[time-nuts] Fix Trimble Oscillator??

J. L. Trantham jltran at att.net
Fri Apr 22 12:08:00 UTC 2011


I couldn't tell from the picture but it looks like there is a diode from +12
VDC to ground and trimpot is connected to ground through a resistor.
Mislabeled GND and +12 VDC?  Or am I misinterpreting the picture?

Also, could not make out what the small orange/black components are, one
from +12 VDC to ground.

Joe

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of John Miles
Sent: Friday, April 22, 2011 6:39 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Fix Trimble Oscillator??



> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of J. L. Trantham
> Sent: Friday, April 22, 2011 3:34 AM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] Fix Trimble Oscillator??
>
>
> John,
>
> Perhaps it is there and I did not see it, but do you have a schematic 
> of the connections to the Trimble oscillator to go along with the 
> picture?
>
> Thanks,
>
> Joe

There's not much to it -- just bypass both power pins near the point where
they enter the can, and (if you want to do what I did) connect the wiper of
a 10-turn trimpot to the tuning input.  If you do that, and you want to
drive the trimpot from the +12 supply, you need to use a resistor to limit
the max voltage at the wiper to +5.  Use a bypass capacitor where the
resistor connects to the trimpot, and ground the 'cold' end of the
potentiometer.

For better stability, you should use an independently regulated supply to
tune the oscillator, or at least don't drive it from the same supply wire
that feeds the rest of the oscillator and oven.  This unit was set up for
short-term PN testing, so I didn't care about drift caused by slow changes
in oven current.

Another tip: even though they aren't really high-end Dewar-insulated parts,
these types of oscillators are sometimes vacuum-sealed at the factory, and
if you melt the solder at the seam, it will open up with a 'pop' and ruin
the vacuum.  So if you are making temporary solder connections like these
for testing purposes, stay away from the seam.  I don't know that this
really hurts anything, but I imagine it could invalidate some thermal
assumptions made at the factory.

-- john, KE5FX


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