[time-nuts] GPSDO Question

GandalfG8 at aol.com GandalfG8 at aol.com
Sun Sep 2 19:10:24 EDT 2007

In a message dated 02/09/2007 04:20:54 GMT Daylight Time,  
bruce.griffiths at xtra.co.nz writes:

It is  amusing/distressing to see that the myth that using an FLL to lock
an  oscillator to the PPS output of a GPS receiver is a good approach
still  persists.
The optimum solution is a phase lock loop.
Whilst building an  FLL is instructive/educational, if you want the best
GPSDO performance you  should really use a PLL.

Perhaps it depends on how you define a "good" approach.
If you're looking for the very best you can get then it probably  isn't, but 
I don't recall that being claimed in the first place.
However, one of the attractions has to be the simplicity of the  circuit and 
the fact that something offering reasonable performance can be  knocked up 
very quickly.
Without the divider and buffers, the circuit proposed by Bertrand  Zauhar, 
VE2ZAZ, in his QEX article reduces to just three ICs.
It may not be optimum but it must be a strong contender for the best  you can 
get for very little effort.
The Idaho State University version is reported on their web page for  the 
project as having been checked over a 13 day period, by the Idaho National 
Laboratories Calibration  Lab, and found to be accurate to 1.2x10^-10.
I  don't think that's too bad for a fun project that could probably  be put 
together in an evening, even for one guilty of causing such  amusement and/or 


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