This is a follow-up entry of this one in ilog. The only difference is I'm injecting 20W instead of 2W into MC.

While students were adjusting squeezing table, I quickly swapped the VCO of H1 from the old one to the aLIGO test unit and measured the MC feed back signal going to the VCO.

New VCO has a smaller range, and I needed to increase VCO gain by 8dB.

Green and blue traces in the attached are the VCO feedback signal (H1:IOO-MC_F) with the old VCO from two different lock stretches, and the red is the same thing with the new VCO but scaled down by -8dB. With this setting, OLG of the MC servo with new VCO was only about 0.4dB smaller than the old one.

The new VCO is not doing any harm. In kHz range it is clearly better than the old one.

Considering the fact that the previous test with 2W into MC showed a smaller improvement, it's also clear that the measurement is limited by the sensing noise of MC.

For a better test you need to wait for the full H1 IFO to come back, but this is already good enough in that nothing seems to be wrong.