[Annalisa, Koji, Manasa]
In order to improve the ALS stability we went ahead to check if we are limited by the sensor noise of ALS.
What we did:
RF signals similar to the beatnote were given at the RF inputs of the beatbox.
The frequency of the RF signal was set such that I_OUT was zero (zero-crossing point of the beatbox).
We measured the noise spectrum of the phase tracker output.
Plot 1: X ALS noise spectrum
Plot 2: Y ALS noise spectrum
The X arm ALS noise is not limited by the sensor noise...which means we shoudl come up with clever ideas to hunt for other noise sources.
But this does not seem to be the case for the Y arm ALS. The Y arm part of the beatbox is noisy for frequencies < 100Hz.
After looking into the details and comparing the X and Y arm parts of beatbox, it looks that amplitude of the beat signal seem to affect the Y arm ALS noise significantly and changes the noise spectrum.
Investigate the effect/limitations of amplitude of the beatnote on the X arm and Y arm beatbox.