CRAF Newsletter 1997/1

CRAF Newsletter 1997/1

February 1997

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
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.


1. The Chairman's Corner

In November this year the World Radio Conference WRC-97 will consider the issue of spurious emissions. Radio astronomers played an important role in placing the issue before the ITU at WARC-92. We worked on it through Task Group 1-3, where it became clear that there are powerful commercial interests in not tightening the limits on spurious limits. For some influential countries the commercial considerations override all others. The output from Task Group 1-3 was deeply disappointing for the radio astronomy service, despite the many friends we found within the group. But this is not the time to give up. A new Task Group 1-5 will continue the work and extend it to out-of-band emissions, that is, those nearest to the operating frequency. We have much we can contribute to the work of the new task group. We need to bring clear evidence of interference when evidence is needed. However we must not expect people to feel sorry for us. We must make the radio community realize that spurious emissions will ultimately be everyone's problem. Even those people who are prepared to cut corners now to gain an advantage in the market place will suffer eventually as the spectrum becomes more congested.

During the final meeting of Task Group 1-3 a remarkable presentation was made which illustrates the point that spurious emissions are a real problem for everybody. It is a sorry tale concerning COSPAS/SARSAT, a satellite-based system designed to save lives by locating emergency beacons at 406MHz. The system has an exclusive worldwide frequency allocation. Yet there are many times and places in the world where your distress signal would not be heard because of interference. An extensive press release was issued to the delegates explaining the interference problems. In some cases spurious emissions from radars were to blame. In other cases it was illegal transmitters. Did any CRAF member see this story reported in the press? Where did all those press releases go? Perhaps the story was felt by the men in grey suits to be too sensitive for public consumption. As a community we must help to raise awareness of radio pollution, not only by contributing to ITU Task Groups and Study Groups, but by widening the debate to include the ordinary men and women who are unwittingly paying the price.

R.J.Cohen - Jodrell Bank

2. CRAF Meeting 22 [25-26 November 1996]

The main subjects discussed at the meeting concerned the threat from MSS and the progress of CRAF's activities in the CEPT SE28 project team dealing with sharing MSS operations with other services, ITU WP7D and TG1-3 progress and ITU policy issues. In addition the strategy concerning a full-time CRAF frequency manager was discussed extensively on the basis of a financial plan proposed by the ESF. CRAF and the ESF will bring this under the attention of the directors of the European radio observatories and investigate their support possibilities.

Results of CEPT SE28 on the methodology to calculate protection zones for radio astronomy observatories were presented at WP7D. However, due to insufficient clarity and quantitative results available at the WP7D meeting, WP7D decided to continue studying the SE28 methodology and reconsider it in June 1997. Among the many discussions in WP7D was also the possible reallocation of frequencies around 95 GHz to accommodate a cloud radar system in that frequency range. No decision was made, but it was clear that radio astronomy did not support the use of these frequencies for cloud radar applications.

Also undecided was the position of radio astronomy regarding the amount of data loss due to interference with and without varying propagation conditions. At present a value of 10% is used in ITU-R literature for use in propagation models, but it is widely felt that this is too large a percentage for general data loss.

Among the recent ITU meetings were a World Telecommunication Policy Forum, WTPF, dealing with "Global Mobile Personal Communication by Satellite", GMPCS, and a meeting on the structure of the ITU by the year 2000, ITU2000. The WTPF agreed on five "opinions" which expressed possible actions to facilitate and harmonize the introduction of GMPCS on a worldwide basis. However, this meeting has no regulatory status.

The ITU2000 project will formulate recommendations to the ITU Plenipotentiary Conference on the rights and obligations of Members and members and on strengthening the financial basis of the ITU, including consequential changes to the structure of the Union. These developments may result in acceptable conditions for non-profit organizations to participate in ITU-sector activities.

The work of TG 1-3 was completed but its results are not satisfactory for radio astronomy. The proposed interference levels are too relaxed, particularly for transmitters on spacecraft. In a follow-up task group some of the issues will be addressed again.

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); interference from an unregistered satellite system at 328.25 MHz, continuing trouble at 10.6-10.7 GHz because of the ASTRA transmissions and a new channel 38 TV transmitter in Denmark. CRAF is working hard on the solution of these problems.

