Transcript No Slide Title

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/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
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.
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
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.
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!)
2. 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.
ITU-R Rec. RA.1272-1 (above 60 GHz)
1. Coordination zones be established around mmwave observatories, for all frequencies above 60
GHz where practicable;
2. Until appropriate criteria are developed, use Rec
RA.1031 to define size of coordination zone.
Sharing with terrestrial services is possible at mmwavelengths 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.
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
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
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)
Lovell Telescope
•
•
•
•
250 ft fully steerable
Upgrade in progress
Consultation zone
Coordination zones
(per frequency band)
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)
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)
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
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.
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.
Earth from Space: Forte satellite,
131 MHz
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.