This article gives a brief introduction to the status of radio astronomy within the International Telecommunication Union (ITU), the body which coordinates global telecommunications. Radio astronomy entered the ITU arena in 1959 as a relative latecomer. By its nature, radio astronomy does not fit into the ITU system very well: regulators are hoping to facilitate commercial development of the radio spectrum, whereas astronomers are hoping to retain quiet frequency bands through which to study the Universe at ever higher sensitivity. Nevertheless there are major long-term goals which radio astronomers can realistically hope to achieve via the ITU in the years ahead, including more favourable frequency allocations and better regulatory protection. The prospects for radio astronomy at the forthcoming World Radio Conference WRC-2000 are reviewed. It is vital that radio astronomers participate in force at this WRC.

The World Radio Conference 2000 must be considered the most important one for radio astronomy since WARC-79. The conference agenda contains about 30 topics of substance, and more than 10 of these have direct impact on radio astronomy frequency allocations. From the perspective of radio astronomy the most important items are: “Allocation of Frequency Bands above 71 GHz to the Earth-Exploration Satellite Service (passive) and Radio Astronomy Service” and the agenda items dealing with Recommendation 66 (Unwanted Emissions). A review of the status of preparations is given.

Radio astronomy was born in the 1930s and matured in the 1950s. The telecommunications environment of those decades was dominated by monopolies (often state monopolies) and a strong regulatory environment. Radio communications were analogue in nature and mostly confined to frequencies below a few hundred megahertz. The worldwide telecommunications environment began to change in the 1960s and has undergone a revolution during the last three decades. Impulse for this revolution, which has not yet ended, was provided by political, as well as by technological developments. The most influential among these were the end of the cold war and the emergence of giant, often multinational telecommunications companies or consortia, that provide services previously reserved to state monopolies. Technically, the new era can be characterized by a host of new types of satellite services, the use of digital communication techniques, the proliferation of low power devices that do not require individual licensing and by a steady move towards higher frequencies. I discuss the evolution of some of these trends and their implications for radio astronomy.

Development of radio technologies will lead to a serious conflict between millimetre-wave astronomy and telecommunication services. I describe characteristics of millimetre-wave astronomy and technical aspects related to radio astronomical observations. Three examples of possible interference to millimetre-wave astronomy are described. It is very important to advertise what millimetre-wave astronomy contributes to human culture and to get support from the non-astronomical community to keep the radio windows open and clean.

Microwave atmospheric radiometry and radio, mm and sub-mm astronomy are “passive” services, i.e. not involved in any man-made transmission but only concerned with the reception of naturally occurring radio waves. The intensity of the radiation received is not subject to human control, unlike the situation for active services. All active services operate in bands occupied by natural signals of atmospheric and cosmic origin and the active service tranmissions may be powerful enough to noticeably interfere with reception of those signals by scientific services. A conflict exists for the coexistence of active and passive services in many frequency bands, which leads to a need for regulating how to share the electromagnetic spectrum. This document gives an overview of the problems of frequency sharing in the longwave region of the electromagnetic spectrum (radio to submillimetre waves).

European radio astronomy has major world-class facilites which operate successfully in a hostile electromagnetic and economic environment. In 1988 the Committee on Radio Astronomy Frequencies (CRAF) was established under the auspices of the European Science Foundation, ‘to keep the frequency bands used for radio astronomical observations free from interference’. Coordination of the European efforts through CRAF adds value through the sharing of expertise and information. Having one recognized voice for European radio astronomy also gives us strength. For example, the agreement concluded with Iridium LLC offered radio astronomy significant concessions compared with agreements reached elsewhere in the world. As Europe moves towards harmonized use of the radio spectrum, CRAF members participate in the discussions alongside representatives of governments and industry, to ensure that radio astronomy will have a secure future in Europe. This paper gives an overview of the European regulatory environment and the ways in which CRAF is working to protect radio astronomy.

Due to the very weak nature of signals from cosmic radio sources, the sensitivity of a radio telescope and receiver is about 40–60 dB higher than those of communications receivers. Hence, radio telescopes are generally located in relatively radio-quiet locations and operate in frequency bands that are protected against radio interference through frequency planning by national governments. Taking advantage of the much lower degree of radio interference in developing countries and the relatively labour-intensive nature of metre-wave radio telescopes, several such radio telescopes have been built and are planned in Argentina, Brazil, China, India, Mauritius and South Africa. Radio telescopes operating at cm-wavelengths are also planned in Egypt and Mexico.