3. CEPT SE28

CRAF participated in the 8th and 9th meetings of this CEPT SE28 project team which were, repectively, held on 5-6 December 1996 in Paris at CNET [R.J.Cohen, E.Gerard, J.E.B.Ponsonby and T.A.Th.Spoelstra] and 10 January 1997 [E.Gerard and T.A.Th.Spoelstra]. Around 15 participants from administrations, MSS organizations and CRAF attended the meetings.

3.1. 8th Meeting of CEPT SE28

On the 8th meeting, the radio astronomy discussions took only place on the second day.

Two items were discussed:

[1] the evaluation of the SE28 report on the methodology to determine coordination zones around radio astronomy observatories;

[2] protection of radio astronomy against out-of-band interference from downlink transmissions from MSS satellites in the band 1613.8-1626.5 MHz.

Cohen explained that WP7D did not reject the SE28 document, but was not able to evaluate it properly because WP7D considered that this complex document was (a) submitted late and nobody present at the WP7D meeting in Geneva (8-16 October 1996) was able to defend the document; (b) explanatory examples of results were lacking; (c) the document explicitly used a value of 10% of data loss due to interference acceptable for radio astronomers. CRAF stated clearly the WP7D did not reach a conclusion about this value: it is still an open question which value of x% would be correct for the MSS case. CRAF discussed this at its 22nd meeting (Bologna, 25-26 November 1996) and prefers a value of about 2% instead of 10%.

Ponsonby is working on a software package based on the document. He made a point in demonstrating a first version of his software in front of the audience. SE28 decided that the document will be improved and it will carry out software validation on the basis of (not yet publicly available) CNET software, similar software developed by INMARSAT and the software developed by Ponsonby.

Concerning the protection of radio astronomy against out-of-band downlink interference Motorola submitted a document in which it explained that on the basis of calculations done for Jodrell Bank, radio astronomy is well-protected. Cohen, who has examined these calculations explained very clearly the non-sense nature of this document: telling radio astronomers that they have to live with interference for some (unknown) amount of time and telling radio astronomers that a "gentle unwanted spectrum across the RAS band with a small ripple" is basically the same as telling a victim that he has to protect the criminal. Motorola places itself on a position to tell radio astronomers what they shall/might/could do but does not want to discuss what Iridium will do. Ponsonby showed that from open literature it is clear that no technical effort is done by Motorola to protect the Radio Astronomy Service against unwanted emission from the Iridium system.

The chairman concluded that no progress is possible in this discussion. The UK administration nevertheless prefers to keep the discussion open as long as possible. The next meeting will prepare a final statement about this topic.

3.2. 9th Meeting of CEPT SE28

The radio astronomy discussions during the 9th meeting addressed the following topics:

[1] in relation to a requested liaison statement to CEPT PT3 the meeting has to inform PT3 what passive space research is done in the band 1660-1670 MHz. CRAF informed the meeting that except radio astronomy no other use of this band is made. This band will be of great importance for VSOP operations, since it is an important band for VLBI.

[2] interference from aircraft earth stations into RAS: A draft document on this subject was presented by Gerard. The U.K. administration presented a document on the applicability of the RAS/MES methodology to aircraft earth stations. SE28 supports the proposal by PT3 to exclude aircraft earth stations from co-frequency operation. As to adjacent frequency operation, if PT3 requires more work on this issue, e.g. attempting to determine a suitable guard band between the Aeronautical Mobile Satellite Service and the Radio Astronomy Service, SE28 is prepared to undertake the work. The Radio Astronomy Service should, therefore, beware of new allocations to "generic" MSS close to Radio Astronomy bands.

The meeting was clear about the fact that in airplanes the use of transmitters and various other electronic equipment is not permitted. Other aspects of this discussion wait for a final CRAF input document.

CRAF introduced an extensive document in which it explained (again) that the levels of harmful interference given in ITU-R literature are indeed very realistic and even friendly to other frequency users.

Motorola's claim that the protection of radio astronomy does not need these levels, was rejected by CRAF by explaining that state of the art observations are done at sensitivity levels much lower than these levels of harmful interference. A Motorola document entitled "Protection of Radio Astronomy Single Dish measurements from Iridium Downlinks" was strongly opposed point by point by CRAF as neither proposing nor providing in fact any significant protection at all. Motorola claims that several possibilities exist for interference mitigation considering e.g. RAS antenna pattern, polarization, nature of interference and noise temperature. Motorola's claim that radio astronomy does not need dual polarization observations and that, when dual polarization observations are done, this will average out the interference effects, were rejected by CRAF on astronomical and antenna-technical grounds.

