At 2/28/2007 08:19 AM, you wrote: >Bob > You seem to want to lump what is characteristically a complex impedance > (R+or-jX) into a single number in order to simplify your argument that a > non conducting RF output transistor is an open circuit because the > transistor is not having any RF drive to the base (as in a class C amp > with no current flowing in the collector / emitter circuit), and ignoring > the Xc or XL remaining which will and is being transformed to an > impedance different than the impedance originally designed to operate > into as a load (50 ohms). > Even then your argument again fails because the transformed complex > impedance (+or-jX) will result in a source impedance from the transistor > into something also complex, either capacitive or inductive, with little > or no resistive component, and is never seen or sourced as a "high > impedance" by any stretch of the imagination.
I use the term "high impedance" loosely here to mean no resistive component, hence quasi-infinite VSWR, low return loss, mag. S11~=1 or however you want to put it. In reality, the impedance at the collector of the transistor is going to be pretty high. Yes it gets transformed around the Smith chart to a capacitance, through a short @ 1/4 wavelength, then inductive & back to an open as you move away from it but I think that's irrelevent to this discussion. > > Why do you think that this (high impedance) is the case? Even in RF > amplifiers operated as class A or AB, there is always current flow thru I'm talking about class C amplifiers, the ones normally found in repeater RFPAs. They draw no current when not TXing. Bob NO6B
