January 2014 – anderswallin.net

allantools

Python code for calculating Allan deviation and related statistics: https://github.com/aewallin/allantools

Sample output:

Cheat-sheet (see http://en.wikipedia.org/wiki/Colors_of_noise).

Phase PSD	Frequency PSD	ADEV
1/f^4, "Black?"	1/f^2, Brownian, random walk	sqrt(tau)
1/f^3 ?, "Black?"	1/f Pink	constant
1/f^2, Brownian, random walk	f^0, White	1/sqrt(tau)
f^0, White	f^2 Violet	1/tau

Phase PSD is frequency dependence of the the power-spectral-density of the phase noise.
Frequency PSD is the frequency dependence of the power-spectral-density of the frequency noise.
ADEV is the tau-dependence of the Allan deviation.

These can get confusing! Please comment below if I made an error!

White Rabbit DIO vs. FDELAY PPS output test

I ran a test to compare the quality of PPS outputs from a DIO (used as GM) and an FDELAY (used as slave) White Rabbit SPEC/FMC combinations. Here is the phase data measured with a Time-interval-counter. The nice clean traces are derived from a H-maser. We then lock a BVA (internally 2x multiplied to 10MHz) to this PPS signal. The GM node is locked to this 10MHz signal.

The average of each trace was removed, and the traces are offset for clarity.

The Allan deviations look like this. Both the DIO and FDELAY PPS outputs have allan deviations about 5x worse than the BVA used as input clock for the GM.