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Message ID: 5464     Entry time: Mon Sep 19 16:44:16 2011
Author: Keiko 
Type: HowTo 
Category: LSC 
Subject: Procedure for the demodulation board check 

 Here I note the procedure for the demodulation board orthogonality check for the future reference.

1. prepare two function generators and make sure I an Q demodulation signals go to the data acquisition system.

2. sync the two generators

3. drive the function generator at the modulation frequency and connect to the LO input on the demod board

4. drive the other function generator at the modulation frequency + 50Hz  the RF in

5. run "orthogonality.py"  from a control computer scripts/demphase directory. It returns the amplitude and phase information for I and Q signals. If necessary, compensate the amplitude and phase by the command that  "orthogonality.py" returns.


If you want to check in the frequency domain (optional):

1. 2. 3 are the same as above.

4. drive the function generator at the LO frequency + sweep the frequency, for example from 1Hz to 1kHz, 50ms sweep time. You can do it by the function generator carrier frequency sweep option.

5. While sweeping the LO frequency, run "orthogonality.py"

6. The resulting plot from "orthogonality.py" will show the transfer function from the RF to demodulated signal. The data is saved in "dataout.txt" in the same directory.

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