Basic conversion formulas for Radioastronomy.
Copyright (C) 2012+ Axel Jessner (jessner@mpifr.de)
2015+ Benjamin Winkel (bwinkel@mpifr.de)
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Johannes Kepler was born on December 27, 1571. To celebrate his 450th anniversary, the government of the state of North-Rhine-Westphalia decides to switch off all artificial light sources on December 27, 2021, so that people can finally enjoy the stars in the sky in the middle of Europe.
Unfortunately, hundreds of amateur astronomers make themselves ready to use their sophisticated and highly automated optical telescopes during this night. It is well known, that especially the Pro-OBS-2000 telescope motorized mount has insufficient shielding and produces radio frequency interference at multiples of an oscillator running at 48.5 MHz. On of the harmonics happens to lie at 1406.5 MHz, close to the important 21-cm HI line at 1420 MHz and well within the protected RAS band.
Therefore, the German administration has asked you, to provide the necessary calculations to determine a protection zone around the 100-m radio telescope at Effelsberg, such that no harm is put to radio observations on that night.
Since HI line observations are planned, we have to use the spectral-line limits of ITU-R RA.769.
The strength of the RFI line is -70 dBm/Hz and it has a width of 2.5 Hz.
Fortunately, Effelsberg is surrounded by some hills, which provide additional shielding.
A group of amateur astronomers builds a camp well outside of the exclusion zone at $(l, b)=(6.9^\circ, 50.57^\circ)$.
Everything goes as planned. However, one day before the event, you get a phone call: a Chinese vendor sold hundreds of LED based flash lights to the amateur astronomers, which leak broadband emission into the L-band. The estimated power level is -50 dBm/MHz over the full protected RAS band. You have 30 minutes to calculate the necessary single-interferer exclusion zone, before it is too late!