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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: 4560     Entry time: Fri Apr 22 11:08:50 2011     In reply to: 4555
Author: kiwamu 
Type: Update 
Category: LSC 
Subject: demod board AS11 : amplitude imbalance 

Amplitude imbalance between I and Q in a demod board, AS11, with the new 90 deg splitter was measured.

It shows roughly 10% amplitude imbalance when the LO power is in a range from 0 to 5 dBm. Not so bad.

 

  With the handmade coil there used to be a huge imbalance (either I or Q goes to zero volt while the other keeps about 1 V rms) as the LO power decreases.

But with the new 90 deg splitter now there are no more such a huge imbalance.

The remaining 10 % imbalance possibly comes from the fact that we are using ERA-5 in each I and Q path. They may have such gain imbalance of 10%.

We should check the ERA-5 gains so that we can confidently say ERA-5 causes the amplitude imbalance.

Then our plan replacing the ERA-5s (see here) will sound more reasonable.

IQamplitude.png

 

Quote from #4555

The new 90 deg splitter works better.

 I will also measure amplitude unbalances between I and Q.

 

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