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Reflected power

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Stephen Rabinowitz

Reflected power

My KPA-1500 switches from operate to standby due to reflected power more
than 200w whenever drive power exceeds about 8 watts on 7 MHz. The forward
power at that point is about 400w. The antenna is a double bazooka that
shows an SWR of about 1.2 on a RigExpert AA-230Pro antenna analyzer. A
Telepost LP-100A digital wattmeter shows SWR 1.3 with Z=52, R=49, Ph=17, and
X=15. The KP1500 tunes to an SWR of what it labels 1.1 on that frequency.
The latest firmware, version 2.27 is installed. This problem does not occur
with double bazooka antennas on 80m or 30m, or with Yagis from 20m to 6m. It
seems to me that there is a brief surge in reflected power at the very onset
of the transmission that triggers the response, but that the reflected power
quickly decreases to normal levels of just a few watts. Any ideas for
dealing with this problem would be much appreciated.
73, Steve K2SN

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Dave wo2x

Re: Reflected power

Check your connections. Loose or poor PL-259s. Also check to see if the
antenna is close to something causing it to arc over. I had one antenna that
used ladder line with solid conductors. Due to it moving around in the wind
one of the conductors developed a break which tested fine under low power or
with an analyzer but would have problems at higher power. I've since moved
to Davis RF copper clad stranded ladder line.

Dave wo2x

-----Original Message-----
From: [hidden email] <[hidden email]> On
Behalf Of Stephen Rabinowitz
Sent: Sunday, September 15, 2019 7:58 PM
To: [hidden email]
Subject: [Elecraft] Reflected power

My KPA-1500 switches from operate to standby due to reflected power more
than 200w whenever drive power exceeds about 8 watts on 7 MHz. The forward
power at that point is about 400w. The antenna is a double bazooka that
shows an SWR of about 1.2 on a RigExpert AA-230Pro antenna analyzer. A
Telepost LP-100A digital wattmeter shows SWR 1.3 with Z=52, R=49, Ph=17, and
X=15. The KP1500 tunes to an SWR of what it labels 1.1 on that frequency.
The latest firmware, version 2.27 is installed. This problem does not occur
with double bazooka antennas on 80m or 30m, or with Yagis from 20m to 6m. It
seems to me that there is a brief surge in reflected power at the very onset
of the transmission that triggers the response, but that the reflected power
quickly decreases to normal levels of just a few watts. Any ideas for
dealing with this problem would be much appreciated.
73, Steve K2SN

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Michael Walker

Re: Reflected power

Steve

40 seems to be the killer band for weird things. Dave's comments are the
first place to look. Try also changing jumper cables.

What also could be happening is RF flowing back on feedline in a common
mode. This RF gets measured as return energy and now, since the power is
higher, the return currents are higher and hence the high SWR reading. You
won't see this with your RigExpert.

Does the same problem happen into a dummy load? If Yes, it is an amp
issue. If no, it is a antenna/feedline issue.

I would try some RF chokes (Mix 43) on both ends of the feedline (antenna
and amp end). I chased strange RF issues for decades until I read this
document by the YCCC/W1HIS.
http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf.
After that I bought about 100 Mix 43 chokes and added them everywhere.

Not only does it help with unique RFI TX issues, it also helps with the
ability to hear. The quieter you are, the more you can copy.

Let us know how you make out.

Mike va3mw

On Sun, Sep 15, 2019 at 8:05 PM <[hidden email]> wrote:

> Check your connections. Loose or poor PL-259s. Also check to see if the
> antenna is close to something causing it to arc over. I had one antenna
> that
> used ladder line with solid conductors. Due to it moving around in the wind
> one of the conductors developed a break which tested fine under low power
> or
> with an analyzer but would have problems at higher power. I've since moved
> to Davis RF copper clad stranded ladder line.
>
> Dave wo2x
>
>
>
>
> -----Original Message-----
> From: [hidden email] <[hidden email]>
> On
> Behalf Of Stephen Rabinowitz
> Sent: Sunday, September 15, 2019 7:58 PM
> To: [hidden email]
> Subject: [Elecraft] Reflected power
>
> My KPA-1500 switches from operate to standby due to reflected power more
> than 200w whenever drive power exceeds about 8 watts on 7 MHz. The forward
> power at that point is about 400w. The antenna is a double bazooka that
> shows an SWR of about 1.2 on a RigExpert AA-230Pro antenna analyzer. A
> Telepost LP-100A digital wattmeter shows SWR 1.3 with Z=52, R=49, Ph=17,
> and
> X=15. The KP1500 tunes to an SWR of what it labels 1.1 on that frequency.
> The latest firmware, version 2.27 is installed. This problem does not occur
> with double bazooka antennas on 80m or 30m, or with Yagis from 20m to 6m.
> It
> seems to me that there is a brief surge in reflected power at the very
> onset
> of the transmission that triggers the response, but that the reflected
> power
> quickly decreases to normal levels of just a few watts. Any ideas for
> dealing with this problem would be much appreciated.
> 73, Steve K2SN
>
> ______________________________________________________________
> 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
> Message
> delivered to [hidden email]
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

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Jim Brown-10

Re: Reflected power

On 9/15/2019 6:05 PM, Michael Walker wrote:
> Steve
>
> 40 seems to be the killer band for weird things. Dave's comments are the
> first place to look. Try also changing jumper cables.
>
> What also could be happening is RF flowing back on feedline in a common
> mode. This RF gets measured as return energy and now, since the power is
> higher, the return currents are higher and hence the high SWR reading.

False. Common mode current is NOT reflected power.

It is a fallacy that antennas like this do not need a serious common
mode choke, and it must be at the feedpoint (that is, up in the air).
Indeed, common mode current may be putting RF in the shack. Is
everything in your station properly bonded? Lots of things that work at
low power break with high power. See

http://k9yc.com/GroundingAndAudio.pdf

There are multiple versions of antennas using this name. Which one are
you using, Steve?

There are also fallacies about the performance of the double bazooka
antenna. Study this report by a very good engineer debunking them.
https://owenduffy.net/antenna/DoubleBazooka/index.htm

You

> won't see this with your RigExpert.
>
> Does the same problem happen into a dummy load? If Yes, it is an amp
> issue. If no, it is a antenna/feedline issue.
>
> I would try some RF chokes (Mix 43) on both ends of the feedline (antenna
> and amp end). I chased strange RF issues for decades until I read this
> document by the YCCC/W1HIS.
> http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf.
> After that I bought about 100 Mix 43 chokes and added them everywhere.

Mix 43 is a very poor material for HF chokes. The reason is complicated,
but it boils down to it's relatively high Q and wide production
tolerances, which make repeatable designs impossible.

Mix 31 is FAR better. W1HIS is right about the significance of chokes to
kill common mode current, but he didn't know about mix 31 when he wrote
the referenced document -- it was a pretty new material at the time. See
the latest version of my Choke Cookbook for detailed recommendations.
http://k9yc.com/2018Cookbook.pdf

> Not only does it help with unique RFI TX issues, it also helps with the
> ability to hear. The quieter you are, the more you can copy.

Yes

73, Jim K9YC

>
> Let us know how you make out.
>
> Mike va3mw
>
>
> On Sun, Sep 15, 2019 at 8:05 PM <[hidden email]> wrote:
>
>> Check your connections. Loose or poor PL-259s. Also check to see if the
>> antenna is close to something causing it to arc over. I had one antenna
>> that
>> used ladder line with solid conductors. Due to it moving around in the wind
>> one of the conductors developed a break which tested fine under low power
>> or
>> with an analyzer but would have problems at higher power. I've since moved
>> to Davis RF copper clad stranded ladder line.
>>
>> Dave wo2x
>>
>>
>>
>>
>> -----Original Message-----
>> From: [hidden email] <[hidden email]>
>> On
>> Behalf Of Stephen Rabinowitz
>> Sent: Sunday, September 15, 2019 7:58 PM
>> To: [hidden email]
>> Subject: [Elecraft] Reflected power
>>
>> My KPA-1500 switches from operate to standby due to reflected power more
>> than 200w whenever drive power exceeds about 8 watts on 7 MHz. The forward
>> power at that point is about 400w. The antenna is a double bazooka that
>> shows an SWR of about 1.2 on a RigExpert AA-230Pro antenna analyzer. A
>> Telepost LP-100A digital wattmeter shows SWR 1.3 with Z=52, R=49, Ph=17,
>> and
>> X=15. The KP1500 tunes to an SWR of what it labels 1.1 on that frequency.
>> The latest firmware, version 2.27 is installed. This problem does not occur
>> with double bazooka antennas on 80m or 30m, or with Yagis from 20m to 6m.
>> It
>> seems to me that there is a brief surge in reflected power at the very
>> onset
>> of the transmission that triggers the response, but that the reflected
>> power
>> quickly decreases to normal levels of just a few watts. Any ideas for
>> dealing with this problem would be much appreciated.
>> 73, Steve K2SN
>>
>> ______________________________________________________________
>> 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
>> Message
>> delivered to [hidden email]
>>
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
>>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

