This morning I adjusted the I-Q balancing of all the demodulators at the AS port (i.e. the ones in ISC R3 rack).
I did the same technique as described here. I did not turn on any of the whitening stages. The gain of the whitening filters were set 21 dB (although I am not sure if this is close enough for the future operational condition.) except for ASAIR_B_RF18 which I set the gain to be 45 dB. The beatnote were ajusted such that they are in between 40-50 Hz. Since the amplitude imbalance were typically smaller than 0.5 % or so, I did not try to correct the amplitude imbalance. Therefore only parameters I adjusted were the phase difference btween the I and Q signals. Here are the results:
= = =
H1:LSC-ASAIR_A_RF45_PHASE_D 93.4
H1:LSC-ASAIR_B_RF18_PHASE_D 89.82
H1:LSC-ASAIR_B_RF18_PHASE_D 89.82
H1:LSC-ASAIR_B_RF18_PHASE_D 89.82
H1:LSC-ASAIR_B_RF90_PHASE_D 88.164
H1:ASC-AS_A_RF36_SEG1_PHASE_D 92.14
H1:ASC-AS_A_RF36_SEG2_PHASE_D 92.87
H1:ASC-AS_A_RF36_SEG3_PHASE_D 91.9086
H1:ASC-AS_A_RF36_SEG4_PHASE_D 92.7
H1:ASC-AS_B_RF36_SEG1_PHASE_D 92.131
H1:ASC-AS_B_RF36_SEG2_PHASE_D 92.951
H1:ASC-AS_B_RF36_SEG2_PHASE_D 92.951
H1:ASC-AS_B_RF36_SEG3_PHASE_D 92.62
H1:ASC-AS_B_RF36_SEG4_PHASE_D 92.411
H1:ASC-AS_A_RF45_SEG1_PHASE_D 91.896
H1:ASC-AS_A_RF45_SEG2_PHASE_D 92.53
H1:ASC-AS_A_RF45_SEG3_PHASE_D 93.1091
H1:ASC-AS_A_RF45_SEG4_PHASE_D 92.867
H1:ASC-AS_A_RF45_SEG4_PHASE_D 92.867
H1:ASC-AS_B_RF45_SEG1_PHASE_D 91.876
H1:ASC-AS_B_RF45_SEG2_PHASE_D 93.105
H1:ASC-AS_B_RF45_SEG3_PHASE_D 92.825
H1:ASC-AS_B_RF45_SEG4_PHASE_D 91.827
Forgot to mention --- I switched two ADC and BIO cables that were connected to the whitening filter of a quad demodulator in ISC R3 rack. This is due to the special modification on the demodulator.
At the very bottom of the rack, there is a quad demodulator which takes care of 18, 90 and 45 MHz LSC signals. From channel 1 to 4, the order of the demodulation frequencies should be 18, 90 and 45 MHz in order to satisfy the planned cable layout (see for example D1200666). However, this quad demodulator (S1001003) has these signals in order of 45, NAN, 18 and 90 MHz. The point is that this is a special mod version, where it has a fancy diplexer in it. So you can not easily swap the modulation frequencies between the channels unless one opens up the box and physically allocates the position of the boards. Because of that, the signal at the ADC were screwed up. For example, I obtained a signal from 18 MHz demodulator at a digital channel which was dedicated for 45 MHz (i.e. LSC-AS_A_RF45). In order to quickly fix it, I decided to swap the two ADC cables that were connected to the back side of the whitening filter. This pf course lead to another modification -- I had to swap the BIO cables.