To make this idea work you need to make a 25Wpep amplifier that is kept in it's linear region so that the IMD from this amplifier does not cause problems in the output of the KPA500.
To make a class A-B 25W amplifier such as this with enough linearity will result in you designing an amplifier capable of 100Wpep at full smoke. The non-linear nature of HF PA's is easily found on the net. Having designed PA's for HF manpacks a number of years ago we simply turned down our 100Wpep design to 25Wpep and pocketed the performance increase at the expense of cost. The K3/100 at 25-35W has excellent linearity (highly likely by design, pat designers on back for this one) which allows a more aggressive approach within the KPA500 for grunt at the expense of "some" linearity. You're not increasing the cost of the KPA500 trying to eeek out every last bit of linearity to get around the rubbish coming from the transceiver. I'm keen to do some measurements in the near future of the SPE 1.3k-fa amplifier being driven by a K3/10. Having measured the IMD of my the K3/100 at 10W (KPA3 disabled) recently I was a little surprised at the result, it was not as clean as when driven at 30W with the KPA3 enabled. I'd not be surprised to see some output degradation in the SPE from the K3/10 c.f K3/100 driven at 20W with a -3dB inline attenuator. This would certainly explain some of the "wide" local signals that I've been seeing in my SDR recently. Engineering is always about compromise, and cascaded amplifiers are one of the more trickier things to strike the right balance with. 73 Matthew VK5ZM On 23 February 2017 at 07:55, Harry Yingst via Elecraft < elecraft@mailman.qth.net> wrote: > > Seeing how the KPA- 500 tends to need less than 25 watts to drive it to > full output (500 watts) It got me thinking about a 25 watt PA Option. > Would it be possible to replace the existing 10 watt PA board with a 25 > watt PA board that would use a larger heatsink instead of the case. > > If the stock Filters and Relays can handle the 25 watts it would seem that > it would be a more inexpensive option for those who plan on going with the > KPA500. > > Just a thought... > > > > > ______________________________________________________________ > 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 vk...@bistre.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
