Committee on Radio Astronomy Frequencies

The Committee on Radio Astronomy Frequencies (CRAF) is a committee of the European Science Foundation (ESF).

Frequency band allocated to the Radio Astronomy Service:

ITU-RR allocations (+ footnotes):


4800 - 4990 MHz: 		FIXED
			MOBILE	5.442
			Radio Astronomy
			
			5.149 5.339 5.443
			

4990 - 5000 MHz: 		FIXED
			MOBILE except aeronautical mobile
			RADIO ASTRONOMY
			Space Research (passive)
			
			5.149
			

5000 - 5010 MHz:		AERONAUTICAL RADIONAVIGATION
			RADIONAVIGATION-SATELLITE (Earth-to-space)

			5.367


5010 - 5030 MHz:		AERONAUTICAL RADIONAVIGATION
			RADIONAVIGATION-SATELLITE (space-to-Earth)(space-to-space) 5.328B 5.443B

			5.367


5030 - 5150 MHz:		AERONAUTICAL RADIONAVIGATION
			
			5.367 5.444 5.444A

National Arrangements for Radio Astronomy different from ITU-R Radio Regulations:

Astrophysical importance of the band 4900 - 5000 MHz

The spectral region around 5 GHz has been one of the widely used frequency ranges in radio astronomy during the last decade. Astronomers have made use of this frequency range in order to study the detailed brightness distributions of both galactic and extragalactic objects. Detailed radio maps of interstellar ionized hydrogen clouds and supernova remnants have assisted our understanding of the nature of such celestial objects. These radio maps define the extent and detailed morphology of radio sources and enable us to make conclusions concerning their structures and dynamics and to derive physical parameters of the sources such as their total masses.

One of the most important uses of the band around 5 GHz is the study of the formaldehyde (H2CO) interstellar clouds at 4829.66 MHz. The H2CO line at this frequency is considered to be one of the most important radio lines in the entire spectrum, primarily because it can be detected in absorption in almost any direction where there is a continuum radio source. This distribution of H2CO clouds can give independent evidence of the distribution of the interstellar material and can help in understanding the structure of our Galaxy. H2CO has also been observed in absorption against the microwave cosmic 3 K blackbody background radiation. H2CO lines from the carbon-12 isotopic and oxygen-18 isotope have been detected and studies of the isotopic abundances of these elements are being carried out.

The band 4950.0 - 4990.0 MHz is used by radio astronomy as an extension of the next higher band which is too narrow (see No. 5.149 and 5.443). Protection would be improved if transmission from aircraft could be excluded.

The primary (exclusive in Region 2) radio astronomy band (4990 - 5000 MHz) is narrow. A much-needed improvement would be to extend the allocation downwards to 4950 MHz by sharing with compatible services. To reduce the risk of interference from aeronautical services above 5000 MHz, exclusion of air-to-ground transmissions from the band 5000.0 - 5010.0 MHz is strongly recommended. This band is used for worldwide VLBI.

Threshold levels of interference detrimental to radio astronomy continuum observations:

System Sensitivity (noise fluctuations)Threshold Interference Levels
TemperaturePower Spectral DensityInput PowerPower Flux DensitySpectral Power Flux Density
Single Dish0.16 mK-267 dB(WHz-1)-207 dBW-171 dB(Wm-2)-241 dB(Wm-2Hz-1)
Interferometer-240 dB(Wm-2Hz-1)
VLBI-198 dB(Wm-2Hz-1)

NOTE:

For further details the reader is referred to ITU-R Recommendation RA769. It should, however, be noted that the observed spectral power flux densities are much lower than the harmful interference levels because they are made in the main beam of the radio astronomy antennas whereas the harmful levels correspond to reception in the sidelobes, i.e. the differences are related to the gain of the antennas. The differences can be of the order of 50 to 80 dB W m-2 Hz-1 (see ITU-R "Handbook on Radio Astronomy", 1995/2003, chapter 4).

In Europe, the band 4900 - 5000 MHz is used by the Radio Astronomy Service in:

Threats to the Radio Astronomy Service:

Last modified: March 21, 2005