Test of the 1PPS stability of an uBlox F9T dev-kit RCB-F9T
CategoryResearch
A new release of AllanTools is now available on PyPi.
The AllanTools functions mtotdev() and htotdev() are now almost 10-times faster, after an update to the code that more efficiently calculates moving averages.
The old code used numpy.mean() for each iteration of a loop:
|
1 2 3 4 |
for j in range(0, 6*m): # summation of the 6m terms. xmean1 = np.mean(xstar[j : j+m]) xmean2 = np.mean(xstar[j+m : j+2*m]) xmean3 = np.mean(xstar[j+2*m : j+3*m]) |
However this can be computed much faster by noticing that the new mean differs from the old (already computed!) mean by just two points, one at the start is dropped, and a new one at the end is added:
|
1 2 3 4 5 6 7 8 9 10 11 |
for j in range(0, 6*m): # summation of the 6m terms. if j == 0: # intialize the sum xmean1 = np.sum( xstar[0:m] ) xmean2 = np.sum( xstar[m:2*m] ) xmean3 = np.sum( xstar[2*m:3*m] ) else: # j>=1, subtract old point, add new point xmean1 = xmean1 - xstar[j-1] + xstar[j+m-1] # xmean2 = xmean2 - xstar[m+j-1] + xstar[j+2*m-1] # xmean3 = xmean3 - xstar[2*m+j-1] + xstar[j+3*m-1] # |
We started trapping in this 2nd-generation VTT MIKES ion trap in early May and we are now working with characterizing the trap and laser cooling. Hopefully the ion stays in the trap for several days!
Single-ion Sr+ trap.
Recently merged plotting-functions for allantools with a look and feel of Stable32 - thanks to yxie.
I should probably run python3 to get special characters like tau and sigma to work..
We got a 350 eur AIM-TTi TF930 frequency counter for less demanding frequency counting. Here's how it looks like on the inside.
See also discussion on the AD forum: https://ez.analog.com/dds/f/q-a/107510/ad9912-ftw-lsb-always-zero
We've tried to measure the frequency resolution of the AD9912 DDS, which when used with a 1 GHz SYSCLK should be 1 GHz / 2**48 = 3.55 uHz.
We tried an ARTIQ Urukul-board and an AD dev-board and got the following results:
ARTIQ Urukul AD9912 DDS output frequency vs. FTW 
AD9912 dev-board output frequency vs. FTW
In both cases the output frequency corresponds to an even frequency tuning word (FTW) although we step the frequency by one LSB. In other words the LSB appears to be zero in all cases, even when we write an odd FTW with '1' as the LSB. Instead of the expected 3.55 uHz frequency resolution we see double-sized steps of 7.1 uHz.
The Urukul measurement was done with a Microsemi 3120A phase-meter and the dev-board was measured using a PICDIV 1PPS-divider followed by a Keysight 53230A time interval counter. The even FTW frequencies agree with the predicted frequency to much better than 0.1 uHz.
Inspired by discussion on time-nuts, here's a revised noise-colour graph. There are a few updates: The PSDs (both phase and frequency) now cross at 1 Hz (with the relation between phase-PSD and frequency-PSD explicitly stated), and the ADEV/MDEV theoretical lines now include the formula for the pre-factor (the old graph only had 'proportional to' here).
Source: example_noise_slopes2.py
It is left as an exercise to the reader to properly explain the ADEV pre-factor for flicker-phase noise :).
© 2019 anderswallin.net
Theme by Anders Norén — Up ↑
Recent Comments