On 1/4/13 10:25 AM, Rick Karlquist wrote:
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.
An excellent point.. After all, what is a crystal oscillator but
essentially a noise source followed by a crystal filter.
Now after considering all that, crystal clean up filters don't
sound like such a great idea unless you have no alternative.
I can't think of a good practical example, but say you had a kind of
noisy source, and a box full of crystals that happened to be at the same
frequency, and for some odd reason, you didn't just build an oscillator
with the crystal. (perhaps some sort of distribution amp system where
you want all the outputs to be coherent to some reference, and the
reference is noisy?)
Rick Karlquist N6RK
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