Very true. There is a tradeoff between efficiency and distortion. The K3 has good cooling, so for a fixed station where power consumption is not an issue, you might as well keep the PS voltage fairly high. It also might give you a little more power output 6 meters which tends to run a little low.
Al N1AL On Wed, 2009-06-03 at 23:42 -0400, Don Wilhelm wrote: > Alan, > > Your analysis is correct - BUT -- > > Efficiency is one thing. but it has been previously discussed that > higher DC voltages result in improved IMD. > So the "best" voltage to be used is a compromise (efficiency alone is > not the only consideration). My preference is to stay with the 13.8 volt > output of my power supply and keep the voltage drop under full load to a > minimum by using #12 or larger conductors and low drop (APP) > connectors. My vote is to stay with a "systems" approach rather than > concentrating on only one parameter. YMMV. > > 73, > Don W3FPR > > Alan Bloom wrote: > > The graphs show: the lower the power supply voltage, the higher the > > efficiency. > > > > The reason: When you set the K3 to, say, 100W it has to put 1.4A into > > the 50-ohm dummy load (P = I^2R = 1.4^2 x 50 = 100). > > > > The DC current through the PA transistors is pretty much directly > > proportional of the RF current through the transistors. Whatever DC > > current the PA transistors require to achieve 1.4A of RF into the load > > doesn't depend on the power supply voltage. > > > > Since the transistor current is the same no matter the power supply > > voltage, you get best efficiency (lowest power dissipation) at the > > lowest voltage that is capable of sustaining the desired power level. > > > > Al N1AL > > > > > > On Wed, 2009-06-03 at 19:04 -0400, Jack Smith wrote: > > > >> I've made some measurements of my K3's efficiency versus DC supply > >> voltage, output and frequency at > >> http://www.cliftonlaboratories.com/elecraft_k3_efficiency.htm > >> > >> Jack K8ZOA > >> www.cliftonlaboratories.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 ______________________________________________________________ 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
