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 be...@bealecorner.com 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 li...@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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