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Message ID: 170     Entry time: Wed Nov 9 15:32:11 2016
Author: Gabriele 
Type: General 
Category: Noise hunting 
Subject: Noise below 2 kHz is not due to the roughing pump, but to the clean air filters 

The two spectra below show basically no difference (blue roughing pump on, red, roughing pump off)

Instead, below is another comparison: blue same as before, standard condition, red with one of the two clean air filters momentarily off. There is some clear improvement. The second filter is too hard to switch off!

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