NAOJ GW Elog Logbook 3.2
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YuhangZhao - 16:43, Thursday 07 January 2021 (2328)
Investigation of 20kHz noise in SHG error signal
Marc and Yuhang
We used signal generator AFG3102 to modu/demodu SHG fields (instead of DDS1). At the same time, all DDS boards were taken out from rack. Then we locked SHG and checked error signal spectrum. We found 20kHz noise disappeared. Figure 1 (SHGNODDS.txt) shows error signal spectrum in this measurement.
After that we also checked the rack voltage, which may change due to large power consumption.
| no DDS | all DDS | |
| +24 | 24.04 | 24.04 |
| -24 | -24.04 | -24.04 |
| +12 | 12 | 12 |
| -12 | -12.03 | -12.03 |
| +6 | 5.837 | 5.837 |
| -6 | -5.995 | -5.995 |
We measured error signals when there were DDS1 only (DDS1.txt), DDS2 only (DDS2.txt), DDS3 only (DDS3.txt) and clock removed (no clock.tx).
Participants : Marc, Yuhang
Here are the figures :
First no DDS board connected to the rack : all the peaks disappear.
Then, DDS board connected one by one we can see that each DDS is causing one of the peak around 20 kHz.
DDS1 -> 18 112 Hz
DDS2 -> 17 728 Hz
DDS3 -> 21 312 Hz