Committee on Radio Astronomy Frequencies
The Committee on Radio Astronomy Frequencies (CRAF) is a committee of the European Science Foundation (ESF).
2520 - 2655 MHz: FIXED 5.409 5.410 5.411 MOBILE except aeronautical mobile 5.384A BROADCASTING SATELLITE 5.413 5.416 5.339 5.403 5.405 5.408 5.412 5.417 5.418 5.418B 5.418Bbis 5.418C 5.418Cbis 2655 - 2670 MHz: FIXED 5.409 5.410 5.411 MOBILE except aeronautical mobile 5.384A BROADCASTING SATELLITE 5.413 5.416 Earth Exploration-Satellite (passive) Radio Astronomy Space Research (passive) 5.149 5.412 5.420 2670 - 2690 MHz: FIXED 5.409 5.410 5.411 MOBILE except aeronautical mobile 5.384A MOBILE-SATELLITE (Earth-to-space) 5.351A Earth Exploration-Satellite (passive) Radio Astronomy Space Research (passive) 5.149 5.412 5.419 5.420 2690 - 2700 MHz: EARTH EXPLORATION-SATELLITE (passive) RADIO ASTRONOMY SPACE RESEARCH (passive) 5.340 5.421 5.422
National Arrangements for Radio Astronomy different from ITU-R Radio Regulations
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Astrophysical importance of the band 2655 - 2690 MHz
A general consideration for the study of the continuum emission of radio sources is the requirement of sampled observations of these sources throughout a very wide frequency range. Observations at many different frequencies help to define the shape of the spectra of the emission from these sources, which in turn can give information on the physical parameters of the radiating sources such as densities, temperatures and magnetic fields, while they also give information on their lifetimes. The knowledge of these physical parameters is essential for our understanding of the physical processes that produce radio radiation. Many extragalactic radio sources show a "break" in their nonthermal spectrum in the region between 1 to 3 GHz and continuum measurements at ~2.7 GHz are essential to define such a spectral characteristic accurately.
The spectral region 2655.0 to 2700.0 MHz is a good band for continuum measurements partly because the galactic background radiation is low, and also because radio astronomy receivers are of excellent quality and have very low noise at such frequencies.
The frequency band 2655.0 to 2700.0 MHz is also useful for galactic studies of ionized hydrogen clouds and the general diffuse radiation of the Galaxy. Since at such frequencies available radio telescopes have adequate angular resolutions (narrow beams, of the order of 10 arc minutes for large telescopes), many useful surveys of the galactic plane have been performed, including the regions of the galactic center, which is invisible at optical wavelengths because of the interstellar absorption by dust particles. The center of our Galaxy is perhaps its most important region and yet it can only be observed at infrared and radio wavelengths, since these wavelengths are not affected by the dust particles in the interstellar space (optical wavelengths are absorbed and scattered by such dust particles). The study of the nuclei of galaxies, including the nucleus of our own Galaxy, is emerging as an extremely important and fundamental topic in astronomy.
Problems that can be studied in these objects include the state of matter and the possibilities of the existence of black holes in galactic nuclei; the explosive activities and the production of intense double radio sources from galactic nuclei; the influence of galactic nuclei on the morphological structure of galaxies; the formation of galaxies and quasars; and many other and major astrophysical subjects.
An important study at radio wavelengths is the polarization of the radiation that is observed from radio sources. It is often found that radio sources are weakly linearly polarized, with a position angle that depends on frequency. This effect is due to the fact that the propagation medium in which the radio waves travel to reach us is composed of charged particles, electrons and protons, in the presence of magnetic fields. The determination of the degree and angle of polarization gives us information on the magnetic fields and electron densities of the interstellar medium and in certain cases on the nature of the emitting sources themselves. The degree of polarization of radio waves is higher at higher frequencies. The frequency bands near 2700 and 5000 MHz are important bands for polarization measurements.
This band is under pressure by Digital Sound Broadcasting from satellites (which will also endanger the next bands upward). Use of this band for radio astronomy (No. 5.149) will be impracticable if it is shared with transmissions in the Broadcasting Satellite Service. Exclusive use for radio astronomy to extend the adjacent higher band to a 2 % bandwidth is highly desirable, but sharing with services transmitting from the ground only seems feasible.
| System Sensitivity (noise fluctuations) | Threshold Interference Levels | ||||
| Temperature | Power Spectral Density | Input Power | Power Flux Density | Spectral Power Flux Density | |
| Single Dish | 0.16 mK | -267 dB(WHz-1) | -207 dBW | -177 dB(Wm-2) | -247 dB(Wm-2Hz-1) |
| VLBI | -204 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 2655 - 2690 MHz is used by the Radio Astronomy Service in:
Sharing problems with the following services:
Out-of-band emission from the following services: