[Sudarshan, Sheila]

We turned off the A2L filters on ETMX last week to see how much of the ADS line shows up in DARM, compared to when the filters are on. At the ADS line frequency, we saw about factor of 30 suppression with the A2L filter engaged (Attached Fig 1). Today we tried similar measurement with ITMY  and measured the suppression by a factor of 165 at the line frequency (Attcahed Fig 2).  The fact that ADS lines with similar amplitude gets suppressed to the noise level  at ITMY and not at ETMX seems to suggest there might be some frequency dependent A2L coupling associated with ETMX (A2L digital filter is currently a scalar). We have additional measurements on the can (and some planned) for further investigations.