[QRO] KPA500 variation of PA current band-by-band
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I have recently assembled KPA500 serial number 641. When testing into a dummy load I find that I get a large variation in the DC power input when driving for 500W CW when I go from band to band. My worst band is 21MHz, where I get the highest current (lowest efficiency). The drive was adjusted to give 500W as indicated by the LCD display. Here are my results:-
1.8MHz DC current 10.0A fan hardly ever comes on 3.5MHz DC current 10.0A fan hardly ever comes on 7MHz 12.0A 10.1MHz 12.4A 14MHz 14.3A 18.1MHz 13.8A 21MHz 16.4A temperature rises rapidly and fan soon gets to full speed 24.9MHz 13.5A 29.7MHz 12.3A I have no results for 50MHz band as I have no transceiver covering that band. The readings drift as the heatsink (and the dummy load) warm up, and so I took readings quickly and allowed time for the heatsink to cool down between each band. I find that the KPA500 current sensor tends to give low readings. I would be interested in knowing how other amplifiers perform. David Park G3PSV ______________________________________________________________ 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 |
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120 or 240 volts supply?
On Feb 4, 2012, at 2:27 PM, david park <[hidden email]> wrote: > I have recently assembled KPA500 serial number 641. When testing into a dummy load I find that I get a large variation in the DC power input when driving for 500W CW when I go from band to band. My worst band is 21MHz, where I get the highest current (lowest efficiency). The drive was adjusted to give 500W as indicated by the LCD display. Here are my results:- > > 1.8MHz DC current 10.0A fan hardly ever comes on > 3.5MHz DC current 10.0A fan hardly ever comes on > 7MHz 12.0A > 10.1MHz 12.4A > 14MHz 14.3A > 18.1MHz 13.8A > 21MHz 16.4A temperature rises rapidly and fan soon gets to full speed > 24.9MHz 13.5A > 29.7MHz 12.3A > > I have no results for 50MHz band as I have no transceiver covering that band. > > The readings drift as the heatsink (and the dummy load) warm up, and so I took readings quickly and allowed time for the heatsink to cool down between each band. I find that the KPA500 current sensor tends to give low readings. > I would be interested in knowing how other amplifiers perform. > > David Park G3PSV > ______________________________________________________________ > 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 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
Jack - WE5ST
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Re: [QRO] KPA500 variation of PA current band-by-band
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Given that the poster is in the UK can probably assume 240Vac.
Regards, Mike VP8NO On 04/02/2012 17:31, Jack Berry wrote: > 120 or 240 volts supply? > > On Feb 4, 2012, at 2:27 PM, david park<[hidden email]> wrote: > >> I have recently assembled KPA500 serial number 641. When testing into a dummy load I find that I get a large variation in the DC power input when driving for 500W CW when I go from band to band. My worst band is 21MHz, where I get the highest current (lowest efficiency). The drive was adjusted to give 500W as indicated by the LCD display. Here are my results:- >> >> 1.8MHz DC current 10.0A fan hardly ever comes on >> 3.5MHz DC current 10.0A fan hardly ever comes on >> 7MHz 12.0A >> 10.1MHz 12.4A >> 14MHz 14.3A >> 18.1MHz 13.8A >> 21MHz 16.4A temperature rises rapidly and fan soon gets to full speed >> 24.9MHz 13.5A >> 29.7MHz 12.3A >> >> I have no results for 50MHz band as I have no