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AM-FM conversions

Commercial radio broadcasting licensees can request AM to FM conversions and/or infill transmitters (repeaters) to go with an existing AM or FM service.

This information does not apply to community radio broadcasting services.

We allow AM to FM conversions by changing the technical details for a transmitter. This is done through a variation to a Licence Area Plan (LAP).

Requests are considered under our General Approach to Analog Planning

LAP variation requests

Our approach allows us to consider requests from licensees in:

  • single licensee (solus) regional licence areas with less than 30% overlap with any other commercial radio licence area
  • other licence areas where we believe the variation will not put existing FM commercial radio broadcasting licensees at a competitive disadvantage

Before varying a LAP, we believe that:

  • A conversion should not result in any existing radio services being affected. They should not have to be retuned, replanned or cancelled, unless a solution can be found that reduces the impact and does not impose costs on affected parties.
  • A conversion should not result in any significant coverage differences for radio listeners in the affected licence areas.

Things we consider

Coverage loss

We look at the number of people in areas who receive AM and FM services. For communities with a population of 200 or more, we measure if AM coverage is likely to be the same as FM. 

There can be a range of factors that affect AM and FM coverage, including:

  • the nature of radio wave propagation
  • adequate signal levels
  • coverage evaluation methodologies
  • assessment of population covered
  • 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:

Table 1: average coverage levels

Environment

For FM planning

For AM planning

Rural

>54 dBµV/m (for stereo)

>54 dBµV/m (0.5 mV/m)

Suburban

>66 dBµV/m

>68 dBµV/m (2.5 mV/m)

Urban

>74 dBµV/m

>80 dBµV/m (10 mV/m)

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

Rural signal levels

AM and FM signals should be received at levels well below what is considered adequate for planning purposes.

Adequate AM signal levels that meet the threshold can become inadequate if high levels of electrical noise are present.

Measuring coverage levels

AM

Field surveys conducted in the 1970s and 1980s, and plotted on maps as contours equating to adequate reception thresholds in rural, suburban and urban environments, can provide AM coverage measurements.

They are, however, based on point-in-time measurements in a limited number of locations.

This approach is sometimes used due to low confidence in computer coverage predictions.

FM

Digital terrain models, details of transmission infrastructure and 1 or more different propagation prediction algorithms can provide FM coverage measurements.

These generally have a greater geographical resolution, and different models can often provide different coverage measurements.

 

Population estimates

Population estimates identify the potential for a 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.

We have 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

LAP variation complete

List of locations with completed LAP variations
State Markets
Tasmania

Burnie

Devonport

Queenstown

Scottsdale

New South Wales

Armidale

Bathurst

Bega

Cooma

Goulburn

Victoria Warrnambool
Northern Territory Katherine
South Australia

Murray Bridge

Port Lincoln

Riverland

Spencer Gulf North

Western Australia

Karratha

Port Hedland

Remote WA (Exmouth, Paraburdoo and Tom Price)

Mandurah

Pending

List of pending LAP variations
State Markets
New South Wales

Grafton

Gunnedah

Inverell

Lismore

Lithgow

Moree

Nowra

Parkes

Tamworth

Taree

Young

Victoria Wangaratta
Western Australia Albany

The progress and timing of AM to FM conversions depends on various factors and cannot always be guaranteed.

For more information on how we prioritise requests, please refer to Assessing and prioritising requests to vary radio licence Area Plans (LAPs).

Starting a FM radio service

The licensee is in charge of the timing for starting a FM radio service, once their request has been approved. 

Licensees can ask for a period (up to 28 days) of simulcasting the AM and FM transmitters. This gives listeners a chance to move to the new FM transmission. 

We may consider allowing continued simulcasting of AM and FM radio services on a case-by-case basis. If we do not, transmission on the AM transmitter must finish at the end of the simulcast period.

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