The Committee on Radio Astronomy Frequencies (CRAF) is a committee of
the European Science Foundation (ESF).
CRAF is the ESF Expert Committee on Radio Astronomy Frequencies. CRAF coordinates the efforts on frequency protection for European radio astronomy, passive remote sensing and related sciences.
CRAF usually holds two meetings per year. In 1997 CRAF had its 23rd meeting in St.Peterburg at Pulkovo Observatory in April 24-25, 1997, while its 24th meeting will be held in Zurich at the ETHZ in October 20-21, 1997.
The main subjects discussed at meeting 23 were again the compatibility of new Mobile Satellite Services with radio astronomy in the 1.6 GHz bands, the associated work of CRAF in the CEPT SE28 project team, progress of the ITU-R Task Group 1/3 and new work in the ITU-R Task Group 1/5. TG1/3 is charged with establishing limits on spurious emissions (including spurious emissions from satellites), while TG1/5 continues the work of TG1/3, while it also discusses coordination methodology. Policy issues regarding mm-wave astronomy were also a main issue on the 23rd CRAF meeting.
At the 24th CRAF meeting CRAF remote sensing colleages will be present. By this CRAF attempts to bring radio astronomers and remote sensing people together to make the activities of both communities as coherent as possible.
The new Mobile Satellite Services will involve uplinks from the user terminals to the satellites at frequencies which overlap the OH 1612 MHz line. Work within the SE28 project team includes a methodology to calculate exclusion zones around radio astronomy observatories, within which mobile uplinks will not operate on the radio astronomy frequencies. This work is being carried forward to the ITU-R and also within the CEPT as a common European position which will protect radio astronomy. The Iridium system also proposes to use a downlink from the satellites to the user terminals at frequencies adjacent to the OH 1612 MHz line. This is proving a more difficult problem to solve. The satellites will generate unwanted emissions due to intermodulation in the power amplifiers, at levels which will cause interference to radio astronomy observations. This problem does not have an easy solution.
CRAF members are also working in project team CEPT SE21, and the worldwide Task Groups 1/5 which are looking at the problem of spurious emissions such as those from Iridium, with the aim of setting limits which are economically and technically feasible and which at the same time will protect radio astronomy and other passive services. TG1/3 was not able to set limits on out-of-band emissions while its limits for spurious emission are not acceptable for the radio astronomy community. Representatives of the space services are not happy with the limits which radio astronomers need for protection. To complete the work of TG1/3 the ITU installed a new Task Group, TG1/5, will also study the applicability of Monte Carlo methods in coordination questions. The first TG1/5 meeting was held in July 1997 in Geneva.
The protection of mm-wave astronomy is becoming an issue for concern. The first serious potential threat of interference has appeared in the form of a proposal for a satellite-borne cloud radar system at 95-GHz. The power levels of the system are such that sensitive radio astronomy detectors could be destroyed if the satellite passed through the telescope's main beam. In a joint project of ESA, Oerlikon-Contraves and CRAF filter technology was developed to protect mm-wave these detectors. CRAF has also prepared a general position paper on the protection requirements for mm-wave astronomy. With this as input IUCAF reviews the frequency requirements and priorities for mm-wave astronomy.
Other topics discussed include the interference problems in Italy at 1.6 GHz (after a discussion of CRAF and Italian radio astronomers the Italian administration took steps to improve the situation for radio astronomy), interference from an unregistered satellite at 328.25 MHz, continuing problems at 10.6-10.7 GHz from ASTRA transmissions in an adjacent band, and a proposed TV transmitter in Denmark on channel 38 (which is used for radio astronomy in several nearby countries - Poland, Sweden, Netherlands, Germany and the UK). CRAF is working hard on the solution of these problems.
CRAF has published the 2nd edition of its "Handbook for Radio Astronomy" in August 1997. The CRAF secrtariat received many positive reactions from industry, administrations and other users of the handbook. Some administrations asked for more copies since they want to study the radio astronomy requirements in more detail (in one case in a special working group).
In addition CRAF informs the world about various aspects on frequency protection for radio astronomy on the WorldWideWeb. This information includes a regular Newsletter. The CEPT having seen this, has installed a direct link between the WWW homepage of the European Radiocommunications Office, ERO, and CRAF. This information has been read already by more than 1000 "visitors" from more than40 countries. US industry (presumably satellite operators) showed great interest in CRAF. p> CRAF continues to act as the European voice on radio astronomy frequency protection matters, to coordinate the activities of its members in frequency protection and to develop new techniques for dealing with interference both by reducing it at source and by rejecting it in data acquisition and data analysis procedures. The work load in all these areas is growing. CRAF therefore is happy that with financial support of the ESF and European radio observatories it has been able to appoint a full-time spectrum manager for European radio astronomy. Dr.T.A.Th.Spoelstra, the present CRAF secretary, has accepted to take this position.
Outside Europe CRAF, its US sister organization CORF and the international sister IUCAF work closely together. Due to activities of CRAF China has also installed a national body to work on the protection of frequencies, while a regional Asia/Pacific Rim "CRAF" is under "construction".
CRAF has liaison persons in various administrations including the US and China.
It is a time of great change in telecommunications and also a time of great opportunity for radio astronomy to stake its claim. The CEPT is working to harmonize European frequency use and standards. By participating in this work CRAF is able to ensure that the new frequency-harmonized Europe will be one where radio astronomy can continue to flourish.