We get the best rejection of 60 Hz (and harmonics) using the 3 kHz high-pass filter with 12 dB/octave rolloff in our Sanford Research SR560 pre-amp. The gain factor is set to 10,000. This frequency spectrum shows an example of the background noise and interference with our coil and this amp/filter setup.

The next spectrum compares background noise/interference at O'Brien, noise in our lab in the basement of the physics building, and noise on the roof of the physics building.

It is clear that there is an excess amount of interference in the basement of the physics building (where we are surrounded by other experiments, etc.). More importantly, we conclude that additional trips to O'Brien are probably not necessary; the roof of the building should suffice.

Anyone seen any lightning lately?