[time-nuts] VCXO center frequency offset
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
> -John Beale
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