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]
