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):


30.01 - 37.5  MHz:	FIXED
			MOBILE
			

37.5  - 38.25 MHz: 	FIXED
			MOBILE
			Radio Astronomy
			
			5.149
			

38.25 - 39.986  MHz:	FIXED
			MOBILE

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

Astrophysical importance of the band 37.5 - 38.25 MHz

The band 37.5 - 38.25 MHz has worldwide a secondary allocation (see No. 5.149). Together with the bands 13.36 - 13.41 MHz and 25.55 - 25.67 MHz this band is very important for research of radiation from Jupiter. Long after all the decametric frequency bands have been allocated and widely used by active services Jovian decametric radiation was discovered. The allocations to the Radio Astronomy Service are extremely narrow since the interesting Jovian phenomena can cover the entire spectrum from 3 - 40 MHz. Jupiter is the only radio-planet observable from the ground and its study is a unique mean of developping theoretical models for the radio emissions of all the other planets.

These three bands (13.36 - 13.41 MHz, 25.55 - 25.67 MHz and 37.5 - 38.25 MHz) are also used for solar observations. Also for this research the allocations are extremely narrow, since the interesting solar phenomena can cover the entire spectrum up to 70 MHz. The Sun is the nearest star and its study enables a closer understanding of the radio emission mechanisms of all other stars.

The allocation of the band 37.5 - 38.25 MHz was modified only slightly by WARC 79. On a worldwide basis the Radio Astronomy Service has a secondary allocation shared with the Fixed and Mobile Services. Despite the secondary allocation, this band is often free of interference and is quite useful for radio astronomy.

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 Dish250 mK-235 dB(WHz-1)-180 dBW-198 dB(Wm-2)-251 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 37.5 - 38.25 MHz is used by the Radio Astronomy Service in:

Threats to the Radio Astronomy Service:

Last modified: March 21, 2005