There are many internationally protected frequency which are used by radio astronomers.
Frequency band Status Radio astronomy use 13.36 - 13.41 MHz 25.55 - 25.67 MHz 37.5 - 38.25 MHz Continuum observations 73 - 74.6 MHz Solar wind observations. Continuum observations. 80.5 - 82.5 MHz Pulsar observations 150.05 - 153 MHz Continuum observations. Pulsar observations. Solar observations. 322 - 328.6 MHz Continuum observations. VLBI 406.1 - 410 MHz Continuum observations. Pulsar observations. 608 - 614 MHz Continuum observations. VLBI 1400 - 1427 MHz Spectral line observations 21cm hydrogen line 1660 - 1660.5 MHz VLBI 1660.5 - 1668.4 MHz VLBI Line observations. Continuum observations. 1668.4 - 1670 MHz 1718.8 - 1722.2 MHz 2655 - 2690 MHz Continuum observations 2690 - 2700 MHz 3260 - 3267 MHz 3332 - 3339 MHz 3345.8 - 3352.5 MHz 4800 - 4990 MHz Continuum observations 4990 - 5000 MHz Continuum observations. VLBI 5000 - 5030 MHz VLBI 6650 - 6675.2 MHz 10.6 - 10.68 GHz Continuum meausurements. VLBI 10.68 - 10.7 GHz Continuum observations. VLBI 14.47 - 14.5 GHz Spectral line observations. VLBI 15.2 - 15.35 GHz VLBI 15.35 - 15.4 GHz Continuum observations. VLBI 22.01 - 22.21 GHz Spectral line observations Water line 22.21 - 22.5 GHz Spectral line observations Water line. 22.91 - 22.86 GHz Spectral line observations Methyl Formate Ammonia 23.07 - 23.12 GHz Spectral line observations 23.6 - 24.0 GHz Spectral line observations Continuum observations Ammonia line 31.2 - 31.3 GHz Continuum observations 31.3 - 31.5 GHz Continuum observations 31.5 - 31.8 GHz Continuum observations 36.43 - 36.5 GHz Spectral line observations Hydrogen cyanide Hydroxil 42.5 - 43.5 GHz Spectral line observations Silicon monoxide and many other lines 48.94 - 49.04 GHz Spectral line observations Carbon monosulphide 51.4 - 54.25 GHz 58.2 - 59 GHz 72.77 - 72.91 GHz Spectral line observations Formaldehyde line. 86 - 92 GHz Spectral line observations. Continuum obserations 92 - 94 GHz Spectral line observations. Diazenylium and many other lines. 95 - 100 GHz Spectral line observations. Continuum observations.