KPA500 PA current
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HI,
I'm new here and new to Elecraft. I have to KPA/KAT500 combo and love it! I do have a question about PA current though... On all bands except 20, when running full power out, my HV sits around 64v and PA current is stable between 10 and 12A. FAn takes it's time coming on and amp just loafs along. On 20, however, even at lower power output levels, the PA current is high and the fan comes on and steps up quickly! At full 500W out on 20, HV is 62v and current runs as high as 16A! Even at 300w out the current runs around 13A, higher than any other band at full 500w out. Question is, is this just how it is or do I have something amiss on 20m? Antenna is doublet 60' in the air and this antenna is the one I use on 80, 40 and 20, so don't think I can blame the antenna. Tuner loafs along during all this, and SWR is no worse than 4:1 on any of these three bands. Harry W4HWD -- Sent from: http://elecraft.365791.n2.nabble.com/ ______________________________________________________________ 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 Message delivered to [hidden email] |
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Harry:
Are these values on a dummy load or feeding the KAT500 or antenna direct? I just quickly checked my KPA500 into a dummy load at 500 watts output. The currents run from 14.0A on 20M to a low of 11.5A depending on band. This is done with 500 watts output as shown on my Bird 43 and Bird 50.5 ohm load in TUNE mode which I have set for 20 watts tune power on all bands from my K3S. The HV runs 60.0 volts or a bit higher under load and 74.5 volts at no load. The amp is sourced from 240VAC. With the amp feeding the KAT500 and a 1.5:1 or better resolved match on the antenna system, the currents run from a high of 16.4 amps to 11.7 amps. Again depending on band and SWR values. Yes the amp is more efficient on some bands, and the load impedance will affect the PA current. As to fans, I run mine in NOR and let the amp take care of itself. Fans do ramp up when running FT-8 at 500 watts. 73 Bob, K4TAX On 8/2/2019 6:03 PM, W4HWD wrote: > HI, > > I'm new here and new to Elecraft. I have to KPA/KAT500 combo and love it! I > do have a question about PA current though... > > On all bands except 20, when running full power out, my HV sits around 64v > and PA current is stable between 10 and 12A. FAn takes it's time coming on > and amp just loafs along. On 20, however, even at lower power output levels, > the PA current is high and the fan comes on and steps up quickly! At full > 500W out on 20, HV is 62v and current runs as high as 16A! Even at 300w out > the current runs around 13A, higher than any other band at full 500w out. > > Question is, is this just how it is or do I have something amiss on 20m? > Antenna is doublet 60' in the air and this antenna is the one I use on 80, > 40 and 20, so don't think I can blame the antenna. Tuner loafs along during > all this, and SWR is no worse than 4:1 on any of these three bands. > > Harry W4HWD > > > > > > -- > Sent from: http://elecraft.365791.n2.nabble.com/ > ______________________________________________________________ > 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 > Message delivered to [hidden email] > ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by W4HWD
"On 20, however, even at lower power output levels, the PA current is high and the fan comes on and steps up quickly!"
As Bob has said, KPA500 PA current (also PA dissipation and PA efficiency) are strongly dependent of the load presented by the antenna system. To understand what is going on you will need to know the complex load presented to the KPA500. SWR is insufficient to characterize the load. Avoid any load with R significantly less than 50 ohm even if the SWR looks ok. Some of my test data is shown here - https://tinyurl.com/y37szlko 73, Andy, k3wyc ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by W4HWD
Harry,
What is your current draw when connected to a 50 ohm dummy load. Connect the load to the KPA500 directly (not through the KAT500). That will tell you whether the KPA500 is OK - and if so, you should investigate your antenna impedances - measure with an antenna analyzer. SWR is not sufficiently informative, you need to know the resistive and reactive components of the load to determine whether the KAT500 is capable of matching it. The KAT500 has a nominal matching capability of up to a 10:1 SWR, but at very low impedance loads, that can break down. 73, Don W3FPR On 8/2/2019 7:03 PM, W4HWD wrote: > > On all bands except 20, when running full power out, my HV sits around 64v > and PA current is stable between 10 and 12A. FAn takes it's time coming on > and amp just loafs along. On 20, however, even at lower power output levels, > the PA current is high and the fan comes on and steps up quickly! At full > 500W out on 20, HV is 62v and current runs as high as 16A! Even at 300w out > the current runs around 13A, higher than any other band at full 500w out. ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by W4HWD
Tell us a bit more about the antenna. How is it fed? Is it properly choked to eliminate RF shield current (this is current flowing on the outside of the shield. It is a bit early to remember the proper term…)?
