[time-nuts] Advantages & Disadvantages of the TPLL Method

Charles P. Steinmetz charles_steinmetz at lavabit.com
Wed Jun 16 03:45:03 UTC 2010

Warren wrote:

>Charles posted:
>>but the locked frequency will be different from both oscillators' 
>>free-running frequency and
>>the EFC will not correctly indicate the test oscillator deviation
>>because it isn't the only control input in the system.
>Good point and No argument  (except for the deviation part)
>Because the EFC is the only control input THAT IS VARYING.

No, it's not.  The strength with which each oscillator pulls on the 
other also varies as the equilibrium frequency (the result of all 
three recursive control inputs) moves around relative to the two 
instantaneous free-running frequencies.  How much EFC is required 
depends, in part, on the strength of the pulling.  There are three 
varying inputs.

Magnus suggested that the effect of injection locking may be enough 
smaller than the EFC input that it has little practical 
significance.  That may be so, but when dealing with measurement 
accuracy in the hundreds or tens ot ppt, this needs to be verified by 
the results of carefully constructed experiments and hopefully also 
supported by mathematical analysis.

Best regards,


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