Jennie W, Sina K, Jim W,

Yesterday we continued the checking we have been doing of the digital signal chain in CDS. We found that a lot of channels appear to be zero due to the decimation filters used on OUT16 channels and also that these were set to round the displayed channel to 1 significant figure. We corrected most of these on the main screen but I still have to go through the subsidiary screens and cross-check that we got all of these. Here are the new digital LO readout channels we introduced the other day (alog #91504) and here are the changes we made to monitored channel yesterday.

In the process we checked the calculation of the magnitude and phase of the reference and measurement interferometers (this is displayed in the 'monitor' block on the main SPI overview screen). The phase seems ok and indeed the 'phase unwrap' button that can be pressed to reset the phase of the IFO to zero after it accumulates more that 2pi of phase, seems to work well. We checked all the filtering done on the demodulated signals and those seem ok too.

Once we had checked all the signal routing we got signals out for the efficiency calculation. These seemed very low (~25%). After checking the raw PD into CDS against the calculated mean and peak to peak ampltiude of the beat signals which are used to calculate the efficiency, we realised that the efficiency should be above 80% but there is something wrong with the calculation of the peak to peak amplitude. To fix this we will try removing the phase rotator block in the interferometer simulink model as we think these blocks are unnecessary and might be doing something unexpected.

We also double checked the signal processing of the QPD channels and confirmed that these still need calibrated into radians of ISI motion. Per Jim's suggestion we will use the ISI sensors to calibrate these.

Summary: Most parts of SPI medm and model checked - still need to debug demodulation of signals for heterodyne interferometer.