So far not much has been done to do tilt decoupling on the the HAM ISI's, because we weren't sure it was necessary. I took some measurements yesterday to check, and I think that's still right. If you just look at my first attached plot, it seems reasonable to think that maybe we should. The GS13-Y/ISO-Y transfer function shows what looks like a  ~1/f^2 low frequency component then the normal f^3 component above 10mhz. But looking at Hugh's measurments on the BSC's the tilt component for the ETMX T240-X/ISO-X looks different (second attached plot). I also looked at Fabrice's calculations in alog 8284 and his data there looks like Hugh's BSC data, not my HAM data. Made me think I'm looking at something else. My third plot shows calbrated spectra, and I think I just looking at sensor noise at 10mhz. My calibration could be a bit  off, but the specrta going flat at 10mhz on the red trace is suspicious. I don't know what the bubble below is, maybe actual tilt? If it is, that doesn't look like an easy measurement to make, or worth doing.