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General survey of radio astronomy problems
Adv. Space Ree. Vol.2, No.3, pp.23—24, 1982 Printed in Great Britain. All rights reserved.
0273—1177/82/03002302$03.OO/O
copyright © COSPAR
4a. GENERAL SURVEY OF RADIO ASTRONOMY PROBLEMS R. Wielebinski Max-Planck-Insrilut für Radioasfronomie, Bonn, FRG
The whole field of radio astronomy is potentially threatened in its very existence by radio transmissions from space. Radio astronomy, which is operated in the passive receiver mode, has always had to co-exist with man-made radio signals emitted from the ground or from aeroplanes. Direct emissions from space, however, lead to new problems. The transmissions from space transmitters are in the direct field of view of radio telescopes. In fact, these latter recently actually interfered with the reception of radio-astronomicaJ. spectral line signals, i.e. cosmic emissions at fixed frequencies. Therefore, an effective cooxdination of frequency allocations is urgently needed. The radio signals interesting radio astronomers are either continuum emissions (ground-based observations from 1 MHz to 300 GHz are possible) or line emissions at fixed frequencies due either to spin transitions (e.g. that of hydrogen HI at l~+20MHz), or to emissions of radicals (e.g. CH, OH) or from molecules (1120, 00, H
2CO, etc.).
Since radio astronomy is
recognised by ITU as a “radio—service”, protection rules for the radio frequencies which must be used when observing these natural phenomena are fixed by the World Administrative Radio aonference (wARO) and can be found in the International Telecommunication Union (I’m) Radio Regulations. For continuum observations, radio bands are allocated in steps across the radio-frequency spectrum. With receivers of limited bandwidth, the broad spectrum of a radio source can be determined by measuring in numerous frequency bands. Most of these are allocated the so— called “shared primary status”, the sharing being usually with low-power transmitters at fixed locations. After negotiation with the go~ernmentaladministrations responsible for national frequency allocations, most radio-astronomical observatories have been able to secure a low level of interference. A few line frequencies only (]Jf20 MHz, 115 GHz) are reserved for radio astronomy by worldwide exclusive allocation. In these bands no transmitters should be operating at all. Many other cosmic emission lines have either “shared primary”, “shared secondary” or so—called “footnote” status in the Radio Regulations. In spite of the fact that the latter status is rather vague, it has usually been possible to reach a reasonable solution with local transmitters on a national basis. The potentially dangerous development is the placing of an increasing number of radio transmitters in space, particularly if these are broadcast or television transmitters.
It is
then possible that the transmitter will cross the main beam of the receiving antenna or a
24
R. Wielebinski
secondary lobes when this occurs the directivity of the antenna no longer provides the protection that it should. Unfortunately, natural radio signals, particularly the emissions from distant extragalactic sources, are extremely weak, and sharing the same frequency band with a space transmitter is not acceptable.
Interference detrimental to radio astronomy was,
and still is, generated by certain transmissions found experimentally in the case of the ATS-6 and SMS-l series of satellites. This was in spite of planned sharing of adjacent frequency bands. The transmitter technolo~rwas, unfortunately, such that serious out-ofband interferen~e was generated (see 4b below; detailed reports are available). Detrimental space transmissions were even found in the protected 1~4O0MHz band as shown by Oanadian experience.
A further problem arises from harmonics of transmitters in space.
To a large extent, the administrations responsible for telecommunications in different countries appreciate these problems and try to find solutions. The most important aspects are summarised in Report 224 - 4 of the COIR (xIvth Plenary Assembly, Kyoto 1978). The recommendations are internationally recognised, but they lead to the conclusion that harmful interference to radio—astronomy observations cannot be avoided only by the coordination of frequency allocations~ it is necessary that transmission from space to ground should be prohibited, not only in bands which are allocated for the radio-astronomy service, but also in adjacent bands. It is important that planning of space transmitters be undertaken more carefully, taking account of harmonics and of the locations where radio-astronomical observations are cuzTently made. In particular, the power of space transmitters should be kept low. A continuous coordination of frequency sharing between space transmissions and radio astronomy must be achieved; otherwise this field of research will be seriously affected. coordination has been recommended for many Allocation of Frequencies, set up by URSI, Administrative Radio Conference the status this body was and is to collect the wishes
Such
years by IUCAF (Inter-Union Commission on the IAU and COSPAR). Unfortunately, in the World of the Commission is only advisory. The task of of radio scientists, and to provide proposals for
international agreemeats which might then be presented to the WARC by sympathetic national administrations.
