[time-nuts] VCXO center frequency offset

beale beale at bealecorner.com
Fri Jan 20 13:20:56 EST 2012

Yes... if the C217 trimmer was not already at the very minimum setting! I was thinking of possibly removing it altogether, maybe adding back a smaller fixed C.  All three of my units are pretty low in VCXO center frequency, and in fact I wonder if that's the reason they were on the surplus market in the first place.

>  -------Original Message-------
>  From: Bob Camp <lists at rtty.us>
>  Based on the frequency plot of your unit, it swings about 35 Hz high and
>  about 170 Hz low as it sweeps. You could bump the trimmer on the VCXO and
>  move it up by about 70 Hz or so to keep it from running out of range. Since
>  the VCXO is trending down in frequency as it warms up, this may be needed
>  sooner rather than later ...
>  -----Original Message-----
>  Great detective work Scott! I'll bet Channel 4 is voltage to the VCXO. It
>  is driven up and down at startup searching for the lock, then it settles
>  down, but the oscillator components are also affected by temperature so the
>  VCO voltage would logically track the temperature too.  At least it seems a
>  reasonable theory.
>  For example, look at this plot of the 10 MHz output frequency after
>  powerup. It has a similar look to your Channel 4, except for the post-lock
>  drift.
>  https://plus.google.com/photos/109928236040342205185/albums/5680473650837554
>  113/5681715799377076466?banner=pwa
>  -John Beale

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