The theory states that Power in = U I Power out ~ I*I*r So power-in is linear with current. Power-out is quadratic with current.
Driving hard helps efficiency but hurts linearity. Max efficiency with LDMOS is about 60% with reasonable linearity and no feedback, but could be > 70% with predistortion. Higher efficiency can be obtained in class C for CW/RTTY however wideband SS designs are not suitable for class C. For low efficiency at lower power the best approach is to reduce the supply voltage. SPE gives a choice of 25V (1/3 power), 35V (half power) and 48V (full power). New 4O3A (Flex) amplifier is supposed to adjust supply voltage automatically for highest efficiency at a given power. Another choice is to use an external tuner for max power, not low SWR, as e.g. at 1/4 power the optimum output impedance is 200 Ohms not 50 Ohms. Elecraft is using a trick in KX3 where at > 12 V and 5 W another ratio is used in the final transformer, reducing power input by almost one half. Ignacy, NO9E -- 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: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
