fine tuning amp pi-network

Mike Silva mjsilva at JPS.NET
Mon Jun 28 09:44:27 EDT 1999

First off, I'm no Pi network expert, and I'll be interested in hearing what
others have to say, but my understanding is that by varying the L for a
given power output (transformation ratio) and frequency (resonance), you're
varying the loaded Q of the network.  You're probably not going to see much
difference in P out or Ip, but you may notice a difference in your harmonic
output.  Maybe it's best just to pick a recommended loaded Q value (12-15?)
and use the book value of L for that chosen Q.

Mike, KK6GM

>Anyway, in optimizing the L for the output pi-net what are the recommended
>methods? I see not much difference btwn 1.8 and 1 uH of L on the output
>tuning the 10 meter band. I did use a roller inductor to determine what the
>optimized L was but that was with full out of the deck on each band and I
>just know there must be a better way. I have the coils right now for 10
>through 40 meters including 17 and 12 meters having their own switch
>positions. The value of L does not seem to be really critical in the
>resultant output power. Also does not seem to vary the Ip all that much
>Anyway, just wondered how some of you HB'ers have optimized your tank
>circuits for each desired band.
>Sorry I am not much of an engineer but I am learning a lot as I go. I
>homebrewed a quad 572B but it was rather poorly built so I thought I would
>do things right this time.
>BTW I will have the front panel completely taken down to parade rest and
>re-silkscreened. I will snail mail pictures to Larry W7IUV for his amps
>photos web page when it is all done.
>So how do we optimize the tank guys? I do have a lab quality grid dipper as
>well as the MFJ 259 SWR Analyzer.
>San Diego
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