40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  PSL  Not logged in ELOG logo
Entry  Fri Nov 1 17:54:47 2019, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD RF Ouput under inspection NFSS_RFPD_Output_Oscilloscope.pdfSFSS_RFPD_Output_Oscilloscope.pdfNFSS_RFPD_RF_OUT_COUPLED.pdfSFSS_RFPD_RF_OUT_COUPLED.pdf
    Reply  Tue Nov 5 18:37:59 2019, anchal, DailyProgress, FSS, FSS Diagnostics - TTFSS Testpoint Spectrum Data FSS_TP_Spectrum.pdf
       Reply  Sat Nov 9 19:28:36 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Loop nonlinearity Test NFSS_NonLinearity_Test.pngSFSS_NonLinearity_Test.pngsignal-attachment-2019-11-09-195635.jpeg
          Reply  Mon Nov 11 20:42:49 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Two Tone Test NFSS_RFPD_SN009_TF_11-11-2019_183131.pdfSFSS_RFPD_SN010_TF_11-11-2019_203310.pdfFSStwoToneTest.pdf
             Reply  Tue Nov 12 18:36:59 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Two Tone Third Order Intermodulation Test FSStwoToneThirdOrderIM.pdf
                Reply  Thu Nov 14 12:19:32 2019, rana, DailyProgress, FSS, FSS Diagnostics - Two Tone Third Order Intermodulation Test 
                   Reply  Tue Nov 19 18:51:02 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Second-order Distortion Calculation FSSDistortionCalc.pdfFSSDistortion.zip
                      Reply  Mon Dec 9 19:54:44 2019, anchal, DailyProgress, FSS, FSS Diagnostics - How much distortion affects the functioning of PDH? 
       Reply  Wed Nov 27 13:59:24 2019, anchal, DailyProgress, FSS, FSS Diagnostics - TTFSS TP1 TimeSeries NFSS_TP1_Oscilloscope.pdf
          Reply  Wed Nov 27 15:17:51 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Quick HF OLTF of NFSS NFSS_OLTF_HF.pdf
             Reply  Wed Nov 27 16:31:20 2019, rana, DailyProgress, FSS, FSS Diagnostics - Quick HF OLTF of NFSS 
                Reply  Wed Dec 4 18:11:09 2019, anchal, DailyProgress, FSS, Free running laser frequency noise spectrum PMCErrorSignals.pdf
                   Reply  Thu Dec 5 18:25:11 2019, rana, DailyProgress, FSS, Free running laser frequency noise spectrum 
                   Reply  Tue Dec 17 18:29:58 2019, anchal, DailyProgress, FSS, Need for ISS? 
                      Reply  Wed Dec 18 18:40:32 2019, anchal, DailyProgress, FSS, Maybe the NPRO Laser isn't bad after all NorthLaserRINAnalysis.pdf
                         Reply  Wed Dec 18 22:03:17 2019, rana, DailyProgress, FSS, Maybe the NPRO Laser isn't bad after all 
                            Reply  Fri Dec 20 15:00:30 2019, anchal, DailyProgress, FSS, PZT, EOM to RIN TF Measurement NorthLaserPZTEOMtoRINTF.pdf
                               Reply  Fri Dec 20 18:08:44 2019, anchal, DailyProgress, FSS, PZT, EOM to RIN TF Measurement Through FSS NorthLaserPZTEOMtoRINTFThruFSS.pdf
                                  Reply  Tue Jan 7 17:59:20 2020, anchal, DailyProgress, FSS, NPMC TF NPMC_TF.pdf
       Reply  Thu Dec 12 19:15:55 2019, anchal, DailyProgress, FSS, FSS Diagnostics - Beatnote Spectrum wrt Laser Power and Modulation Index BeatnoteSpectrumwrtPowerandModindex.pdf
       Reply  Tue Dec 17 16:55:07 2019, anchal, DailyProgress, FSS, FSS Diagnostics - TTFSS North U7 Boost Stage Input-Output TimeSeries NFSS_UT_TS_Analysis.pdf
    Reply  Tue Nov 12 11:39:48 2019, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD RF Ouput under inspection 
    Reply  Fri Dec 13 16:24:02 2019, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD Circuit Latest Available Photos SN009.jpgSN010.jpgSN009.jpgSN010.jpg
    Reply  Fri Dec 13 17:44:05 2019, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD RF Coupled Output Offset 
       Reply  Mon Jan 13 19:04:38 2020, anchal, DailyProgress, FSS, FSS Diagnostics - SN009 (North RFPD) Notch Improvement Attempt SN009.jpgSN009_D980454-00-C.pdfSN009_Notch_Improvement_Attempt.pdf
          Reply  Tue Jan 14 18:19:33 2020, anchal, DailyProgress, FSS, FSS Diagnostics - SN009 (North RFPD) Notch Improved! SN009.jpgSN009_D980454-00-C.pdfSN009_Notch_Improvement_Attempt.pdf
             Reply  Thu Jan 16 11:17:15 2020, anchal, DailyProgress, FSS, FSS Diagnostics - SN010 (South RFPD) Notch Improvement Attempt SN010.jpgSN010_D980454-00-C.pdfSN010_Notch_Improvement_Attempt.pdf
                Reply  Thu Jan 16 20:18:44 2020, anchal, DailyProgress, FSS, FSS Diagnostics - SN010 (South RFPD) Notch Improved SN010.jpgSN010_D980454-00-C.pdfSN010_Notch_Improved.pdf
                   Reply  Mon Jan 27 18:29:19 2020, anchal, DailyProgress, FSS, FSS Diagnostics - RFPD RF Out Spectrum FSS_RFPD_RFOut_Spectrum.pdf
Message ID: 2481     Entry time: Tue Nov 19 18:51:02 2019     In reply to: 2480     Reply to this: 2490
Author: anchal 
Type: DailyProgress 
Category: FSS 
Subject: FSS Diagnostics - Second-order Distortion Calculation 