transceiver covering that band. >> >> The readings drift as the heatsink (and the dummy load) warm up, and so I took readings quickly and allowed time for the heatsink to cool down between each band. I find that the KPA500 current sensor tends to give low readings. >> I would be interested in knowing how other amplifiers perform. >> >> David Park G3PSV >> ______________________________________________________________ >> 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 > ______________________________________________________________ > 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 > 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 |
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In reply to this post by G3PSV
Guys,
I'm also curious about this-- especially what's going on on 15M. My values at 500 W out into a dummy load are: (amp), [volts], {efficiency} 1.8MHz DC (11.5) [63.1] {70} 3.5MHz (11.2) [63.5] {71} 7MHz (12.2) [62.5] {67} 10.1MHz (not measured) 14MHz (13.4)[61.8] {60} 18.1MHz (12.9)[62.8] (63} 21MHz (15.8)[61.2] {52} 24.9MHz (14.6) [60.1] {56} 29.7MHz (14.7)[60.4] {56} These are in reasonable agreement with David's except for perhaps 10M. The problem with these measurements are the wattmeter accuracy (10%?) and the current measurement inaccuracy. Default wattmeter calibration factors were used above. Elecraft is using a Hall effect device to measure PA current. It would be nice to know just what accuracy to expect from it. The efficiencies appear to be in the right ballpark. They tend to fall on a straight line log plot vs frequency, decreasing at higher freq's. If nothing else, the above numbers serve as a benchmark for future comparisons down the road for my amp. Note: The current measurement can be significantly affected by RF on the outside shield of the coax. Until a choke was employed on the feedline, the 24.9 MHz current with a real antenna measured 3 amps too low. With the choke it agreed with the above dummy load value. I suspect lots of KPA-500 users do have this condition-- given the types of antennas/tuners et al described by uses on this reflector. 73 de Brian/K3KO On 2/4/2012 20:27, david park wrote: > I have recently assembled KPA500 serial number 641. When testing into a dummy load I find that I get a large variation in the DC power input when driving for 500W CW when I go from band to band. My worst band is 21MHz, where I get the highest current (lowest efficiency). The drive was adjusted to give 500W as indicated by the LCD display. Here are my results:- > > 1.8MHz DC current 10.0A fan hardly ever comes on > 3.5MHz DC current 10.0A fan hardly ever comes on > 7MHz 12.0A > 10.1MHz 12.4A > 14MHz 14.3A > 18.1MHz 13.8A > 21MHz 16.4A temperature rises rapidly and fan soon gets to full speed > 24.9MHz 13.5A > 29.7MHz 12.3A > > I have no results for 50MHz band as I have no transceiver covering that band. > > The readings drift as the heatsink (and the dummy load) warm up, and so I took readings quickly and allowed time for the heatsink to cool down between each band. I find that the KPA500 current sensor tends to give low readings. > I would be interested in knowing how other amplifiers perform. > > David Park G3PSV > ----- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1424 / Virus Database: 2112/4794 - Release Date: 02/07/12 ______________________________________________________________ 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 |
Re: [QRO] KPA500 variation of PA current band-by-band
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When the KPA100 (the K2's 100w amplifier stage) came out, some of us noted similar issues.
