[Takase, Ushiba]

This is the log of yesteday's work.

Abstract:
We measured DAC noise of ITMY TM actuators.
Measured DAC noise level is 4e-4 cnts/rtHz, which is corresponding to 1.24e-7 V/rtHzand seems too small.
We need to investigate what was wrong.

detail:
We measured DAC noise by using ADC and whitening filters, which has already been on IYV rack.
We disconnected the cable between DAC to coil driver and connected DAC output directly to whitening filter input.
Then, whitening filter output is connecte to ADC and measured the spectra with several whitening configurations.

Figure 1 shows the spectra after dewhitening of the raw spectra data.
Red, blue, and pink lines have a larger floor, which implies that whitening is not enough.
The others have a same floor level but somehow green line shows the better noise level at low frequencies.
So, probably it is better to use this configuration (FM1+FM2 ON: +36dB in all frequency band) for the DAC noise measurment.

Measured DAC noise floor is 4e-4 cnts/rtHz, which is corresponding to 0.124 uV/rtHz.
This value seems too small compared to the theoretical limit of DAC noise (~1uV/rtHz).
So, probably the measurement is wrong somewhere but I haven't confirmed yet.