AM-FM conversions

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 using the document below, which outlines our approach to broadcast planning and varying licence area plans.

153.13 KB

ACMA approach to broadcast planning and varying LAPs

We assess requests for conversions in line with our planning principals seen below.

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.

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:

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).

In 2016, we commenced a program to convert AM services to FM in solus (single licensee) regional radio licence areas.

In September 2022, we expanded our conversion program to include competitive regional radio licence areas.

We have adopted the below set of planning principles to help guide conversions.

The principles apply to commercial radio conversions in the remaining regional solus licence areas and to regional competitive licence areas.

They help to identify eligibility for inclusion in the conversion program for industry and to assist our prioritisation of conversion requests.

We expect industry participants to apply these planning principles when identifying which commercial services to convert, and when engaging consultant engineers to identify frequencies for conversion.

LAP variation complete

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 the broadcast planning and LAP variation guidelines below.

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.