# Remote Interference

03 February 2008

### Instructions

Tune the radio to a silent spot between stations

Try getting someone to phone your mobile phone while it is near the radio.

What do you hear?

### Result

When you press a button on the remote control you should hear strange sounds like this:

Remote control electronic interference noise

And when your phone is being called, before it starts ringing you may hear a noise like:

Mobile phone electronic interference noise

### Explanation

You can hear what the presenter is saying on a radio set because the sound waves are used by the radio transmitter to alter how an electric current runs up and down the transmitter aerial. If electrons are accelerated (change speed) they will emit what is known as electromagnetic radiation, in this case they will emmit a type of electromagnetic radiation called radio waves.

These radio waves then travel out from the aerial at the speed of light and when they meet the aerial of your radio at home they make tiny electric currents flow up and down it. The electronics in the radio then convert them into sound so you can listen to your favourite program.

 The transmitter emits radio waves which are picked up by your radio at home. It does this by making electrons accelerate up and down the aerial which creates electromagnetic radiation.

A remote control is an electronic device, and when you press a button a small infra-red light on the front flashes a signal to your TV. In order to power this flashing light various electric currents have to start or strop flowing, this will create weak electromagnetic  waves, but they are produced so close to the radio that it can still pick them up, and you can hear the currents inside the remote.

Try using different pieces of electronic equipment you should be able to hear a variety of different sounds.

### Why does the mobile phone make such a noise

Your mobile phone is a radio transmitter but works at between 1.7 and 2.5 GHx (billion vibrations a second) a completely different frequency to your radio which is designed to pick up radio waves at between 150kHz (thousand vibrations a second) and 1500kHz. Despite this your radio will pick up some of this signal if it is strong enough, eg when it is sitting on top of it.

Sometimes you will find this doesn't work very well, you will often find this is because you are near a phone mast. The phone is very clever, if it is near the phone mast it doesn't transmit with as much power saving your batteries, and not interfering with other phones. This means that it is sometimes not powerful enough to be picked up on the radio.

It also means that if you talk on your phone a lot you and want to minimise your exposure to mobile phone radiation, it may well be best to live near to a phone mast.

Thankyou to Andrew Steer, who suggested this experiment on our forum

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