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Radio interference


What does radio interference sound like?

Weak signals on AM and FM radio

Radio reception becomes noisy and distorted.



With FM a common symptom of this problem is a harsh edge or loud scratching noise distorting the sound, often accompanied by the stereo light flashing on the radio receiver. It may also cause a flutter effect on car radio FM reception when the vehicle is moving.

With AM there are two types of effect noticed. The first effect is where the audio sound fades away into a hiss. The second effect is where the sound becomes very distorted and unpleasant to listen to. In both cases the sound continuously varies between clear and distorted.


Radio transmitter interference

On AM and FM a common symptom of this problem is a buzzing, rasping type noise or you may hear distorted voices or other audio sounds, often accompanied by the stereo or signal light flashing on the radio receiver.


Co-channel interference

For FM vertical layering of moisture content and temperature in the atmosphere (inversion layers) can occasionally cause signals to travel hundreds or thousands of kilometres further than usual.

With FM radios, and in particular radios fitted in moving vehicles, the primary signal suddenly disappears and is replaced by the unwanted signal. This is often noticed as both signals alternatively taking over from each other on a random basis as the vehicle is moving. There is often scratchy distortion preceding the changeover.

With AM radios the interference appears as whistle (a beat note) or loud tone mixed in with the required audio.


Electrical interference

Is usually caused by power lines, electric motors/thermostats, microprocessors, switch mode power supplies, etc. Indeed anything using electric power may cause interference.

On AM and FM radios, the interference is characteristically heard as a buzzing noise, wine or hiss affecting mains and battery operated radios. AM reception is more prone to interference than FM reception. For AM the source of the interference may be many hundreds of metres away


LED radio interference

Importers, distributors and users should be aware that the increased use of LED lights in both fixed and mobile installations are producing greater risk of noise across the radio spectrum.

Consumers should ensure that their products are compliant with standards AS/NZS CISPR15 or EN55015 and check with their supplier if they have any concerns prior to purchasing.

Below are two videos showing the interference effects of poorly performing LED lighting.

Last updated 22 June 2016