[time-nuts] 10 MHz -> 16 MHz clock multiplier

Rick Karlquist richard at karlquist.com
Fri Jan 4 18:25:00 UTC 2013


Chris Albertson wrote:

> My question is about the phase noise of the final 16MHz signal.  Do
> crystal filters "clean up" the signal.  It seems that after several
> 16MHz crystals in series the output should look a lot like an XO.
>

For offsets out to 100 Hz or so, using a crystal filter will cause
the signal to have the same flicker noise that an oscillator built
with that crystal would have.  Thus don't try to use some junky
clock crystals to make a crystal filter as described in numerous
ham radio articles about receiver IF filters.  If you have a
residual phase noise measurement system like the Agilent E5505A
and a very low flicker noise source, you can actually measure your
filter crystals.  Of course, the crystal time base in the source
has to be better than the crystals you are measuring.  You also
have to avoid overdriving the crystal.  This will require a low
noise buffer amplifier to bring the signal back up to a high
level.

Now after considering all that, crystal clean up filters don't
sound like such a great idea unless you have no alternative.

Rick Karlquist N6RK





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