Vic Rosenthal

Re: Reflected power

He didn’t say common mode current WAS reflected power. He said that common mode current can cause incorrect SWR measurements, and that is true.

Victor 4X6GP

> On 16 Sep 2019, at 7:37, Jim Brown <[hidden email]> wrote:
>
>> On 9/15/2019 6:05 PM, Michael Walker wrote:
>> Steve
>> 40 seems to be the killer band for weird things. Dave's comments are the
>> first place to look. Try also changing jumper cables.
>> What also could be happening is RF flowing back on feedline in a common
>> mode. This RF gets measured as return energy and now, since the power is
>> higher, the return currents are higher and hence the high SWR reading.
>
> False. Common mode current is NOT reflected power.
>
> It is a fallacy that antennas like this do not need a serious common mode choke, and it must be at the feedpoint (that is, up in the air). Indeed, common mode current may be putting RF in the shack. Is everything in your station properly bonded? Lots of things that work at low power break with high power. See
>
> http://k9yc.com/GroundingAndAudio.pdf
>
> There are multiple versions of antennas using this name. Which one are you using, Steve?
>
> There are also fallacies about the performance of the double bazooka antenna. Study this report by a very good engineer debunking them. https://owenduffy.net/antenna/DoubleBazooka/index.htm
>
> You
>> won't see this with your RigExpert.
>> Does the same problem happen into a dummy load? If Yes, it is an amp
>> issue. If no, it is a antenna/feedline issue.
>> I would try some RF chokes (Mix 43) on both ends of the feedline (antenna
>> and amp end). I chased strange RF issues for decades until I read this
>> document by the YCCC/W1HIS.
>> http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf.
>> After that I bought about 100 Mix 43 chokes and added them everywhere.
>
> Mix 43 is a very poor material for HF chokes. The reason is complicated, but it boils down to it's relatively high Q and wide production tolerances, which make repeatable designs impossible.
>
> Mix 31 is FAR better. W1HIS is right about the significance of chokes to kill common mode current, but he didn't know about mix 31 when he wrote the referenced document -- it was a pretty new material at the time. See the latest version of my Choke Cookbook for detailed recommendations. http://k9yc.com/2018Cookbook.pdf
>
>
>> Not only does it help with unique RFI TX issues, it also helps with the
>> ability to hear. The quieter you are, the more you can copy.
>
> Yes
>
> 73, Jim K9YC
>> Let us know how you make out.
>> Mike va3mw
>>> On Sun, Sep 15, 2019 at 8:05 PM <[hidden email]> wrote:
>>> Check your connections. Loose or poor PL-259s. Also check to see if the
>>> antenna is close to something causing it to arc over. I had one antenna
>>> that
>>> used ladder line with solid conductors. Due to it moving around in the wind
>>> one of the conductors developed a break which tested fine under low power
>>> or
>>> with an analyzer but would have problems at higher power. I've since moved
>>> to Davis RF copper clad stranded ladder line.
>>>
>>> Dave wo2x
>>>
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: [hidden email] <[hidden email]>
>>> On
>>> Behalf Of Stephen Rabinowitz
>>> Sent: Sunday, September 15, 2019 7:58 PM
>>> To: [hidden email]
>>> Subject: [Elecraft] Reflected power
>>>
>>> My KPA-1500 switches from operate to standby due to reflected power more
>>> than 200w whenever drive power exceeds about 8 watts on 7 MHz. The forward
>>> power at that point is about 400w. The antenna is a double bazooka that
>>> shows an SWR of about 1.2 on a RigExpert AA-230Pro antenna analyzer. A
>>> Telepost LP-100A digital wattmeter shows SWR 1.3 with Z=52, R=49, Ph=17,
>>> and
>>> X=15. The KP1500 tunes to an SWR of what it labels 1.1 on that frequency.
>>> The latest firmware, version 2.27 is installed. This problem does not occur
>>> with double bazooka antennas on 80m or 30m, or with Yagis from 20m to 6m.
>>> It
>>> seems to me that there is a brief surge in reflected power at the very
>>> onset
>>> of the transmission that triggers the response, but that the reflected
>>> power
>>> quickly decreases to normal levels of just a few watts. Any ideas for
>>> dealing with this problem would be much appreciated.
>>> 73, Steve K2SN
>>>
>>> ______________________________________________________________
>>> 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
>>> Message
>>> delivered to [hidden email]
>>>
>>> ______________________________________________________________
>>> 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
>>> Message delivered to [hidden email]
>>>
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]

