I wanted to get a rough number for the JAC error signal in Hz, this it to allow Jeff and I to measure the frequency noise of the JAC as an independent monitor of the IMC frequency noise which will allow us to compare the IMC length noise to the SPI length noise.

I think Masayuki calculated this back in March LHO alog #89399  but I wanted to recheck it as the Guardian settings have been changed since then.

I measured the unlocked error signal Vpp at H1:JAC-L_SERVO_IN1_DQ to be 1.01365V.

The value in metres is the half-width at half-maximum of the cavity.

First calculate the HWHM in Hz:

HWHM = FSR/2*Finesse  = 0.595 MHz.

The finesse was measured by Masdayuki and I at Caltech for our JAC which is unit 008 (see E2500324).

The FSR of the JAC I got from T0900616 to be 148.5MHz (couldn't find the exact FSR for this specific unit mentioned anywhere so used the one quoted in the PMC design document).

This means to measure the frequency noise we need to multiply the signal at 

H1:JAC-L_SERVO_IN1_DQ by 0.587 e6Hz/V to measure frequency noise.