I did some theoretical calculations using the datasheet value of second harmonic SFDR from MAX4107 and the transfer function I measured from Test IN ports of RFPDs (using 100 kOhm series resistance).

Calculation:

  • Attached notebook has all the calculations. In all places, "Omega" refers to the modulation frequency.
  • I first calculated power at 0, 1-Omega and 2-Omega from the resonance frequency in the light incident on the cavity using Bessel functions.
  • I used reflection function from the cavity (using transmittance of 5 ppm, cavity length of 1.45" and assuming lossless cavity):
    \LARGE R = \frac{- r(1 - e^{\iota \omega/\nu})}{1 - r^2 e^{\iota \omega /\nu}}
  • Using this, I calculated reflected power at  0, 1-Omega and 2-Omega from the resonance frequency.
  • Then I used -40 dBc SFDR for second harmonic generation mentioned in MAX4107 datasheet when used with a gain of 10. I used following formula to calculate this:
    \LARGE P_{1\Omega Dist} = \frac{(V_{1\Omega}V_{2\Omega})}{100}10^{-\frac{SFDR}{10}}
  • Finally, I also calculated ratio of 1-Omega signal (actual beat between Sideband and Carrier) and the 1-Omega Distortion signal (generated) due to the non-linearity of MAX4107.

Inferences:

  • These are purely theoretical calculations but I can put in the second harmonic SFDR by measurement tomorrow.
  • The suppression of 2nd harmonics by the notch in the RFPD circuits is very bad. It only suppresses the second harmonic by 25-30 dB.
  • This is not enough as this 2-Omega signal would mix a lot with 1-Omega and would also go forward into the TTFSS box after downconversion.
  • The ratio of Signal at 1-Omega to the distortion at 1-Omega is about just 8 at 100 Hz. This doesn't reach 100 even till 1 kHz.
  • And below 10 Hz, the distortion dominates the 1-Omega signal from RF out.
  • This looks like a big limitation to our FSS loop. The notch filters in the RFPDs need to be doing much better job then they are doing.

Edited Wed Nov 20 14:43:07 2019: Corrected an error in code.

Attachment 1: FSSDistortionCalc.pdf  30 kB  Uploaded Wed Nov 20 14:36:29 2019  | Hide | Hide all
FSSDistortionCalc.pdf FSSDistortionCalc.pdf FSSDistortionCalc.pdf FSSDistortionCalc.pdf FSSDistortionCalc.pdf FSSDistortionCalc.pdf
Attachment 2: FSSDistortion.zip  51 kB  Uploaded Wed Nov 20 14:42:54 2019
ELOG V3.1.3-