[Miyakawa, Ushiba, Komori]

We measured the electrical noise around several CMSs using a loop antenna to check the effect of the RF local oscillator.
The critical oscillator is the one producing 5.6 MHz to generate sidebands used in the main IFO control.
Turning on and off the other oscillators do not have clear impact.

Figures 1 and 2 show the spectra around the CARM CMS with and without the 5.6 MHz oscillator, respectively.
Figures 3 and 4 represent those around the green PDH CMS with and without the oscillator.
Turning off the oscillator removed the most prominent peak at 50 MHz, corresponding to 3*f1, as well as several other peaks.
While we cannot turn off the oscillator during IFO operation, we successfully identified the origin of these peaks.

There are many other peaks in the spectra, but they are still present (Fig. 5) even when measured far from the CMS cables, such as on the desk in front of the rack (Fig. 6).
Therefore, these peaks might originate not from a specific CMS but from the entire electrical system.