A particularly severe problem arises for the radio astronomy service and other passive services below 2 GHz from the possibility of unacceptable emissions from satellites in unwanted bands (out-of-band and spurious emissions), due to the specific modulation schemes used in satellite transmitters. It is noted that this can be circumvented within the existing technologies if the satellite transmitters employ suitable bit-shaping or filtering techniques or use modulation schemes like Gaussian-filtered Minimum-Shift Keying (GMSK) which produce very little out-of-band emission. Although radio astronomy started in the western world at low frequencies, much low frequency radio astronomy is now planned or operational in developing countries. In order to protect the interests of these and other passive services within developing nations, it is important that suitable regulations be recommended to UNISPACE-III to provide appropriate protection.

Future radio telescopes will feature large increases in sensitivity, not only to celestial sources but also to man-made interference. In addition, they will need to measure spectral lines as a function of redshift and hence observe at arbitrary frequencies. Current international regulations governing the use of the radio spectrum are in principle inappropriate to these science-driven needs. There are still a few places on Earth that are relatively interference-free, but the coming generation of telecommunications satellites in low orbit will compromise even those sites. The Organization for Economic Cooperation and Development (OECD) has recently sponsored a working group on the future of radio astronomy, which recommended that the possibility of establishing one or more formally recognized International Radio Quiet Zones (IRQZ) be studied seriously. First results of that effort will be discussed.

We have carried out a series of measurements at some locations in Guizhou Province and one additional site at the Urumqi Astronomical Station in the Xinjiang autonomous region, to check on their suitability, from the point of view of interference, for the construction of a Five-hundred-meter Aperture Spherical Telescope (FAST). This large facility will in some sense act as a prototype for the Square Kilometer Array (SKA). Measurements were made using a commercial receiver in the frequency range 25–1500 MHz. The results in Guizhou look quite promising. A protected radio quiet zone in Guizhou would make it an ideal location for an international radio astronomical facility, and would establish the FAST site as a natural SKA location.

As a complement to spectrum management efforts by radio astronomers a number of observatories and research groups around the world have begun looking into technical solutions to the problem of separating weak cosmic radiation from man-made radio signals. Some of the technical research now getting underway includes: high dynamic range receivers, low-noise superconducting filters, passive digital filtering, adaptive filters, adaptive sidelobe nulling, multi-feed correlation of RFI, and various techniques for signal blanking.

Increased technical support to spectrum management can also be provided in the form of accurate and statistically significant characterization of the radio environment, empirical and theoretical improvement of over-the-horizon propagation models, and timely measurements of spurious radiation falling in the protected radio astronomy bands.

Finally, credibility of our spectrum management effort can only be maintained by making sure that local radiation under the control of our radio observatories is in compliance with the field strength limits of Recommendation ITU-R R.A.769. This requires sensitive radiation measurements and often shielding of digital equipment, microwave ovens, test equipment, local oscillators, etc.

In this paper, we first describe the situation of radio interference at the Miyun station in Beijing Astronomical Observatory, and then new developments in both hardware and software techniques of interference rejection for the Miyun Synthesis Radio Telescope (MSRT) are described.

For astronomers, monitoring of the radio spectrum is an obvious necessity in order to do observations which are free of interfering signals. Recent practice has shown that the installation of dedicated RFI surveillance antennas at radio astronomy sites has virtually become a necessity. Data obtained with such antennas have carried significant weight in discussions with other radio spectrum users. Furthermore, the growing number of dedicated antennas for RFI surveillance at radio observatories has opened the possibility for the establishment of common RFI databases. Such databases can provide objective numbers showing the degradation of the effective use of protected frequencies due to interference, to be used by astronomers as well as by their partners in frequency protection. As it is all too easy to drown in such a sea of data, discussions between astronomers themselves and with their partners are clearly necessary to define the form, implementation and use of such databases.

Fixed and mobile RFI search facilities at the Medicina radio astronomy station are described. A complex system of wide-band antennas that can be steered, has been designed and installed on the top of a 25-m high tower and connected with a wide-band sweeping receiver system. At present it works from 0.08 GHz up to 2.5 GHz in continuous mode. Low-noise front ends are used in the radio astronomy bands. A mobile system, equipped with a similar receiving system, has been designed to facilitate the interfering transmitter's position localization.

