[Tomura, Kamiizumi, Aoumi, Komori]

We succeded in stopping the oscillation around 27 MHz by wrapping ferrite cores around the BNC cables connected to the CMS of GrPDH, PLL, the summing node, and CARM.

According to the AEL team, they stopped the oscillation reported in klog:29568 by wrapping ferrite cores (ZCAT2032-0930, ZCAT1518-0730, DC-2810N) around the BNC cables in their lab.
Therefore, we applied this method to the actual CMS of GrPDH, PLL, summing node, and CARM.

These ferrite cores effectively stopped the oscillation around 27 MHz.
The attached six figures show the spectra measured by a loop antenna before and after wrapping the ferrite cores around the cables for GrPDH, PLL, and between the summing node and CARM, respectively.
All 27 MHz peaks and several other peaks present before this work disappeared.

However, there are still standing peaks at 17 MHz, 50 MHz, and 90 MHz.
These might originate from harmonics of the sidebands: f1, 3*f1, and 2*f2.
We will identify the origin by measuring the spectra with the local oscillator turned off tomorrow.