Scientific discovery

Subhash Sharma

Cellphone

Walking and talking, working on the train, always in contact, never out of touch, cellphones have dramatically changed the way we live and work. No one knows exactly how many little plastic handsets there are in the world, but the best guess is that there over 7 billion subscriptions. That’s more than the planet’s population! In developing countries, where large-scale land line networks are few and far between, over 90 percent of the phones in use are cellphones.
Cellphones are radio telephones that route their calls through a network of masts linked to the main public telephone network.
Let’s take a closer look at how they works!

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Photo: A typical Nokia cellular phone
Cellphones use wireless technology
Although they do the same job, land lines and cellphones, work in a completely different way. Land lines carry calls along electrical cables. Cut out all the satellites, fiber-optic cables, switching offices, and land lines are not that much different to the toy phones you might have made out of a piece of string and a couple of baked bean cans. The words you speak ultimately travel down a direct, wired connection between two handsets. What’s different about a cellphone is that it can send and receive calls without wire connections of any kind. How does it do this? By using electromagnetic radio waves to send and receive the sounds that would normally travel down wires.
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Photo: Phones to go: you can use a mobile phone wherever you can get a signal.
Whether you’re sitting at home, walking down the street, driving a car, or riding in a train, you’re bathing in a sea of electromagnetic waves. TV and radio programs, signals from radio-controlled cars, cordless phone calls, and even wireless doorbells all these things work using electromagnetic energy: undulating patterns of electricity and magnetism that zip and zap invisibly through space at the speed of light .Cellphones are by far the fastest growing source of electromagnetic energy in the world around us.
How cellphone calls travel
When you speak into a cellphone, a tiny microphone in the handset converts the up-and-down sounds of your voice into a corresponding up-and-down pattern of electrical signals. A microchip inside the phone turns these signals into strings of numbers. The numbers are packed up into a radio wave and beamed out from the phone’s aerial. The radio wave races through the air at the speed of light until it reaches the nearest cellphone mast.
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Photo: Engineers repair a cellphone mast.
The mast receives the signals and passes them on to its base station, which effectively coordinates what happens inside each local part of the cellphone network, which is called a cell. From the base station, the calls are routed onward to their destination. Calls made from a cellphone to another cellphone on the same network travel to their destination by being routed to the base station nearest to the destination phone, and finally to that phone itself. Calls made to a cellphone on a different network or a land line follow a more lengthy path. They may have to be routed into the main telephone network before they can reach their ultimate destination.
How cellphone masts help
At first glance, cellphones seem a lot like two-way radios and walkie talkies, where each person has a radio (containing both a sender and a receiver) that bounces messages back and forth directly, like tennis players returning a ball. The problem with radios like this is that you can only use so many of them in a certain area before the signals from one pair of callers start interfering with those from other pairs of callers. That’s why cellphones are much more sophisticated and work in a completely different way.
A cellphone handset contains a radio transmitter, for sending radio signals onward from the phone, and a radio receiver, for receiving incoming signals from other phones. The radio transmitter and receiver are not very high-powered, which means cellphones cannot send signals very far. That’s not a flaw— it’s a deliberate feature of their design! All a cellphone has to do is communicate with its local mast and base station; what the base station has to do is pick up faint signals from many cellphones and route them onward to their destination, which is why the masts are huge, high-powered antennas (often mounted on a hill or tall building). If we didn’t have masts, we’d need cellphones with enormous antennas and giant power supplies—and they’d be too cumbersome to be mobile. A cellphone automatically communicates with the nearest cell (the one with the strongest signal) and uses as little power to do so as it possibly can (which makes its battery last as long as possible and reduces the likelihood of it interfering with other phones nearby).
The world of cellphones
Cellphones are changing the way the world connects. In the early 1990s, only one per cent of the world’s population owned a cellphone; today nearly a quarter of people make their phone calls this way. In developing countries, there are on average only five telephones (either land lines or cellphones) per hundred people and cellphones are much more popular; in Cambodia, over 90 percent of all phones are cellphones.
Cellphones are also used in different ways around the world. In the United States, mobiles are still mostly used for voice conversations. In Europe, more people send “texts” (also known as SMS) from mobile phones than use the Internet on personal computers. In Asia, where high-speed “third-generation” (3G) mobile networks and cutting-edge phones are more widely available, more people surf the Web and send emails from mobile phones than in any other way; over a quarter of all Japanese people now use the Internet like this. Since the arrival of high-end cellphones (such as iPhones and Android phones), lots of people now go online by tapping their phones and “cellphones” have now effectively become fully fledged pocket computers.

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