The gain available from a transistor varies in the opposite direction to frequency, and the circuits include feedback mechanisms to try to balance it. The characteristics of real components have some effect on the behavior of the feedback network; in the case of the KPA100, some resistors had more inductance than expected, which resulted in a severe drop in gain on some bands. I guess what I'm saying is that gain variations are expected, and unless the efficiency is bad enough to endanger the devices, I wouldn't worry about it. On 2/7/2012 5:35 AM, Brian Alsop wrote: > Guys, > > I'm also curious about this-- especially what's going on on 15M. > My values at 500 W out into a dummy load are: > (amp), [volts], {efficiency} > 1.8MHz DC (11.5) [63.1] {70} > 3.5MHz (11.2) [63.5] {71} > 7MHz (12.2) [62.5] {67} > 10.1MHz (not measured) > 14MHz (13.4)[61.8] {60} > 18.1MHz (12.9)[62.8] (63} > 21MHz (15.8)[61.2] {52} > 24.9MHz (14.6) [60.1] {56} > 29.7MHz (14.7)[60.4] {56} > > These are in reasonable agreement with David's except for perhaps 10M. > > The problem with these measurements are the wattmeter accuracy (10%?) > and the current measurement inaccuracy. Default wattmeter calibration > factors were used above. Elecraft is using a Hall effect device to > measure PA current. It would be nice to know just what accuracy to > expect from it. > > The efficiencies appear to be in the right ballpark. They tend to fall > on a straight line log plot vs frequency, decreasing at higher freq's. > > If nothing else, the above numbers serve as a benchmark for future > comparisons down the road for my amp. > > Note: The current measurement can be significantly affected by RF on the > outside shield of the coax. Until a choke was employed on the feedline, > the 24.9 MHz current with a real antenna measured 3 amps too low. With > the choke it agreed with the above dummy load value. I suspect lots of > KPA-500 users do have this condition-- given the types of > antennas/tuners et al described by uses on this reflector. > > 73 de Brian/K3KO > > On 2/4/2012 20:27, david park wrote: >> I have recently assembled KPA500 serial number 641. When testing into a dummy load I find that I get a large variation in the DC power input when driving for 500W CW when I go from band to band. My worst band is 21MHz, where I get the highest current (lowest efficiency). The drive was adjusted to give 500W as indicated by the LCD display. Here are my results:- >> >> 1.8MHz DC current 10.0A fan hardly ever comes on >> 3.5MHz DC current 10.0A fan hardly ever comes on >> 7MHz 12.0A >> 10.1MHz 12.4A >> 14MHz 14.3A >> 18.1MHz 13.8A >> 21MHz 16.4A temperature rises rapidly and fan soon gets to full speed >> 24.9MHz 13.5A >> 29.7MHz 12.3A >> >> I have no results for 50MHz band as I have no transceiver covering that band. >> >> The readings drift as the heatsink (and the dummy load) warm up, and so I took readings quickly and allowed time for the heatsink to cool down between each band. I find that the KPA500 current sensor tends to give low readings. >> I would be interested in knowing how other amplifiers perform. >> >> David Park G3PSV >> > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1424 / Virus Database: 2112/4794 - Release Date: 02/07/12 > > ______________________________________________________________ > 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 -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ ______________________________________________________________ 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 |
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In reply to this post by alsopb
Is your dummy load absolutely a flat 1.0:1 from 1.0MHz to 30MHz? 73, Tom Amateur Radio Operator N5GE ARRL Lifetime Member QCWA Lifetime Member "Only the white eyes would believe they could cut the top off a blanket, sew it to the bottom and have a longer blanket." -- American Indian comment about Daylight Saving Time -- On Tue, 07 Feb 2012 13:35:47 +0000, Brian Alsop <[hidden email]> wrote: >Guys, > >I'm also curious about this-- especially what's going on on 15M. >My values at 500 W out into a dummy load are: > (amp), [volts], {efficiency} > 1.8MHz DC (11.5) [63.1] {70} > 3.5MHz (11.2) [63.5] {71} > 7MHz (12.2) [62.5] {67} > 10.1MHz (not measured) > 14MHz (13.4)[61.8] {60} > 18.1MHz (12.9)[62.8] (63} > 