Radio Astronomy Frequencies List
On behalf of the Radioastronomy Commission 40 of the International Astronomical Union (IAU) representing about 100 countries, International Telecommunications Union (ITU), who represents more than 350 nations, allocated frequencies bands that are strictly reserved to scientific, militaries and public usage. All the spectrum from 9 kHz to 275 GHz is covered and allocated to specific services in order to avoid any interferences.
However, side effects called "harmful interferences" appear from time to time due to parasits generated by unprotected devices or the lack of national regulation.
Some of these bands are reserved for radio astronomy purposes, mainly for the study of spectral lines like the water hole, OH molecule, etc. You will find on the European Radiocommunications Office website, ERO, the complete list of allocated frequencies with their description.
Here is the global list updated in 2003 of allocated bands in which all emissions are prohibited. Unfortunately most are shared with other services :
however that Rules and Procedures from ITU specify that there is no
allocation to radio astronomy in the next bands, whatever nationals
regulations, so interferences can exist in these bands if they are used
for that purpose :
Hereunder the detail of each band allocated to Radio Astronomy as defined by IAU, modified Dublin 2003 :
According to ITU, interference levels are considered to be harmful to the Radio Astronomy Service when the rms fluctuations of the system noise increase at the receiver output by 10 % due to the presence of interference.
ITU-R RA.769-1 gives the levels of harmful interference for the Radio Astronomy Service based on this criterion and the adopted integration time of 2000 seconds. It should be noted that in practice it depends completeley on the type of telescope and the operating parameters used whether interferences is considered harmful. For example: the conditions are different for single dish observations, radio interferometry and Very Long Baseline Interferometry (VLBI); or whether observations are done of spectral lines or in a broadband continuum mode. Usualy each instruments has a number of different operating parameters. The values given in ITU-R RA.769-1 general "averages" and give an indication of the levels at which an interfering signal degrades the observations significantly.
Percentage of time lost by the Radio Astronomy Service due to harmful interference
In cases where the strength of an interfering signal varies as a result of time-varying propagation conditions, for example in the case of propagation by tropospheric scatter, the usual practice in interference calculations for radio astronomy is to consider the level for which the propagation loss is exceeded for 90 % of time. Thus the harmful threshold would be exceeded for 10 % of time, and in removing contaminated data 10 % of the observations would be lost. Radio astronomers generally agree that this is the maximum tolerable loss. In general this figure applies to interference which intermittently exceeds the harmful threshold for time periods such that no more than 10 % of the data is contaminated. In terms of the time averaging no more than 10 % of the initially-averaged data (for example of tens of milliseconds to tens of seconds) should be lost when contaminated data is rejected. Thus, for example, interference from a radar signal, the mean power of which exceeds the harmful threshold, would not be tolerable even if the duty cycle of the transmitter is less than 10 % (according to ITU-R Handbook on Radio Astronomy).
For more information
IAU list of important spectral lines (on this site)
List of Discovered Interstellar Molecules, Obs. Paris.