical properties and length of the ladder line,
>> one can do the impedance transformations and determine just what
>> impedances the balun sees. One may end up with entirely different
>> conclusions from above. The G5RV is an example of a "doublet" antenna
>> where the ladder line length is pruned to find an acceptable match on
>> several bands.
>>
>> 73 de Brian/K3KO
>>
>>
>>
>>
>>
>> On 1/9/2013 13:41, Jim Miller wrote:
>>> I strongly suspect you have a common mode problem. These can be very
>>> frequency dependent.
>>>
>>> Read: http://audiosystemsgroup.com/RFI-Ham.pdf especially the section on
>>> common mode chokes. There is a cookbook near the end for band specific
>>> chokes.
>>>
>>> For more details on the math read:
>>> http://fermi.la.asu.edu/w9cf/articles/balun.pdf
>>>
>>> I'd also recommend you take out the 4:1 transformer.
>>>
>>> Good luck
>>>
>>> jim ab3cv
>>>
>>> On Tue, Jan 8, 2013 at 8:06 PM, Ron W3ZV <[hidden email]> wrote:
>>>
>>>> At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and
>>>> the
>>>> KPA500 connected as recommended with Elecraft DB15HD cables. The
>>>> antenna is
>>>> a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of
>>>> coax to
>>>> the KAT500. I have a comment point ground to a ground rod six foot
>>>> from the
>>>> shack. I have operated the amp at 400+ watts from 80m to 6m. The
>>>> only band
>>>> that gives me a problem is 12m. When I am operating at 400 watts
>>>> ssb, the
>>>> amp will fault with a high swr indication within 5 to 20 seconds.
>>>> Immediately prior to the fault the swr on the amp display was 1.2:1.
>>>> Reducing power to below 300 watts seems to avoid the problem.
>>>>
>>>> Assuming the consensus is that this is RFI, what would be the most
>>>> likely
>>>> suspect? Coax cables in/out? DB15HD cable? Power cable? What's the
>>>> easiest
>>>> way to diagnose and correct the problem? Thanks
>>>>
>>>> Ron W3ZV
>>>>
>>>>
>>>>
>>>>
>>>> ______________________________________________________________
>>>> 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
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>>>>
>>>>
>>> ______________________________________________________________
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>>>
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>>>
>>> -----
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>>> Checked by AVG - www.avg.com
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>>> 01/08/13
>>>
>>>
>>
>>
>>
>> -----
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>> Checked by AVG - www.avg.com
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>>
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>
> ______________________________________________________________
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> Checked by AVG - www.avg.com
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>
>

David Gilbert

Re: KPA500 RFI problem

From a troubleshooting point of view jumping right to the balun
requires making a lot of assumptions, most of them unwarranted given
what little we know so far from his post. More importantly, a balun
with a ruined core is going to look bad for SWR no matter what power
level is fed to it, and he says that things look fine at 300 watts but
go south at 400 watts. That's an arc over problem somewhere ...

Dave AB7E

On 1/9/2013 10:53 AM, Brian Alsop wrote:

