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## Re: [TowerTalk] coax stubs /bandpass filter

 To: "Tower and HF antenna construction topics." Re: [TowerTalk] coax stubs /bandpass filter "Jim Brown" "Tower and HF antenna construction topics." Tue, 30 Mar 2010 16:58:08 -0700 mailto:towertalk@contesting.com>
 ```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 _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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