Spark image

Mobile phones (mobiles)

When you make a call using your mobile the phone sends a digital signal at a frequency in the region of 900 MHz, this is in the microwave region of the electromagnetic spectrum. A local transmitting/receiving station receives this call via a selected frequency and reroutes via other stations, if needed, to the receiving phone.

The country is divided into cells with each cell containing one "relay" station. In regions where the phone traffic is high more cells are needed in a given area. In cities one station covers around 2 km whereas in the country this may extend to over 25 km. You will probably have seen some of these relay stations springing up all over the place if you travel around the country. The size of the cell (hence the name cellular phones) also depends on the frequency of that particular band. Higher frequencies do not travel so far without distortion and so the cells are smaller. The frequency bands used by mobile phones in Britain are from 872 MHz to 9670 MHz, 1710 MHz to 1875 MHz and 1920 to 2170 MHz.

A mobile phone is really just a low powered radio which is why you need so many of the relay stations and cells to cover the country.

I tried to make a call using my mobile while coming home across the channel from France last summer. Although there are plenty of stations on either side of the channel in France and England I was out of range of all of them and so could not make the call.

Texting has become very popular since it is brief, makes no noise and does not require you to have the phone up against your head.

Photographic phones
These mobiles are a combination of a mobile phone and a digital camera. A digital picture is transmitted as well as the audio signal. These days many phones are capable of taking not only still pictures but also video clips. In fact it is quite difficult to buy a mobile that is not also a camera. Some even include a GPS facility and allow Internet access.

See also: Mobile phones (14-16)
© Keith Gibbs 2011