> Dave,
>
> Most likely a tuner is being used.
> If the balun failed one might not notice that since one generally
> tunes to min SWR. Unless one recognizes something changed, one
> wouldn't know it failed. This is especially true for auto tuners.
>
> This "not knowing it failed" is wide spread for bead baluns-- although
> this isn't the case here.
>
> 73 de Brian/K3KO
>
>
> On 1/9/2013 17:26, David Gilbert wrote:
>>
>> If that balun had overheated and become ruined on 12m it almost
>> certainly would have affected other bands as well. A ruined balun is a
>> changed balun.
>>
>> Dave AB7E
>>
>>
>>
>> On 1/9/2013 7:26 AM, Brian Alsop wrote:
>>> Sounds like the 4:1 balun may be overheating on 12M. Chances are if
>>> you've been doing this for a bit, it's ruined. Heat anneals the core
>>> and changes it's electrical properties for the worse. Heat may have
>>> cracked it.
>>>
>>> Now whether a 4:1 balun is the thing to use is another issue.
>>> You don't say how long your open wire line is so it is impossible to
>>> estimate the impedance seen by the balun.
>>>
>>> Here are the approximate antenna feedpoint impedances for a 120'
>>> double 50' up.
>>>
>>> 80M 47 -j188 SWR=17:1 4:1 balun at antenna feedpoint makes
>>> situation worse
>>> 40M 1724 +j1869 SWR =75:1 4:1 balun at antenna helps
>>> 20M 415 + j880 SWR =45:1 4:1 balun at antenna helps
>>> 15M 186+281j SWR =13:1 4:1 balun at antenna helps
>>> 12M 1293-155j SWR =63:1 4:1 balun at antenna helps
>>> 10M 122.4-j100 SWR =4:1 4:1 balun at antenna helps
>>>
>>> It is clear that 12M may be close to the worst of the lot
>>>
>>> If one knew the electrical properties and length of the ladder line,
>>> one can do the impedance transformations and determine just what
>>> impedances the balun sees. One may end up with entirely different
>>> conclusions from above. The G5RV is an example of a "doublet" antenna
>>> where the ladder line length is pruned to find an acceptable match on
>>> several bands.
>>>
>>> 73 de Brian/K3KO
>>>
>>>
>>>
>>>
>>>
>>> On 1/9/2013 13:41, Jim Miller wrote:
>>>> I strongly suspect you have a common mode problem. These can be very
>>>> frequency dependent.
>>>>
>>>> Read: http://audiosystemsgroup.com/RFI-Ham.pdf especially the
>>>> section on
>>>> common mode chokes. There is a cookbook near the end for band specific
>>>> chokes.
>>>>
>>>> For more details on the math read:
>>>> http://fermi.la.asu.edu/w9cf/articles/balun.pdf
>>>>
>>>> I'd also recommend you take out the 4:1 transformer.
>>>>
>>>> Good luck
>>>>
>>>> jim ab3cv
>>>>
>>>> On Tue, Jan 8, 2013 at 8:06 PM, Ron W3ZV <[hidden email]> wrote:
>>>>
>>>>> At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and
>>>>> the
>>>>> KPA500 connected as recommended with Elecraft DB15HD cables. The
>>>>> antenna is
>>>>> a 120ft. doublet fed with ladder line to a 4:1 balun and 10ft of
>>>>> coax to
>>>>> the KAT500. I have a comment point ground to a ground rod six foot
>>>>> from the
>>>>> shack. I have operated the amp at 400+ watts from 80m to 6m. The
>>>>> only band
>>>>> that gives me a problem is 12m. When I am operating at 400 watts
>>>>> ssb, the
>>>>> amp will fault with a high swr indication within 5 to 20 seconds.
>>>>> Immediately prior to the fault the swr on the amp display was 1.2:1.
>>>>> Reducing power to below 300 watts seems to avoid the problem.
>>>>>
>>>>> Assuming the consensus is that this is RFI, what would be the most
>>>>> likely
>>>>> suspect? Coax cables in/out? DB15HD cable? Power cable? What's the
>>>>> easiest
>>>>> way to diagnose and correct the problem? Thanks
>>>>>
>>>>> Ron W3ZV
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ______________________________________________________________
>>>>> 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
>>>>>
>>>>>
>>>> ______________________________________________________________
>>>> 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
>>>>
>>>>
>>>> -----
>>>> No virus found in this message.
>>>> Checked by AVG - www.avg.com
>>>> Version: 2012.0.2221 / Virus Database: 2637/5519 - Release Date:
>>>> 01/08/13
>>>>
>>>>
>>>
>>>
>>>
>>> -----
>>> No virus found in this message.
>>> Checked by AVG - www.avg.com
>>> Version: 2012.0.2221 / Virus Database: 2637/5519 - Release Date:
>>> 01/08/13
>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>>> Post: mailto:[hidden email]
>>>
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>>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
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>>
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>>
>>
>> -----
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>> Checked by AVG - www.avg.com
>> Version: 2012.0.2221 / Virus Database: 2637/5519 - Release Date:
>> 01/08/13
>>
>>
>
>
>
> -----
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> Checked by AVG - www.avg.com
> Version: 2012.0.2221 / Virus Database: 2637/5519 - Release Date: 01/08/13
>
> ______________________________________________________________
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>
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Rick WA6NHC

Re: KPA500 RFI problem

I agree that the balun should be checked but that it is likely NOT the issue
here as it works on the other bands. If it is replaced, using a 1:1 common
mode choke (not just a voltage balun or series of ferrite cores on the coax)
would be a good thing to try. I opted for the 10KW rated version as I never
want to have an issue and I only run <700 watts.

