Keita, Evan

We installed a mixer-based 45 MHz RFAM monitor using two spare 45 MHz spigots on the distribution amplifier on the ISC rack. This provides an unobtrusive way to look for 45 MHz amplitude glitches on the ISC rack (i.e., it does not require inserting anything into the main 45 MHz drive that goes to the EOM driver and the EOM). On the other hand, if the glitches are only on the main 45 MHz drive, this monitor will not tell us anything.

Set-up is as follows:

• Spigot #7 is attenuated by 5 dB and goes to mixer LO. Spigot #8 is attenuated by 12 dB and goes to mixer RF. The spigots are nominally 13 dBm, so the mixer (ZAD-1, level 7) should get 8 dBm in its LO port and 1 dBm in its RF port.
• IF of mixer is sent through an 11 MHz minicircuits LPF, and then is terminated with 50 Ω. The dc component of this output is 175 mV.
• The output is then sent into an ac-coupled SR560 with a gain of 1000. This produces a signal whose voltage ASD is 18 µV/Hz^1/2 at 100 Hz, as measured with an SR785. If the SR560 is terminated at the input with 50 Ω, the voltage ASD is 5 µV/Hz^1/2 at 100 Hz.
• The output of the SR560 is sent into LSC-EXTRA_AI_1. This should add an additional 4 µV/Hz^1/2 of noise.

I have calibrated LSC-EXTRA_AI_1_OUT so that it is in volts. This channel is not dequeued, but if we have another hours-long episode of glitching we can watch the test points in real time.