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Entry  Fri Apr 1 01:58:25 2011, tara, Notes, BEAT, beat and UPDH gain on ACAV loop 7x
    Reply  Mon Apr 4 19:48:51 2011, tara, Notes, BEAT, beat and UPDH gain on ACAV loop rcav_errnoise.png
    Reply  Tue Apr 5 22:32:08 2011, tara, Notes, BEAT, beat and UPDH gain on ACAV loop errnoise.pngnoise_prj_beat.png
Message ID: 564     Entry time: Mon Apr 4 19:48:51 2011     In reply to: 560
Author: tara 
Type: Notes 
Category: BEAT 
Subject: beat and UPDH gain on ACAV loop 

I check the noise projection from RCAV's error signal. It is still lower than the beat frequency. So the limiting noise source is not from RCAV loop.

From previous entry, I measured the slope of the error signal for RCAV loop. The value is 0.275 MHz/V. So I can calculate the frequency noise level from RCAV loop by measureing the noise at the error point, then multiplying the noise by the slope of the error signal.

rcav_errnoise.png

The noise level is about 2*10^-2 Hz/rtHz which is lower than the current beat noise (~0.1 Hz/rtHz).

Since the beat signal contains all noise from RCAV ACAV, and PLL loop, and I verified that the noise contributions from RCAV and ACAV loop are smaller than the measured noise. The limiting noise must come from the readout part.

So the next thing to look into is the noise in PLL loop.

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