[time-nuts] Advantages & Disadvantages of the TPLL Method
Charles P. Steinmetz
charles_steinmetz at lavabit.com
Tue Jun 15 16:05:21 UTC 2010
>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.
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