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 <[email protected]> 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 <[email protected]> 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 <[email protected]> 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: [email protected] < > [email protected]> > >>>> On > >>>> Behalf Of Stephen Rabinowitz > >>>> Sent: Sunday, September 15, 2019 7:58 PM > >>>> To: [email protected] > >>>> 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:[email protected] > >>>> > >>>> This list hosted by: http://www.qsl.net > >>>> Please help support this email list: http://www.qsl.net/donate.html > >>>> Message > >>>> delivered to [email protected] > >>>> > >>>> ______________________________________________________________ > >>>> Elecraft mailing list > >>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft > >>>> Help: http://mailman.qth.net/mmfaq.htm > >>>> Post: mailto:[email protected] > >>>> > >>>> This list hosted by: http://www.qsl.net > >>>> Please help support this email list: http://www.qsl.net/donate.html > >>>> Message delivered to [email protected] > >>>> > >>> ______________________________________________________________ > >>> Elecraft mailing list > >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft > >>> Help: http://mailman.qth.net/mmfaq.htm > >>> Post: mailto:[email protected] > >>> This list hosted by: http://www.qsl.net > >>> Please help support this email list: http://www.qsl.net/donate.html > >>> Message delivered to [email protected] > >> ______________________________________________________________ > >> Elecraft mailing list > >> Home: http://mailman.qth.net/mailman/listinfo/elecraft > >> Help: http://mailman.qth.net/mmfaq.htm > >> Post: mailto:[email protected] > >> > >> This list hosted by: http://www.qsl.net > >> Please help support this email list: http://www.qsl.net/donate.html > >> Message delivered to [email protected] > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[email protected] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > Message delivered to [email protected] > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
