The electronics has been studied with the cavity BPMs of #3 and #4 which are nearby ML10 and ML11, respectively. In this case, the combiner/converter was set near the BPMs and the detector was set outside of the extraction line, where the two electronics were connected with long cables . Since the signals were down-mixed to 700MHz before the long transmission, their attenuation was less than 10%. The calibration constant was estimated to be 300 counts/um. With null signals, RMS of noise was measured to be 5 counts. Therefore, the resolution is estimated to be 17nm.
Replacing the 1/25 attenuator with 1/4 one, the noise RMS became 19.6 counts, while the scaled RMS shall be 31.3 counts. So, the resolution must be 11nm without the large attenuation. Since the estimated resolution is worse than the requirement of less than 1nm, NF (noise figure) of first amplifier must reduce 1/10 of the present one.
Vacuum effect in the laser transmission has been measured in the four laser-BPM system with 2m length. Improvement of laser spot fluctuation was clearly observed.