Jim Brown-10

Re: Reflected power

I disagree, Vic. He said "the return currents are higher." SWR describes
what is going on INSIDE the transmission line -- the differential
current. Common mode current is OUTSIDE the coax (or, in the case of
2-wire line, the difference between the current on the two conductors.

Now, common mode current CAN de-tune the antenna to the extent that the
feedline becomes part of the antenna, but the resulting SWR would be
correctly measured by the LP100A. It might NOT be correctly measured by
the RigExpert, because it breaks up the common mode circuit.

Further -- standing waves on the feedline exist inside the feedline (or
between the conductors), and voltage and when there is SWR, current and
voltage vary along the line in a manner determined by the VF of the
feedline. But in the common mode circuit, the feedline acts as a single
wire with a VF near 0.98, depending on diameter and insulation, and
common mode current and voltage vary along the line just as they would
on any other antenna.

73, Jim K9YC

On 9/15/2019 9:53 PM, Vic Rosenthal wrote:

Alan Bloom

Re: Reflected power

In reply to this post by Vic Rosenthal

As long as everything is well-shielded, the common-mode currents do not
make the SWR reading incorrect. They may affect the actual SWR just due
to the additional radiation from the feedline common-mode currents, and
the SWR meter will reflect that, but the reading is correct.

Alan N1AL

On 9/15/19 9:53 PM, Vic Rosenthal wrote:

