Radio-Quiet Zones

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Radio-Quiet Zones
R. J. Cohen
13th June 2002
Jodrell Bank Observatory University of Manchester
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• Susceptibility of Radio Astronomy
• to Interference
• Cosmic signals are weak (billions of times
  weaker than man-made signals) and noise-like 1
  Jy 10-26 W/m2/Hz
• Redshifts carry spectral lines to lower
  frequencies (because of expanding Universe)
• Harmful interference levels are very low
• Results of measurements are usually
  unpredictable interference may look like new
  science
• mm-wave receivers easily destroyed (1µm
  junctions) and filtering techniques are not
  mature

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Protection for Radio Astronomy - 1
Effective protection of radio astronomy requires
coordinated action at all levels. The threats
can be global, regional, national or local.
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Protection for Radio Astronomy - 2

• GLOBALLY - International Telecommunications
  Union (ITU) and Radio Regulations (quiet
  frequency bands for RA worldwide, limits on
  satellite emissions)
• REGIONALLY - international agreements on
  harmonized spectrum use (e.g. how to share
  bands) and standards (good neighbours)
• NATIONALLY planning by telecommunications
  authority spectrum management can create and
  maintain a radio-quiet zone
• LOCALLY remote site for observatory, liaise
  with local authorities about developments in RQZ

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ITU-R Rec. RA.769-1 (RFI levels) 1.
Radio astronomers should be encouraged to choose
sites as free as possible from interference 2.
Administrations should afford all practicable
protection to RA frequency bands, taking due
account of the interference levels given in Annex
1 3. Administrations should take all
practicable steps to reduce unwanted emissions
into RA bands, particularly from aircraft,
spacecraft and balloons 4. Administration
should take into account the difficulties of
sharing frequencies with transmitters in direct
line-of-sight to observatories.
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• ITU-R Rec. RA.1031-1 (shared bands)
• 1. In making assignments administrations should
  take all practicable steps to avoid interference
  to RA (e.g. dont assign the frequencies to
  active services shared bands dont have to be
  shared!)
• Consideration be given to protecting RA sites by
  establishing coordination zones (dont assign
  the frequencies within a calculated distance of
  the radio observatory)
• 3. That the size of the coordination zone be
  calculated taking account of the protection
  criteria in Rec. RA.769-1 and suitable
  propagation model.

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• ITU-R Rec. RA.1272-1 (above 60 GHz)
• 1. Coordination zones be established around
  mm-wave observatories, for all frequencies above
  60 GHz where practicable
• Until appropriate criteria are developed, use Rec
  RA.1031 to define size of coordination zone.
• Sharing with terrestrial services is possible at
  mm-wavelengths because of atmospheric
  attenuation, shielding by topography, and since
  there are only a small number of remote sites to
  protect. Also, at present the radio astronomers
  are almost the only people using the bands.

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Need for Radio-Quiet Zones
In-band transmitters Most radio astronomy
frequency bands are shared with active users
(transmitters), some roaming! Need good
coordination process. Out-of-band interference
Signals can leak into passive bands
(pollution) powerful transmitters can block RA
receiver (including IF amplifiers, e.g. IRAM
radar). Need coordination of transmitters at
any frequency. Non-radio transmitters
Electrical or electronic devices (e.g.
computers, microwave ovens) need better EMC
standards
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Radio-Quiet Zones

• Natural Radio Quiet Zones
• Sun-Earth Lagrangian point L2
• Shielded zone of Moon
• Terrestrial Radio Quiet Zones
• Typical radio observatory (Jodrell Bank)
• Greenbank USA
• SKA (possible Australian site)
• ALMA

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VSA (Very Small Array)

• 14-element array at Observatorio del Teide
  (Tenerife)
• UK (Jodrell Bank and Cambridge) and Spanish
  collaboration
• maps cosmic µ-wave background at 31 GHz
• RFI screen (very small radio-quiet zone)

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Lovell Telescope

• 250 ft fully steerable
• Upgrade in progress
• Consultation zone
• Coordination zones
• (per frequency band)

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Jodrell Bank Consultation Zone

• Direction from the Department of the Environment
  to local planning authorities 6 mile
  consultation zone established 10 years after
  telescope built
• Jodrell Bank Observatory automatically consulted
  about any new buildings or developments , within
  the Consultation Zone (as part of the normal
  planing permission process)
• Also, UK Radiocommunications Agency provides
  protection from certain radio transmitters
  anywhere in the UK (coordination to agreed
  levels depending on frequency band)

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Greenbank Radio-Quiet Zone - 1

• Act to amend the code 1931 of West Virginia,
  passed in August 1956, enacting zoning
  restrictions governing the use of electrical
  equipment within 10 miles of any radio astronomy
  facility
• CHAPTER 37-A. ZONING Article 1. Radio
  Astronomy Zoning Act
• Within 2 miles it is illegal to operate any
  electrical equipment that causes interference
• Protection within 10 miles based on field
  strengths of emissions (graded limits for
  equipment within 3,4, 5, 6, 7, 8, 9 and 10 miles)

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Greenbank Radio-Quiet Zone - 2

• National Radio Quiet Zone established with FCC
  rule making document No. 11745, Nov 1958
• 13,000 square miles of Virginia and West
  Virginia
• NRAO automatically consulted about new radio
  transmitters within the Radio-Quiet Zone (as
  part of the normal licencing process)
• If an ERP limit is not acceptable to the
  applicant, NRAO will assist in finding a
  mutually acceptable alternative
• The laws were set up before the radio telescopes
  and before any frequency allocations to RAS

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ALMA and mm-wave Astronomy The global situation
is very good since WRC-2000. Generous allocations
above 71 GHz for passive services (24 of
spectrum to remain passive and a further 43
allocated to radio astronomy on primary basis).
Most useable frequencies can be protected. Radio
astronomy use of frequencies up to 1 THz is now
officially acknowledge through Footnote
S5.565. Frequency allocations above 275 GHz are
on the agenda for WRC-2006. First regulatory
limits on unwanted emissions from satellites.
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ALMA Radio-Quiet Zone

• International frequency allocations for ALMA are
  very favourable, but need careful
  implementation when frequencies are assigned
  nationally (and regionally harmonized).
• Any electrical equipment can cause interference,
  not just radio transmitters, so need to involve
  local planning authorities as well as national
  telecommunications authority.
• ALMA Radio-Quiet Zone needs to be set up as soon
  as possible.

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Earth from Space Forte satellite, 131 MHz
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Square Kilometre Array

• Consortium aims to select a site by 2005.
• Measurement programmes underway in China,
  inland Australia and elsewhere (0-2 GHz).
• Investigating option to have main building and
  astronomers away from telescope (optical fibre
  connection).
• OECD Task Force on Radio Astronomy is
  investigating ways to establish an
  internationally recognized radio-quiet zone, and
  ways to deal with satellites.
• Tasso Tzioumis will say more.