Page 590 - Ultimate Visual Dictionary (DK)

THE MODERN WORLD
Cellphones Top Front

microphone camera
IN THE EARLY 1990s, THE CELLPHONE (or mobile Receiver
phone) was a rare luxury, but in recent years it
Status bar
has outsold almost every other electrical gadget—
as a professional tool, domestic convenience, and Earpiece
even a fashion accessory. Cellphones have also
generally shrunk in size, due to improvements
in rechargeable batteries, which now store more
electricity for longer in a smaller package, and
to smaller, more efficient electronics that use less
electricity. A “cellphone” is basically a low-power
radio receiver-transmitter, plus a tiny microphone
to convert sounds into electrical signals, and a
small speaker that does the reverse. When the
cellphone is activated, it sends out a radio signal that
is answered by nearby mast transmitter -receivers.
The phone locks onto the clearest signal and uses
this while within range (the range of each
transmitter is known as a cell). The phone
continuously monitors signal strength and
switches to an alternative transmitter when
necessary. The phone’s liquid crystal display
(LCD) shows numbers, letters, symbols, and color
pictures. Newer models have a larger screen for
more complex color images, and commonly
incorporate a camera, radio, and MP3 functionality. Bottom Home Speaker
Smartphones, which are increasingly widespread, microphone button
contain additional software and more may be
I-PHONE 4
downloaded. Smartphones typically offer Menu Home Back Search
internet and email access, PDA-like functions key key key key
(see pp. 568–569), and may even contain GPS
LG OPTIMUS 2X
navigation software.

HOW A CELLPHONE WORKS Recipient’s landline
Caller sends call phone (fixed at wall
signal to nearest socket or cordless
Phone locks onto cell tower with base-set) emits
signals from local ring tone Cells are smaller
mast within home cell
in areas where
many calls occur
simultaneously
Phone out of (cities, suburbs)
signal range—
no reception
Activated phone
auto-switches to
signals from Landlines (or
next cell as it tower-to-tower Recipient’s cellphone
moves across links) carry emits ring tone
cell boundary phone signals
to local Local cell- Main telephone Signals forwarded Signals forwarded
exchange phone network network to non-cellphone to relevant cell for
exchange exchange transmission

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