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 > > > > Alan Bloom wrote: > > On Wed, 2009-06-03 at 10:59 -0700, hb9brj wrote: > > ... > > > >> Guess the major problem resulting from voltage drop is a reduced efficiency > >> of the KPA3. > >> > > > > Actually, for a given power level the KPA3 probably has better > > efficiency. For lowest heat in the PA, the supply voltage should be as > > low as possible that still works at the selected power level. But the > > system efficiency is lower because of the power loss in the cables. > > > > Al N1AL > > > > > > ______________________________________________________________ > > 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
