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[Amps] Relationship between Q and SWR in PI network.

To: amps@contesting.com
Subject: [Amps] Relationship between Q and SWR in PI network.
From: Paul Baldock <paul@paulbaldock.com>
Date: Wed, 23 May 2018 15:09:52 -0700
List-post: <mailto:amps@contesting.com>
Does anybody know the relationship between Q and SWR for a PI network?

For example let's say I design my amp PI output network for 7.0MHz. I simulate the Tube Impedance with a 1K resistor. I put my MFJ259 on the output of the PI and tweak the load and tune caps for a perfect 1:1 (50 Ohm) SWR. I now leave the caps where they were and adjust the frequency to show the upper and low 2:1 SWR points and they are 7.2MHz and 6.8MHz. (2:1)=Fo/(Fu-Fl)=7.0/(7.2-6.8)=17.5. In practice this is in fact about 1.5 times my design Q, but I would like to know what theory says.

- Paul  KW7Y

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