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Radio-Quiet Zones

Radio-Quiet Zones. R. J. Cohen. 13th June 2002. Jodrell Bank Observatory University of Manchester. 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/m 2 /Hz

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Radio-Quiet Zones

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  1. Radio-Quiet Zones R. J. Cohen 13th June 2002 Jodrell Bank Observatory University of Manchester

  2. 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

  3. 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.

  4. 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

  5. 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.

  6. 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. don’t assign the frequencies to active services: shared bands don’t have to be shared!) • Consideration be given to protecting RA sites by establishing coordination zones; (don’t 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.

  7. 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.

  8. 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

  9. 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

  10. 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)

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

  12. 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)

  13. 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)

  14. 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

  15. 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.

  16. 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.

  17. Earth from Space:Forte satellite,131 MHz

  18. 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.

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