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What radio interference sounds like
This page has audio and video demonstrations of what different types of 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.
Audio example of multi-path interference [MP3, 361 KB]
With AM there are 2 types of effect noticed. In both cases the sound continuously varies between clear and distorted:
- The sound fades away into a hiss.
- The sound becomes very distorted and unpleasant to listen to.
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. This is often accompanied by the stereo or signal light flashing on the radio receiver.
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.
This is usually caused by power lines, electric motors/thermostats, microprocessors, switch mode power supplies, etc. Anything that uses electric power may cause interference.
On AM and FM radios, the interference is characteristically heard as a buzzing noise, whine or hiss. It affects both 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.
Example of power line interference [MP3, 421 KB]
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 before buying.
Below are two videos showing the interference effects of poorly performing LED lighting.
Paul Salter demonstrates the practical effect of interference generated by LED lights.
Radio detective Mathias Coinchon from EBU Tech investigates how LED lights block (digital) radio reception.