We succeeded in locking the X arm with the C1LSC digital control.
As we did on the day before yesterday, the feedback signal goes to MCL (#4141), but this time the signal is transfered from C1LSC through the RFM.
- checking the state of the analog whitening filters at C1LSC rack.
We took the transfer function of them and found that they were always on regardless of the clicking any buttons on medm.
To cancel the filter shape of the whitening, we put an unWhitening filter so that these transfer functions becomes flat in total.
The whitening filter approximately has : pole:150Hz, pole:150Hz, zero:15Hz, zero:15Hz (although these numbers came from by our eye ball fitting)
- demodulation phase adjustment
We performed the same measurement as that of Suresh and Koji did yesterday (#4143) to adjust the phase of the PDH demodulation.
By changing the cable length we roughly adjusted the I-phase to eventually ~10 deg, which is close enough to 0 deg.
(probably some more efforts should be made as a part of daytime tasks)
Note that we are currently using the REFL33 demodulation board for this purpose (#4144). The LO power we put is about 16dBm.
The angle between I and Q at 11MHz is actually almost 90 deg.
This fact has been confirmed by putting a sinusoidal signal with a slightly different frequency (~100Hz) from that of the LO onto the RF input.
- attenuation of RF signal
Since the PDH signal taken by C1LSC's ADC had been saturated somewhat, we introduced a ND filter of 10 on the photo diode to attenuate the RF signal.
As a result the amplitude of the PDH signal on dataviewer became more reasonable. No more saturations.
unWhitening filter pole:15Hz. pole:15Hz, zero:150Hz, zero:150Hz
C1LSC_MC_FM1 pole:1kHz, zero:10Hz
Gain in digital control G ~ -1
measured UGF ~ 200-300 Hz
measured RFM delay ~ 125 usec