Radio astronomy uses extremely sensitive radio antennas to detect very faint radio signals of cosmic origin. It is highly susceptible to interference by unwanted emissions from other radiocommunication services in nearby or even distant spectrum bands. To minimise such interference, radio astronomy antennas are usually placed in remote locations. The radio astronomy service is the only entirely passive radiocommunication service defined by the ITU-R.
The Australian Radiofrequency Spectrum Plan contains specific radio astronomy allocations covering areas of the spectrum of particular astronomical importance. These allocations cover a relatively small part of the spectrum, whereas significant cosmic radio emissions occur over the whole radio spectrum. Hence, radio astronomy facilities often operate in bands not specifically allocated to the radio astronomy service.
The Mid West Radio Quiet Zone
The Australian Communications and Media Authority (the ACMA) established Australia's first Radio Quiet Zone (RQZ) on 11 April 2005. The RQZ aims to maintain the current ‘radio-quietness’ of a site in remote Western Australia (near Boolardy Station, around 200 km East of Meekatharra). The area has very low levels of radiofrequency energy because of its low population and remote location. The RQZ is intended to facilitate the development and use of new radio astronomy technologies at that location, and is the central core of the Australian component of the international Square Kilometre Array (SKA) project.
In the period since 2005, the Murchison Radio astronomy Observatory (MRO) has been developed at the centre of the RQZ. Major national and international radio astronomy projects already under construction at that site include:
- the Australian SKA Pathfinder telescope - a testing facility for Square Kilometre Array technology (see www.atnf.csiro.au for more details)
- the Murchison Widefield Array (MWA) telescope (see www.mwatelescope.org for more details.
The ACMA introduced several measures to protect radioastronomy services in the RQZ, including a frequency band plan, coordination arrangements and licence conditions.
Radiocommunications (Mid West Radio Quiet Zone) Frequency Band Plan 2011
The band plan, introduced in July 2011, outlines the purpose for which spectrum may be used within 150 km of the MRO. It also defines geographic zones, applying to the frequency range 70 MHz to 25.25 GHz, as follows:
- Inner zone: Within 70km of the MRO, radioastronomy services are the primary service in the zone, with any other services deemed to be secondary. Applicants for new apparatus licences must consult with the MRO before applying for a licence.
- Outer zone: The new outer zone would operate within a radius of 70-150km from the MRO. In practical terms, licence applications in this zone will be considered in light of the spectrum plan and the relevant licence condition but licence applicants must consult with the MRO.
Radiocommunications Assignment and Licensing Instruction (RALI) MS32
In December 2014, the ACMA updated RALI MS32 Coordination of Apparatus Licensed Services Within the Mid West Radio Quiet Zone. The RALI was developed to refine the Radio Quiet Zone initially created by Spectrum Embargo 41, which is now also defined by the band plan. Embargo 41 was also updated to reflect the distances set out in the band plan. For more information, see IFC 32/2013.
Prospective frequency assignments for transmitters that lie within the scope of the RALI (up to 260km from centre of the RQZ) are analysed to determine whether the use of the planned transmitter might produce signal levels above prescribed thresholds at the MRO. If the analysis finds that potential signals are above the prescribed threshold then the licensee must take reasonable measures to reduce the signal level reaching the centre of the RQZ, or within 50km of the centre, to below the threshold levels. For example, transmitter antennas may be modified, alternative transmitter locations may be used to take advantage of terrain shielding, or transmitter EIRP may be reduced.
In cases where the potential signal level reaching the centre of the RQZ, or within 50km of the centre, (as determined by the method prescribed in the draft RALI) cannot be reduced below the threshold levels, the prospective licensee shall enter discussions with the users of facilities within the RQZ to achieve a mutually agreeable solution. Where agreement is not possible the ACMA will prescribe a solution.
Class licensed services should not cause harmful interference to other radiocommunications services, including the radioastronomy services in the RQZ. In July 2011, the ACMA amended three class licences to ensure that all relevant class licences contained explicit conditions that would protect the MRO.
Under the band plan, licence applicants in the RQZ are required to consult with the MRO before applying to the ACMA for an apparatus licence. Relevant technical arrangements, negotiated and agreed between the licence applicant and the MRO, are applied to the apparatus licence as a licence condition.
Spectrum licences granted in areas around the RQZ will be subject to a licence condition designed to prevent harmful interference to radioastronomy services at the site. The ACMA also intends to exclude the proposed SKA site at the centre of the RQZ from all new spectrum licences granted nationally.
Consultation on Spectrum access in the RQZ
The regulatory framework for protection of the RQZ requires consultation between the MRO and other spectrum users or spectrum seekers in the region. The ACMA supported the development of a co-existence agreement between the Australian and Western Australian Government, which outlines agreed principles for spectrum sharing and sets out processes for negotiation and dispute resolution. The CSIRO has committed to operate consistently with the management framework in performing its SKA functions.
In making its regulatory decision, the ACMA will take into account all relevant circumstances, including an agreement by the interested parties to operate in accordance with the co-existence agreement.
The Square Kilometre Array
The RQZ is the core site for the Australian-New Zealand SKA radio telescope project.
The SKA is a proposed radio telescope with a collecting area of one square kilometre. The design criteria call for a large central collecting antenna array and additional receiving arrays remote from the central cluster. The SKA is planned to operate over a frequency range of around 70 MHz to 25 GHz and to have 50 times the sensitivity of the best radio astronomy telescopes currently in use. The broad mission of the SKA is to address fundamental questions in research on the origin and evolution of the universe. The SKA is anticipated to operate until 2050.
In May 2012, the SKA Organisation announced that both Australia and southern Africa will jointly host the SKA. Further information can be found at www.ska.gov.au.
Radio Sensitive Zones
The ACMA has established "Radio Sensitive Zones" around key Australian radio astronomy facilities, to provide the operators of the facilities the opportunity to seek better outcomes for radio astronomy when new radio transmitters are planned to be installed near these facilities.
Before a new transmitter is turned on it must obtain a radiocommunications licence from the ACMA. If, during the process of obtaining the licence, certain criteria are met then the CSIRO will be notified. The CSIRO may then assess the likely impact of the proposed transmitter on radio astronomy facilities, and opt to negotiate with the prospective licensee for a more favourable outcome for radio astronomy.
The Radio Sensitive Zones and notification procedures are defined in RALI MS31 Notification Zones for Apparatus Licensed Services Around Radio Astronomy Facilities (PDF [104 kB]).