[time-nuts] WTB: Oscilloquartz 8607, 8600 or similar OCXO

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Jun 7 19:01:19 EDT 2008

Andreas Tschammer wrote:
> Bruce,
> thanks for the valuable information.
> I am aware of the importance of the zero crossing slope to noise ratio in this kind of setup.
> I will only use this design as a first step, because it is easy to replicate and seems to have
> a sufficiently low noise floor for my applications. I also have to build the isolation amps with 
> transformer coupling. But the most difficult part seems to find a good reference oscillator ...
> Andreas, DL2KCL
> _______________________________________________

The LT1028 filter has some essential details missing like the source 
impedance (ie mixer IF port termination circuit).
JPL and NIST favour an LC PI filter low pass filter to attenuate Rf 
above 100kHz or so followed by an RC low pass filter.

The LM161has a maximum differential input of 5V before destruction.
At least add a pair of inverse parallel diodes across its inputs to 
avoid potential destruction.
Comparators with totem pole output stages (like the LM161) tend to 
oscillate when the input signal has a relatively low slew rate (this may 
be why such a complex output circuit is used).
Driving the comparator from a relatively high impedance source (Thevenin 
equivalent = 5K in parallel with 10K) doesnt help,

Even the early NIST designs:


are better, although far from optimum.
Note that all amplifier/filter stages are diode clamped.

JPL favour optically isolated outputs:

US patents 44011953, 4425543
Don't copy their isolation amplifier its not that good (besides the 
LH0033 is out of production).

For isolation amplifier designs with high performance see:


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