AM–FM conversions and infill transmitters for commercial radio broadcasters | ACMA

AM–FM conversions and infill transmitters for commercial radio broadcasters


This guidance applies to commercial radio broadcasting licensees seeking AM–FM conversions and/or infill transmitters (repeaters) to supplement an existing AM or FM service in a licence area.

The ACMA authorises AM-FM conversions by changing the technical specifications for the transmitter through a variation to a Licence Area Plan (LAP). Read more about the ACMA’s approach to planning for broadcast services.

The guidance does not apply to requests for AM–FM conversion or infill transmitters from licensees of community radio broadcasting services. These requests will be considered on a case-by-case basis, having regard to the General Approach to Analog Planning (the general approach). The ACMA will have regard to previous decisions of the ACMA and its predecessors when considering any applications for AM to FM conversions for AM community radio broadcasting services.

AM–FM conversions

The ACMA’s approach to AM-FM conversions and infill transmitters for commercial radio broadcasting services (the AM–FM guidance) provides that the ACMA will consider requests for variations to LAPs to enable AM–FM conversion of existing AM commercial radio broadcasting services when the requests are from licensees in:

  • single licensee (solus) regional licence areas with less than 30 per cent overlap with any other commercial radio licence area
  • other licence areas where the ACMA considers that the circumstances do not put existing FM commercial radio broadcasting licensees at a competitive disadvantage.

Before varying a LAP, the ACMA notes that:

  • A conversion should not result in any existing radio services being adversely affected—in their use of spectrum and the technical parameters of their radio transmissions. Other existing radio services should not have to be retuned, replanned or cancelled, unless a solution can be found that mitigates these impacts without imposing any undue costs on the affected parties.
  • A conversion should not result in any significant coverage differences for radio listeners within the affected licence areas. The vast majority of radio listeners who were able to receive services in AM should be able to continue to do so.

Consideration of AM–FM coverage loss

The ACMA looks at the proportion of the population within the licence area who receive the AM service that is predicted not to receive the same service in FM, and the distribution of that population—particularly in communities with a population of 200 people or more.

The ACMA assesses the proportion of the population within the licence area likely to be covered by the new ‘main’ FM transmission, in comparison to the population coverage of the current AM transmitter. Approximating AM coverage may require FM in-fill translators as well as a main transmitter. Factors that affect the potential coverage loss of an FM conversion, compared to the original AM service, include the nature of radio wave propagation, adequate signal levels, coverage evaluation methodologies, assessment of population covered, and the presence of other signals that may provide alternative coverage.

Signal characteristics

AM and FM radio signals have different characteristics, resulting in coverage differences:

  • AM signals spread by means of ‘ground waves’, which are dependent on good ground conductivity, and at night can also travel as ‘sky waves’. AM is more susceptible to interference from power lines, electric lighting and electric motors.
  • FM signals spread via a transmitter sited on a high location such as a hill, mountain, building or tower. FM signals are less susceptible to electrical noise interference.

Adequate coverage levels

Coverage is assessed in different types of electrical noise environments. The minimum field strengths for adequate reception in the presence of radio noise resulting from human activities alone are:


Acceptable signal level


For FM planning

For AM planning


>54 dBµV/m (for stereo)

>54 dBµV/m (0.5 mV/m)


>66 dBµV/m

>68 dBµV/m (2.5 mV/m)


>74 dBµV/m

>80 dBµV/m (10 mV/m)[1]

[1] Australian Broadcasting Authority, Technical Planning Parameters and Methods for Terrestrial Broadcasting, April 2004.

With rural signal levels:

  • listenable AM and FM signals should be received at levels well below what is considered adequate for planning purposes, because signal quality gradually declines
  • they often extend well outside the licence area boundary—particularly for AM services—as the suburban signal level was typically used in determining the licence area boundary
  • reception of signals outside the licence area boundary is ‘fortuitous’ and not protected from interference in the planning of other services.

Note: AM signal levels that would ordinarily meet the threshold for adequate reception could be inadequate if high levels of electrical noise are present.

