[time-nuts] femtosecond jitter anyone?

Magnus Danielson magnus at rubidium.dyndns.org
Wed Apr 8 23:07:07 UTC 2009

Bruce Griffiths skrev:
> Magnus
> For examples of the use of crystals in filters for cleaning up the
> output of a crystal oscillator look at the circuit schematics for some
> of the early crystal frequency standards.
> Crystal filters were used quite liberally in some of these to clean up
> the outputs.

It's used in the step-up chain of the SR620 for instance. The SR620 has 
a 10 MHz oscillator (TCXO or as in my case a Wenzel OCXO) which is 
stepped up to 90 MHz using a fairly ordinary odd-order stepup and 
filtering chain. The ECL logic counter frontend use this as coarse 
counter frequency. The analog interpolators is a bit interesting in a 
few peculiarities but nothing really exciting.

The crystal filters of that chain is setup in PI-filter style with the 
crystals in serial mode.

> However it may be necessary to control the temperature of these crystals.

Indeed. I wonder if he really needs that level of sine purity. An LC 
tank should be sufficient to get started.


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