CRAF explained the developments of the GLONASS system given the agreement between the GLONASS administration and IUCAF. GLONASS transmissions are still above the levels of harmful interference for radio astronomy, but the progress anticipated and already made promises a reduction of GLONASS interference into radio astronomy observations below these harmful interference levels in a few years from now.

Motorola's own simulations explain that Iridium will cause harmful interference at levels exceeding 20 dB above the levels of harmful interference to radio astronomy.

Motorola discussed in response a document in which Iridium was compared with GLONASS. It simply stated that when GLONASS transmits 20-30 dB above the levels of harmful interference for radio astronomy, radio astronomers do not experience significant interference. Furthermore, comparing the unwanted emission levels for GLONASS and Iridium, Motorola did not present reliable data for GLONASS emissions: i.e. the data presented by Motorola gave the impression that GLONASS is about 20 dB/W/m2 worse than it is in reality. Based on this incorrect information Motorola stated that the mitigation factors for unwanted emissions into RAS from Iridium satellites will not pose a particular problem.

CRAF rejected this opinion and will react to this position at the next SE28 meeting by providing further elements on the polarization issue and the GLONASS absolute spectral power flux density within the RAS band.

The next CEPT SE28 meeting will be on 11/12 March 1997 in Dwingeloo.

4.Interference to COSPAS-SARSAT

Unwanted emissions from radio transmitters are a troublesome source of interference to radio astronomy. For some people interference from unwanted emissions can be life-threatening. ITU-R Task Group 1-3, meeting in Santa Rosa California last October, heard that unwanted emissions from transmitters in some parts of the world are hampering the work of the COSPAS-SARSAT Search and Rescue Satellite System. COSPAS-SARSAT is a multi-national system which uses earth-orbitting satellites and ground stations to locate emergency distress beacons and pass the information to the nearest search and rescue centre. The radio beacons are triggered by an impact (aircraft) or by immersion in water (ships), whereupon they transmit a short distress message every 50 seconds in the band 406.0-406.1 MHz. The band has an exclusive allocation worldwide because of the safety- of-life implications. More than 6000 lives have already been saved.

The COSPAS-SARSAT system regularly suffers from interference, resulting in the loss of beacon messages. Unless at least four beacon messages are received and properly decoded the beacon location fails. Interference in some parts of the world is so bad the beacon reception is disrupted over areas as large as 100,000,000 square kilometres. The interference is sometimes persistent enough for the source to be located precisely using the same techniques intended for emergency beacons. The COSPAS-SARSAT community are now investigating ways to automate the interference location and to deal with the problem on a global basis to eliminate the present interferers and to ensure that no new interferers come on line. It is a sorry tale. Let us hope that lives are not lost before the interference problems are solved.

R.J.Cohen - Jodrell Bank

5. The Satellite-Borne Cloud Radar at 3-mm Wavelength

ESA is presently investigating the design of a satellite for Earth Radiation measurements. This is part of ESA's Earth Observation Programme and the satellite is intended to be launched sometime between 2003 and 2005 with an estimated mission duration of 4 years. The satellite would have in its payload a Cloud Profiling Radar (CPR) which would provide vertical active sounding of cloud-layer structure down to the terrestrial surface ( Newsletter 1996-2 ).

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 ( IUCAF report of ITU-R WP7D meeting, 8-16 October 1996).

A meeting between representatives of ESA, Oerlikon-Contraves, and CRAF took place at ESTEC on Oct. 28, 1996. This was the second progress meeting (PM2) within project 'RATEP' to investigate methods to protect mm-wave astronomy from harmful interference due to the CPR.

The theoretical calculations on loss-less waveguide filters by Oerlikon-Contraves had been assessed by ESTEC. CRAF considers it a formidable technological achievement when this kind of filters can be manifactured. The shrinking of the material when it is being cooled to cryogenic temperatures has to be taken into consideration in addition to a general overall size tolerance of about 1 micron.

Further theoretical calculations including estimates of the influence of losses were presented by Oerlikon-Contraves. Samples of mandrels for manufacturing of a 15-slot corrugated filter and of a 3-double-ring loaded filter were shown. Technical problems concerning the electroforming of the latter type of filter were discussed. A few breadboarding versions of both types of filters will be manufactured and tested at ambient temperature. Two "double-ring" filters have been made and measured until now. The result is that a "band-stop filter" has a promising perspective (Arcetri radio observatory is making preparations for tests of this filter in the near future).

