Dave, Cao, Evan

We wanted to check briefly how the electronics noise of the PUM coil drivers compares to the excess noise in DARM.

With an SR785, we measured the voltage noise spectra out of the IX and IY coil driver chassises (going to the satellite boxes), and below 80 Hz we found them all to be below to the noise floor of the SR785 (40 nV/rtHz at 10 Hz, 10 nV/rtHz at 100 Hz). On the other hand, in order to explain a 1/f⁴ DARM noise of 1×10⁻¹⁹ m/rtHz at 30 Hz, this would require a white voltage noise at the coil output of 190 nV/rtHz for a single coil, or 50 nV/rtHz for 16 coils with uncorrelated noise.

If we want a good measurement (not just an upper limit) of this coil driver noise, we should use a FET-buffered preamp for reading out the signal.