I hadn't considered phase noise, thanks for bringing that up! I know tempo can also be an issue with high Q filters.
These aren't significant issues for my current application, which is to clean up a synthesizer running at a slight offset from the nominal 10.000 MHz frequency. So I'm starting with much more noise than an OCXO. John On Nov 15, 2010, at 4:43 PM, "Richard (Rick) Karlquist" <[email protected]> wrote: > A friendly warning about crystal filters. Crystals, whether > used in an oscillator or filter, have intrinsic phase noise. > You cannot improve the phase noise of a crystal oscillator > with a crystal filter unless the filter crystals have lower > phase noise than the oscillator crystals. In general, post > filtering of an oscillator is rarely done for the reasons > I mentioned. One place where it made sense was in the HP > 8662 with the 640 MHz output option where a 10811 is multiplied to 80 > MHz and then filtered to reduce the noise floor. It is further > multiplied to 640 MHz and filtered again by a SAW filter, > that was made at HP in those days. As others have mentioned, > filter characteristic impedance is a function of the crystal > physics. There is a specific impedance that you must use for > a given bandwidth. Fortunately, it is easy to put transformers > at the ports to convert to 50 ohms. > > Rick Karlquist > N6RK > > On 11/15/2010 7:44 AM, John Ackermann N8UR wrote: >> I'd like to find a couple of 5.0 and/or 10.0 MHz crystal filters, >> preferably configured for use in-line with 50 ohm coax. >> >> I've done some googling but don't find anyone selling these as a stock >> item. Do they exist? Any pointers would be appreciated. Used/surplus is >> fine (even preferable). >> >> Thanks! >> >> John >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
