[Shimode, Enomoto]

This log entry is to summarize a couple of works on RFPDs and RFQPDs done in the last one month.
In summary, all the RFPDs and RFQPDs are ready.

= Modification of RFPDs for 2f/3f use =
I did some soldering and some modification on existing RFPD boards (see also 7947).
- 2f PD: HI out has resonance at 90 MHz, and LO out has resonance at 34 MHz. Both have notches at 17, 28, 45, 62 MHz.
- 3f PD: HI out has resonance at 135 MHz, and LO out has resonance at 51 MHz. Both have notches at 17, 28, 34, 45, 62, 90 MHz.

For 3f mod, I modified non-inverting amplifier part for HI out in addition to modifications on notches.
This was because Shimode-san pointed out that 3f PD was about to oscillate as is; if the resonance of HI out is slightly off-tuned to 140 MHz, oscillations can be seen.
It turned out that this oscillation was due to the limited negative feedback range of the op-amp (LMH6624). The range is 100 MHz when it is used with the gain of 10.
In fact, LTspice simulation showed similar oscillation-like behavior if small capacitive load is intentionally added to the output of the op-amp.
According to the LTspice simulation, to decrease the gain by a factor of ~< 2 and add 1.5 pF capacitance parallel to the feedback resistance will be a good solution, so I changed the feedback resistance from 453 Ohm to 240 Ohm, and added 1 pF parallel to it (See also JGW-S1504187).
This modification relieved the oscillating behavior.

= Tune and meaasurement of RFPDs and RFQPDs =
MIF group asked AEL group to do tuning and measurement of RFPDs and RFQPDs, and Shimode-san has perfomed them.
Up to now, he has tuned and measured 7 normal RFPDs, 7 RFQPDs, 3 RFPDs for 2f, and 2 RFPDs for 3f, which means we have the required numbers plus one spare for each. 
Here I attach some example results of transimpedance measurements.
I am going to upload the results of each RFPD or RFQPD to S-number page of the board in JGWdoc.

= Installation =
[Izumi, Michimura, Nakano, Sugimoto, Enomoto and maybe more]
I have installed all the RFPDs and RFQPDs that are planned to be used in bKAGRA (except for RFAM monitor at IMMT2 trans).
Currently we have 1f PD and 3f PD on REFL table, 1f PD and 2f PD on POP table, and 1f PD and 2f PD on AS table.
We also have 2 QPDs on each table.
Cabling for all the PDs and QPDs have been done.
For those on REFL table and POP table, I have checked that DC outputs are working.
For those on AS table, cabling has been done but not yet powered since no power is available in OMC1 rack, where RFPD/RFQPD interfaces are installed.