Nowadays we have a massively increasing use of radio techniques in a wide variety of application fields. Meanwhile state-of-the-art receiver technology dramatically increases the sensitivity of modern radio telescopes. This situation produces a worrying vulnerability of ground-based radio telescopes to Radio Frequency Interference (RFI). In order to monitor the RFI scenario within the frequency bands reserved for radio astronomy activities, a monitoring system, based on a quite new approach, has been developed and is presented here.

We first very briefly introduce the major radio facilities for astronomical research in China, and then report on the present interference situation at major radio observatories. Some of the radio interference problems are caused by paging services, mobile phone satellites, telemetry services for power supply, waterpower and earthquake activity, or radar systems, but some causes are unknown. In the worst case, harmful to radio astronomy, the Sesan VLBI station has not been able to do any observations at 92 cm due to serious radio interference problems since 1992. Still more serious interference coming from satellites can be expected in the next decade. International efforts on frequency protection should be urgently pursued if ground-based radio astronomy is to survive.

Shahe Station of our Solar Radio Group has suffered from radio interference in recent years, so we decided to move our solar radio telescopes to Huairou Station of BAO. We measured radio interference at both sites recently and found that the radio interference is more serious in Shahe than in Huairou. Although the interference is low at the single working frequency, we do find some radio interference within the working band at Shahe. It is comparatively radio quiet at Huairou and suitable for placement of the solar radio instruments there.

Based on the data observed by a solar radio spectrometer at 2.6–3.8 GHz and other measurements at Shahe Station, we analyze the radio interference and its influence on observations. We have identified three different types of interference: (a) from antenna; (b) from IFs; and (c) internal signals, etc. Corresponding measures can be taken to reject or correct these errors and to improve the observations.

Civil users of the NAVSTAR Global Positioning System (GPS) in Hungary occasionally experience interference at the 1575.42-MHz GPS signal frequency. As the application of the GPS technique spreads rapidly in our country, radio frequency interference (RFI) should be considered a serious threat. The new geodetic control network (OG-PSH) in Hungary is based on GPS measurements and incorporates more than 1100 sites. The paper reports the experiences gained during the establishment of the network. Interference sources were tracked to ground-based digital data transmissions for telecommunications, which operate mostly in the Western part of Hungary. Telecommunication regulations exceptionally allow such transmissions in specified countries. In order to warn potential GPS users, the interference sources are being mapped.

This paper outlines some of the radio frequency interference issues related to radio astronomy performed with space-based radio telescopes. Radio frequency interference that threatens radio astronomy observations from the surface of Earth will also degrade observations with space-based radio telescopes. However, any resulting interference could be different than for ground-based telescopes due to several factors. Space radio astronomy observations significantly enhance studies in different areas of astronomy. Several space radio astronomy experiments for studies in low-frequency radio astronomy, space VLBI, the cosmic microwave background and the submillimetre wavelengths have flown already. The first results from these missions have provided significant breakthroughs in our understanding of the nature of celestial radio radiation. Radio astronomers plan to deploy more radio telescopes in Earth orbit, in the vicinity of the L2 Sun-Earth Lagrangian point, and, in the more distant future, in the shielded zone of the Moon.

About 40 hours of observing data received by the space radio telescope HALCA at L-band (1.6 GHz) were analyzed in order to investigate interference received by the space radio telescope. Autocorrelation spectra for this study were specially prepared at the DRAO S2-correlator with a 7.8125 kHz frequency resolution in each 16 MHz channel. It was found that during 20% of the observing time the interfering signal was above the tolerable level of 1% of total receiver noise in a 16 MHz channel. The major source of interference is identified with uplink communication from ships to geostationary satellites in the International Maritime Satellite service (INMARSAT). The frequency range allocated for INMARSAT is 1636.5–1645.0 MHz. INMARSAT uses four geostationary satellites, two of which are located above the Atlantic Ocean where the strongest interference was observed. To avoid this interference it is recommended to move the HALCA observing frequency range from the currently used 1634–1666 MHz to 1645–1677 MHz. A simple criterion is proposed to predict harmful interference from INMARSAT. This criterion may be used in scheduling of future HALCA observations at L-band.