Evaluating coverage levels

The extent of coverage is evaluated through either measurements taken at various points within a coverage area, or computer predictions of signal levels using propagation algorithms and digital terrain elevation models: 

  • AM coverage has been evaluated based on field survey measurements conducted in the 1970s and 1980s, and plotted on maps as contours equating to adequate reception thresholds in rural, suburban and urban environments. They have the limitation that they are based on point-in-time measurements at a limited number of locations. Nevertheless, this approach has been used due to low confidence in computer coverage predictions. (Because of limited available data on ground conductivity.)
  • Coverage predictions for new FM services use digital terrain models, details of the transmission infrastructure and one or more different propagation prediction algorithms. Consequently, FM coverage predictions generally have a much greater geographical resolution. It should be noted, however, that different prediction models will provide different coverage estimates. Experience with the models and knowledge of their underlying assumptions are needed to consider which model is likely to give the best result.

Population estimates

This is used to identify the potential for the conversion to result in coverage loss and can be done in a few different ways.

The simplest way is to classify the centroid point of each geographic unit and assign the entire population of that unit to the classification. This works reasonably well in populated areas and in aggregating populations in large geographic areas, but is less precise in analysis of small, sparsely distributed populations.

The ACMA has developed a more granular method, which is likely to give a more accurate result. The census data for each geographic population unit is distributed across a grid. The population assigned to each cell in the grid is weighted by taking into account the distribution of address information contained in the Geocoded–National Address File (G–NAF).

Current conversion program

After consulting with industry, the ACMA has received a number of applications for AM–FM conversions in regional solus markets. A list of the regional solus markets (as agreed by industry) is set out below. The ACMA will consider those requests for Licence Area Plan (LAP) variations to facilitate AM–FM conversions in accordance with the guidance. The ACMA will also take the opportunity to deal with non-conversion-related variation requests already made in relation to the relevant LAP, wherever this is feasible, and will not unduly delay the LAP variation process for AM–FM conversion.

As the ACMA is utilising the assistance of an industry-appointed consultant engineer to perform the engineering work for most applications, the progress and timing of AM–FM conversions is dependent on industry’s sponsored work program.

FM service on-air

State Markets
New South Wales
  •  Bathurst
  • Warrnambool

Western Australia


  • Karratha
  • Port Hedland
  • Remote WA (Exmouth, Paraburdoo and Tom Price)
  • Mandurah

LAP variation complete

State Markets
  • Burnie
  • Devonport
  • Queenstown

Currently consulting

State Markets
New South Wales
  • Bega 
  • Cooma
  • Goulburn
Northern Territory
  • Katherine
  • Scottsdale


State Markets

New South Wales

  • Armidale
  • Grafton
  • Gunnedah
  • Inverell
  • Lismore
  • Lithgow
  • Moree
  • Nowra
  • Parkes
  • Tamworth
  • Taree
  • Young

South Australia

  • Murray Bridge
  • Port Lincoln
  • Riverland
  • Spencer Gulf North


  • Wangaratta                

Western Australia

  • Albany                

For more general information on the ACMA’s approach to prioritising radio LAP variations, please refer to Assessing and prioritising requests to vary radio licence Area Plans (LAPs).

Broadcaster implementation

While the ACMA may facilitate an AM–FM conversion, the timing for commencement of the FM radio service is a decision for the licensee. Licensees requesting AM–FM conversion may seek a simulcasting period of the AM and FM transmitters in order to transition listeners to the FM transmission. As a general rule, the ACMA will permit simulcasting of the AM and FM services for a period of 28 days. The ACMA may consider permitting continued simulcasting of AM and FM radio services on a case-by-case basis in accordance with the policy. If the ACMA does not permit dual coverage, transmission on the AM transmitter must cease at the end of the simulcast period.


In 2015, Commercial Radio Australia put a proposal to the Minister for Communications to support AM-FM conversions in single licensee (solus) regional markets where (in most cases) the licensee holds both a licence for a commercial AM service and supplementary commercial license for an FM service (issued pursuant to section 39 of the Broadcasting Services Act 1992) (BSA). The minister was supportive of this proposal, subject to certain caveats, and asked the ACMA to consider his request to prioritise AM-FM conversions in the context of the ACMA’s broadcast planning responsibilities under Part 3 of the BSA.

In 2016, the ACMA published a consultation paper about issues relevant to implementing AM–FM conversions and infill transmitters. Details of how the ACMA considered those issues in revising its approach is outlined in the consultation paper, A new approach to AM–FM conversions and in-fill transmitters for commercial radio broadcasting services.


Last updated: 05 July 2019