Anders,
On 04/03/2015 11:49 AM, Anders Wallin wrote:
Hi all,
I ran some tests on a new 53230A counter that just arrived:
http://www.anderswallin.net/2015/04/keysight-53230a-noise-floor-test/
The time-interval single-shot noise and resulting ADEV seems easy enough to
explain.
I didn't yet have time to look closely at Enrico Rubiola's notes over here:
http://rubiola.org/pdf-slides/2012T-IFCS-Counters.pdf
There is probably a good explanation for the ADEV-level in standard
(pi-counting?) reciprocal frequency counter mode as well as the roughly
1/sqrt(10) enhancement in ADEV when increasing the gate-time 10-fold.
When using new counters with Delta (HP53132A) or Omega (Pendelums
Least-Square) estimators for refined frequency resolution, they work by
doing a filtered weighing which has a lower bandwidth than the brute
force counter, and this will give a lower reading for white and flicker
phase noise (see their formulas), and this causes the deception that the
ADEV is lower, just because you get the reading, that the noise-type is
lower, but all which is happening is that you lower the reading for that
noise-type, not that you have a better noise situation.
on another note:
The discussion on phase-noise <-> ADEV calculations earlier was
interesting. Datasets (synthetic or real) with known correct ADEVs and
phase-noise-spectra would be a good addition to allantools and a motivation
to add code for the phase-noise <-> ADEV conversion.
Do look at the NIST SP 1065 for a noise-generator with known properties
for a number of algorithms.
Cheers,
Magnus
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