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Entry  Tue Mar 2 19:52:46 2021, gautam, Update, LSC, REFL55 demod board rework 
    Reply  Wed Mar 3 22:13:05 2021, gautam, Update, LSC, REFL55 demod board rework 
       Reply  Thu Mar 4 23:16:08 2021, Koji, Update, LSC, REFL55 demod board rework D990511-00_REFL55.pdfP_20210304_215602.jpgP_20210304_222400.jpgP_20210304_222412.jpg20210304234400_IMG_0526.jpg
          Reply  Fri Mar 5 13:53:57 2021, gautam, Update, LSC, REFL55 demod board rework 
             Reply  Fri Mar 5 15:31:23 2021, Koji, Update, LSC, REFL55 demod board rework 
                Reply  Fri Mar 5 16:24:24 2021, gautam, Update, LSC, REFL55 demod board re-installed in 1Y2 REFL55.pdfdemodNoise.pdf
                   Reply  Fri Mar 5 22:25:13 2021, gautam, Update, LSC, PRMI 1f SB locking recovered PRMI1f_noArmssensMat.pdf
Message ID: 15871     Entry time: Fri Mar 5 16:24:24 2021     In reply to: 15869     Reply to this: 15873
Author: gautam 
Type: Update 
Category: LSC 
Subject: REFL55 demod board re-installed in 1Y2 

I don't have a good explanation why, but I too measured similar numbers to what Koji measured. The overall conversion gain for this board (including the +20dB gain from the daughter board) was measured to be ~5.3 V/V on the bench, and ~16000 cts/V in the CDS system (100Hz offset from the LO frequency). It would appear that the effective JMS-1-H conversion loss is <2dB. Seems fishy, but I can't find anything else obviously wrong with the circuit (e.g. a pre-amp for the RF signal that I missed, there is none).

I also attach the result of the measured noise at the outputs of the daughter board (i.e. what is digitized by the ADC), see Attachment #2. Apart from the usual forest of lines of unknown origin, there is still a significant excess above the voltage noise of the OP27, which is expected to be the dominant noise source in this configuration. Neverthelesss, considering that we have only 40dB of whitening gain, it is not expected that we see this noise directly in the digitized signal (above the ADC noise of ~1uV/rtHz). Note that the measured noise today, particularly for the Q channel,  is significantly lower than before the changes were made

Attachment 1: REFL55.pdf  194 kB  | Hide | Hide all
REFL55.pdf
Attachment 2: demodNoise.pdf  159 kB  | Hide | Hide all
demodNoise.pdf
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