And, do you have chokes on the coax at the KAT500 or KPA500? I think we need a bit more info to determine what is going on here. RF return currents flowing back into the station and combining at the KAT500 connector could account for something like this. Note that I don’t discount that the 20m LPF is noticeably less efficient than those on the other bands. Each KPA is unique in this sense - we tune the LPFs for best efficiency for each band. I suspect your KPA is just fine, but the more info we get from you, the more we can tell what is going on. In any case, welcome to Elecraft products! We work hard to bring delight to your radio experience. 73! Jack, W6FB > On Aug 2, 2019, at 4:03 PM, W4HWD <[hidden email]> wrote: > > HI, > > I'm new here and new to Elecraft. I have to KPA/KAT500 combo and love it! I > do have a question about PA current though... > > On all bands except 20, when running full power out, my HV sits around 64v > and PA current is stable between 10 and 12A. FAn takes it's time coming on > and amp just loafs along. On 20, however, even at lower power output levels, > the PA current is high and the fan comes on and steps up quickly! At full > 500W out on 20, HV is 62v and current runs as high as 16A! Even at 300w out > the current runs around 13A, higher than any other band at full 500w out. > > Question is, is this just how it is or do I have something amiss on 20m? > Antenna is doublet 60' in the air and this antenna is the one I use on 80, > 40 and 20, so don't think I can blame the antenna. Tuner loafs along during > all this, and SWR is no worse than 4:1 on any of these three bands. > > Harry W4HWD > > > > > > -- > Sent from: http://elecraft.365791.n2.nabble.com/ > ______________________________________________________________ > 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 > Message delivered to [hidden email] ______________________________________________________________ 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 Message delivered to [hidden email] |
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On 8/4/2019 9:20 AM, Jack Brindle via Elecraft wrote:
> And, do you have chokes on the coax at the KAT500 or KPA500? I hope not -- to be effective, a choke must be that the antenna's feedpoint. A choke on an antenna in the shack does nothing. 73, Jim K9YC ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by ANDY DURBIN
"Note that I don’t discount that the 20m LPF is noticeably less efficient than those on the other bands. Each KPA is unique in this sense - we tune the LPFs for best efficiency for each band. I suspect your KPA is just fine, but the more info we get from you, the more we can tell what is going on."
In the time I have owned and used my KPA500 I have noticed that 20 m band requires a higher drive level than other bands. This thread prompted me to do some more analysis of data I had recorded last year. Data here - https://tinyurl.com/y5oygtlp The data show that my KPA500 is significantly less efficient on 20 m than on the other bands tested. Is this a characteristic of all KPA500 and, if so, why would that be the case? Note that my dummy load shows variation of characteristics with frequency and heating. I have the load complex values for every data point but I used a test run average R and X to name each test plot. 73, Andy, k3wyc ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by Jim Brown-10
I have to argue with my friend Jim on this one. The coax itself can be an antenna, and can pick up RF along its path from the antenna to the radio. The best example is a vertical antenna which will use any metal it can find for return currents, which includes the coax after the antenna-mounted choke. This current will combine with the internal shield current at the first place they are connected (which very well may be the SO239 on the back of the ATU). A choke at this point will protect against the problem. This may not be common-mode currents, which is one of the reasons I hesitated in calling it that in my previous email.