0273—1177/82/03002302$03.OO/O
copyright © COSPAR
4a. GENERAL SURVEY OF RADIO ASTRONOMY PROBLEMS R. Wielebinski Max-Planck-Insrilut für Radioasfronomie, Bonn, FRG
The whole field of radio astronomy is potentially threatened in its very existence by radio transmissions from space. Radio astronomy, which is operated in the passive receiver mode, has always had to co-exist with man-made radio signals emitted from the ground or from aeroplanes. Direct emissions from space, however, lead to new problems. The transmissions from space transmitters are in the direct field of view of radio telescopes. In fact, these latter recently actually interfered with the reception of radio-astronomicaJ. spectral line signals, i.e. cosmic emissions at fixed frequencies. Therefore, an effective cooxdination of frequency allocations is urgently needed. The radio signals interesting radio astronomers are either continuum emissions (ground-based observations from 1 MHz to 300 GHz are possible) or line emissions at fixed frequencies due either to spin transitions (e.g. that of hydrogen HI at l~+20MHz), or to emissions of radicals (e.g. CH, OH) or from molecules (1120, 00, H
2CO, etc.).
Since radio astronomy is
recognised by ITU as a “radio—service”, protection rules for the radio frequencies which must be used when observing these natural phenomena are fixed by the World Administrative Radio aonference (wARO) and can be found in the International Telecommunication Union (I’m) Radio Regulations. For continuum observations, radio bands are allocated in steps across the radio-frequency spectrum. With receivers of limited bandwidth, the broad spectrum of a radio source can be determined by measuring in numerous frequency bands. Most of these are allocated the so— called “shared primary status”, the sharing being usually with low-power transmitters at fixed locations. After negotiation with the go~ernmentaladministrations responsible for national frequency allocations, most radio-astronomical observatories have been able to secure a low level of interference. A few line frequencies only (]Jf20 MHz, 115 GHz) are reserved for radio astronomy by worldwide exclusive allocation. In these bands no transmitters should be operating at all. Many other cosmic emission lines have either “shared primary”, “shared secondary” or so—called “footnote” status in the Radio Regulations. In spite of the fact that the latter status is rather vague, it has usually been possible to reach a reasonable solution with local transmitters on a national basis. The potentially dangerous development is the placing of an increasing number of radio transmitters in space, particularly if these are broadcast or television transmitters.
It is
then possible that the transmitter will cross the main beam of the receiving antenna or a
24
R. Wielebinski
secondary lobes when this occurs the directivity of the antenna no longer provides the protection that it should. Unfortunately, natural radio signals, particularly the emissions from distant extragalactic sources, are extremely weak, and sharing the same frequency band with a space transmitter is not acceptable.
Interference detrimental to radio astronomy was,
and still is, generated by certain transmissions found experimentally in the case of the ATS-6 and SMS-l series of satellites. This was in spite of planned sharing of adjacent frequency bands. The transmitter technolo~rwas, unfortunately, such that serious out-ofband interferen~e was generated (see 4b below; detailed reports are available). Detrimental space transmissions were even found in the protected 1~4O0MHz band as shown by Oanadian experience.
A further problem arises from harmonics of transmitters in space.
To a large extent, the administrations responsible for telecommunications in different countries appreciate these problems and try to find solutions. The most important aspects are summarised in Report 224 - 4 of the COIR (xIvth Plenary Assembly, Kyoto 1978). The recommendations are internationally recognised, but they lead to the conclusion that harmful interference to radio—astronomy observations cannot be avoided only by the coordination of frequency allocations~ it is necessary that transmission from space to ground should be prohibited, not only in bands which are allocated for the radio-astronomy service, but also in adjacent bands. It is important that planning of space transmitters be undertaken more carefully, taking account of harmonics and of the locations where radio-astronomical observations are cuzTently made. In particular, the power of space transmitters should be kept low. A continuous coordination of frequency sharing between space transmissions and radio astronomy must be achieved; otherwise this field of research will be seriously affected. coordination has been recommended for many Allocation of Frequencies, set up by URSI, Administrative Radio Conference the status this body was and is to collect the wishes
Such
years by IUCAF (Inter-Union Commission on the IAU and COSPAR). Unfortunately, in the World of the Commission is only advisory. The task of of radio scientists, and to provide proposals for
international agreemeats which might then be presented to the WARC by sympathetic national administrations.