It has been decided that the CPR will be nadir looking rather than 'push-broom'. ESTEC had checked on the calculations of Oerlikon-Contraves on interference levels using a simple and practical approach. The findings of Oerlikon-Contraves were more or less verified. It was suggested that the CPR be shut down whenever the satellite is within a zenith distance of 14 degrees as seen from a mm-wave telescope.

A. Winnberg - Onsala Space Observatory

6. Cloud radar frequencies

CRAF was asked by the CEPT FM meeting on February 7, 1997, to inform that meeting about its position concerning a possible re-allocation of the band 92-95 GHz, because of spectrum need for cloud profiling radar. The position of CRAF is as follows:

The issue of the frequency choice for cloud profiling radar has been discussed extensively within the radio astronomy community, e.g. during the October meeting of ITU-R WP7D (8-16 October 1996) in Geneva ( IUCAF report of ITU-R WP7D meeting, 8-16 October 1996).

In relation to this subject the following observations can be made:

[1] ITU-R Doc.9D/41-E states that a 1 GHz allocation at 95 GHz for space based active earth sensors is necessary for this application. After discussions with space agencies and remote sensing colleagues it became clear that instead of 1 GHz one should read 100 MHz. There is no need at all for more bandwidth.

[2] Virtually all of the microwave spectral lines of molecules present in the interstellar medium are at frequencies above 20 GHz and access to them for research is limited only by their intrinsic intensities and the absorption of the terrestrial atmosphere. The band considered is in this spectral domain and located in a "forest" of spectral lines (of which each adds in its own specific way to the story which physics is explaining to mankind).

[3] Astronomers are fortunate in the availability of wideband receiving systems spanning almost the entire atmospheric spectral windows. For instance, all current mm-wave antennas are outfitted with sensitive systems commonly used Superconductor-Insulator-Superconductor (SIS) mixers) operating in the range 70-116 GHz, approximately. This provides astronomers access to a large number of molecular spectral lines - a 1992 compilation lists detections of about 30-40 lines/GHz near 95 GHz, and the numbers are now much higher. Many spectral lines now considered of astrophysical importance by astronomers are outside bands in which the Radio Astronomy Service has a primary allocation (such as 86-92 GHz, 98.77-98.08 GHz and 105-116 GHz): e.g. five spectral lines of methanol at frequencies between 94.405 and 94.542 GHz. But there has been no opportunity to obtain appropriate protection in the Radio Regulations since 1979 (quoted from ITU-R Doc.7/86-E).

[4] Emissions from spaceborne or airborne stations can be particularly serious sources of interference to the Radio Astronomy Service. Allocations of a band near 95 GHz for use by space-based radar systems, would produce several undesirable consequences for 3-mm RA observations using currently installed receivers:

a. If a subband near 95 GHz is allocated to active sensors, RA observations could no longer be conducted near frequencies of satellite transmitters, and interference at levels exceeding threshold limits considered detrimental for RA observations, as listed in Recommendation ITU-R RA.769-1, might be experienced in the 86-92 GHz, 98.77-98.08 GHz and 105-116 GHz bands, whenever satellites were above the horizon of mm-wave observations.

b. SIS receivers can saturate at very low input leveles, and active sensor transmissions could affect the operation of the receivers over their total frequency band. In addition, calculations suggest that in the event of a satellite transmission into the mean beam of a mm-wave antenna, the SIS receiver would be destroyed.

Additional comments:

Depending on the installation, SIS mixers are destroyed if 0.01 mW to 10 mW of power is input. The saturation level is typically of the order of -110 dBW.

A damage to the SIS receiver could occur when a RA receiver is within the cloud profiling radar main beam and the RA antenna is pointing directly to the satellite of very close to it (< 3 degrees), hence to the zenith.

A saturation could occur when: (a) the RA receiver is within a +/- 14 degree vertical cone centered on the satellite with RA antenna is pointing directly to the satellite (+/- 0.01 degree). The validity of this result is conditional, depending on the cloud profiling radar and radio astronomy antenna patterns. Hence, updates will be necessary as better knowledge on the antenna patterns become available.

Remaining interference possibilities are:

i) a possible saturation when the RA antenna exactly points to the distant satellite, which could be eliminated by avoiding the known satellite path at known time (orbit information needed at RA site).

ii) signal interferences during the horizon-to-horizon appearances of the satellite, at a level which depends on the relative orientations of the respective antennas and the frequency separation between the cloud profiling radar transmit signal and the RA observation band.