Perhaps the best way to make sure there is no current flowing on the outside of coax shield would be to add ferrites along the entire path, a solution that is way to expensive to be practical. 73! Jack, W6FB > On Aug 4, 2019, at 10:29 AM, Jim Brown <[hidden email]> wrote: > > On 8/4/2019 9:20 AM, Jack Brindle via Elecraft wrote: >> And, do you have chokes on the coax at the KAT500 or KPA500? > > I hope not -- to be effective, a choke must be that the antenna's feedpoint. A choke on an antenna in the shack does nothing. > > 73, Jim K9YC > > > ______________________________________________________________ > 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 > Message delivered to [hidden email] ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by ANDY DURBIN
Andy;
This is the effect of not being able to obtain perfect components. It is easy to forget that the toroid cores used for the inductors vary, as do the windings and capacitors. There will be variances because of this which will be different from KPA to KPA. They are set up for best case operation, but then as components age things will change. As it is, the design is outstanding. With efficiencies greater than 50%, the designers did a super job! 73! Jack, W6FB > On Aug 4, 2019, at 10:34 AM, Andy Durbin <[hidden email]> wrote: > > "Note that I don’t discount that the 20m LPF is noticeably less efficient than those on the other bands. Each KPA is unique in this sense - we tune the LPFs for best efficiency for each band. I suspect your KPA is just fine, but the more info we get from you, the more we can tell what is going on." > > In the time I have owned and used my KPA500 I have noticed that 20 m band requires a higher drive level than other bands. This thread prompted me to do some more analysis of data I had recorded last year. > > Data here - https://tinyurl.com/y5oygtlp > > The data show that my KPA500 is significantly less efficient on 20 m than on the other bands tested. Is this a characteristic of all KPA500 and, if so, why would that be the case? Note that my dummy load shows variation of characteristics with frequency and heating. I have the load complex values for every data point but I used a test run average R and X to name each test plot. > > 73, > Andy, k3wyc > > > > > ______________________________________________________________ > 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 > Message delivered to [hidden email] ______________________________________________________________ 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 Message delivered to [hidden email] |
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"This is the effect of not being able to obtain perfect components. It is easy to forget that the toroid cores used for the inductors vary, as do the windings and capacitors. There will be variances because of this which will be different from KPA to KPA. They are set up for best case operation, but then as components age things will change. As it is, the design is outstanding. With efficiencies greater than 50%, the designers did a super job!"
Jack, I understand that there will be variation between different KPA500. However, 2 owners have reported that 20 m stands out as being less efficient than other bands. I was asking if that is typical of all KPA500. I don't really expect to get an answer though as I doubt many owners have test data as comprehensive as mine. I just did a spot check on 20 m and, despite my line voltage being down to 118.1 V with the high air conditioning load in the area, I saw 60% efficiency with load R 51 X 0.4: PA voltage=58.9 PA current=13.8 PA input=812 RF out=490 PA diss=322 PA effic=60 Of course this is not typical of normal operating conditions. 73, Andy, k3wyc ______________________________________________________________ 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 Message delivered to [hidden email] |
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In reply to this post by Elecraft mailing list
On 8/4/2019 10:57 AM, Jack Brindle wrote:
> I have to argue with my friend Jim on this one. The coax itself can be an antenna, and can pick up RF along its path from the antenna to the radio. Yes, it can, and it is good practice to break up feedlines to high dipoles to prevent their interaction with adjacent vertical antennas; a choke acts as an egg insulator. I first published this recommendation about ten years ago. It is also good practice on long runs from receiving antennas to prevent noise and TX RF from coupling to the inside of the coax by a limitation of the shield quantified as its transfer impedance. This is especially important with the relatively thin shields of CATV coax we commonly use for RX antennas, which are especially poor shields below VHF. But, again, these chokes should be along the line outside the shack. But NOT on a feedline in the shack! Think about it -- coax feedlines should be bonded to the premises ground system at the point of entry. > The best example is a vertical antenna which will use any metal it can find for return currents, which includes the coax after the antenna-mounted choke. An antenna should NEVER depend on the feedline to carry return current, and an effective choke prevents this. Further, a path for return current should be provided by some sort of counterpoise, the most effective of which is a radial system. Also, you're describing a type of vertical fed from the base. There are many vertical antennas that approximate center feed. They are discussed in these slides for another talk I've given at Pacificon, Visalia, and some ham clubs. http://k9yc.com/VerticalHeight.pdf and in this pdf, which ran in The Jug several years ago. http://k9yc.com/AntennaPlanning.pdf > This current will combine with the internal shield current at the first place they are connected (which very well may be the SO239 on the back of the ATU). If that's the first point of connection, you've got a VERY unsafe station with respect to lightning! RUN, do not walk, to buy N0AX's recent ARRL book on Grounding and Bonding, to which I contributed extensively. Or study these slides for a talk I've given at Visalia, Pacificon, and several local clubs. You'll find it referenced in Ward's book. http://k9yc.com/GroundingAndAudio.pdf <http://k9yc.com/GroundingAndAudio.pdf> > A choke at this point will protect against the problem. The only thing chokes do in the shack is reduce RF current from coupling to or from poorly designed equipment by a mechanism called "The Pin One Problem" by the audio professional who first described it, Neil Muncy, ex-W3WJE (SK) in 1994. I've seen it in virtually every piece of ham gear where I've looked for it, including all the Elecraft products I've examined, even the KRC2 band decoder. 73, Jim K9YC ______________________________________________________________ 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 Message delivered to [hidden email] |
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