21MHz (15.8)[61.2] {52} > 24.9MHz (14.6) [60.1] {56} > 29.7MHz (14.7)[60.4] {56} > >These are in reasonable agreement with David's except for perhaps 10M. > >The problem with these measurements are the wattmeter accuracy (10%?) >and the current measurement inaccuracy. Default wattmeter calibration >factors were used above. Elecraft is using a Hall effect device to >measure PA current. It would be nice to know just what accuracy to >expect from it. > >The efficiencies appear to be in the right ballpark. They tend to fall >on a straight line log plot vs frequency, decreasing at higher freq's. > >If nothing else, the above numbers serve as a benchmark for future >comparisons down the road for my amp. > >Note: The current measurement can be significantly affected by RF on the >outside shield of the coax. Until a choke was employed on the feedline, >the 24.9 MHz current with a real antenna measured 3 amps too low. With >the choke it agreed with the above dummy load value. I suspect lots of >KPA-500 users do have this condition-- given the types of >antennas/tuners et al described by uses on this reflector. > >73 de Brian/K3KO > >On 2/4/2012 20:27, david park wrote: >> I have recently assembled KPA500 serial number 641. When testing into a dummy load I find that I get a large variation in the DC power input when driving for 500W CW when I go from band to band. My worst band is 21MHz, where I get the highest current (lowest efficiency). The drive was adjusted to give 500W as indicated by the LCD display. Here are my results:- >> >> 1.8MHz DC current 10.0A fan hardly ever comes on >> 3.5MHz DC current 10.0A fan hardly ever comes on >> 7MHz 12.0A >> 10.1MHz 12.4A >> 14MHz 14.3A >> 18.1MHz 13.8A >> 21MHz 16.4A temperature rises rapidly and fan soon gets to full speed >> 24.9MHz 13.5A >> 29.7MHz 12.3A >> >> I have no results for 50MHz band as I have no transceiver covering that band. >> >> The readings drift as the heatsink (and the dummy load) warm up, and so I took readings quickly and allowed time for the heatsink to cool down between each band. I find that the KPA500 current sensor tends to give low readings. >> I would be interested in knowing how other amplifiers perform. >> >> David Park G3PSV >> > > >----- >No virus found in this message. >Checked by AVG - www.avg.com >Version: 10.0.1424 / Virus Database: 2112/4794 - Release Date: 02/07/12 > >______________________________________________________________ >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 ______________________________________________________________ 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
Amateur Radio Operator N5GE
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Hmmm,
Given that ham-affordable components are full of minor and harmless frequency dependent characteristics, INCLUDING the antennas and dummy loads used, is there really any good reason to EXPECT 1.8-30 power output uniformity beyond what is commonly measured? Quite contrary to amps which were designed, built and certified to a broadband tight uniformity (and appropriately priced), if one WANTS exactly 500.0 watts from a KPA500 for some purpose, and you actually trust your output measuring instrument to deliver an accurate measurement to four figures, one just adjusts the drive, does one not? This is ham gear, not lab instruments, but I would be intrigued to hear what purpose this debated level of accuracy serves, other than light entertainment. I have sometimes heard some very interesting stuff coming from the other side of what I thought was the left field foul line. One never knows. ??? 73, Guy. On Tue, Feb 7, 2012 at 3:23 PM, <[hidden email]> wrote: > > Is your dummy load absolutely a flat 1.0:1 from 1.0MHz to 30MHz? > > 73, > Tom > Amateur Radio Operator N5GE > ARRL Lifetime Member > QCWA Lifetime Member > > "Only the white eyes would believe they could cut the top > off a blanket, sew it to the bottom and have a longer > blanket." > > -- American Indian comment about Daylight Saving Time -- > > > On Tue, 07 Feb 2012 13:35:47 +0000, Brian Alsop <[hidden email]> wrote: > > >Guys, > > > >I'm also curious about this-- especially what's going on on 15M. > >My values at 500 W out into a dummy load are: > > (amp), [volts], {efficiency} > > 1.8MHz DC (11.5) [63.1] {70} > > 3.5MHz (11.2) [63.5] {71} > > 7MHz (12.2) [62.5] {67} > > 10.1MHz (not measured) > > 14MHz (13.4)[61.8] {60} > > 18.1MHz (12.9)[62.8] (63} > > 21MHz (15.8)[61.2] {52} > > 24.9MHz (14.6) [60.1] {56} > > 29.7MHz (14.7)[60.4] {56} > > > >These are in reasonable agreement with David's except for perhaps 10M. > > > >The problem with these measurements are the wattmeter accuracy (10%?) > >and the current measurement inaccuracy. Default wattmeter calibration > >factors were used above. Elecraft is using a Hall effect device to > >measure PA current. It would be nice to know just what accuracy to > >expect from it. > > > >The efficiencies appear to be in the right ballpark. They tend to fall > >on a straight line log plot vs frequency, decreasing at higher freq's. > > > >If nothing else, the above numbers serve as a benchmark for future > >comparisons down the road for my amp. > > > >Note: The current measurement can be significantly affected by RF on the > >outside shield of the coax. Until a choke was employed on the feedline, > >the 24.9 MHz current with a real antenna measured 3 amps too low. With > >the choke it agreed with the above dummy load value. I suspect lots of > >KPA-500 users do have this condition-- given the types of > >antennas/tuners et al described by uses on this reflector. > > > >73 de Brian/K3KO > > > >On 2/4/2012 20:27, david park wrote: > >> I have recently assembled KPA500 serial number 641. When testing into > a dummy load I find that I get a large variation in the DC power input when > driving for 500W CW when I go from band to band. My worst band is 21MHz, > where I get the highest current (lowest efficiency). The drive was > adjusted to give 500W as indicated by the LCD display. Here are my > results:- > >> > >> 1.8MHz DC current 10.0A fan hardly ever comes on > >> 3.5MHz DC current 10.0A fan hardly ever comes on > >> 7MHz 12.0A > >> 10.1MHz 12.4A > >> 14MHz 14.3A > >> 18.1MHz 13.8A > >> 21MHz 16.4A temperature rises rapidly and > fan soon gets to full speed > >> 24.9MHz 13.5A > >> 29.7MHz 12.3A > >> > >> I have no results for 50MHz band as I have no transceiver covering that > band. > >> > >> The readings drift as the heatsink (and the dummy load) warm up, and so > I took readings quickly and allowed time for the heatsink to cool down > between each band. I find that the KPA500 current sensor tends to give low > readings. > >> I would be interested in knowing how other amplifiers perform. > >> > >> David Park G3PSV > >> > > > > > >----- > >No virus found in this message. > >Checked by AVG - www.avg.com > >Version: 10.0.1424 / Virus Database: 2112/4794 - Release Date: 02/07/12 > > > >______________________________________________________________ > >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 > > ______________________________________________________________ > 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 > 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 |
Re: [QRO] KPA500 variation of PA current band-by-band
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> On Tue, Feb 7, 2012 at 3:23 PM, <[hidden email]> wrote:
> >> >> Is your dummy load absolutely a flat 1.0:1 from 1.0MHz to 30MHz? ================ Suppose that the SWR is 1.2. This means that 0.8% of the power is reflected (80 milliwatts reflected for 10 forward). If the SWR is 1.1, the reflected power is 0.2%. A simple coax jumper can sometimes cause an impedance bump large enough to reflect more power than that. A few minutes spent on a test bench with even the fanciest precision equipment will quickly disabuse one of the notion that a dummy load can be trusted to be "absolutely flat 1.0:1 from 1.0MHz to 30MHz." Tony KT0NY ______________________________________________________________ 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 |
Re: [QRO] KPA500 variation of PA current band-by-band
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In reply to this post by Guy, K2AV
Guy and all,
