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.
Contents
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
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.
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.
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
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
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.
Conclusion:
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.
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.
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