> 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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