To make clear an earlier statement of mine, without the added coax, the
untuned VSWR was 24:1, with the added coax it is under 10:1. The KAT500
tuned the wire in both cases here but in the original configuration tuned
my EDZ to 1:1 at low power then faulted out at anything above 300 watts.
Adding more coax solved the issue (I tried a shorter run too, no change) by
shifting the 80M voltage peak to someplace else on the feed.

Is your wire antenna insulated or bare? Is there a chance that it is arcing
(wet tree, mast ???)? With the voltages produced at QRO, the potential is
there. Ditto your window line, insulated or bare? Is rain or snow
impacting it? You'd know because it would need retuning.

Rick wa6nhc

-----Original Message-----
From: David Gilbert

From a troubleshooting point of view jumping right to the balun
requires making a lot of assumptions, most of them unwarranted given
what little we know so far from his post. More importantly, a balun
with a ruined core is going to look bad for SWR no matter what power
level is fed to it, and he says that things look fine at 300 watts but
go south at 400 watts. That's an arc over problem somewhere ...

Dave AB7E

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Igor Sokolov-2

Re: KPA500 RFI problem

If it is RFI problem (as it was initially suspected) I would first
disconnect the control cable between K3 and KPA500. I would use only
separate PTT line to the amd and see if the problem is gone on the affected
band.

73, Igor UA9CDC

----- Original Message -----
From: "Rick Bates" <[hidden email]>
To: "'David Gilbert'" <[hidden email]>; <[hidden email]>
Sent: Thursday, January 10, 2013 1:19 AM
Subject: Re: [Elecraft] KPA500 RFI problem

>I agree that the balun should be checked but that it is likely NOT the
>issue
> here as it works on the other bands. If it is replaced, using a 1:1
> common
> mode choke (not just a voltage balun or series of ferrite cores on the
> coax)
> would be a good thing to try. I opted for the 10KW rated version as I
> never
> want to have an issue and I only run <700 watts.
>
> To make clear an earlier statement of mine, without the added coax, the
> untuned VSWR was 24:1, with the added coax it is under 10:1. The KAT500
> tuned the wire in both cases here but in the original configuration tuned
> my EDZ to 1:1 at low power then faulted out at anything above 300 watts.
> Adding more coax solved the issue (I tried a shorter run too, no change)
> by
> shifting the 80M voltage peak to someplace else on the feed.
>
> Is your wire antenna insulated or bare? Is there a chance that it is
> arcing
> (wet tree, mast ???)? With the voltages produced at QRO, the potential is
> there. Ditto your window line, insulated or bare? Is rain or snow
> impacting it? You'd know because it would need retuning.
>
> Rick wa6nhc
>
> -----Original Message-----
> From: David Gilbert
>
> From a troubleshooting point of view jumping right to the balun
> requires making a lot of assumptions, most of them unwarranted given
> what little we know so far from his post. More importantly, a balun
> with a ruined core is going to look bad for SWR no matter what power
> level is fed to it, and he says that things look fine at 300 watts but
> go south at 400 watts. That's an arc over problem somewhere ...
>
> Dave AB7E
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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Jim Brown-10

Re: KPA500 RFI problem

In reply to this post by David Gilbert

On 1/9/2013 10:59 AM, David Gilbert wrote:
> More importantly, a balun with a ruined core is going to look bad for SWR

Please delete the word "balun" from this discussion, and use the words
"unknown black box" instead. That's because the word "balun" is used to
describe at least a half dozen circuit components, most of which are
very different from each other.

A so-called "current balun" is really a common mode choke formed by
either placing a lot of ferrite beads on coax, or by winding multiple
turns of coax around/through a ferrite core. The most common failure
mode of such a choke is overheating of the coax, causing it to deform,
and in the extreme, to short (between center and shield).

A common mode choke fails when it's choking impedance is too low to
limit common mode current to a value that does not limit dissipation to
a safe value. Excessive common mode current is caused by high common
mode voltage, which results from antennas that are unbalanced
(especially "Windom" style antennas, and, of course, by running higher
power.

