40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Entry  Sat Sep 10 14:55:28 2011, Keiko, Update, LSC, 3f demodulation board check 
    Reply  Sat Sep 10 16:10:42 2011, Keiko, Update, LSC, 3f demodulation board check REFL33-input-filter.png
       Reply  Sat Sep 10 18:57:52 2011, Keiko, Update, LSC, 3f demodulation board check 
          Reply  Sun Sep 11 15:19:39 2011, kiwamu, Update, LSC, phase delay in RF signals 
       Reply  Sun Sep 11 22:36:32 2011, Keiko, Update, LSC, 3f demodulation board check REFL33.pngREFL165.png
          Reply  Mon Sep 12 13:24:07 2011, Keiko, Update, LSC, 3f demodulation board check 
             Reply  Mon Sep 12 16:27:01 2011, Keiko, Update, LSC, 3f demodulation board check 
                Reply  Mon Sep 12 18:40:35 2011, Keiko, Update, LSC, 3f demodulation board check 
                   Reply  Tue Sep 13 15:00:25 2011, Keiko, Update, LSC, 3f demodulation board check WF33.pdfWF165.pdf
                      Reply  Tue Sep 13 23:08:51 2011, Keiko, Update, LSC, 3f demodulation board check REFL33-modified.pngREFL165-modified.png
                         Reply  Thu Sep 15 01:06:20 2011, Keiko, Update, LSC, 3f demodulation board check 
                            Reply  Fri Sep 16 21:26:12 2011, Keiko, Update, LSC, 3f demodulation board check 
Message ID: 5380     Entry time: Sat Sep 10 18:57:52 2011     In reply to: 5378     Reply to this: 5384
Author: Keiko 
Type: Update 
Category: LSC 
Subject: 3f demodulation board check 

The phase delay due to the RF input filter on the demodulation board will not bother the resulting PDH signals.

I quickly calculated the below question (see the blue sentence in the quote below). I applied an arbitrary phase delay (theta) due to the filter I measured, on the detected RF signal by the photo detector. Then the filtered RF signal is multiplied by cos(omega_m) then filter the higher (2 omega_m) freqency as the usual mixing operation for the PDH signal. As a result, the I signal is delayed by cos(theta) and the Q signal is delayed by sin(theta). Therefore the resulting signals and its orthogonalitity is kept ok. From the sideband point of view, theta is applied on both upper and lower and seems to make the unbalance, however, as it is like a fixed phase offset on both SBs at the modulation frequency, the resulting signals is just multiplied by cos or sin theta for I and Q, respectively. It won't make any strange effect (it is difficult to explain by sentence not using equations!).

Quote:

There is a LP filter just after the RF input of an demodulation board (its schematic can be found as D990511-00-C on DCC). I have checked if the 3f freq, 33MHz, can pass  this filter. The filter TF from the RF input to RF monitor (the filter is between the input and monitor) on REFL33 demo-board was measured as shown in Fig. 1. At 33MHz, the magnitude is still flat and OK, but the phase is quite steep. I am going to consider if it is ok for the PDH method or not.

 Fig. 1 Transfer function from the RF input to RF monitor on the REFL33 demodulation board. At 33MHz, a very steep phase is applied on the input signal.

Quote:

 To check the demodulation boards for REFL33 and REFL165, a long cable from ETMY (SUS-ETMY-SDCOIL-EXT monitor) is pulled to the rack on Y side.

(1) A filter just after the RF input and (2) transfer function from the RF input to the demodulated signal will be checked for the two 3f demod boards to confirm that they are appropriate for 33 and 165 MHz.

 

 

ELOG V3.1.3-