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):


4500 - 4800  MHz:		FIXED
			FIXED-SATELLITE (space-to-Earth) 5.441
			MOBILE
			

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

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

Astrophysical importance of the band 4800 - 4900 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.

There is a continuing use of the band 4800 - 4810 MHz by radio astronomy in some countries (No. 5.149 and 5.443).

The importance of the formaldehyde line at 4829.66 is such that at least a strong footnote is needed (see No. 5.149 and 5.443) to protect radio astronomy in the band 4825 - 4835 MHz. A wide band (e.g. 4850 - 4890 MHz) is favourable for continuum measurements in this part of the spectrum being located to include the formaldehyde line (see ITU-R Recommendation RA.314-8, table 1).

Threshold levels of interference detrimental to radio astronomy spectral-line observations:

System Sensitivity (noise fluctuations)Threshold Interference Levels
TemperaturePower Spectral DensityInput PowerPower Flux DensitySpectral Power Flux Density
Single Dish2.20 mK-255 dB(WHz-1)-218 dBW-183 dB(Wm-2)-230 dB(Wm-2Hz-1)

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 4800 - 4900 MHz is used by the Radio Astronomy Service in:

Threats to the Radio Astronomy Service:

Last modified: March 21, 2005