WEBVTT - Why is a cell phone called a cell phone?

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<v Speaker 1>Welcome to brain Stuff from how stuff Works dot com

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<v Speaker 1>where smart Happens. Hi Am Marshall Brain with today's question,

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<v Speaker 1>how does a cell phone work in your pocket? You

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<v Speaker 1>have an amazing device. It's a communicator that allows you

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<v Speaker 1>to talk instantly to almost anyone on the planet. Plus

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<v Speaker 1>it may also give you instant stock quotes, help you

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<v Speaker 1>read your email, and let you play games. Your cell

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<v Speaker 1>phone truly is an achievement. But how does it do it?

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<v Speaker 1>A little history can help here. Remember when you were

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<v Speaker 1>a kid and you played with a walkie talkie. A

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<v Speaker 1>walkie talkie is an incredibly simple toy that can send

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<v Speaker 1>your voice to a friend who's a quarter of a

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<v Speaker 1>mile away or so. It does this with about twenty

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<v Speaker 1>five cents worth of parts. The parts take your voice,

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<v Speaker 1>change it from sound waves to electric waves, and then

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<v Speaker 1>amidst those electronic waves with the antenna at the other end,

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<v Speaker 1>your friends walkie talkie receives the waves and converts them

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<v Speaker 1>to sound waves with the speaker your friend, here's your voice,

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<v Speaker 1>and vice versa. What if you want to transmit for

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<v Speaker 1>more than a quarter of a mile, you increase the

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<v Speaker 1>power A toy walkie talkie transmits at about a tenth

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<v Speaker 1>of a watch. A CB radio, which can transmit several miles,

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<v Speaker 1>uses four watts. Before there were cell phones, there were

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<v Speaker 1>car radios, which were essentially very very large walkie talkies

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<v Speaker 1>using twenty five watts or more. These things were huge.

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<v Speaker 1>But you can't stick at wat radio in your pocket.

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<v Speaker 1>It would need a gigantic battery. So how did engineers

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<v Speaker 1>solve the problem and create the tiny cell phones we

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<v Speaker 1>have today. The genius of the cell phone system is

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<v Speaker 1>the idea of a cell At the time it was conceived,

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<v Speaker 1>the idea was incredibly audacious. The idea for poses that

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<v Speaker 1>cell phone companies would put up cell phone towers, which

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<v Speaker 1>cost on the order of a million dollars each, on

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<v Speaker 1>a grid approximately four miles apart. A large city would

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<v Speaker 1>need dozens and dozens of these towers. But if you

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<v Speaker 1>put up all those towers, it means that the radio

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<v Speaker 1>and the cell phone only has to transmit at most

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<v Speaker 1>about two miles or so. The radio doesn't have to

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<v Speaker 1>be much more powerful than the radio in a walkie talkie,

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<v Speaker 1>which keeps it and its battery requirements small. There was

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<v Speaker 1>another part of the original cell phone idea that was

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<v Speaker 1>also audacious. A normal Wakie talkie can only transmit on

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<v Speaker 1>one frequency. Cell phones can transmit on hundreds of frequencies.

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<v Speaker 1>That means that one tower can handle dozens of simultaneous

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<v Speaker 1>calls without people interfering with each other. Each cell phone

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<v Speaker 1>uses a different frequency to talk to the tower, so

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<v Speaker 1>the different people can't hear each other, and each cell

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<v Speaker 1>phone actually uses too frequencies simultaneously for a call, so

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<v Speaker 1>you and your friend can talk simultaneously without the walkie

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<v Speaker 1>talkies push to talk button. And there is a third

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<v Speaker 1>radio in your phone that's always talking to the tower

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<v Speaker 1>even if you aren't on a call. This radio handles

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<v Speaker 1>the control channel. When a call comes in, the tower

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<v Speaker 1>talks to your phone on the control channel to set

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<v Speaker 1>the call up. The tower tells your phone what frequencies

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<v Speaker 1>do you use for the call, and also sends stuff

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<v Speaker 1>like the caller I D to the phone. The control

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<v Speaker 1>channel also handles one other important feature of cell phones.

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<v Speaker 1>Let's say that you're in your car driving down the

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<v Speaker 1>road while talking on the phone. Your phone is connected

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<v Speaker 1>to one tower, but it's driving away from it. As

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<v Speaker 1>you get closer to the next tower, the towers communicate

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<v Speaker 1>and arrange a handoff your phone gets a message on

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<v Speaker 1>the control channel telling it to change frequencies as your

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<v Speaker 1>driveing along. Your phone might switch between ten different towers

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<v Speaker 1>on a single call and you don't even know it.

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<v Speaker 1>The original cell phones were called analog cell phones. That

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<v Speaker 1>was the first generation. These were replaced by digital cell

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<v Speaker 1>phones because several digital calls can fit in the space

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<v Speaker 1>of one analog call. Digital cell phones were the second generation.

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<v Speaker 1>Now we're in the third generation, or three G, where

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<v Speaker 1>the towers and phones can handle calls as well as

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<v Speaker 1>high speed data connections. The data connection allows a phone

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<v Speaker 1>to browse web pages, get stock quotes, read email, watch videos,

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<v Speaker 1>and so on. When you think about it, it's truly

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<v Speaker 1>amazing that in your pocket you can have a mini

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<v Speaker 1>laptop computer that's always connected to the Internet, combined with

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<v Speaker 1>the ability to talk to anyone in the world. Be

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