[time-nuts] Re: Practical relation between Phase Noise and ADEV

[Bob kb8tq]

Hi

Since ADEV is a “broadband” measure, mapping it to phase noise is … errr ….
non-trivial. In fact HP ran into a brick wall trying to do this on one of their devices
back in the early 1970’s. This was for ADEV -> Phase Noise. 

If you want to go from xDEV to phase noise, it turns out that the Hadamard variance
is a better starting point. There still is a bit of math involved. You can’t just look at
1 sec and get to 1 Hz.

Going the other way ( phase noise -> xDEV ) is a bit more practical. The issue there
is still the broadband stuff. In one case, close in dominates. In another case far removed
drives what you see. The “general” answer is to push a wide range of frequencies 
into the measurement. 

No this is not as crazy as a jitter measure, but it shares a lot of the same sorts of issues. 

Bob

> On Jul 22, 2022, at 7:50 AM, Erik Kaashoek via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Both ADEV and Phase Noise can be measured around 1 to 10Hz so for my own understanding I made an empirical graph that relates a certain phase noise with its impact on the ADEV to allow checking for consistency in measurements.
> All data mentioned is only correct for a signal at 10MHz
> The table was made by generating a 10MHz test signal with just the right level of phase noise at the wanted frequency and measuring the ADEV of the test signal. Of course it should be possible to calculate this relation but these calculations are not my strongest point.
> And I did not verify how the summing of noise impacts the total ADEV
> Phase noise with frequency f has maximum contribution to ADEV at frequency f*2.
> Phase noise of -60dBc at 1Hz contributes maximum 1E-10 to ADEV at 0.5Hz
> Every 20dB of decrease in noise level decreases ADEV contribution with a factor 10
> Every factor 10 increase in frequency increases the ADEV contribution with a factor 10.
> A simple graph showing the relation can be found here: http://athome.kaashoek.com/time-nuts/PNvsADEV.PNG
> Erik.
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com