| Quote from #5930 |
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Right now the fluctuation of the green beat-note seems mostly covered by unknown noise which is relatively white.
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The 2nd trial of the Y arm ALS noise budgeting :
(Removal of broad band noise)
+ The broad band noise decreased somewhat after I fixed a broken connection in the discriminator.
+ I took a look at the frequency discriminator setup and found one of the SMA-BNC adapter was broken.
This adapter was attached to one of the outputs of the 4-way power splitter, which splits the signal into the coarse and find discriminator paths.
And this broken adapter was in the coarse path, which actually I am not using for the noise budget.
Depending on the stress acting on the adapter it was creating broadband noise, even in the fine path.
So I threw it away and put another SMA-BNC adapter.
Here is a plot of the latest noise : high frequency noise is still unknown.
I will add the dark noise of the broad-band beat-note PD and the MFD read out noise on the budget. |