As other devices in our daily life, a mobile phone is a mystery to most people. Indeed, a mobile phone is not really a phone, but if a radio that works similarly to a radio amadora, or a portable CB.
The big difference is in the CB band facto use just one frequency for talking and listening, which leads to that when someone is talking on the other side you can only listen and vice versa. A mobile phone uses two different frequencies: one to speak and another to listen, allowing a normal conversation. A CB radio has 40 channels, a mobile phone communicates via thousands. However, as mobile phones operate in a cell system, and a CB radio transmitting directly to another device, the radio has to be much stronger, despite having a range of just over six miles.
The radiotelephones
Before the invention of the cells, people used radios that transmitted to a satellite office in each city with 25 available channels. An antenna isolated in this manner required a powerful transmitter, or enough to transmit 60 or 80 miles. This meant that not everyone could use radio telephones: not only was expensive and simply did not exist sufficient frequency.
Cells
In the 70 and 80 was invented cell system. Someone decided one day that cities could be divided into smaller spaces, circles called cell transmission, allowing extensive use of frequencies in all cities, no problems, through reuse.
How do you process this? The operator divides the area into several areas, in various cells, usually hexagonal (geometric shape that can occupy all the space and is very close to the circumference), as in a board game, raising a huge network of hexagons. In each cell is a base station transmitter, typically, a simple antenna. Each cell gets to use several dozens of channels, giving the possibility of several dozen people communicate simultaneously in each cell. When a person moves from one cell to another, shifting to the frequency of the new cell, freeing the previous cell to be used by someone else.
As transmission distances are not large, mobile phones can be transmitted with little energy, then with small batteries that allow for reduced size and weight. They are, therefore, cells that make possible cell phones as we know them today. Hence the expression: cell phones.
