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W2DU's Reflections III is now available from CQ Communications,...
Cecil Moore, W5DXP wrote:
"Seems to me, the highest efficiency would be achieved by a source with zero source impedance." Me too, but zero source impedance does not match the load as required for maximum power transfer. The best combination is then a source impedance matching the load and which is also pracrically lossless. The Class C amplifier does this by acting as a switch which is infinite in impedance when open during a large part of the RF cycle and a near short circuit to a low impedance (near zero Z) D.C. power source for the short part of the RF cycle it is switched on. It is the time averaged impedance which counts. Is this linear? No way, but the tank circuit is able to remove the harmonics and turn current pulses into a low distortion sine wave. Efficiency? Terman says on page 450 of his 1955 opus that Class C eddiciency is typically 60% to 80%. Compare that with 50% efficiency in a Class A amplifier. Best regards, Richard Harrison, KB5WZI |
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