[KPA500] Low Power Use Cases
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I love my KPA500. I don't use it enough because of all the low power digital I do. I was wondering if the quality of my signal would better if I let the KPA500 produce the output even if the wattage is 50 or less watts. If I drive it with 1 to 5 watts, it produces 10 to 50 watts. I like the thought of offloading the thermal load of my long JT65 & JT9 duty cycles onto the KPA rather than my main rig which is a Flex 6700.
Does the KPA500 make a much cleaner signal than the built in barefoot amp because its running at such a higher voltage? I'm not too concerned about power efficiency comparisons, because we know its not more efficient doing it this way. :) Thx -Chris ______________________________________________________________ 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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On 7/18/2013 3:08 PM, Chris Johnson wrote:
> I love my KPA500. I don't use it enough because of all the low power > digital I do. I was wondering if the quality of my signal would > better if I let the KPA500 produce the output even if the wattage is > 50 or less watts. If I drive it with 1 to 5 watts, it produces 10 > to 50 watts. I like the thought of offloading the thermal load of > my long JT65 & JT9 duty cycles onto the KPA rather than my main rig > which is a Flex 6700. You're likely to stimulate more replies than the "Why is aeronautical VHF comm still AM?" did. :-) I don't know anything about a Flex <anything> but, all amplifiers have non-zero distortion figures. Putting two "in series" will add up at least some if not all of them. The amp in your Flex followed by the KPA500 will most likely produce a poorer signal quality than just your Flex for the same power output. Secondly, the KPA500 was designed to produce several hundred watts with a few tens of watts drive [500W on any band for me takes between 25 and 30 watts drive]. That's probably the optimum operating point. Driving it with 5 watts should produce somewhere in the 50+ watts output range. 73, Fred K6DGW - Northern California Contest Club - CU in the 2013 Cal QSO Party 5-6 Oct 2013 - www.cqp.org ______________________________________________________________ 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 Chris Johnson-2
On Thu, 18 Jul 2013 15:08:14 -0700, Chris Johnson wrote:
> Does the KPA500 make a much cleaner signal than the built in barefoot amp because > its running at such a higher voltage? No. As the other person told you, the quality will not be made better by going through another amplifier. Every piece you go through adds to the decline in quality, albeit probably only a very small amount. > I'm not too concerned about power efficiency comparisons, because we know its not > more efficient doing it this way. :) As you said, it is less efficient, as it is not operating within the designed parameters. Some amplifiers actually run hotter if you run less than the design level. I'm not saying the KPA does at all, just making a point that "some" amps can actually run hotter when the power is turned down than they do when running full output. Gary ______________________________________________________________ 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: [KPA500] Low Power Use Cases
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In reply to this post by k6dgw
I think the best solution would be to try it both ways and see what kind of
signal report you get. I'd be interested to see the two JT waterfalls compared side by side. 73, Frank KG6EYC On Thu, Jul 18, 2013 at 3:47 PM, Ron D'Eau Claire <[hidden email]> wrote: > I think it's a good question, but I cannot answer it. > > Most amps produce more distortion the more power they run. > > The question is whether the sum of distortion from both amps at lower power > is less than one amp running at higher power. > > 73, Ron AC7AC > > -----Original Message----- > > > On 7/18/2013 3:08 PM, Chris Johnson wrote: > > I love my KPA500. I don't use it enough because of all the low power > > digital I do. I was wondering if the quality of my signal would > > better if I let the KPA500 produce the output even if the wattage is > > 50 or less watts. If I drive it with 1 to 5 watts, it produces 10 > > to 50 watts. I like the thought of offloading the thermal load of > > my long JT65 & JT9 duty cycles onto the KPA rather than my main rig > > which is a Flex 6700. > > You're likely to stimulate more replies than the "Why is aeronautical VHF > comm still AM?" did. :-) > > I don't know anything about a Flex <anything> but, all amplifiers have > non-zero distortion figures. Putting two "in series" will add up at least > some if not all of them. The amp in your Flex followed by the > KPA500 will most likely produce a poorer signal quality than just your Flex > for the same power output. > > Secondly, the KPA500 was designed to produce several hundred watts with a > few tens of watts drive [500W on any band for me takes between 25 and > 30 watts drive]. That's probably the optimum operating point. Driving it > with 5 watts should produce somewhere in the 50+ watts output range. > > 73, > > Fred K6DGW > - Northern California Contest Club > - CU in the 2013 Cal QSO Party 5-6 Oct 2013 > - www.cqp.org > > ______________________________________________________________ > 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 > -- FHC #4224 | 30MDG #6370 | DMC #5698 NAQCC #6554 | SKCC #10435 | FISTS #16155 ______________________________________________________________ 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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Hi Frank,
