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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: 8199     Entry time: Thu Feb 28 05:54:54 2013     In reply to: 8094     Reply to this: 8200
Author: yuta 
Type: Update 
Category: RF System 
Subject: phase tracker: calibration 

I swept the frequency of RF input to the beatbox to calibrate and check linearity range of phase tracker.
Calibration factors are;
  C1:ALS-BEATX_FINE_PHASE_OUT    52.1643 +/- 0.0003 deg/MHz
  C1:ALS-BEATY_FINE_PHASE_OUT    51.4788 +/- 0.0003 deg/MHz


There was systematic error to the linearity check, but at least, calibration factor changes less than 50 % in the frequency range of 10 MHz to more than 500 MHz.


What I did:
  Used network analyzer(Aligent 4395A) to sweep the frequency RF input to the beatbox and getdata of phase tracker signal. I swept from 10 Hz to 500 MHz with 501 points in 50 sec. This sweep is slow enough considering we could lock the 40m arms (typical speed of a mirror is 1 um/s, so bandwidth of the phase tracker should be more than 1 um/sec / 40 m * 3e14 Hz = 75 MHz/s).
  RF amplitude was set to be -3 dBm and splitted into BEATX and BEATY.


Result:
  Plots for BEATX and BEATY are below;
ALS-BEATX_FINE_PHASE_OUT.pngALS-BEATY_FINE_PHASE_OUT.png


Discussion:
  - Considering delay line length is ~30m, expected calibration factor is;

    2*pi*l/v = 2*pi * 30 m / (2e8 m/s) = 0.94 rad/MHz = 54 deg/MHz

so, this calibration is reasonable.

  - Since frequency sweep of network analyzer is not continuous, phase tracker output is like steps with some ringdown. This makes some systematic error for checking linearity. I'm planning to do slower sweep or continuous sweep. Also, the phase tracker seems like he can exceed 500 MHz.

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