[time-nuts] 53230A noise floor

Magnus Danielson magnus at rubidium.dyndns.org
Fri Apr 3 12:46:59 EDT 2015


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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