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LOFAR Dynamic Spectrum Art

Submitter: Menno Norden
Description: Because of the ever-present possibility(*) of little problems like hardware failure, software bugs, or even human error, the LOFAR system is being monitored 24 hours a day. Sometimes we notice strange features in the inspection plots. This time Science Support asked me to find out why the HBA-ONE (Serdes Ring 01) was showing behaviour that was completely different from the much cleaner HBA-ZERO (Serdes Ring 00). It is obvious that the signal in the two messy plots is not real (although some might think of SETI).

Since I could not find a clear hardware issue in station CS026C, I asked the Duty Observer to repeat the observation, and discovered a multi-problem bug. Thanks to plots made by Richard Fallows (Inspection Plots) and Pieter Donker (Live Plots) I noticed that 25% of the HBA tiles of this station had the wrong spectral inversion setting, which mirrorred the frequency band. The second problem was an oscillating tile (T28 in HBA-ONE) that occasionally disrupted the station beam, causing the art-like structures in the beamlet inspection plots.

The spectral inversion issue has now been resolved, but tile T28 will be temporarily ignored in LOFAR observations while it is being repaired. The latter will certainly be the case by the time you read this daily image (which has taken its own good time to get posted).

(*) Editor's note: An electronic beam-forming system like LOFAR (or SKA Low) is somewhat more complex than a dish-based system, and thus has somewhat more scope for little problems like this one. Of course that is amply compensated by the advantages of multi-beaming. One just has to be vigilant, like a doting young mother.
Copyright: Astron
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