A new noise appeared in our external magnetometer ENV_EXT_MAG_N on December 6, at 14:00 UTC.
This noise is a couple of wide sidebands around the mains line at 50 Hz, 15 Hz apart from it.
No equivalent noise is visible in Hrec, nor in our internal CEB magnetometers.
In fact, the noise level in ENV_EXT_MAG_N is much higher also at low frequency (plot1) and at high frequency (plot2).
There is a vague (~ 0.1) coherence with one (and only one) of the magnetometers that are near the towers: ENV_WI_MAG. None visible in all others, and none in CEB IPS and UPS sensors.
The noise has period of high and low sidebands level, as well as disappearances, such as the one that occurred today at 10:00 UTC that lasted 4 minutes. .
The noise that plagued our external magnetometer seems to have disappeared today between 09:20 (amplitude reduction) and 09:40 (disappeared).
