The European Science Foundation is an association of its 62
member research councils and academies in 21 countries. The ESF brings European scientists together to work on
topics of common concern, to co-ordinate the use of expensive facilities, and to discover and define new endeavors that will benefit from a co-operative approach
On behalf of European radio astronomers, the ESF Committee on Radio Astronomy Frequencies, CRAF, coordinates activities to keep the frequency bands used
by radio astronomers free from interference.
The scientific work sponsored by ESF includes basic research in the natural sciences, the medical and biosciences, the humanities and the social sciences.
The ESF links scholarship and research supported by its members and adds value by cooperation across national frontiers. Through its function as coordinator, and also by holding workshops and conferences and by enabling researchers to visit and study in laboratories throughout Europe, the ESF works for the advancement of European science.
On behalf of European radio astronomers, the ESF Committee on Radio Astronomy Frequencies, CRAF, coordinates activities to keep the frequency bands used
by radio astronomers free from interference.
The World Radio Conference WRC-97 is to be held in Geneva later this year, from 27th October to 21st November. At first sight the Agenda may seem to have little in it to concern radio astronomy. The Radio Astronomy Service is not even mentioned. Yet the outcome of this WRC could have a major impact on our science. Under agenda item 1.9.1 the WRC will consider possible new frequency allocations for the mobile-satellite and fixed-satellite services. Many bands are under consideration at this moment, including bands 1390-1400, 1427-1429 and 1429-1432 MHz which are close to the hydrogen 21-cm line. Earlier generations of frequency managers took some care that bands adjacent to the hydrogen line band 1400-1427 MHz were themselves kept fairly quiet. For that reason these relatively quiet bands now look attractive to incoming mobile-satellite services, who need to find a home without disturbing too many people. The experience we have at 1612 MHz with interference from GLONASS and GPS, and the interference levels predicted for the Iridium constellation, give great cause for concern. A new satellite downlink close to the hydrogen line band (the single most important band allocated to radio astronomy) would be a recipe for disaster. Radio astronomers need to be sure to brief their national administrations on the importance of this band and the difficulty of protecting radio astronomy bands from unwanted emissions from satellites.
Task Group 1-3 was convened to deal with the problem of unwanted emissions, including those from satellites. Under agenda item 1.7 the WRC will consider the results of Task Group 1-3 on spurious emissions, which are a subset of unwanted emissions, and will decide whether or not to accept the recommendations of the group. The discussions within Task Group 1-3 were often extremely polarised between the Europeans, who have adopted tight standards for new systems, and the Americans, who have older, looser standards, which seem to work in the wide open spaces. Satellite operators are used to having no limits at all on their unwanted emissions, and they asked for an exemption, to give them more time to study the implications of adopting the limits proposed by Task Group 1-3. In fact radio astronomy will need more than the proposed limits to achieve protection from satellites (see Section 5 of this Newsletter).
We must hope that the WRC will see the connection between these two agenda items. If new allocations are sought for satellite downlinks, and if the satellite operators cannot accept limits on their unwanted emissions, then the new allocations need to be placed in parts of the spectrum where any unwanted emissions will not cause undue interference. At the present time it would be extremely poor spectrum engineering to place new space-to-Earth allocations close to passive bands.
R.J.Cohen - Jodrell Bank
The report of CEPT SE28 on the downlink aspect of the sharing problem between MSS and Radio Astronomy was considered by CRAF but rejected, since it reflected too strongly the opinion of Motorola. The meeting discussed the question of non-disclosure agreements and MoUs, and prepared a strategy to deal with possible requests for discussions between Motorola and individual radio astronomy observatories on the MSS sharing issue at 1.6 GHz. In all discussions CRAF insists on the levels of harmful interference as given in ITU-R RA769-1 (for 1.6 GHz: -238 dBW m-2 Hz-1).
ITU-R TG1-3 has concluded its studies on spurious emission levels, but has not been able to recommend generic spurious emission levels which will protect the Radio Astronomy Service. TG1-3 is now succeeded by TG1-5, which will consider limits on out-of-band emissions and review the new TG1-3 limits on spurious emissions. TG1-5 will also the discussions started within TG1-3 on the applicability of Monte Carlo methods to these problems.