> He didn’t say common mode current WAS reflected power. He said that common mode current can cause incorrect SWR measurements, and that is true.
>
> Victor 4X6GP
>
>> On 16 Sep 2019, at 7:37, Jim Brown <[hidden email]> wrote:
>>
>>> On 9/15/2019 6:05 PM, Michael Walker wrote:
>>> Steve
>>> 40 seems to be the killer band for weird things. Dave's comments are the
>>> first place to look. Try also changing jumper cables.
>>> What also could be happening is RF flowing back on feedline in a common
>>> mode. This RF gets measured as return energy and now, since the power is
>>> higher, the return currents are higher and hence the high SWR reading.
>> False. Common mode current is NOT reflected power.
>>
>> It is a fallacy that antennas like this do not need a serious common mode choke, and it must be at the feedpoint (that is, up in the air). Indeed, common mode current may be putting RF in the shack. Is everything in your station properly bonded? Lots of things that work at low power break with high power. See
>>
>> http://k9yc.com/GroundingAndAudio.pdf
>>
>> There are multiple versions of antennas using this name. Which one are you using, Steve?
>>
>> There are also fallacies about the performance of the double bazooka antenna. Study this report by a very good engineer debunking them. https://owenduffy.net/antenna/DoubleBazooka/index.htm
>>
>> You
>>> won't see this with your RigExpert.
>>> Does the same problem happen into a dummy load? If Yes, it is an amp
>>> issue. If no, it is a antenna/feedline issue.
>>> I would try some RF chokes (Mix 43) on both ends of the feedline (antenna
>>> and amp end). I chased strange RF issues for decades until I read this
>>> document by the YCCC/W1HIS.
>>> http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf.
>>> After that I bought about 100 Mix 43 chokes and added them everywhere.
>> Mix 43 is a very poor material for HF chokes. The reason is complicated, but it boils down to it's relatively high Q and wide production tolerances, which make repeatable designs impossible.
>>
>> Mix 31 is FAR better. W1HIS is right about the significance of chokes to kill common mode current, but he didn't know about mix 31 when he wrote the referenced document -- it was a pretty new material at the time. See the latest version of my Choke Cookbook for detailed recommendations. http://k9yc.com/2018Cookbook.pdf
>>
>>
>>> Not only does it help with unique RFI TX issues, it also helps with the
>>> ability to hear. The quieter you are, the more you can copy.
>> Yes
>>
>> 73, Jim K9YC
>>> Let us know how you make out.
>>> Mike va3mw
>>>> On Sun, Sep 15, 2019 at 8:05 PM <[hidden email]> wrote:
>>>> Check your connections. Loose or poor PL-259s. Also check to see if the
>>>> antenna is close to something causing it to arc over. I had one antenna
>>>> that
>>>> used ladder line with solid conductors. Due to it moving around in the wind
>>>> one of the conductors developed a break which tested fine under low power
>>>> or
>>>> with an analyzer but would have problems at higher power. I've since moved
>>>> to Davis RF copper clad stranded ladder line.
>>>>
>>>> Dave wo2x
>>>>
>>>>
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: [hidden email] <[hidden email]>
>>>> On
>>>> Behalf Of Stephen Rabinowitz
>>>> Sent: Sunday, September 15, 2019 7:58 PM
>>>> To: [hidden email]
>>>> Subject: [Elecraft] Reflected power
>>>>
>>>> My KPA-1500 switches from operate to standby due to reflected power more
>>>> than 200w whenever drive power exceeds about 8 watts on 7 MHz. The forward
>>>> power at that point is about 400w. The antenna is a double bazooka that
>>>> shows an SWR of about 1.2 on a RigExpert AA-230Pro antenna analyzer. A
>>>> Telepost LP-100A digital wattmeter shows SWR 1.3 with Z=52, R=49, Ph=17,
>>>> and
>>>> X=15. The KP1500 tunes to an SWR of what it labels 1.1 on that frequency.
>>>> The latest firmware, version 2.27 is installed. This problem does not occur
>>>> with double bazooka antennas on 80m or 30m, or with Yagis from 20m to 6m.
>>>> It
>>>> seems to me that there is a brief surge in reflected power at the very
>>>> onset
>>>> of the transmission that triggers the response, but that the reflected
>>>> power
>>>> quickly decreases to normal levels of just a few watts. Any ideas for
>>>> dealing with this problem would be much appreciated.
>>>> 73, Steve K2SN
>>>>
>>>> ______________________________________________________________
>>>> 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
>>>> Message
>>>> delivered to [hidden email]
>>>>
>>>> ______________________________________________________________
>>>> 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
>>>> Message delivered to [hidden email]
>>>>
>>> ______________________________________________________________
>>> 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
>>> Message delivered to [hidden email]
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
> ______________________________________________________________
> 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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Michael Walker

Re: Reflected power

I only post stuff on this reflector so Jim can tear me a new one.

Mike va3mw

On Mon, Sep 16, 2019 at 1:21 AM Alan <[hidden email]> wrote:

