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I read in sci.electronics.design that gwhite wrote
(in ) about '1/4 vs 1/2 wavelength antenna', on Thu, 3 Mar 2005: By definition, conj-match insists RL = Ri = 110 ohms. Again we are limited in our clipping constraint by static drain current, and supply voltage, specifically 10 V. Our negative swing limit is, as ever, 10 V (the drain voltage). positive swing = Id*rL = 1*55 = 55 V This would breakdown the device, but the lower negative swing will force us to back down the drive to meet the design defined clipping constraint. Pload = 10^2/(2*110) = 0.455 W And the power dissipated in the device is also 0.445 W. Matching according to the 'maximum power theorem' or conjugate matching, results in equal power in the PA and load. That's why it isn't useful for power amplifiers. Doesn't everyone know that an audio amplifier that id designed to feed an 8 ohm load MUST have an output source impedance of 0.0000001 ohms or less. An output source impedance of 8 ohms would dramatically decrease the electromagnetic damping on the loudspeaker voice-coil - by the huge factor of .... two!(;-) -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
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