[AMPS] Pi-L networks

[John Fielding]

Hi Carl - I am currently designing my "ultimate amplifier" using a Pi-L
network.  Like you I struggled to calculate the necessary values, that is
until I used the ARRL Radio Designer software!

I designed the Pi section to match into 300 ohms first of all, and then
having optimised the values (comparing them to the values published in the
ARRL Handbook).   I then "fixed" these in the program and optimised the L on
the output.   Works pretty good, the predicted response is always better
than 30dB down at twice the working frequency.  Input match (as the anode
sees it) is better than -30dB and S22 is about the same.

Thought this may be of interest to all on the net.

John    ZS5JF


-----Original Message-----
From: km1h@juno.com <km1h@juno.com>
To: amps@contesting.com <amps@contesting.com>
Date: Saturday, November 14, 1998 6:29 AM
Subject: Re: [AMPS] Pi-L networks


>
>
>
>On Fri, 13 Nov 1998 12:47:23 -0000 Peter Chadwick
><Peter_Chadwick@mitel.com> writes:
>>
>>Does anyone have any comments about the Q of the L network section in
>>Pi-L
>>networks? I have seen it suggested that the impedance at the middle of
>>the
>>pi-L should be the geometric mean of the input and output impedances:
>>the Q
>>of the L will then be given by
>>
>>Q = sq.rt.(Ri - Rl)/Rl
>>
>>where Ri is the intermediate impedance in the Pi-L (i.e. the geometric
>>mean)
>>and Rl is the load impedance (usually 50 ohms)
>>
>>For an 1800ohm plate load, this gives a Q of 5 for the L section,
>>which
>>appears to be the right order of magnitude.
>>
>>Of course, the Pi section would run at the usual Q - 10 to 15, or so.
>>
>>Comments, please?
>>
>>73
>>
>>Peter G3RZP
>
>Peter,
>I thought the same until I started to actually use that concept
>Peter....wound up with higher than expected voltage at the Load
>capacitor....read "arcs".
>By formula that should not have occured leading me to believe that there
>is more to it than static design on a piece of paper.
>I now "design" for a Q of 2 to 3 in the L and have had no further bad
>experiences. The spectrum analyzer confirms the L is performing as
>expected.
>
>73  Carl  KM1H
>
>
>
>>
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>>
>
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