ACMA’s study of aeronautical interference from FM broadcast transmission

enadmin, 12th June 2013

The Australian Communication and Media Authority has conducted an audit program involving inspections of transmitter sites for community radio services in the FM band. This program was part of an ACMA exercise to identify the causes of interference that was being reported to aeronautical radiocommunications in the VHF band. Both the ACMA and Airservice Australia were concerned about an increasing number of reports of interference that appeared to involve FM broadcast transmitters.

A representative sample of transmitters across the country was inspected with the assistance of the community broadcast industry.

Of the community radio stations inspected, the ACMA found that 28% of transmitters were producing spurious emissions. A significant number of those transmitters were emitting into the aeronautical radiocommunication band of 108-136 MHz.

The safe operation of aircraft that operate in relative close proximity to each other is fundamentally dependent on radio communications from ground stations and passing aircraft.

Consequently, these communications services require special measures to prevent harmful interference. Licensees of community broadcast stations can contribute to safeguarding the aeronautical band from harmful interference by regularly inspecting and maintaining their transmitters.  

External filters are a widely used method of limiting the radiation of unwanted spurious signals.  This involves the connection of an external radiofrequency filter between a broadcast transmitter and the associated aerial. The ACMA’s audit found less than 20% of community radio stations were using filters. External filters are regarded as an ingredient of good site engineering practice and will benefit the broadcast radio licensee by avoiding unnecessary disruption to its service by reducing the risk of interference to other services.

Here are some simple tips to check the health of your radio transmissions:

  • Are there any changes in transmitter meter readings?
  • Is the transmitting equipment overheating?
  • Is there a change in transmitter power levels?
  • Is there any damage or deterioration to the antenna or antenna cable?

Spurious emissions are easily detected with a spectrum analyser.  This means that an assessment by a technical expert is the often the most effective method of identifying spurious emissions. Using a “scanning” type receiver across the aeronautical band may give an indication of spurious emissions.

Licensees or operators of community based radio broadcast services who need advice on interference resolution matters can contact the ACMA or Airservices Australia.


Airservices Australia 

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A community radio pilot scheme was run in the UK during 2002 and the pilot stations have been allowed to continue operating pending the first full licensing process, which took place in 2005 and 2006.

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Licence renewal application update for permanently licensed broadcasters.