Potential techniques to minimize these interferences without appreciably reducing the signal integration time (which is certainly not a trivial undertaking), have to be developed.

Adding appropriate filters to RA receivers is difficult or is not feasible, because:

a. Currently, there is no adequately low-loss 3-mm wavelength filter technology available and the prospects for such technology becoming available are at present uncertain.

b. Addition of a notch filter into the RA receiver band would permanently prevent RA observations at frequencies covered by the filter.

ITU-R WP7D suggested several possible solutions to this problem, such as: - operate the space-based active Earth sensors in the 78 GHz band already allocated to this application. However, operation of a cloud profiling radar in a higher frequency bands (e.g. 120-130 GHz) may have less impact on RA operations. Compared with operations at 95 GHz, the decreased scattering losses would result in a 5 dB gain in sensitivity, and the atmospheric attenuation is comparable.

- regarding the current proposal, suggestions that satellite systems could switch off transmissions, or that RA observations could cease, for the short period that a satellite is in the line-of-sight of mm-wave observatories might be a possible solution if only one cloud profiling radar satellite was involved, but appears untenable if several systems of satellites were to use the allocated band.

ITU-R WP7D suggested furthermore that in the event that an allocation is made at WRC97 in the frequency band 94-95 GHz for cloud profiling radars, the allocation should cover only the 94.0-94.1 GHZz band, which appears to have relatively few spectral lines. Furthermore, WP7D suggests that to prevent the proliferation of space-based radars, such an allocation be restricted to cloud profiling radars, possibly through a footnote to the Radio Regulations.

- Finally, concerning the transmissions of such systems, a pulsed signal would have lower impact on RA observations than a chirp-type transmission.

An other astronomical argument in favour of the subband 94.0-94.1 GHz which was not mentioned in ITU-R Doc.7/86-E is that the band 94.9-95.0 GHz subband is close to a strong CH3OH transition at 95.169 GHz which can be observed in extragalactic objects. Usually extragalactic sources are red- shifted (frequencies become lower due to the Doppler effect) by more than 100-200 MHz. By using e.g. VLBI measurements we can use the CH3OH maser line to measure distances of such extragalactic sources (difficult to obtain by other means). Measurement of distance is one of the most fundamental studies in astronomy. Around 94.0-94.1 GHz no such strong maser lines exist.


In case an allocation of 100 MHz for cloud profiling radars near 94-95 GHz has to be made, the ESF Committee on Radio Astronomy Frequencies, CRAF, informs you that the 94.0-94.1 GHz subband is preferred on the basis of both astronomical arguments and technical radio astronomical arguments as given above.

In addition, CRAF strongly supports a solution (mentioned above) that cloud profiling radar transmitter is shut down whenever a mm-wave RA- telescope is within +/- 14 degrees from nadir of the satellite. This would eliminate the possibilities of damaging the SIS receiver and a largest part of saturation occurrences.

7. Iridium and radio astronomy

Motorola has approached several key people at various observatories about the interference from the Iridium system in the protected 1612 MHz RAS band. Iridium with its downlink in the 1620 - 1626.5 MHz band [in Europe the band 1616 - 1626.5 is planned for both up- and downlink] is by design unable to reach the RAS harmful spfd levels as described in ITU.R-R.769. The purpose of these Motorola contacts is to discuss the predicted time periods Iridium cannot reach the RAS harmful limits at each observatory site and to draw up a Memorandum of Understanding. The modelling that Motorola has done for each site is based on traffic models for nearby metropolitan areas with a 1.5 safety factor.

On June 12th, 1994, NRAO and Motorola had signed a Memorandum of Understanding (e.g.: Newsletter 1996-1 ) which implies that NRAO accepted to observe at 18 cm wavelength during low traffic hours only.

However, one should note that MSS (uplink) has a primary allocation shared with RAS in the band 1610.6 - 1613.8 MHz [MSS has a primary allocation for the uplink in the band 1610 - 1626.5 MHz], while the MSS downlink has a secondary allocation in the band 1613.8 - 1626.5 MHz. Also FN733E holds. Shortly before WARC92 Motorola approached radio astronomy observatories for a memorandum of understanding (MoU). Calculations done for Jodrell Bank show that during about 4 hours in the night the interference would be below -240 dB W m-2 Hz-1. Else it is at least about -210 dB W m-2 Hz-1, being similar to the GLONASS interference. Any spectrum at 1612 MHz would show spurious features of a few tenths of a Kelvin. The MoU proposed by Motorola to Jodrell Bank is similar to the one signed by NRAO. If accepted the best situation would be a window of about 4 hours in the night during which sensitive radio astronomical observations can be done.