As a follow up of the 1996 World Telecommunication Policy Forum, WTPF, a Memorandum of Understanding for Global Mobile Personal Communication by Satellite, GMPCS, had been prepared by the ITU. This document radiates potential threats for radio astronomy when satellite operators are given too much support. CRAF informed the European Radiocommunications Committee, ERC, in Copenhagen about the threats by Mobile Satellite systems to the Radio Astronomy Service and asked for a Europe wide political solution.
The 2nd edition of the CRAF Handbook for Radio Astronomy will be published in June 1997 (see section 3).
Among the other topics discussed were the severe interference problems in Italy at 1.6 GHz (which prevent Italy to be a reliable and full participant in the VLBI operations at this frequency). With Italian radio astronomers and the CNR lawyer, CRAF discussed this problem with the Italian administration with the result that the latter undertook action to remove the interference out of the affected band. Interference from an unregistered satellite system at 328.25 MHz and the ASTRA-trouble at 10.6-10.7 GHz remain of continuous concern.
The 24th CRAF meeting is on October 20-21, 1997, in Zürich, Switzerland.
The 2nd edition of the CRAF Handbook for Radio Astronomy will be published in July 1997.
This document reviews the radio astronomical needs. It is conceptually based on the continuation of the protection of this service.
For the sake of the continuation and progress of the science of radio astronomy, CRAF takes the starting-point that frequency protection should be maintained at least to the level the Radio Astronomy Service has enjoyed until now.
This Handbook for frequency allocations in connection with radio astronomy has been prepared by CRAF. It provides a comprehensive review of matters related to spectrum management and the protection of the science of radio astronomy against harmful interference. This review is placed within the historical and technological context within which the Radio Astronomy Service operates.
This book addresses a wide readership outside the professional radio astronomy community.
The Table of contents of the 2nd edition of this Handbook is in summary:
Since January 1997, CRAF participated in three CEPT SE28 project team meetings. Usually around 25 participants from administrations, MSS organizations and CRAF attended the meetings.
The radio astronomy discussions addressed the following topics:
 software program of FT simulations implementing the SE28 methodology.
This methodology to be used for the determination of coordination zones around radio observatories to avoid radio interference from mobile earth stations is based on the Monte Carlo method. The CNET, INMARSAT and J.E.P.Ponsonby (Jodrell Bank) wrote software programs on the basis of algorithms from the SE28 methodology.
The present status of this is that software validation has not yet been done to sufficient extent. The software produced at CNET and INMARSAT will (at least for the time being) only be made available as executable files - not as source code. It is already known that the three programs have been written with different scopes in mind, which implies that some work has to be done to compare the different simulations in detail. Furthermore, at present the software is still in the debug-phase. Real simulation comparison cannot be done yet.
The third phase in this process should be a direct comparison with reality or site testing to confront its results with the software calculations. At present no action plan has been developed for this.
 downlink of MSS satellites and radio astronomy.
SE28 was not yet able to prepare a document presenting its conclusions to the SE Working Group of the CEPT. The opinions of Motorola and CRAF are very different. Furthermore, it is observed that Motorola uses SE28 meetings to quarrel ITU-R RA769-1. The positions are in fact clear: Motorola is not able to accept the protection criteria for radio astronomy and CRAF cannot accept the Motorola conditions which imply that giving away measurement quality and telescope efficiency is synonym with "interference protection". Motorola proposals do only state obligations and concessions from the Radio Astronomy Service without any obligation or concession by Motorola. Furthermore, Motorola could not discuss technical details showing to which extent the Iridium system takes the protection criteria for radio astronomy into account.
A new ITU-R Task Group has been initiated to succeed TG1-3: TG1-5. This task group will continue the study of out-of-band emissions. The conclusions on transmissions from spacecraft remained unresolved in TG1-3 because of strong opposition of space operators. Europe at least tries to keep the discussion about spurious and the distinction line (+/- 250%) open. This task group will also investigate the applicability of Monte Carlo methods for coordination purposes. It has been registered by CRAF in the TG1-3 chairman's report that he is aware of the fact that "Radio astronomy and space services using passive sensors are particularly sensitive as shown in annex 3 of the recommendation. In no way would Category A limits provide adequate protection to these services. Therefore, other mitigation techniques should be brought to the attention of the administrations to take care of this issue."
