The Cell Phone

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The Cell phone
Cell phones are becoming popular day by day. People of all ages use them. They carry it
in their hands, pockets or purses. One can find advertisements related to cell phones
anywhere: roads, newspapers, and television. A person carrying a cell phone can be
contacted almost anywhere, anytime.
The handset of cell phone is normally no bigger than 12x 5x1 cm. It has a small screen at
one end and a panel of buttons below it. Some handsets have a small antenna that is
protruding out from its, but it is not universal. Some modern handsets are foldable so that
when not in use the panel of buttons is not visible, these handsets have a larger screen
that can display colour pictures also.


How it works
Cell phones are based on networks of many radio transmitters/receivers. Each cell phone
company has a network of this kind. You know that our body is made up of many cells.
These networks are also cellular akin to the body of any animal.



SID and ESN
All cell phones have special codes associated with them. There is a phone numbers
allocated to each cell phone user. In India these numbers have 9 as their first digit.
Then there are other code numbers that are used to identify the phone, the phone's
owner and the service provider. SID (System Identification Code) is a unique 5-digit
number that is assigned to each cell phone company by the government. When a cell
phone is switched on, it listens for an SID on the control channel. The control
channel is a special frequency that the phone and base station use to talk to one
another. If the phone cannot find any control channels to listen to, it knows it is out
of range and displays a "no service" message. When it receives the SID, the phone
compares it to the SID programmed into the phone. If the SIDs match, the phone
knows that the cell it is communicating with is part of its parent company..


Inside a handset
A cell phones handsets is somewhat like a palmtop computer. It is the most intricate
device common people play with daily. But, if you were to take a cell phone apart, you
will be surprised to discover very few parts inside it. They are:
· A circuit board that has several chips (IC’s) on it.
· An antenna
· A liquid crystal display (LCD)
· A keyboard (not unlike the one you find in a TV remote control)
· A microphone
· A speaker
· A battery
Let us explore the function of each one of them. One chip on the circuit board translates
the sound that is spoken near the microphone from analog to digital and the incoming
digital signal back to sounds that can be heard through its speaker. Cell phones have such
tiny speakers and microphones that it is incredible how well most of them reproduce
sound. As you can see, the speaker is about the size of a 25p coin and the microphone is
even smaller. The keyboard allows the user to enter information like the telephone
number etc.