I would not expect the waterfalls for the JT modes to change because the JT modes transmit only one tone at a time. Apart from turning the tx on and off, the amplitude of the signal does not change. Therfore there is no source for IMD that could result in a broader signal or splatter. You could even use a class C amplifier like you could for a fm transmitter. Greetings Ralf, DL6OAP Am 19.07.2013 um 00:55 schrieb Frank Precissi <[hidden email]>: > I think the best solution would be to try it both ways and see what kind of > signal report you get. I'd be interested to see the two JT waterfalls > compared side by side. > > 73, > > Frank KG6EYC > > > On Thu, Jul 18, 2013 at 3:47 PM, Ron D'Eau Claire <[hidden email]> wrote: > >> I think it's a good question, but I cannot answer it. >> >> Most amps produce more distortion the more power they run. >> >> The question is whether the sum of distortion from both amps at lower power >> is less than one amp running at higher power. >> >> 73, Ron AC7AC >> >> -----Original Message----- >> >> >> On 7/18/2013 3:08 PM, Chris Johnson wrote: >>> I love my KPA500. I don't use it enough because of all the low power >>> digital I do. I was wondering if the quality of my signal would >>> better if I let the KPA500 produce the output even if the wattage is >>> 50 or less watts. If I drive it with 1 to 5 watts, it produces 10 >>> to 50 watts. I like the thought of offloading the thermal load of >>> my long JT65 & JT9 duty cycles onto the KPA rather than my main rig >>> which is a Flex 6700. >> >> You're likely to stimulate more replies than the "Why is aeronautical VHF >> comm still AM?" did. :-) >> >> I don't know anything about a Flex <anything> but, all amplifiers have >> non-zero distortion figures. Putting two "in series" will add up at least >> some if not all of them. The amp in your Flex followed by the >> KPA500 will most likely produce a poorer signal quality than just your Flex >> for the same power output. >> >> Secondly, the KPA500 was designed to produce several hundred watts with a >> few tens of watts drive [500W on any band for me takes between 25 and >> 30 watts drive]. That's probably the optimum operating point. Driving it >> with 5 watts should produce somewhere in the 50+ watts output range. >> >> 73, >> >> Fred K6DGW >> - Northern California Contest Club >> - CU in the 2013 Cal QSO Party 5-6 Oct 2013 >> - www.cqp.org >> >> ______________________________________________________________ >> 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 >> > > > > -- > FHC #4224 | 30MDG #6370 | DMC #5698 > NAQCC #6554 | SKCC #10435 | FISTS #16155 > ______________________________________________________________ > 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: [KPA500] Low Power Use Cases
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In reply to this post by Chris Johnson-2
Chris,
I cannot answer how well the KPA500 will run when driven 1 to 5w, but JT65 does NOT require a linear amp. It runs the same as CW, only stepping in frequency (makes different tones in a SSB receiver), so one can use a class-C amp if they want to with JT65. Therefore, there is no concern about intermod distortion (any more than if one ran CW). How efficient the KPA100 runs when lightly driven is another topic which I cannot answer. It does reason that the heat sink should easily take care of the heat at 50w, if designed for operation at 500w. If the KPA500 runs in class-AB it will dissipate some minimum level without RF drive. If it were class-A it would dissipate full power all the time. I run my 8877 far into class-B so there is almost no idle current without drive. In class-C it would be biased at cutoff. One might measure the current draw without drive, but often much of this is attributed to digital control components that have nothing to do with dissipation of the finals. Perhaps the Elecraft engineers have that number? 73, Ed - KL7UW Date: Thu, 18 Jul 2013 15:08:14 -0700 From: Chris Johnson <[hidden email]> To: "[hidden email] Reflector" <[hidden email]> Subject: [Elecraft] [KPA500] Low Power Use Cases Message-ID: <[hidden email]> Content-Type: text/plain; charset=us-ascii I love my KPA500. I don't use it enough because of all the low power digital I do. I was wondering if the quality of my signal would better if I let the KPA500 produce the output even if the wattage is 50 or less watts. If I drive it with 1 to 5 watts, it produces 10 to 50 watts. I like the thought of offloading the thermal load of my long JT65 & JT9 duty cycles onto the KPA rather than my main rig which is a Flex 6700. Does the KPA500 make a much cleaner signal than the built in barefoot amp because its running at such a higher voltage? I'm not too concerned about power efficiency comparisons, because we know its not more efficient doing it this way. :) Thx -Chris 73, Ed - KL7UW http://www.kl7uw.com [hidden email] "Kits made by KL7UW" ______________________________________________________________ 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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