You are so correct. This is ham radio, and precision instrumentation for power output levels is not the norm - a 20% error potential should always be considered. Yes, I personally have power instrumentation that is calibrated to the 5 % level up to 30 MHz. That level of precision has come at a goodly cost and effort. In general, amateur quality power measurement gear should be given a +/- 20% range of error. There are variations due to frequency, variations due to changes in the dummy load actual impedance, and if one is using an antenna, any common mode RF current can substantially influence the readings on the meters. In other words, what you see on your power meter may or may not reflect reality. If there is any doubt about your results, tell me what your results are when driving a known good 50 ohm non-reactive dummy load (measure it with your antenna analyzer), and if a problem is indicated with that load, then you can conclude that you have a transceiver problem. If it is OK into that dummy load, but gives problems driving your antenna, then you will have to solve the problem in your antenna field. These are generalized statements and not directed at any particular installation. If you and your indications are suspect, then investigate your particular situation carefully (it is possible that we can help). 73, Don W3FPR On 2/7/2012 9:40 PM, Guy Olinger K2AV wrote: > Hmmm, > > Given that ham-affordable components are full of minor and harmless > frequency dependent characteristics, INCLUDING the antennas and dummy loads > used, is there really any good reason to EXPECT 1.8-30 power output > uniformity beyond what is commonly measured? Quite contrary to amps which > were designed, built and certified to a broadband tight uniformity (and > appropriately priced), if one WANTS exactly 500.0 watts from a KPA500 for > some purpose, and you actually trust your output measuring instrument to > deliver an accurate measurement to four figures, one just adjusts the > drive, does one not? > > This is ham gear, not lab instruments, but I would be intrigued to hear > what purpose this debated level of accuracy serves, other than light > entertainment. I have sometimes heard some very interesting stuff coming > from the other side of what I thought was the left field foul line. One > never knows. > > ??? > > 73, Guy. > > On Tue, Feb 7, 2012 at 3:23 PM,<[hidden email]> wrote: > >> Is your dummy load absolutely a flat 1.0:1 from 1.0MHz to 30MHz? >> >> 73, >> Tom >> Amateur Radio Operator N5GE >> ARRL Lifetime Member >> QCWA Lifetime Member >> >> "Only the white eyes would believe they could cut the top >> off a blanket, sew it to the bottom and have a longer >> blanket." >> >> -- American Indian comment about Daylight Saving Time -- >> >> >> On Tue, 07 Feb 2012 13:35:47 +0000, Brian Alsop<[hidden email]> wrote: >> >>> Guys, >>> >>> I'm also curious about this-- especially what's going on on 15M. >>> My values at 500 W out into a dummy load are: >>> (amp), [volts], {efficiency} >>> 1.8MHz DC (11.5) [63.1] {70} >>> 3.5MHz (11.2) [63.5] {71} >>> 7MHz (12.2) [62.5] {67} >>> 10.1MHz (not measured) >>> 14MHz (13.4)[61.8] {60} >>> 18.1MHz (12.9)[62.8] (63} >>> 21MHz (15.8)[61.2] {52} >>> 24.9MHz (14.6) [60.1] {56} >>> 29.7MHz (14.7)[60.4] {56} >>> >>> These are in reasonable agreement with David's except for perhaps 10M. >>> >>> The problem with these measurements are the wattmeter accuracy (10%?) >>> and the current measurement inaccuracy. Default wattmeter calibration >>> factors were used above. Elecraft is using a Hall effect device to >>> measure PA current. It would be nice to know just what accuracy to >>> expect from it. >>> >>> The efficiencies appear to be in the right ballpark. They tend to fall >>> on a straight line log plot vs frequency, decreasing at higher freq's. >>> >>> If nothing else, the above numbers serve as a benchmark for future >>> comparisons down the road for my amp. >>> >>> Note: The current measurement can be significantly affected by RF on the >>> outside shield of the coax. Until a choke was employed on the feedline, >>> the 24.9 MHz current with a real antenna measured 3 amps too low. With >>> the choke it agreed with the above dummy load value. I suspect lots of >>> KPA-500 users do have this condition-- given the types of >>> antennas/tuners et al described by uses on this reflector. >>> >>> 73 de Brian/K3KO >>> >>> 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 |
Re: [QRO] KPA500 variation of PA current band-by-band
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In reply to this post by Tony Estep
Tony,
