[ARC5] R-25 dial nonlinearities

Sun Jan 8 18:50:53 EST 2017

The HP 204C audio sig gen uses elliptical gears to achieve a linear dial scale. Picture the small radius end of the dial gear meshed with the large radius side of the capacitor gear and you can see how one gear speeds up or slows down depending on the mesh point.

The Remler 631 "butterfly" variable capacitor has square shaped plates.  Each set of plates (two rotors, no stator) rotates at one corner and are both geared to a central dial shaft to mesh and unmesh with each other.  This action produces the sum-of-the-squares for linear frequency change with dial rotation.

None of this applies to ARC-5, but interesting anyway.  Mike, W6MAB

  ----- Original Message ----- 
  From: Bruce Long via ARC5 
  To: Clare Owens ; Discussion of AN/ARC-5 military radio equipment. 
  Sent: Sunday, January 08, 2017 2:04 PM
  Subject: Re: [ARC5] R-25 dial nonlinearities

  Nice reference Clare.  I had not heard before about using eccentric pulleys tor linear tuning.

------------------------------------------------------------------------------
  From: Clare Owens <clare.owens at gmail.com>
  To: Discussion of AN/ARC-5 military radio equipment. <arc5 at mailman.qth.net> 
  Sent: Sunday, January 8, 2017 3:50 PM
  Subject: Re: [ARC5] R-25 dial nonlinearities

  The math in this article is somewhat beyond my somewhat ancient brain but perhaps it might inspire some of you younger folks:

  http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/hr/1990/01/page53/

  In any case it looks interesting...

  Clare  N2RJB

  On Sun, Jan 8, 2017 at 2:27 PM, Richard Knoppow <1oldlens1 at ix.netcom.com> wrote:

       Capacitor plate shape is covered in many older engineering books. I will see if I can generate a list.  Many older books are available on line from tubebooks.org and archive.org   These are free.
       Variable caps used to be available in three or four standard types:
    Straight line capacitance, straight line wavelength, straight line frequency and compromise. Straight line frequency requires that the plat shape be rather extreme so were not very often used.  Receivers mostly used "mid-line" caps which provided some extension on the low capacitance side in order not to compress the high end dial too much but still retain a more practical plate shape.
        One thing to look for when the dials seem far out of calibration is the centering of the rotor.  The variation in capacitance changes when the rotor is off center and is not linear.  At the center the capacitance is minimum. Remember the capacitance is a square law function of area so the change in variation with spacing is somewhat critical. If you can measure the capacitor on a bridge you can adjust the end bearings to get it exactly centered.  This is assuming that no serious plate bending has been done. Plate bending is legit on some devices and not on others. For instance, the handbook for the Hewlett-Packard 200CD oscillator gives specific instructions for bending the plates (but the factory bending should usually be left alone) while in the Hammarlund SP-600-JX the plates should NEVER be bent. If they are you can never get the dial to track.
        I would suggest looking at the cap in the R-25 to see if its correctly centered. I don't know whether they are supposed to have bent plates.

    On 1/8/2017 10:55 AM, Mike Everette via ARC5 wrote:

      Gordon White wrote:

          Unfortunately I did not hear that he had died until his heirs tossed
      out his design notebooks.

      And so, more knowledge and history is lost forever.

      Guys, if you have stuff like this, please please PLEASE make sure
      someone in your family knows its value and significance.

      73

      Mike

      WA4DLF

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    -- 
    Richard Knoppow
    1oldlens1 at ix.netcom.com
    WB6KBL

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