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Entry  Sat Feb 16 18:32:01 2013, yuta, Summary, RF System, phase tracker: OLTF BEATXFINEPHASE_OLTF.pngBEATYFINEPHASE_OLTF.pngphasetracker.png
    Reply  Thu Feb 28 05:54:54 2013, yuta, Update, RF System, phase tracker: calibration ALS-BEATX_FINE_PHASE_OUT.pngALS-BEATY_FINE_PHASE_OUT.png
       Reply  Thu Feb 28 06:51:17 2013, yuta, Update, RF System, phase tracker: noise level frequencynoise.png
          Reply  Sat Mar 2 20:09:12 2013, yuta, Update, RF System, phase tracker: DAQ noise limited frequencynoisewhitening.png
Message ID: 8214     Entry time: Sat Mar 2 20:09:12 2013     In reply to: 8200
Author: yuta 
Type: Update 
Category: RF System 
Subject: phase tracker: DAQ noise limited 

[Koji, Yuta]

We found that our phase tracker noise is currently limited by the noise introduced in DAQ.
We confirmed that the frequency noise was improved from 2 Hz/rtHz to 0.4 Hz/rtHz by increasing the gain of the whitening filter.
The whitening filters should definitely be refined.

What we did:
  1. Put constant frequency RF input to the beatbox from Marconi and measured noise spectrum of the beatbox output(BEATX I) after the whitening filter with a spectrum analyzer. Noise floor level was ~0.2 Hz/rtHz at carrier frequency range of 15-100 MHz. Calibration factor of the beatbox output was ~380 mV/MHz.

  2. Measured noise spectrum of C1:ALS-BEATX_FINE_I_OUTPUT(figure below). The noise floor didn't change when there was RF input of 100 MHz from Marconi(blue) and DAQ input was terminated (green). Also, C1:ALS-BEATX_FINE_I_IN1(which is before unwhitening filter) showed a flat spectrum. These show our spectrum is limited by DAQ noise, which is introduced after the whitening filter.

  3. We increased the gain of whitening filter by x20 to show frequency noise performance can be improved by better whitening filter(red). But we can not use this setup as the other quadrature will be saturated by a too much gain at DC. Thus we need to carefully consider the signal level and the gain distribution of the whitening filters.
frequencynoisewhitening.png


Next:
  - Better whitening filters. The current one consists of zero 1 Hz and pole 10 Hz with DC gain of 5 using SR560.
  - Better beatbox. We can increase the RF input power to the mixer and unify the preamplifier and the whitening filter in the box.

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