[Fujimoto, Hirose, Yokozawa, Ushiba]

Abstract:

We changed IMC and IFO local oscillators' amplitude to 10.4 dBm and 13.0 dBm, which were 7.4 dBm and 10.0 dBm, respectively.
After that, we measured the OLTF of IMC and IRX loops, and confirmed that they are almost consistent with those measured before.

Detail:

As reported in klog37656, IMC UGF is lower than before (klog35394), so we investigated the reason.
Though IMC LO amplitude is nominal (7.4 dBm, which is written on the signal generator), LO amplitude was 10.4 dBm after the planned power outage in March according to the photo in notion page.
So, we set LO amplitude to 10.4 dBm and measured the OLTF (fig1).
Then, the UGF becomes 120 kHz, which is almost same as before.

After that, we increased IFO LO amplitude from 10 dBm to 13 dBm, which should be nominal according to the spec of the harmonic generator (JGW-D1808028-v5).
Though IRX could not be locked with 13 dBm amplitude the day before yesterday, it can be locked without any problems this time.
Figure 2 shows the OLTF of IRX loop with 13 dBm LO amplitude, whose UGF is 11 kHz that is same or slightly high compared with the previous measurement (though we didn't measure IRX OLTF for a long time, it should be -20dB around 100kHz according to klog35455).

After increasing LO amplitude, we locked PRMI and confirmed that POP90 value is slightly higher than before (fig3: Y cursor in the top left pannel shows the POP90 when PRMI was locked with 3F before the blackout).
We are not so sure the reason but it might be due to the LO amplitude is slightly higher than before the unexpected blackout (which was 12.3 dBm after the planned power outage on March 2026).

Anyway, the strange points in IMC, IRX, and PRMI seemed to be resolved by increasing LO amplitude.

Note:

For the future references, I summarized current ISC related signal generator setting in the nortion page.