[ARC5] R-25 dial nonlinearities

[J Mcvey]

Robert, the good news for you is that the NC270 scale was DESIGNED to calibrate to that scale.It will align pretty well if you follow the mfr alignment instructions,
I did a couple of Hallicrafters lately and they pick fequencies that are NOT at the extreme ends of the dial to align against. Of coarse, it is critical that the mechanical mesh and dial are are the correct place before you start the electrical alignment.Then they use the cap trimmers for the high end and the coil slug for the low end, then repeat two or three times until the calibration tracks the dial.
We had a discussion here a few month ago when I was struggling with an ARC-5 transmitter that had been tinkered with and the tracking was off by quite a bit.Someone ( I forget who) told me to use calibration points at 1/3 and 2/3 of the dial and use the cap at the high end and inductor at the low end much like what was described by Hallicrafters.So, for ad-hoc systems, this method is a pretty good rule of thumb.for dials that are off by any significant amount. ...worked for me!
 

    On Sunday, January 8, 2017 2:39 PM, Robert Eleazer <releazer at earthlink.net> wrote:
 

  I've been trying to align a National NC-270 and I'm having a dial nonlinearity problem.  I get the frequency set on the top end of each band and the bottom ends are always off.  The receiver has a sliding dial so you can align it as required by using the 100 KHZ marker signal.  But the amount it is off can be beyond the ability of the dial to slide.  You set the coils for the top end of each band, but there is only one trimmer cap for all the bands.  I plan to add some individual trimmer caps for each band and see if that helps.
WayneWB5WSV           
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