Rich said:
>1. Pi-networks are never operated at resonance, they are operated
close to resonance. Low-pass Pi-networks resonate a bit lower than
the operating freq and high-pass Pi-networks resonate above it.<
If it isn't resonant i.e. volts and amps are in phase, then you won't get
maximum output and will likely get worse IMD. I am aware that the US Extra
Class licence exam defines resonance as XL = XC, but this is only an
approximation, and falls apart very badly when the working Q is low. If you use
the only definition of resonance which holds up under all conditions i.e. the
input impedance of the network is resistive (as far as the tube sees it -
strays will have some effect if you calculate and compare with reality,
especially on the higher bands), then the pi network is resonant. So is the L
network, but if you use XL = XC, then both cases suggest that the circuit isn't
resonant.
Operating into a non-resonant load leads to an elliptical load line - see
Pappenfus et al.
73
Peter G3RZP
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