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

[Paul Baldock]

Thanks for the info. The calculator I used gave 
the answer 6:1. but my test circuit gave about 
4:1 on my 
MFJ259 
http://chemandy.com/calculators/return-loss-and-mismatch-calculator.htm

- Paul


At 10:12 AM 5/26/2018, sm0aom at telia.com wrote:
>There is a relationship between SWR bandwidth, 
>and Q which is valid for "simple" circuits and 
>for limited excursions from the center frequency.
>It uses the limit of |X| = R of the input impedance, and is
>
>Q = center frequency/SWR bandwidth at the 2.6:1 points.
>
>For a pi-network, it is somewhat approximate, as 
>it does not take the asymmetry of the real part 
>around the resonance point into account.
>
>A discussion  and a detailed derivation can be found at:
>
>https://owenduffy.net/blog/?p=12152& and
>https://owenduffy.net/blog/?p=1736
>
>73/
>Karl-Arne
>SM0AOM
>
>
>
>----Ursprungligt meddelande----
>Från : paul at paulbaldock.com
>Datum : 2018-05-24 - 00:09 (UTC)
>Till : amps at contesting.com
>Ämne : [Amps] Relationship between Q and SWR in PI network.
>
>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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