Hannah, EvanStefan

Since we redid the AS_A_RF36 re-phasing (alog 19572), we never re-did a src coupling test while moving the SRC1_YAW offset (see alog 18436), so this was on the menu today - before redoing the SRCL decoupling.

- First we lowered the AS_A_RF36 whitening gain from 21dB to 18dB because some quadrants had too much signal.
- Again we found that for the matrix (see alog 19572)
    H1:ASC-AS_A_RF36_I_MTRX_2_1    0
    H1:ASC-AS_A_RF36_I_MTRX_2_2    0
    H1:ASC-AS_A_RF36_I_MTRX_2_3    -2
    H1:ASC-AS_A_RF36_I_MTRX_2_4    2
  an offset of -2500 counts in H1:ASC-SRC1_Y_OFFSET gives the lower POP90, higher AS90, and lower high frequency SRCL coupling. (see plot)
- Since I don't like running with offsets in WFS loops, I tried the following sensing matrix, which puts us to the same position:
    H1:ASC-AS_A_RF36_I_MTRX_2_1    0
    H1:ASC-AS_A_RF36_I_MTRX_2_2   -1
    H1:ASC-AS_A_RF36_I_MTRX_2_3    0
    H1:ASC-AS_A_RF36_I_MTRX_2_4    3
  This admittedly looks odd - it should also have a pitch content - but in alog 19572 we saw that the pitch signal is in a different phase anyway... whatever...
 - With that new lock point we observed:
  - The same SRCL coupling at low frequencies - this one seems steady
  - A lower average SRCL coupling at high frequencies - as a result the notch moved up in frequency from ~75Hz to ~110Hz
  - The high frequency part is also the more variable part - before and after the offset shift. Thus - even though the coupling now seems worse around the old notch frequency - that disadvantage should easily be compensated by the SRCLFF path.

 - We also updated the FM8 cut-off filter in SRCL - it is now a less aggressive low pass filter starting at 80Hz. This still kills the variable part of the coupling, but also reduces gain peaking in the SRCL loop - which before made the coupling worse.