Many years ago, before I had learned about what was inside an unknown
black box called a balun at the feedpoint of a dipole, I fried one by
tying both sides of the feedline together to feed it as a top-loaded
long wire, and running 100W for a weekend 160M contest.

73, Jim K9YC
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Guy, K2AV

Re: KPA500 RFI problem

In reply to this post by Ron W3ZV

Part of the difficulty is an assumption that 1) there really is an antenna
that will work on all bands, 2) that balanced feedlines do not have common
mode current, and 3) that just about any feedline and transformer
combination will work. There is an awful lot of "all-band" stuff that is
really snake oil, and depends on LOSS to push down the SWR. True,
efficient all-banding is work, requires the good components and scanning RF
analyzers to work and adjust them into shape.

Both a transformer or any wire plus ferrite device and an auto-tuner that
are subjected to the stresses from an "all-band" application can 1) be
ineffective due to no in-range solution at a given frequency, 2) overheated
due to common mode current or high current, or 3) in the extreme destroyed
by heat or arcing paths.

An antenna that is tunable on all bands including WARC has an element of
luck to it, even with antennas claimed to be all-band. To be efficient as
well means that extremes in R, X and Z are presented in full strength to
stress points, and are not soaked up by potentially lossy elements in the
antenna system such as feedlines, transformers, and wire/ferrite devices.
Destructive possibilities are made worse by cores and coax that barely can
stand constant key down 100 watts with extreme R, X, and Z. While I doubt
this for the KAT500, an awful lot of stuff peddled as "baluns", "ununs",
etc., is really cr*p. This is particularly true for the inexpensive
devices. Add to this some unlucky antenna implementations.

Now the odds of working at 100 watts and then failing at 500 watts are
remarkably common. You have multiplied prior heat loss by 5. You have
better than doubled current at high current points, and you have better
than doubled the voltage at possible breakdown points. Stuff that was
made as cheap as possible, and blow-up tested at 100 watts for the low end,
now becomes questionable.

And even if you were previously lucky, adding a half dozen feet of
miscellaneous conductors to insert an amp and/or auto-tuner to the string
can present R, X, or Z that is now out of range or destructive, especially
considering the higher power.

Just wanted you to know that if you are doing one antenna multiband, you
are in the swamp and there are alligators. Nothing that can't be managed,
you just need to know that all-band antenna design has sharp teeth, and
will bite. Forewarned and all that.

There are other analyzers that can do this, I have an AIM4170 scanning RF
analyzer. The 4170 can be set to scan from 3 to 30, or 1.5 to 30, or any
continuous range of frequencies that is your target range.

The entire range at one time can be displayed graphically on the PC
connected to the 4170. Ham bands can have a darker gray background to make
it easier to see it all at one time. Then the sweep display of R, X and Z
will tell you what is going to happen. One can dink around with wire
lengths and open wire lengths, and inclusions of 4:1 transformers (or not).
What you are looking for is neither really high or really low extremes of
R, or X or Z in the ham bands. High extremes will defeat tuner matching,
cause arcing in connectors, and low extremes will cause overheating when
presented to transformers.

You need to do the viewing anywhere you intend to insert a device, and at
either end of coax runs. In particular, before coax do the all frequency
scan WITH and WITHOUT a 4:1 or 9:1. Also consider running dual coax, with
the two center conductors as a balanced line with the shields connected
together at both ends and grounded at entry to the shack. Dual RG-11 (150
ohms balanced) is good for terminating open wire for coax runs, and may
moderate impedances (and loss) seen at the tuner end.

When an extreme is close or in a ham band, seemingly small changes in
feedline or even antenna height and changes in proximity to conductors,
just a small change can move an extreme point just enough to hit a
frequency you are using.

If you haven't bought a 4170 or equivalent, or borrowed a friend with a
4170 or its equivalent, basically you are flying blind, and just hoping you
didn't drop an extreme in a band you want. An SWR meter is really not
sufficient to the problem unless you are lucky.

73, Guy
K2AV

On Tue, Jan 8, 2013 at 8:06 PM, Ron W3ZV <[hidden email]> wrote: