[time-nuts] Low Phase Noise buffer

[WarrenS]

Magnus said
>White noise goes down into the lower range and do contribute to the 
>ADEV....

Can you put some numbers to it to show how much effect there is.
If the 10 MHz had an  incredible total of 10 ns (10%) white noise at say 100 
MHz bandwidth, what would be the Phase noise for the 1 sec ADEV optimum BW 
of 5 Hz?

ws

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The white noise which is the only dominant noise at higher frequencies
goes down into the lower range and do contribute to the ADEV measures
there, even if filtered. This filtering will affect lower-tau measures
more than mid or high tau measures. Telecom standards prescribe
filtering and tau0 for their reference measures for repeatable measures.

The filtering has been debated. The estimators will filter themselves
regardless when m has become a number of multiples, essentially when the
filter bandwidth becomes large compared to the inverse of the tau.

If the noise is benign white noise it should be kept at a low level, but
work on flicker noise is where most effort should be spent.

Cheers,
Magnus

*****************
WarrenS wrote:
>
> T&F Nut question
>
> Is the high frequency phase noise of a buffer important when the 
> Oscillator is used just as the Reference for taking ADEV data?
> The current (2005) writings say that ADEV phase data should be bandpass 
> filtered which removes all the High freq edge jitter.
> If that is the case, Does a buffer's added HIGH FREQUENCY phase noise and 
> jitter have any effect on the ADEV numbers when using modern, high 
> resolution, mixer type, Time interval counters? Of course the low 
> frequency type of buffer noise would still be important.
>
> Previously there was some confusion and disagreement on the subject. What 
> are the latest opinions?