Detection system (Detection system)swinkels, tacca - 20:59 Tuesday 21 June 2011 (29715)
Print this reportSwitch flat -> shape with excited 6 and 8HzAround 15:20 UTC, while locked at step 12, we switched B1 from the flat to the shaped ADCs. At that moment, some lines around 18, 20 and 22 Hz appear in the spectrum of B1, see fig 1. These are probably caused by harmonic distortion, since we were only locked for a short time and both the 6 and 8 Hz resonances were very excited (but not enough to saturate, max voltage on shaped signals +- 3.5 Volt). The lines are different combinations of harmonics (3*6 = 18, 2*6+8 = 20, 6+2*8=22). Fig 2 shows the spectra before and after. Before the switch, the lines are only visible in the shaped signals, which are out of lock at that moment. After the switch, the lines decrease in the shaped signals and appear in the flat signals, which is probably the effect of the lines being introduces in the ITF by the lock of DARM. Fig 3 compares d2_flat with d2_shap before the switch.
