[time-nuts] Fix Trimble Oscillator??

[John Miles]

> I couldn't tell from the picture but it looks like there is a
> diode from +12
> VDC to ground...

That's just for reverse-power protection.  I loaned this unit out for a few
weeks, so I added the diode to make it less accident-prone.

> and trimpot is connected to ground through a resistor.

Right, top to +12 through a resistor, bottom to ground, wiper to the VTune
input pin.

> Mislabeled GND and +12 VDC?  Or am I misinterpreting the picture?

Ah, correct -- here's a fixed version.  I guess that's why you need the
diode, in case you actually hook it up as specified in the earlier photo. :)

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

Those are just 0.1 uF capacitors.  One in series with the output pin for AC
coupling, and another located at one or both power pins for bypassing.

The blue capacitor underneath the trimmer is a 4.7 uF tantalum electrolytic.

-- john, KE5FX

> -----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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