Welcome to brain Stuff from how stuff Works dot com where smart Happens. Hi Am Marshall Brain with today's question, how does a cell phone work in your pocket? You have an amazing device. It's a communicator that allows you to talk instantly to almost anyone on the planet. Plus it may also give you instant stock quotes, help you read your email, and let you play games. Your cell phone truly is an achievement. But how does it do it? A little history can help here. Remember when you were
a kid and you played with a walkie talkie. A walkie talkie is an incredibly simple toy that can send your voice to a friend who's a quarter of a mile away or so. It does this with about twenty five cents worth of parts. The parts take your voice, change it from sound waves to electric waves, and then amidst those electronic waves with the antenna at the other end, your friends walkie talkie receives the waves and converts them to sound waves with the speaker your friend, here's your voice,
and vice versa. What if you want to transmit for more than a quarter of a mile, you increase the power A toy walkie talkie transmits at about a tenth of a watch. A CB radio, which can transmit several miles, uses four watts. Before there were cell phones, there were car radios, which were essentially very very large walkie talkies using twenty five watts or more. These things were huge. But you can't stick at wat radio in your pocket.
It would need a gigantic battery. So how did engineers solve the problem and create the tiny cell phones we have today. The genius of the cell phone system is the idea of a cell At the time it was conceived, the idea was incredibly audacious. The idea for poses that cell phone companies would put up cell phone towers, which cost on the order of a million dollars each, on a grid approximately four miles apart. A large city would
need dozens and dozens of these towers. But if you put up all those towers, it means that the radio and the cell phone only has to transmit at most about two miles or so. The radio doesn't have to be much more powerful than the radio in a walkie talkie, which keeps it and its battery requirements small. There was another part of the original cell phone idea that was also audacious. A normal Wakie talkie can only transmit on one frequency. Cell phones can transmit on hundreds of frequencies.
That means that one tower can handle dozens of simultaneous calls without people interfering with each other. Each cell phone uses a different frequency to talk to the tower, so the different people can't hear each other, and each cell phone actually uses too frequencies simultaneously for a call, so you and your friend can talk simultaneously without the walkie talkies push to talk button. And there is a third radio in your phone that's always talking to the tower
even if you aren't on a call. This radio handles the control channel. When a call comes in, the tower talks to your phone on the control channel to set the call up. The tower tells your phone what frequencies do you use for the call, and also sends stuff like the caller I D to the phone. The control channel also handles one other important feature of cell phones. Let's say that you're in your car driving down the road while talking on the phone. Your phone is connected
to one tower, but it's driving away from it. As you get closer to the next tower, the towers communicate and arrange a handoff your phone gets a message on the control channel telling it to change frequencies as your driveing along. Your phone might switch between ten different towers on a single call and you don't even know it. The original cell phones were called analog cell phones. That
was the first generation. These were replaced by digital cell phones because several digital calls can fit in the space of one analog call. Digital cell phones were the second generation. Now we're in the third generation, or three G, where the towers and phones can handle calls as well as high speed data connections. The data connection allows a phone to browse web pages, get stock quotes, read email, watch videos,
and so on. When you think about it, it's truly amazing that in your pocket you can have a mini laptop computer that's always connected to the Internet, combined with the ability to talk to anyone in the world. Be sure to check out our new video podcast, Stuff from the Future. Join how Stuff Work staff as we explore the most promising and perplexing possibilities of tomorrow. The Houstufforks iPhone app has arrived. Download it today on iTunes.