[AMRadio] National PW Dial

John Coleman ARS WA5BXO wa5bxo2006 at pctechref.com
Tue Mar 13 01:09:18 EST 2007

I was able to get another tuning capacitor to work pretty close to the
desired 1-500KC span once on the linier dial by making the tuning capacitor
as a small part of the total capacitance of the circuit and by placing the
tuning capacitor across only a portion of the coil and the larger part of
the total capacitance across the whole coil.  I could actually spread the
band out on the high end if I wanted to.  I was going to build a receiver
using this circular linier dial I think it came from a surplus frequency
meter or generator.  Some one once told me that it had been done once and
the individual that did it actually filed the plates down to calibrate it.
I was going to do this as well I had mine working to within a few KCs from
one end to the other (700 to 1200) KCs I was going to get out the files when
the flood came and washed it all away.  I even had a program for the
computer to do a least squares analysis on the capacitor which I inputted
data from a capacitance meter for 100 places on the dial.  With some
manipulation of some formulas and with the help of a Visual Basic Programmer
friend, I was able to get it to draw a graph of the frequency to dial
reading X,Y..  

I was an intense project but a fun one.

John, WA5BXO     

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