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  Tue Aug 15 14:49:27 2017, Craig, awade, DailyProgress, PD, 35.5 MHz RFPDs Transfer Functions Aug-15-2017_143644_35p5MHz_RFPD_TFs.pdfRFPDTF_Setup.jpgRFPDTFs.tar.gz
    Reply  Wed Aug 16 12:51:21 2017, rana, DailyProgress, PD, 35.5 MHz RFPDs Transfer Functions 
       Reply  Wed Aug 16 13:50:26 2017, awade, DailyProgress, PD, 35.5 MHz RFPDs Transfer Functions 
          Reply  Thu Aug 17 00:01:00 2017, rana, DailyProgress, PD, 35.5 MHz RFPDs Transfer Functions 
Message ID: 1860     Entry time: Tue Aug 15 14:49:27 2017     Reply to this: 1861
Author: Craig, awade 
Type: DailyProgress 
Category: PD 
Subject: 35.5 MHz RFPDs Transfer Functions 

I took the transfer function through our two 35.5 MHz RFPDs.

RFPD B, labeled "Low Q" on top, has lived up to it's name.  It is the orange curve below.  We opened up the two PDs to see if there were obvious differences, and there were.  We also discovered these differences were documented.

On the PSL wiki, there is an altered schematic of the 35.5 MHz RFPDHere is the original schematic on the DCC.  In order to produce a PD with a lower Q, it seems that some inductors were shorted or replaced by tunable coilcraft inductors.  A resistor and capacitor to ground were also removed.

Now we wonder if we should lower the Q of RFPD A or increase the Q of RFPD B.  Andrew says that the higher the Q, the lower the bandwidth of our controller.  I can barely understand him sometimes, but he's always right about these things.  We've decided to seek out Koji the PD master and ask his opinion.  Remember that the purpose of these PDs is to read out sidebands for PDH locking to the PMCs.

I also attached a tar containing the data, python script which makes this plot, and the plot itself.  It is located in the git repo CTN_noisebudget/RFPDTFs.

Attachment 1: Aug-15-2017_143644_35p5MHz_RFPD_TFs.pdf  122 kB  | Hide | Hide all
Attachment 2: RFPDTF_Setup.jpg  2.103 MB  | Hide | Hide all
Attachment 3: RFPDTFs.tar.gz  385 kB  Uploaded Thu Aug 17 11:52:55 2017
ELOG V3.1.3-