> As long as everything is well-shielded, the common-mode currents do not
> make the SWR reading incorrect. They may affect the actual SWR just due
> to the additional radiation from the feedline common-mode currents, and
> the SWR meter will reflect that, but the reading is correct.
>
> Alan N1AL
>
>
>
> On 9/15/19 9:53 PM, Vic Rosenthal wrote:
> > He didn’t say common mode current WAS reflected power. He said that
> common mode current can cause incorrect SWR measurements, and that is true.
> >
> > Victor 4X6GP
> >
> >> On 16 Sep 2019, at 7:37, Jim Brown <[hidden email]> wrote:
> >>
> >>> On 9/15/2019 6:05 PM, Michael Walker wrote:
> >>> Steve
> >>> 40 seems to be the killer band for weird things. Dave's comments are
> the
> >>> first place to look. Try also changing jumper cables.
> >>> What also could be happening is RF flowing back on feedline in a common
> >>> mode. This RF gets measured as return energy and now, since the power
> is
> >>> higher, the return currents are higher and hence the high SWR reading.
> >> False. Common mode current is NOT reflected power.
> >>
> >> It is a fallacy that antennas like this do not need a serious common
> mode choke, and it must be at the feedpoint (that is, up in the air).
> Indeed, common mode current may be putting RF in the shack. Is everything
> in your station properly bonded? Lots of things that work at low power
> break with high power. See
> >>
> >> http://k9yc.com/GroundingAndAudio.pdf
> >>
> >> There are multiple versions of antennas using this name. Which one are
> you using, Steve?
> >>
> >> There are also fallacies about the performance of the double bazooka
> antenna. Study this report by a very good engineer debunking them.
> https://owenduffy.net/antenna/DoubleBazooka/index.htm
> >>
> >> You
> >>> won't see this with your RigExpert.
> >>> Does the same problem happen into a dummy load? If Yes, it is an amp
> >>> issue. If no, it is a antenna/feedline issue.
> >>> I would try some RF chokes (Mix 43) on both ends of the feedline
> (antenna
> >>> and amp end). I chased strange RF issues for decades until I read this
> >>> document by the YCCC/W1HIS.
> >>> http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf.
> >>> After that I bought about 100 Mix 43 chokes and added them everywhere.
> >> Mix 43 is a very poor material for HF chokes. The reason is
> complicated, but it boils down to it's relatively high Q and wide
> production tolerances, which make repeatable designs impossible.
> >>
> >> Mix 31 is FAR better. W1HIS is right about the significance of chokes
> to kill common mode current, but he didn't know about mix 31 when he wrote
> the referenced document -- it was a pretty new material at the time. See
> the latest version of my Choke Cookbook for detailed recommendations.
> http://k9yc.com/2018Cookbook.pdf
> >>
> >>
> >>> Not only does it help with unique RFI TX issues, it also helps with the
> >>> ability to hear. The quieter you are, the more you can copy.
> >> Yes
> >>
> >> 73, Jim K9YC
> >>> Let us know how you make out.
> >>> Mike va3mw
> >>>> On Sun, Sep 15, 2019 at 8:05 PM <[hidden email]> wrote:
> >>>> Check your connections. Loose or poor PL-259s. Also check to see if
> the
> >>>> antenna is close to something causing it to arc over. I had one
> antenna
> >>>> that
> >>>> used ladder line with solid conductors. Due to it moving around in
> the wind
> >>>> one of the conductors developed a break which tested fine under low
> power
> >>>> or
> >>>> with an analyzer but would have problems at higher power. I've since
> moved
> >>>> to Davis RF copper clad stranded ladder line.
> >>>>
> >>>> Dave wo2x
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> -----Original Message-----
> >>>> From: [hidden email] <
> [hidden email]>
> >>>> On
> >>>> Behalf Of Stephen Rabinowitz
> >>>> Sent: Sunday, September 15, 2019 7:58 PM
> >>>> To: [hidden email]
> >>>> Subject: [Elecraft] Reflected power
> >>>>
> >>>> My KPA-1500 switches from operate to standby due to reflected power
> more
> >>>> than 200w whenever drive power exceeds about 8 watts on 7 MHz. The
> forward
> >>>> power at that point is about 400w. The antenna is a double bazooka
> that
> >>>> shows an SWR of about 1.2 on a RigExpert AA-230Pro antenna analyzer. A
> >>>> Telepost LP-100A digital wattmeter shows SWR 1.3 with Z=52, R=49,
> Ph=17,
> >>>> and
> >>>> X=15. The KP1500 tunes to an SWR of what it labels 1.1 on that
> frequency.
> >>>> The latest firmware, version 2.27 is installed. This problem does not
> occur
> >>>> with double bazooka antennas on 80m or 30m, or with Yagis from 20m to
> 6m.
> >>>> It
> >>>> seems to me that there is a brief surge in reflected power at the very
> >>>> onset
> >>>> of the transmission that triggers the response, but that the reflected
> >>>> power
> >>>> quickly decreases to normal levels of just a few watts. Any ideas for
> >>>> dealing with this problem would be much appreciated.
> >>>> 73, Steve K2SN
> >>>>
> >>>> ______________________________________________________________
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Jim Brown-10

Re: Reflected power

On 9/16/2019 4:42 AM, Michael Walker wrote:
> I only post stuff on this reflector so Jim can tear me a new one.

Nothing personal. I only try to correct flawed ideas.

73, Jim K9YC
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