[ARC5] R-25 dial nonlinearities

[Bruce Long]

Some of the old 1930 vintage radio design handbooks have useful information on that topic but I have not seen any stand alone written treatments.  My draft - which I think I can still find included a method and equations to determine the formula for the radius of a straight line tuning capacitor plate.  The plan was to scribe the right shape on the plates of a straight line capacity  capacitor ( ie semi-circular plates) and then carefully file off the edge of the capacitor plate to match the scribed line.
If you can find the stuff you received from Paul I would like to be able to have a copy.  Maybe you and I can find the time to write an article for Electric radio to expose and preserve Mr Farnham's work.
In any event the first practical thing I can think of for your radio linearity problem would be to remove yet more plates from the variable cap and adjust the remaining LC components as required.


      From: gordon white <gewhite at crosslink.net>
 To: Bruce Long <coolbrucelong at yahoo.com>; J Mcvey <ac2eu at yahoo.com>; "ARC5 at mailman.qth.net" <ARC5 at mailman.qth.net> 
 Sent: Sunday, January 8, 2017 12:05 PM
 Subject: Re: [ARC5] R-25 dial nonlinearities
   
   Back in the day I spoke to the receiver designer, Paul Farnham, if have the name right,  about  designing the variable capacitor plate shape and he gave me some formulae and diagrams, which I may have somewhere, though not in reach at the moment. 
  
      Unfortunately I did not hear that he had died until his heirs tossed out his design notebooks.
  
   - Gordon White
  

   
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