To check how much second harmonic of 7MHz CC/LO beat note affects 14MHz CCSB beat note, I put TAMA RFPD before AMC and detected LO and CC at the same time. CC is directly injected from OPO and CC1 is locked. I compared 14MHz peak height with only CC or CC+LO. Pic. 1,2 shows 14MHz signal with only CC or CC+LO. Apparently 14MHz peak height is almost same.

Then I demodulated the 14MHz signal with 14MHz and measured spectrum of the demodulated signal (Pic. 3). Spectrum with CC+LO has some excess noise compared with only CC and the noise shape seems similar to CC2 phase noise. This noise should come from second harmonic of 7MHz.