Radio-Quiet Zones

1. Radio-Quiet Zones R. J. Cohen 7th March 2002 Jodrell Bank Observatory University of Manchester

2. Outline of Talk What is Radio Astronomy? Susceptibility to Interference Protection of Radio Astronomy Examples of Radio-Quiet Zones Conclusions

3. What is Radio Astronomy? - 1 • Only two windows for ground-based astronomy: • Optical window 0.4 to 0.8 microns wavelength Needs clear skies (no light pollution) The night sky is part of our heritage • The radio window: 30m to 0.3mm wavelength • Needs clear radio skies: no radio pollution • The radio spectrum is rapidly filling up! • Radio pollution is invisible

4. What is Radio Astronomy? - 2 • The radio window opened to us in the 20th century. • The invisible universe: things we couldn’t see before • Interstellar molecules and origin of life • Birth of stars and planets • Death of stars, neutron stars, black holes • Dark haloes in galaxies: missing mass • Active galaxies and massive black holes • Cosmic microwave background radiation

5. 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

6. 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.

7. 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

8. Radio Astronomy within ITU-R The International Telecommunications Union (ITU) allocates frequency bands to services, in 3 regions. The Radio Astronomy Service entered the Radio Regulations at WARC-59: “Astronomy based on the reception of radio waves of cosmic origin”. The RAS is allocated 2% of spectrum below 50 GHz and much more above 50 GHz. “All emissions are prohibited” in passive bands, but most bands are shared with active services. Ten ITU-R recommendations (guidelines) on RAS protection but no mandatory regulations.

9. ITU-R RA Recommendations 314-8 Preferred frequency bands 1031-1 Protection in shared bands 517-2 Protection from adjacent band transmitters 611-2 Protection from spurious emissions 1237 Protection from unwanted emissions 769-1 Protection criteria 1272 Protection above 60 GHz 479-4 Protection of shielded zone of Moon 1417-1 Protection of L2 Sun-Earth Lagrange Point 1513-1 Percentage of time criteria for data loss

10. 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.

11. 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.

12. 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.

13. 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

14. 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

15. 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)

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

17. 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)

18. 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)

19. 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

20. 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

21. Earth from Space:Forte satellite,131 MHz

22. GSO satellites pollute passive band

23. 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.

24. Conclusions • International frequency allocations for ALMA are very favourable, but need careful implementation when frequencies are assigned nationally (and regionally hamonized). • Any electrical equipment can cause interference, not just radio transmitters, so need to involve local planning authorities as well as national telecommunications authority. • Set up the ALMA Radio-Quiet Zone as soon as possible: don’t wait until interference appears. There is time to get it right, since mm-waves not much used at present .

25. Protection for Radio Astronomy - 3 • GLOBALLY – the status of radio astronomy is rising within the ITU, with better frequency allocations and better recommendations on how to protect us. • REGIONALLY – however, when it comes to implementing the recommendations, administrations are often more concerned with telecommunications than with astronomy. • NATIONALLY – some individual countries cherish radio astronomy. • LOCALLY – radio observatories can be good for small isolated communities.

26. Interference from Satellites • In the sky: can’t shield telescopes against them! • Global coverage: all terrestrial sites affected • Spread spectrum: radio pollution of passive bands • Malfunctions are difficult to repair in space • Long timescale for change, once launched • More than 100 satellites launched per year • First limits to unwanted emissions agreed in 2000, but as yet no pre-launch check on total emissions (environmental impact)