[Koji Den EricG]
We inspected the {REFL, AS, POP}55 demodulators.
Short in short, we did the following changes:
- The REFL55 PD RF signal is connected to the POP55 demodulator now.
Thus, the POP55 signals should be used at the input matrix of the LSC screens for PRMI tests.
- The POP55 PD RF signal is connected to the REFL55 demodulator now.
- We jiggled the whitening gains and the whitening triggers. Whitening gains for the AS, REFL, POP PDs are set to be 9, 21, 30dB as before.
However, the signal gain may be changed. The optimal gains should be checked through the locking with the interferometer.
- Test 1
Inject 55.3MHz signal to the demodulators. Check the amplitude in the demodulated signal with DTT.
The peak height in the spectrum was calibrated to counts (i.e. it is not counts/rtHz)
We check the amplitude at the input of the input filters (e.g. C1:LSC-REFL55_I_IN1). The whitening gains are set to 0dB.
And the whitening filters were turned off.
REFL55
f_inj = 55.32961MHz -10dBm
REFL55I @999Hz 22.14 [cnt]
REFL55Q @999Hz 26.21 [cnt]
f_inj = 55.33051MHz -10dBm
REFL55I @ 99Hz 20.26 [cnt] ~200mVpk at the analog I monitor
REFL55Q @ 99Hz 24.03 [cnt]
f_inj = 55.33060MHz -10dBm
REFL55I @8.5Hz 22.14 [cnt]
REFL55Q @8.5Hz 26.21 [cnt]
----
f_inj = 55.33051MHz -10dBm
AS55I @ 99Hz 585.4 [cnt]
AS55Q @ 99Hz 590.5 [cnt] ~600mVpk at the analog Q monitor
f_inj = 55.33051MHz -10dBm
POP55I @ 99Hz 613.9 [cnt] ~600mVpk at the analog I monitor
POP55Q @ 99Hz 602.2 [cnt]
We wondered why the REFL55 has such a small response. The other demodulators seems to have some daughter board. (Sigg amp?)
This maybe causing this difference.
-----
- Test 2
We injected 1kHz 1Vpk AF signal into whitening board. The peak height at 1kHz was measured.
The whitening filters/gains were set to be the same condition above.
f_inj = 1kHz 1Vpk
REFL55I 2403 cnt
REFL55Q 2374 cnt
AS55I 2374 cnt
AS55Q 2396 cnt
POP55I 2365 cnt
POP55Q 2350 cnt
So, they look identical. => The difference between REFL55 and others are in the demodulator. |