> There are resonant pi networks and low pass filter pi networks......
> These are resonant. If you perform a frequency plot of the output vs the
> input you will
> get a small signal up to the point of resonance ( the low pass part of the
> frequency plot) and then a peak at resonance that produces a much larger
> signal and as you increase frequency further the output continues to drop.
> The magnitude of this peak compared with that at lower frequencies is
> related to the Q of the network.If your pi network in your tube output
> transceiver was simply a low pass filter you could not peak the output
> power when tuning it.
>
Yes, quite right on the output PI network, Bill. However, if you plug the
values for Q=1 into a circuit simulator (I just ran them), the frequency
response of a tuned input PI looks a lot like a classic chebyshev
low-pass filter with a ripple of about 0.2dB (values taken from
Orr's Radio Handbook, K8RA 3CX800A7 amp, 14 MHz tuned
input). For Q=2 (taken from my Drake L-7 schematic), the frequency
response is starting to look more like a resonant PI (2 dB ripple).
Not sure why Pittenger used Q=1 (seems like I hear people generally
recommending Q=2). But if a 3 pole Q=1 resonant PI network
provides enough energy storage to be useful as a tuned input, but
only has 0.2dB frequency response ripple, then why wouldn't a 5
pole low-pass with the same 0.2dB ripple provide some useful
storage? Perhaps I need to break out the Spice simulator and run
some half cosine pulses thru said 0.2 ripple low-pass to find out.
BTW, just for the record I am defining Q=1 to be Xc1=Xc2=50 ohms.
Not sure if that is a correct definition when the Q gets this low.
73 de Mike,
W4EF.............................................................
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