Could be they are over 9 years old and I think FE only ever suggested 7 years or less. Granted we run till they are dead. Then fix'em and run'em some more. So with that in mind I noticed something on start up today after adding a large heat sink. Nothing to do with what I saw. When the 10 Mhz signal sweeps downward before lock I actually saw the signal die for a fraction of a second in the sweep. So perhaps what you are running into is indeed a failure mode for the worst case. Take the cap out and see what happens. (That should be a challenge its awful small) Regards Paul WB8TSL
On Fri, Jan 20, 2012 at 1:20 PM, beale <[email protected]> wrote: > 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 <[email protected]> > > 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 > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
