We used AM laser to check up the ALSX WFS.
AM laser output: 1.8mW (measured with old ophir power meter, 978nm, filterr out)
Modulation source was set to 0.1vpp 24.389310MHz (this frequency was set before fixing the 1.002MHz that was mentioned in another alog).
WFS DC interface was set to low DC gain mode and the DC offset zero-ed.
Demod whitening gain was 21dB, first and the second whitening filter were on and the third off, a-whites were turned on though I don't know if they're put in yet (turns out that the awhites were not yet there when we did this measurement, so the "demod" numbers in the table below are 33dB higher than they should be.).
| WFSA DC | WFSA demod (both I and Q) | WFSB DC | WFSB demod (both I and Q) | |
| SEG1 | 3000 cts | +-20k cts | 2600 | +-19k |
| SEG2 | 3070 | +-20k | 2900 | +-9k |
| SEG3 | 2395 | +-12k | 2740 | +-20k |
| SEG4 | 2930 | +-18k | 2960 | +-20k |
Seems like the demod signal out of WFSA SEG3 and WFSB SEG2 are both about a factor of 2 smaller than the others. On the scope it seemed that the RF signal coming from the WFS head was already small for these segments.
We confirmed that the whitening gain and filters are working.
Jax found that depending on how the cables were strained on the AM laser the amplitude of AM varies greatly (from nothingness to full). Crappy RF connection?
I didn't see such an effect when I used it at ISCT1 a month ago and the AM power was reproducable. This could be a new issue.
There may have been a miscommunication between me and Keita. When the cables were strained, they applied a torque to the laser, twisting it out of alignment with the WFS aperture (maybe 45 degrees rather than head-on? didn't exactly measure it, just corrected it.) So the power level issues were caused by cable strain, but on a purely mechanical level.