Today I carried on the tests for the BS_TX loop using EDB_B1s_QD1_50MHz_Y_I that started a while back (entry 66104).

Giving a quick look at the spectra of the in-loop signal and the new one, back when the last test was done and today, no big difference can be spotted (Figures 1 and 2 respectively).

I first used the line at 3.1 Hz to verify the last measurement: line amplitude 2e-3 since 15:53:00 UTC onwards, while in LOW_NOISE_3. After finding the weight (with ASC_BS_TX_INPUT, not ASC_BS_TX otherwise the loop gain will cause a miscalibration) I attempted the handoff, failing twice (LOW_NOISE_3 and _2 respectively). The measurement is also not obvious given that the DIFFp_TX line nearby (3.3 Hz) muddles the reading.

A good attempt was done injecting the line (amplitude 5e-3) from 17:42:12 UTC to 17:56:40 UTC, while in LOW_NOISE_2; I found a ratio between the weighted in-loop ASC_BS_TX_INPUT and B1s_QD1_50MHz_Y_I equal to 0.015 (Figure 3).

At 18:01:33 UTC I made a successful handoff, while in LOW_NOISE_2, from the blending B1p_QD1_50MHz_V_I_LP/B4_QD1_6MHz_V_HP to B1s_QD1_50MHz_Y_I. Clean data from 18:01:40 UTC to 18:13:15 UTC.

At 18:13:17 UTC I injected again the same line, with the same amplitude; the line was turned off at 18:23:30 UTC, clean data afterwards.

In Figure 4 the in-loop signals with the usual one (in purple) and the B1s one (in blue).

At 19:01:53 UTC I moved on towards LOW_NOISE_3 with this configuration; clean data in LOW_NOISE_3 starting from 19:11:59 UTC.

I leave the interferometer in this configuration, which is not macroscopically detrimental to the sensitivity (Figure 5); at the next unlock the lock acquisition will bring back the usual loop configuration.