All you say is true. and should be heeded by all hams. I have dummy loads that are known to be flat (within 5%) to 1 GHz, and I have several more that are flat to within 500 MHz. Others will display the same characteristics to 60 MHz. I know which ones are which, and I rely on them to give me precision power measurement capability. I do not depend on anything other than the RF voltage measured across that known good dummy load for true calculation of RF power (although I do have one wattmeter calibrated to NIST standards that I use as a secondary standard to calibrate my other meters). In other words, I have become more and more distrustful of in-line wattmeters which may be in error by a substantial amount (20% of the full scale reading) - just try to measure 5 watts with a wattmeter having a 200 watt scale - the error may be as much as 40 watts anywhere on the scale - so a reading of 5 watts might be anywhere between zero and 45 watts actual power - does that seem ridiculous - certainly, but it is true - some wattmeters can be in error by that much when used at levels considerably less than their full scale reading. OK, this is my wattmeter inaccuracy rant for Feb 2012 - thanks for listening. 73, Don W3FPR On 2/7/2012 10:09 PM, Tony Estep wrote: >> On Tue, Feb 7, 2012 at 3:23 PM,<[hidden email]> wrote: >> >>> Is your dummy load absolutely a flat 1.0:1 from 1.0MHz to 30MHz? > ================ > Suppose that the SWR is 1.2. This means that 0.8% of the power is > reflected (80 milliwatts reflected for 10 forward). If the SWR is 1.1, > the reflected power is 0.2%. A simple coax jumper can sometimes cause > an impedance bump large enough to reflect more power than that. A few > minutes spent on a test bench with even the fanciest precision > equipment will quickly disabuse one of the notion that a dummy load > can be trusted to be "absolutely flat 1.0:1 from 1.0MHz to 30MHz." > > Tony KT0NY > 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 |
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In reply to this post by Don Wilhelm-4
Guys,
On the other hand, there nothing wrong with trying to characterize the beastie you have as best you can. If for no other reason to see if something changes with time and how much. Also, how does my kit comparing to other kits which presumable have similar but not identical characteristics? Note with the exception of the dummy load impedance, all instrumentation used is within the KPA-500. For what it is worth, my measurements were made with a WATERS 1.5 kW dummy load which the KPA-500 thinks is 1.1 to 1 across the 9 HF bands. Even if it were 1.5 :1 you're talking about introducing 20 watts of reflected power. I assume the KPA-500 is reading forward power and not forward-reflected. Thus these kinds of error would make the output power read higher than reality, not lower. Also look it at a learning experience. This is my first solid state amp. I know what to expect from tube amps but not solid state ones. How does a solid state amp behave in the efficiency department vs frequency? When one sees it takes 16 amps on one band to produce "500" watts and 11 on another, there is plenty reason to raise questions and want to understand why. One thing uncovered already is that current is measured by a Hall effect device instead of the time honored low value series resistor/voltmeter combo. What is it's accuracy? Could that device's accuracy explain a significant amount some of the variations seen. To me it's about understaning my beastie. Certainly people should not be castigated for asking questions. We are not all EE's with 50 years experience and a shop full of precision measuring equipment. 73 de Brian/K3KO On 2/8/2012 03:19, Don Wilhelm wrote: > Guy and all, > > You are so correct. This is ham radio, and precision instrumentation > for power output levels is not the norm - a 20% error potential should > always be considered. > Yes, I personally have power instrumentation that is calibrated to the 5 > % level up to 30 MHz. That level of precision has come at a goodly cost > and effort. > > In general, amateur quality power measurement gear should be given a +/- > 20% range of error. There are variations due to frequency, variations > due to changes in the dummy load actual impedance, and if one is using > an antenna, any common mode RF current can substantially influence the > readings on the meters. > > In other words, what you see on your power meter may or may not reflect > reality. If there is any doubt about your results, tell me what your > results are when driving a known good 50 ohm non-reactive dummy load > (measure it with your antenna analyzer), and if a problem is indicated > with that load, then you can conclude that you have a transceiver > problem. If it is OK into that dummy load, but gives problems driving > your antenna, then you will have to solve the problem in your antenna field. > > These are generalized statements and not directed at any particular > installation. If you and your indications are suspect, then investigate > your particular situation carefully (it is possible that we can help). > > 73, > Don W3FPR > > On 2/7/2012 9:40 PM, Guy Olinger K2AV wrote: >> Hmmm, >> >> Given that ham-affordable components are full of minor and harmless >> frequency dependent characteristics, INCLUDING the antennas and dummy loads >> used, is there really any good reason to EXPECT 1.8-30 power output >> uniformity beyond what is commonly measured? Quite contrary to amps which >> were designed, built and certified to a broadband tight uniformity (and >> appropriately priced), if one WANTS exactly 500.0 watts from a KPA500 for >> some purpose, and you actually trust your output measuring instrument to >> deliver an accurate measurement to four figures, one just adjusts the >> drive, does one not? >> >> This is ham gear, not lab instruments, but I would be intrigued to hear >> what purpose this debated level of accuracy serves, other than light >> entertainment. I have sometimes heard some very interesting stuff coming >> from the other side of what I thought was the left field foul line. One >> never knows. >> >> ??? >> >> 73, Guy. >> >> On Tue, Feb 7, 2012 at 3:23 PM,<[hidden email]> wrote: >> >>> Is your dummy load absolutely a flat 1.0:1 from 1.0MHz to 30MHz? >>> >>> 73, >>> Tom >>> Amateur Radio Operator N5GE >>> ARRL Lifetime Member >>> QCWA Lifetime Member >>> >>> "Only the white eyes would believe they could cut the top >>> off a blanket, sew it to the bottom and have a longer >>> blanket." >>> >>> -- American Indian comment about Daylight Saving Time -- >>> >>> >>> On Tue, 07 Feb 2012 13:35:47 +0000, Brian Alsop<[hidden email]> wrote: >>> >>>> Guys, >>>> >>>> I'm also curious about this-- especially what's going on on 15M. >>>> My values at 500 W out into a dummy load are: >>>> (amp), [volts], {efficiency} >>>> 1.8MHz DC (11.5) [63.1] {70} >>>> 3.5MHz (11.2) [63.5] {71} >>>> 7MHz (12.2) [62.5] {67} >>>> 10.1MHz (not measured) >>>> 14MHz (13.4)[61.8] {60} >>>> 18.1MHz (12.9)[62.8] (63} >>>> 21MHz (15.8)[61.2] {52} >>>> 24.9MHz (14.6) [60.1] {56} >>>> 29.7MHz (14.7)[60.4] {56} >>>> >>>> These are in reasonable agreement with David's except for perhaps 10M. >>>> >>>> The problem with these measurements are the wattmeter accuracy (10%?) >>>> and the current measurement inaccuracy. Default wattmeter calibration >>>> factors were used above. Elecraft is using a Hall effect device to >>>> measure PA current. It would be nice to know just what accuracy to >>>> expect from it. >>>> >>>> The efficiencies appear to be in the right ballpark. They tend to fall >>>> on a straight line log plot vs frequency, decreasing at higher freq's. >>>> >>>> If nothing else, the above numbers serve as a benchmark for future >>>> comparisons down the road for my amp. >>>> >>>> Note: The current measurement can be significantly affected by RF on the >>>> outside shield of the coax. Until a choke was employed on the feedline, >>>> the 24.9 MHz current with a real antenna measured 3 amps too low. With >>>> the choke it agreed with the above dummy load value. I suspect lots of >>>> KPA-500 users do have this condition-- given the types of >>>> antennas/tuners et al described by uses on this reflector. >>>> >>>> 73 de Brian/K3KO >>>> >>>> > ______________________________________________________________ > 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 > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1424 / Virus Database: 2112/4794 - Release Date: 02/07/12 > > ----- No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1424 / Virus Database: 2112/4795 - Release Date: 02/07/12 ______________________________________________________________ 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 |
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