Hi The trick is that a good 125 MHz OCXO has better phase noise at 100 Hz than a multiplied 5 or 10 MHz OCXO. By the time you get to 30 Hz, usually the lower frequency multiplied up wins. By the time you get to 3 Hz, the much higher Q HF OCXO always wins. (Yes, you could have a great 125 MHz and an utterly trash 5 MHz where this would not apply. For the OCXO’s used in the big old telecom GPSDO’s it does apply).
This also *assumes* the noise floor in your phase detector and noise floor in your dividers is not limiting what you do. That *probably* is true for most of the parts you would reasonably decide to use. Again, something that is worth measuring on the device you build up. Now - in *your* application, how much does 30 Hz phase noise matter? Maybe it is a big deal, maybe it does not matter at all. If it does not matter, then indeed do the GPSDO straight up with the 125 ( or 250 or …. ) MHz oscillator. It very much depends on what the system you are designing up requires. Bob > On Feb 12, 2019, at 10:34 PM, jimlux <[email protected]> wrote: > > On 2/12/19 4:41 PM, Jeff Blaine wrote: >> OK. I would still be interested to see if anyone has plots on the close in >> noise profile of the Lucents. The XO part has an Efrom OCXO and I can >> assume it's similar to a generic OCXO. But the RB is an unknown - I have no >> idea what to expect from that. >> On a separate task, one of these days I would like to build up a set of 125 >> & 500 Mhz sources for lab and gear use disciplined by a GPSDO 10Mhz feed. >> The current source is a 125 Mhz homebrew OCXO and a pair of >> doubler/amp/filter sets. I assume they are pretty clean close in but the >> frequency moves around a bit more than I would like as the OCXO part of the >> equation is nothing special. They drive some SDR and DDS sig gens here in >> the shack so the PN is a factor as well as the frequency accuracy. > > what about disciplining the 125 MHz OCXO? > or a really narrow PLL? > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
