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

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 > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >