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

Charles P. Steinmetz charles_steinmetz at lavabit.com
Tue Jun 15 16:05:21 UTC 2010

Warren wrote:

>The thing that you  (and maybe Adler?) are missing is that effect 
>goes away when the two frequencies ARE exactly the same.
>I'm not talking close, I'm talking the exact same freq with phase 
>held in quadrature within single digit femtoseconds.
>BIG difference, Once that is understood, then that sort of answers 
>your other comments.

Actually, this is not true.  If either or both oscillators are 
affected by injection locking (and they pretty much all are, to some 
degree -- in this connection, note that you want to make measurements 
down to E-12 or better [I thought you mentioned E-14 somewhere early 
on], so even the least bit of IL will affect the results), what you 
have is two control inputs to the controlled oscillator (the EFC and 
the reference oscillator) and one control input to the "reference" 
oscillator (the oscillator under test, which is itself controlled by 
both EFC and the reference oscillator).  They will reach equilibrium 
(unless the recursive feedback is unstable), 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.

Best regards,


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