On Jun 4, 2006, at 1:26 AM, Peter Chadwick wrote:
> 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.
In a parallel-resonant tank, true, in a (low-pass) Pi-network, the E-
I relationship between C1 and L are not quite in phase, and the sane
thing is true for L and C2, however the current and the voltage at
the output are in phase, so all's well that ends well. As I see it,
an L network is a cross between a transformer and a tuned circuit.
> 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.
My dummy load is non-resonant, so that's a problem?
> Peter G3RZP
R L MEASURES, AG6K. 805-386-3734
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