¶ Power Line (60 Hz)
In the United States, the mains power is alternating current (AC) at a frequency of 60 Hz. Because of this, quasi-periodic frequencies of 60 Hz and its harmonics (120, 180, etc.) are present in the LIGO data. Additionally, when large equipment that runs on this AC power, such as heater units or air compressors, switch on or off, glitches can occur at 60 Hz or one of its harmonics. In time-frequency plots these usually look narrow in frequency, and last for about 0.2-0.5 seconds in time (sometimes longer), centered around 60 Hz or one of its harmonics.
- For an example of finding and fixing one source of 60 Hz glitches at LHO, see https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=23483
- For an O2 example (long story) of fixing 60Hz glitches from EX at LLO, see https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=32389
¶ Examples
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Audio of Paired Doves (with associated spectrogram) Make sure to wear good headphones!
