On Tue, 30 Mar 2010 18:56:34 EDT, TexasRF@aol.com wrote:
>Wonder how you go about determining where that is? Could you assume the
>plate load capacitor is a point of minimum impedance and go from there?
I see it as far more complex than that. The output of a tube stage is
essentially the output Z of the tube transformed by the output network,
where the output network is the plate tank and everything between it, the
coax connector, and the transmission line. And, because it's a passive
network, the TX end of the transmission line is part of the filter! And, of
course, the transformation that the network provides is different at every
frequency.
>If so, the high impedance points would occur every odd quarter wavelength
>(at the suppression frequency) along the cable, right?
Well, they certainly vary with that spacing, but it's hard to know where
"zero" is. :)
Another point. Any filter that you build from discrete components presents
equivalent problems with respect to analysis. It's convenient to design a
filter assuming fixed values of source and load impedance, but that is a
LONG way from the real world. You could easily measure 60 dB of attenuation
from a 50 ohm generator into 50 ohms resistive, but if the source is 30 -j10
and the load is really 500 - j300 you'll get a LOT less attenuation!
73,
Jim Brown K9YC
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