Test & measurement


Ultra-clean signal handling and nanosecond data precision leads to unprecedented sensitivity of the world’s largest Cherenkov telescopes...


T


he MAGIC telescopes on the Canary Island of La Palma were built to observe cosmic objects that emit high- energy gamma rays, i.e. supernovae or black holes. Astronomers also use the twin telescope to measure the diameter of stars to investigate the processes throughout their life cycle. This is a challenging task for


earthbound telescopes, since the angular diameter of stars is extremely small: only a few milli-arc-seconds. That is about the size of a coin on top of the Eiffel Tower as seen from New York! Not even the largest telescopes in the world are able to measure them directly. Instead, the researchers record the light intensity of an object by combining the light from several telescopes at a distance of tens of meters – a technique called intensity interferometry. However, the signals are very weak so any spurious signals and crosstalk would swamp them. Having evaluated several makes of digitiser card, Spectrum Instrumentation M4i.4450-x8 digitiser cards were selected. “We found that these cards not only had the lowest


levels of spurious signals and crosstalk of all the PC cards that we tested,” said David Fink from the Max Planck Institute for Physics, who is in charge of Electronic Development on the project, “but the performance of each card was also identical. The latter is so important as you are trying to compare the differences between the signals from each telescope. The technique


Measuring distant stars


34 January 2022 Instrumentation Monthly


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