At the WRC97 only the category A limits will be considered. The reference to radio astronomy will be very minute. According to CRAF, this reference should be enhanced. The US view is that the category B limits should be rejected: these work in Europe but the US cannot meet them. The US interprets this discrepancy as trade war between the US and Europe. The Radio Astronomy Service should become involved in this discussion. One can even argue that it is cheaper not to waste power.
TG1-5 will probably form a sub-group with special reference to radio astronomy and downlink aspects.
The UK Radiocommunications Agency commissioned a technical study on unwanted emissions from other services into Radio Astronomy Service application, for consideration by TG1-5.
The ITU-R working party 7D (Radio Astronomy) met at ITU headquarters in Geneva during June 2-6, 1997. 15 persons actively participated in the meeting: 11 of these were radio astronomers (half of them CRAF members).
The topic which was most extensively discussed, was sharing between the Radio Astronomy Service and Mobile-Satellite Service in the 1.6 GHz frequency domain. A liaison statement from WP8D, containing a Draft New Recommendation on sharing the bands 1610.6 - 1613.8 MHz and 1660 - 1660.5 MHz using Monte Carlo based interference assessment tools, and a French input document with almost identical content, were intensively discussed throughout the whole week. This discussion had filled already two preceeding 7D meetings, parallelled by CEPT-SE28, CPG and CPM activities. WP7D considered the proposed new recommendation still unacceptable and kept it as a Temporary Document. In a liaison statement back to Study Group 8 and to WP8D approval of the general methodology was confirmed and a joint group to work out acceptable input parameters and test of the software realization was proposed.
In the same context a New Question has been adopted, which asked to study the impact of the loss of a certain fraction of observing time due to interference onto radio astronomical research. This study shall come to conclusions before 1st December 1998 and will provide one of the most critical input parameters for Monte Carlo calculations.
One of the surprises for the meeting was a paper submitted by Inmarsat, in which proof was offered that a certain MSS system could share the band 1660.5 - 1668.4 MHz without harmfully interfering with a radio astronomical satellite system (VSOP), currently being installed. The real surprise concerned not false assumptions made, but the frequency band envisaged. This band is a primary PASSIVE band, and the secondary allocation to the Mobile Service even excludes aeronautical mobiles. Therefore, WP7D considered this paper irrelevant, but feared strongly that some firms may start to run amuck.
The other important topics were mm-wave bands and unwanted emissions. A New Question was adopted, asking with which active services - and under which conditions - radio astronomy could share bands above 70 GHz. The study shall be completed before 1st December 1998, in order to provide input to the CPM preparing the WRC 1999.
Also aiming at the WRC 1999 conference, liaison statements were written to the newly formed Task Group 1/5, expressing general concern about too relaxed limits for unwanted emissions and specific problems with respect to one proposed system (i.e. Sky Station).
K. Ruf - Bonn
A cloud-radar is one of the instruments investigated within the ESA Earth Observation Prepatory Program (EOPP). It is a potential candidate for a future Earth Observation mission. Such an active instrument is of high interest as it can provide data about the vertical profile within the cloud structure. It will most likely operate near 95 GHz, with a transmit power (pulsed) near to 1 kW, using a highly directive sensor (an antenna with about 2.5 m diameter reflector).
The frequency band near 95 GHz is of interest to other (passive) users: e.g. the radio astronomy community has strong interest in observations in the mm-wave domain. The spectral line observations are done to study the physical conditions within the source of the related line emission. This work is done at a number of mm-wave observatories spread all over the world. mm-Wave radio telescopes make use of a ultra-sensitive wide band receivers. At present, mm-wave astronomical observations are done at frequencies up to about 1 THz. However, the unique information each spectral line provides about the physics and also the chemistry of the Universe implies that observations in one frequency domain cannot be a substitute for those in a different frequency domain. At present more than 100 different molecules have been detected and are subject to daily investigation. The spectral line observations reveal not only the physical conditions within the radio source but also about the kinematics in the celestial object within which the source resides and about even the distance scale of the Universe as a whole (as derived from maser emission).
