Virgo Logbook

Reports 1-1 of 1

AdV-COM (AdV commissioning (1st part) )

casanueva - 9:50 Tuesday 22 May 2018 (41500)

56MHz modulation loss

As noticed by Paolo and others, the level of 56 MHz is slowly decreasing since last septembre, when we increased the modulation depth from 7dBm to 12 dBm. In order to confirm and evaluate this loss I have plotted the trend data of the 112MHz during this time. As it can be seen in the first three figures, we start with 0.035 and we end up with 0.023 in two months.

Then we recovered the level of the sidebands with the power increase (Figure 4).

Figures 5 and 6 show the level of the sidebands during the recovery of February and the present one, and the level has further decreased to 0.013.

The signal used for monitoring is coming from the B4 photodiode 2f signal. It depends on many parameters, but the trend over these months is clear.

Images attached to this report

Comments to this report:

Paoletti - 11:13 Wednesday 23 May 2018 (41526)

A quick check of the RF 56MHz chain does not show any deviation from what expected.

LNFS signal generator is set at +12dBm, RF distribution sends -3dBm to the power amplifier, and the latter has a gain of 33.6dB which provides +30.6dBm (~1W) to the cable that goes at the EOM on the optical bench.

Note that the usual -3dB SMA power attenuator in front of the EOM has been removed since the beginning of the RF power increase.

Note also that the power amplifier for the 56MHz is not the usual (+30dBm ZHL-3A+), because it was modified with a +33dBm ZHL-1-2W+ to allow the power increase within a safety margin.