[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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
[Elecraft] Reflected power
Many thanks to all of those who responded to my message and shared their experiences and thoughts: Dave WO2X, Mike VA3MW, Bob K4TAX, Jim K9YC, Victor 4X6GP, and Alan N1AL. With a dummy antenna (Cantenna) on 7MHz, and a 1.1:1 match, using 10w drive the KPA-1500 puts out 605w at first, then settles down two seconds later to 384w with 8w reflected power. With 25w drive, the initial output is 1431w, settling down to 1105w after two seconds, with 20w reflected power. So, the fault seems to be in the antenna, not in the amplifier. The same initial power surge occurs on 14MHz using the dummy antenna. I don't know if it originates in the transceiver or the amplifier, but it doesn't have much effect on reflected power except with the defective antenna. Answering some of the questions that were posed, the double bazooka in this case is the high power version from Radiowavz, two years old. A common mode choke from DX Engineering sits between the end of the feed coax and the antenna. Several Mix 31 snap-on chokes from Palomar are on various short coax jumpers in the shack, and the ground system is very good. The double bazookas I use on 80m and 30m work well and are from iacantennas.com. I am ordering a 40m version from them to replace the one that seems to be faulty. I will try to report the result after I install it. Many thanks again to all, 73, Steve K2SN __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] 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: elecraft-boun...@mailman.qth.net On Behalf Of Stephen Rabinowitz Sent: Sunday, September 15, 2019 7:58 PM To: elecraft@mailman.qth.net 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to rocke...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] 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 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: elecraft-boun...@mailman.qth.net > On > Behalf Of Stephen Rabinowitz > Sent: Sunday, September 15, 2019 7:58 PM > To: elecraft@mailman.qth.net > 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:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message > delivered to rocke...@gmail.com > > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to va...@portcredit.net > __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] 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 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: elecraft-boun...@mailman.qth.net On Behalf Of Stephen Rabinowitz Sent: Sunday, September 15, 2019 7:58 PM To: elecraft@mailman.qth.net 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to rocke...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to va...@portcredit.net __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to j
Re: [Elecraft] 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 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 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: elecraft-boun...@mailman.qth.net >>> On >>> Behalf Of Stephen Rabinowitz >>> Sent: Sunday, September 15, 2019 7:58 PM >>> To: elecraft@mailman.qth.net >>> 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 >>> >>> ___
Re: [Elecraft] 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: 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 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. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Reflected power
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 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 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: elecraft-boun...@mailman.qth.net On Behalf Of Stephen Rabinowitz Sent: Sunday, September 15, 2019 7:58 PM To: elecraft@mailman.qth.net 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to rocke...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@m
Re: [Elecraft] 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 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 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 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: elecraft-boun...@mailman.qth.net < > elecraft-boun...@mailman.qth.net> > >>>> On > >>>> Behalf Of Stephen Rabinowitz > >>>> Sent: Sunday, September 15, 2019 7:58 PM > >>>> To: elecraft@mailman.qth.net > >>>> Subject: [Elecraft] Reflected power > >>>&
Re: [Elecraft] 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 __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Reflected power
Steve, What radio are you using to drive the amp? Are you using ALC? Sounds like power setting on radio is such you see the higher power until ALC drops exciter power. Dave wo2x Sent from my iPad > On Sep 16, 2019, at 10:58 AM, Stephen Rabinowitz wrote: > > Many thanks to all of those who responded to my message and shared their > experiences and thoughts: Dave WO2X, Mike VA3MW, Bob K4TAX, Jim K9YC, Victor > 4X6GP, and Alan N1AL. With a dummy antenna (Cantenna) on 7MHz, and a 1.1:1 > match, using 10w drive the KPA-1500 puts out 605w at first, then settles > down two seconds later to 384w with 8w reflected power. With 25w drive, the > initial output is 1431w, settling down to 1105w after two seconds, with 20w > reflected power. So, the fault seems to be in the antenna, not in the > amplifier. > The same initial power surge occurs on 14MHz using the dummy antenna. I > don't know if it originates in the transceiver or the amplifier, but it > doesn't have much effect on reflected power except with the defective > antenna. Answering some of the questions that were posed, the double bazooka > in this case is the high power version from Radiowavz, two years old. A > common mode choke from DX Engineering sits between the end of the feed coax > and the antenna. Several Mix 31 snap-on chokes from Palomar are on various > short coax jumpers in the shack, and the ground system is very good. > The double bazookas I use on 80m and 30m work well and are from > iacantennas.com. I am ordering a 40m version from them to replace the one > that seems to be faulty. I will try to report the result after I install it. > Many thanks again to all, > 73, Steve K2SN > > __ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to rocke...@gmail.com __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