The spectral power flux density, spfd, generated on the Earth surface by an orbiting cloud-radar can reach such a level, which would lead to interference with significant consequences for the radio astronomical observations: If the radio telescope pointing direction and the direction of pointing of the radar would be co-aligned (which could occur with a certain low probability) the interference could even be destructive for the ultra sensitive receiver front-end, if no precautions are taken, although frequencies of operations are slightly different from the radar frequency. An interference situation could occur also when a sidelobe-sidelobe coupling scenario would be present, in certain situations it could lead to interferences, causing a loss of observations and degradation of data quality.
This situation was well recognized in ESA and in order to study such interference scenario and to investigate possible means to improve upon such situation, a study was initiated by EOPP, for which Oerlicon Contraves SpA is responsible. The activity is being carried out in close cooperation with CRAF.
Within the scope of this activity, it has been possible to explore the potential and limitations of certain band stop filter configurations, which could provide reduction of the signal level into the ultra sensitive radio telescope receiver. This approach is one of the possible approaches to prevent interference and more work is needed to provide operational scenarios for users of the electromagnetic spectrum without interferences.
Initial results for such filter configuration are promising and an initial proof of capabilities demonstrated by a realised bread-board component, is available. In fact, this activity has contributed to significant progress in the accurate design and realisation of specialised millimetre wave components, not only for this application: For the first time it was possible to design, accurately manufacture and test a millimetre wave (near 95 GHz) stop band filter with indicatively promising results. Design tools were derived from antenna design tools already developed for highly accurate corrugated horn antennas, with a capability to analyse a number of different configurations for the separate corrugations and with a capability to analyse a high number of such cascaded corrugations (as in a corrugated horn). Based on mode matching approaches, these tools are well advanced, making use of a variety of modesets and in fact numerical approaches for situations as encountered in non-rotational structures (like available in polarisers) were already handled as well. This approach has been necessary, as the usual approaches in filter design do not normally foresee to handle configurations as employed here. In fact, the use of coaxial mode sets as needed in ring-loaded corrugations, still has to appear in several filter design tools. Band stop filters are also not frequently encountered and their application at these frequencies makes the situation not more easy in realisation and so as a result the design process deserves to some extent some respect. A short trade-off study led to a proposed design which was investigated in more detail and which has been realised.
C.G.M. van 't Klooster - ESTEC
As part of ESA's Earth Observation Programme, ESA is presently investigating the design of a satellite for Earth radiation measurements (see Section 7.1). This satellite is intended to be launched sometime between 2003 and 2005 with an estimated mission duration of 4 years. The satellite will have in its payload a Cloud Profiling Radar (CPR) which will provide vertical active sounding of cloud-layer structure down to the terrestrial surface (Newsletter 1997-1).
The band 78 - 79 GHz has been allocated for this purpose already during WARC-79. Due to Rayleigh scattering of the radar signal on the cloud droplets the echo amplitude goes as the fourth power of the frequency. This is counteracted by the atmospheric attenuation which also is increasing with increasing frequency. Therefore the meteorologists want to change the allocation to 94 - 95 GHz in order to gain a factor of 2 in sensitivity. However, this frequency band is close to the middle of the 3-mm atmospheric window and of great interest for radio astronomy.
ESA, Oerlikon-Contraves and CRAF collaborated to investigates methods to protect radio astronomy from harmful interference due to the CPR. The final meeting of phase 1 of this project was held at ESTEC on March 24, 1997. The project, however, will continue with a "Phase II" (until January 1998) in which wave-guide band-stop filters will be carefully manufactured and measured at both room and cryogenic (about 20 K) temperatures and a new type of corrugated horn will be designed, manufactured, and tested. The Osservatorio di Arcetri will participate in this part of the project.
During the FM at ESTEC the following 'highlights' were noted during the discussions.
* ESA prefers a nadir-looking satellite radar. Since all millimetre-wave telescopes have alt-azimuth mounts, they all have a circular cone centred at zenith within which they cannot track a radio source, because the angular speed in azimuth would become higher than the maximum possible speed. The size of this 'zone of avoidance' thus depends on this maximum speed. Therefore when the CPR passes directly over an observing millimetre-wave telescope, a mainlobe-to-mainlobe coupling will not be possible. The decision of ESTEC to interrupt radar transmission when the CPR is within 14 degrees from zenith as seen from a millimetre-wave telescope will further relieve the danger of destroying the SIS element. However, it was pointed out that some millimetre-wave telescopes are parked in the zenith position for maintenance and repair work. An investigation as to which telescopes fall into this category will have to be made.
* The manufacturing and testing of two circular wave guide stopband filters were described: one 15-slot corrugated filter and one 3-double ring-loaded filter. The tests had been carried out in November 1996 using a Hewlett-Packard 8510 C network analyzer. The results look promising but there is still a lot of work to be done regarding rejection level and insertion loss. Also a comparison between the measured values and simulated values was presented. The conclusion was that a size tolerance of 2 - 3 micrometres would be necessary for the 15-slot corrugated filter whereas about 10 micrometres would be sufficient for the 3-double ring-loaded filter.
A. Winnberg - Onsala <
Under the auspices of IUCAF, the Inter-Union Commission on Frequencies Allocations, a working group will investigate the spectrum needs for mm-wave astronomy. It will address the question of frequency usage by the different observatories, scientific priorities for use of frequency bands, the nature of mm-wave astronomy compared with radio astronomy at longer wavelengths and its related protection criteria and requirements. The goal of this working group is a frequency table indicating required frequency allocations for mm-wave astronomy up to 1 THz.
The first meeting of this working group will take place during the General Assembly of the International Astronomical Union, IAU, which is held in Kyoto during August 18 - 30, 1997. CRAF input to this working group is a document on astronomy above 30 GHz in the mm-wave domain.
By the end of September 1995, the Ministry of PTT in Rome had decided that private repeaters of radio or TV channels can be allocated in the 1660.5 - 1668.4 MHz band to be used by channelised FM stations spaced 200 kHz. The Ministry added in a footnote the "priority to the Radio Aastronomy Service when appropriate". The local authority for the region Emilia-Romagna in which Bologna and Medicina are located had discussions with the Bolognese radio astronomers to protect the Radio Astronomy Service effectively. However, since each regional authority can act independent from other regions, fixed link applications in these regions may have severe impact on radio astronomy in Bologna and Medicina. Outside the Emilia-Romagna region, several tens of FM stations have been spotted causing harmful interference to radio astronomy. These stations are located from Trieste and Venice to places in Toscane.
The opinion of the Ministry was initially that the licenses were provisional. Bolognese radio astronomers brought their concerns to the attention of the PTT Ministry in Rome.
IUCAF had written a letter to endorse this concern, especially because of the Italian role in the European VLBI Network and as a partner in the operations of space VLBI in general and the VLBI Space Observatory Programme, VSOP, in particular. The Italian Ministry replied (May, 1996) that it started to investigate in deep each interference situation, revoking licenses to fixed services were necessary.
On November 27th, 1996, representatives of the Istituto di Radioastronomia in Bologna, the CNR legal office and the CRAF secretary discussed this problem with representatives of the Italian PTT (Directorate General for Frequency management) in much detail. The discussion addressed also future developments in Italy and Europe (like the DSI project of the CEPT). The Italian PTT explained the local problems it has to solve. However, some legal aspects might have needed some more attention. The meeting concluded with several action items on all parties.
Following the results of this meeting, the Director General of the Italian Ministry of Posts and Telecom, Ing. G. Guidarelli Mattioli, informed on February 27th, 1997, that it had brought the case to the attention of all Directors of Regional PTTs of Northern and Central Italy. The contents of this information is in summary, that as a follow up of previous decisions of the Ministry with respect to the utilisation by private radio links of the band 1660-1670 MHz, it informed these directors that as a consequence of the contacts between CNR and Ing. Guidarelli Mattioli, emerges that in order to protect the Radio Astronomy Service from interference, a 'respect distance' of at least 400 km is considered necessary. [Note: This is the minimum distance was based on calculations of Bolognese radio astronomers]. He stated: "We invite, therefore, the local PTT offices to stop any further allocation of private radio links in the above mentioned band in the Regions of respective competence and to initiate the withdrawal of all previously given allocations giving maximum priority to those already signalled as interfering by the Institute of Radioastronomy." With the latter institute, the Istituto di Radioastronomia in Bologna and its operations in Medicina were meant.
