Detecting loss of Coherence based on Telescope Calibration results in ALMA

摘要

The ALMA telescope will be composed of 66 high precision antennas; each antenna producing 8 times 2GHz bandwidth signals (4 pairs or orthogonal linear polarizations signals). Detecting the root cause of a loss of coherence issue between pairs of antennas can take valuable time which could be used for scientific purposes. This work presents an approach for quickly determining, in a systematic fashion, the source of this kind of issues. Faulty sub-system can be detected using the telescope calibration software and the granularity information. In a complex instrument such as the ALMA telescope, finding the cause of a loss of coherence issue can be a cumbersome task due to the several sub-systems involved on the signal processing (Frequency down-converter, analog and digital filters, instrumental delay), the interdependencies between sub-systems can make this task even harder. A method based on the information provided by the TelCal sub-system (in specific the Delay Measurements) will be used to help identify either the faulty unit or the wrong configuration which is causing the loss of coherence issue. This method uses granularity information to help find the cause of the problem.