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Entry  Wed Apr 22 11:48:30 2015, manasa, Summary, General, Delay line frequency discriminator for FOL error signal 
    Reply  Wed Apr 22 14:56:18 2015, manasa, Summary, General, Delay line frequency discriminator for FOL error signal 
       Reply  Mon May 4 10:21:09 2015, manasa, Summary, General, Delay line frequency discriminator for FOL error signal DFD.pngDFD_resp.png
       Reply  Mon May 4 12:42:34 2015, manasa, Summary, General, Delay line frequency discriminator for FOL error signal DFD_cosfit.png
          Reply  Mon May 18 14:46:20 2015, manasa, Summary, General, Delay line frequency discriminator for FOL error signal DFDnoise.pngDFDnoise_AC.pngFreqResp.pngDFD.zip
Message ID: 11235     Entry time: Wed Apr 22 11:48:30 2015     Reply to this: 11236
Author: manasa 
Type: Summary 
Category: General 
Subject: Delay line frequency discriminator for FOL error signal 

Since the Frequency counters have not been a reliable error signal for FOL PID loop, we will put together an analog delay line frequency dicriminator as an alternative method to obtain the beat frequency.

The configuration will be similar to what was done in elog 4254 in the first place.

For a delay line frequency dicriminator, the output at the mixer is proportional to cos(\theta_{b}) where \theta_{b} = 2 \pi f_{b}L/v

L - cable length asymmetry, fb - beat frequency and v - velocity of light in the cable.

The linear output signal canbe obtained for  0< \theta_{b}<\pi

For our purpose in FOL, if we would like to measure beat frequency over a bandwidth of 200MHz, this would correspond to a cable length difference of 0.5 m (assuming the speed of light in the coaxial cable is ~ 2x108m/s.

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