[time-nuts] GPSDO Question

[Bert]

He everyone,

Just a few points/questions I would like to make regarding the discussion FLL vs PLL vs my design.

One question that I have is regarding FLL vs PLL. The statement that a PLL is better than a FLL on a GPSDO may make sense when looked at from an analog loop and discrete phase comparator signal perspective, but what about the software that closes the loop? For example, the software may provide the ability to not make a frequency adjustment if the frequency difference (or phase difference) is too small. How does this come into play when comparing the two approaches? In other words can we make the software-based FLL a better perfromer so that the claim that PLL is better may not be as obvious?

I have tried to find a detailed comparison PLL vs FLL for GPSDO on the web and in textbooks but could not see anything other than general (qualitative) statements like the ones I have read so far on this mailing list: PLL is better than FLL. Does this information exist? Could anyone direct me to that data? I am truly interested in understanding the behavioral differences.

Finally, just a reminder: I make no claim of mind-blowing
performance with my design. From the beginning, it has been clearly stated
that the expected short term accuracy of the VE2ZAZ design (assuming a
decent OCXO is used) should be better than 1x10^-9. My website also
provides the same information. The feedback that I have received from
the users correlate with this. I like to see my work as allowing the 100+ users to learn more about disciplining an oscillator and obtain a better 10MHz reference. Nothing more than this.

Please keep the discussion open-minded and informative. I like this forum when it is like that. :-)

Bert, VE2ZAZ
http://ve2zaz.net






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