The situation for NRAO is less dramatic than it may be for other observatories such as Jodrell Bank or Nançay observatory where a significant larger fraction of the observing time is dedicated to 18 cm measurements.

Recently, Motorola has made an MoU with Ohio State University Observatory. This puts Motorola in a position to tell the Federal Communications Commission, FCC, of the USA that they have an MoU with all but one US radio observatory. However, Motorola does not tell that the interest of Ohio State University Observatory in 1.6 GHz is nil: no significant 18 cm work is done at this observatory.

It should be noted that Motorola puts much effort in agreements with radio observatories, since the FCC has given a license to Motorola under the condition of coordination with US observatories (the text of the license speaks, however, of "radio observatories" - not restricted to the US only).

Arecibo Observatory is presently in discussion with Iridium on coordination procedures. The situation is as follows:

Iridium and the National Astronomy and Ionosphere Center/Arecibo, NAIC, are under FCC jurisdiction and Iridium has been granted a license to launch and operate 66 satellites in the US. But, as already mentioned, this license in conditioned on coordination with US observatories. Arecibo is the only US observatory that has not signed an MoU with Iridium. As a last effort before requesting arbitration by the FCC, a meeting was held in Washington on January 8, 1997 and was attended by representatives the NAIC and the US National Science Foundation, NSF.

The ground rules for the discussions are found in the FCC Rules as:

47 CFR 25.213(a)(4)

"The Radio Astronomy Service shall avoid scheduling radio astronomy observations during peak MSS/RDSS traffic periods to the greatest extent practicable."

47 CFR 25.213(a)(2)

"Mobile Satellite Service space stations transmitting in the 1613.8-1626.5 MHz band shall take whatever steps necessary to avoid causing harmful interference to [list of observatories, including Arecibo] during periods of observations."

During the January meeting, Arecibo staff presented technical details on the telescope and discussed the OH observing programs from the past. Before the GLONASS situation in 1988, Arecibo used a full 15% of its time on OH observations. It has been found that the roughly 250 Galactic and extragalactic OH observing programs from 1988 can be scheduled between 10 pm and 7 am during weekdays and all day on Saturday and Sunday. These times are considered lower traffic periods for the MSS operators.

The Iridium staff fully understood the fact that the sky turns and that Galactic observations cannot be scheduled in a fixed solar time slot. Furthermore, the idea of night time and weekend access to the band for radio astronomy was accepted as a discussion item. This same proposal from Arecibo had been rejected by Iridium before.

It is expected that the discussions will continue and especially the far-sidelobe levels of Arecibo are being questioned. Iridium thinks it would do better with actual numbers than with the standard -10 dBi from ITU-R RA.769-1 and Rec.509. This is not likely the case for Arecibo.

A Letter of Intent, LOI, has been drafted to serve as a basis for continuing the discussions, which sets some deadlines for exchange of information between the two parties. The draft LOI describes the information exchanges needed to facilitate the protection of the Radio Astronomy Service observations and a basic coordination procedure for handheld Mobile Earth Stations, MES. This draft LOI also states that:

"The parties recognize that the provisions of this letter, and any further coordination agreements, are based on the unique conditions at and facilities of Arecibo Observatory, and may not apply to Motorola's coordination of its Iridium System with any other radio astronomy observatory, in the US or elsewhere. Nevertheless, because the NAIC is a publicly funded institution, the provisions of this letter and any subsequent agreement will not be held as confidential."

Arecibo has requested from Iridium information on the "Technical and organizational actions proposed by Motorola to protect observations when scheduled in the 1610.6-1613.8 MHz band at the Arecibo RAS site" and specifics on the "Spectral signal characteristics of the IRIDIUM System at RAS frequencies".

The Arecibo staff are working very hard to protect the interest of Arecibo and the radio astronomy community. For Arecibo the OH band is of great importance as it is one of its "bread and butter" bands. No obstacles currently exist to prevent a free information exchange on this issue in order to help coordinate similar efforts in other countries.


Last modified: August 27, 1999