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Entry  Fri Apr 15 12:17:39 2011, kiwamu, Update, LSC, 11MHz demod board : funny I-Q phase relativephase.png
    Reply  Fri Apr 15 15:15:08 2011, kiwamu, Update, LSC, 11MHz demod board : 90 degree splitter 
       Reply  Sat Apr 16 02:00:14 2011, rana, Update, LSC, 11MHz demod board : 90 degree splitter 
          Reply  Mon Apr 18 13:05:57 2011, kiwamu, Summary, LSC, demod board modification demod_board.png
             Reply  Mon Apr 18 14:11:44 2011, kiwamu, Update, LSC, RF status RF_Work_Status.png
             Reply  Thu Apr 21 21:24:41 2011, kiwamu, Update, LSC, demod board : new 90 deg splitter DSC_2949_ss.jpgDSC_2951.JPGDSC_2952_ss.jpg
                Reply  Thu Apr 21 21:46:22 2011, kiwamu, Update, LSC, demod board : new 90 deg splitter relativephase.png
                   Reply  Fri Apr 22 11:08:50 2011, kiwamu, Update, LSC, demod board AS11 : amplitude imbalance IQamplitude.png
Message ID: 4530     Entry time: Fri Apr 15 12:17:39 2011     Reply to this: 4533
Author: kiwamu 
Type: Update 
Category: LSC 
Subject: 11MHz demod board : funny I-Q phase 

During checking the 11MHz demod boards I found that the I-Q relative phase showed funny LO power dependence.

It is now under investigation.

relativephase.png

 In the plot above the green curve represents the I-Q phase of a 11MHz demod board (see here).

It showed a strong dependence on the LO power and it changes from -60 deg to -130 deg as the LO power changes.

This is not a good situation because any power modulation on the LO will cause a phase jitter.

For a comparison I also took I-Q relative phase of a 33MHz demod board, which hasn't been modified recently.

 It shows a nice flat curve up to 5 dBm although it looks like my rough measurement adds a systematic error of about -5 deg.

 

 - to do -

* check RF power in every point of LO path on the circuit

* check if there is saturation by looking at wave forms.

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