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Entry  Tue Apr 26 17:06:37 2011, Mingyuan, Tara, DailyProgress, Creak, start crackling 
    Reply  Thu Apr 28 21:55:25 2011, tara, DailyProgress, Creak, start crackling chopping.pdf
       Reply  Fri Apr 29 18:39:37 2011, tara, DailyProgress, Creak, start crackling 
          Reply  Wed May 11 22:17:35 2011, tara, DailyProgress, Creak, start crackling 1khz.pngf_t_response.png
       Reply  Fri Apr 29 21:23:15 2011, tara, DailyProgress, Creak, start crackling ad734_crackle.pdf
          Reply  Thu May 12 23:18:27 2011, ryan, tara, DailyProgress, Creak, start crackling ad734.png
Message ID: 199     Entry time: Wed May 11 22:17:35 2011     In reply to: 191
Author: tara 
Type: DailyProgress 
Category: Creak 
Subject: start crackling 

 I tested the mixer, the demodulated signal from input at 10 - 100 Hz might be too small and too distorted to get reliable data.

 

  As we want to square/demodulate  signal in 10 - 100 Hz BW. a low frequency mixer might be a good tool. I asked Alastair to buy this mixer for me, and it arrived today.

  The lowest acceptable frequency in the design is 500 Hz, but I don't know how well it works at 10 - 100 Hz so I tested it.

   

   ==Setup and result==

   I used  SR785 to generate sine wave, then split it with a T and connected the output to LO and RF of the mixer. 

   I tested that the mixer works fine at the designed frequency.  The plot below shows the result from  1kHz signal input.

1khz.png

Next, I changed the frequency to 10 Hz, 50Hz, and 100Hz.

  The demodulated signal is then observed in frequency domain (left column of the plot) and in time domain ( right column of the plot)

I think the peaks at driving frequencies (10Hz, 50Hz, 100Hz and their harmonics) appear because of the offset of the sine input signal.

f_t_response.png

 

The results for low frequency  seem to be too distorted. We will test the AD734 chips tomorrow. I got the package this afternoon.

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