We performed some noise hunting at the PSL racks today, primariliy looking at the 9MHz and 45MHz RF Amplifier outputs.  Dick assembled a passive RF rectifier which we used to measure the power fluctuations at a low enough frequency to see on the scope.  We applied that signal to a LPF and then amplified it through an SR560 with 100x gain.  An adjustable attenuator was placed before the amplifier to incrementally attenuate the signal.

After some issues with grounding, his diode was conducting too much due to a 74mV DC difference between instrument ground and rack ground, we were able to acquire some data.  Attached is a plot of attenuator value applied vs mVrms noise measured.  We gather that the noise floor is around 2mVrms.  The 45MHz signal sits right on the noise floor, no amount of applied attenuation would push this signal down any lower.  The 9MHz was different, and as we applied attenuation, the mVrms noise decreased.  It was very subtle, but worth mentioning.

D. Gustafson, M. Pirello