Ross, Tega 

We have been using the new h1omcpi and h1susetmxpi models to look at mechanical modes  in OMC DCPD which should be related to parmatetric instabilities. Only the OMC DCPDA is used as subtracting the A and B signals seemed to remove the lines from our spectrum i.e. they must be completely in phase with each other. This signal is being used instead of the QPD transmission signal as it has a much higher SNR for these modes.

Starting in the 64kHz h1omcpi model, the signal (H1:OMC-PI_DOWNCONV_DEMOD_SIG_IN1) is first down converted to DC using a local oscillator set at the frequency of the particular mechanical mode. The I and Q phase signals are then passed via PCIE to the 16kHz h1omc model where they are low passed with a 64Hz corner frequency, multiplexed and sent across to the 16kHz h1pemex model using RFM. The signals are then demuxed and sent to the 64kHz h1susetmxpi model. At this point these signals are low passed again to avoid imaging  and then upconverted back to the frequency of the mode. The I and Q phase signals are then summed which effectively leaves the original signal with a bandpass due to the lowpassed signal being upconverted (H1:SUS-ETMX_PI_OMC_UC1). We are then able to use our linetracking tool iwave to track the particular line you are interested in (H1:SUS-ETMX_PI_MODE_OUT). 

This was process was used to track a selection of lines around 15000 Hz which should be related to some of the mechanical modes. The hope is that we can now use the iwave tracked signals to damp these modes using ESD assuming we know what lines relate to each test mass.