The Radio Astronomy Service has a primary allocation in the band 10.6 - 10.7 GHz. The subband 10.68 - 10.7 GHz has a primary passive allocation (FN: S5.340). However, out-of-band emission into the band 10.6 - 10.7 GHz caused by the GDL-6/ASTRA-1D satellite degrades radio astronomical observations at the Effelsberg Radio Observatory, Germany, dramatically: effectively no observations can be done in this frequency domain. The GDL-6/ASTRA-1D satellites operates in the Fixed Satellite Service and uses the space-to-Earth transmissions for direct-to-home television broadcasting. In 1995 CRAF informed the operator, Société Européenne des Satellites in Luxemburg, about this harmful interference which is documented above 10.695 GHz within the passive band.
ITU-R RA769-1 gives a threshold for harmful interference in the 10.6 - 10.7 GHz band as -160 dBW/m2. The GDL-6/ASTRA-1D out-of-band emission has a spectral power flux density of -158 dBW/m2/100 kHz at 10.7 GHz, falling at about 10 dB per 4 MHz at that point. If it continues to fall at this rate, the total power into the band 10.6 - 10.7 GHz is -145.6 dBW/m2, which is 14.4 dB above the threshold mentioned, and noticeable throughout the whole radio astronomy band. Note that the limits in ITU-R RA769-1 are for terrestrial interferers with an assumed sidelobe level of the radio astronomy antenna of 0 dBi; emitters in the geostationary orbit should stay 15 dB lower in the band allocated to the Radio Astronomy Service.
The operator confirmed the validity of the complaint of CRAF.
The operator informed CRAF that he performed tests using a satellite simulator, and found that the FM uplink signals have a spectrum error after spectrum regeneration to ~ 10 GHz. The plan (explained by the operator) is that the uplink spectrum of the GDL-6/ASTRA-1D is modified to improve the spectrum at ~10.7 GHz. However, the interference is still observed.
CRAF reminded the operator of the problem during a CEPT-FM meeting in May 1996 (Newsletter 1996/2). The operator did make some improvements but so far the Effelsberg Radio Observatory is not able to resume observations in this band due to this interference.
On May 28, 1997, the US Federal Communications Commission, FCC, released a draft recommendation to the WRC97 to allocate non-GSO MSS feeder links in the band 1390-1400 MHz (Earth-to-space) and 1427-1429 MHz (Earth-to-space) and 1429-1432 MHz (space-to-Earth) bands. [FCC Reference No.: ISP-96-005, specifically its Recommendtaion 2]. The draft proposal was open for public comments will June 16, 1997.
CORF, CRAF and IUCAF reacted to this recommendation. CRAF brought the following under the attention of the FCC:
"In brief the concerns are as follows:
"The proposal for a space-to-Earth downlink at 1427-1432 MHz is extremely worrying for European radio astronomers. There is concern that the downlink emissions will not be able to meet the technical limitations which are proposed, viz.
"Stations operating in the Fixed-Satellite Service (space-to-Earth) in the 1429-1432 MHz band shall limit unwanted emissions in the 1400-1427 MHz band to -239 dBW/m2/Hz in any 20 kHz band, and to -255 dBW/m2/Hz averaged over the 1400-1427 MHz band (see ITU-R REC.769)."
"Experience with reference from GLONASS and GPS satellites at similar frequencies suggests that the limits would not be met. Predicted emission levels for the Iridium system reinforce this concern.
"Secondly, there is concern that the European radio astronomy operations would be compromised even if the limits were met. The limits are taken from ITU-R RA.769 and are based on the assumption of 0dBi gain of the radio astronomy telescope in the direction of the interfering transmitter. Taking the ITU-R reference antenna pattern, 0dBi gain is exceeded towards any satellite within 19 degrees of the main beam, which is already 5% of the sky for just one satellite. For a constellation of satellites the interference potential is worse in proportion to the number. For several constellations it would be a coordination nightmare to establish which were the clear times with no satellite near the main beam.
"Finally, the proposal to have Earth-to-space uplinks in the band 1390-1400 MHz could cause difficulties for radio astronomy observations of the red-shifted hydrogen line, for which the Radio Astronomy Service has an allocation in different countries supporting radio astronomy (1330-1400 MHz)."
CRAF also referred to the IUCAF letter to the FCC and stated that it endorsed that response on behalf of the European radio astronomy community.