#### Cell Phone Frequencies

Introduction to Cell-Phone Frequencies:

In the dark ages earlier than cell phones, people who actually required mobile- communications capability installed radio telephones in their cars. There was one central antenna tower in each city in the radio telephone systems, and may be 25 channels presented on that tower. The meaning of this central antenna is that the phone in your car required a powerful transmitter- sufficiently big to transmit 40 or 50 miles (approximately 70km). It also expected that not several people could use radio telephones there just were not sufficient channels.

The cellular system's genius is the division of a city into small cells. This permits extensive frequency reuse beyond a city that is why millions of persons can use cell phones at the same time.

A very good way to understand the sophistication of a cell phone is to evaluate it to a CB radio or a walkie-talkie.

• Full-duplex vs half-duplex:

Both walkie-talkies and CB radios are half-duplex devices. That is, two people communicating on a CB radio or Citizens' Band radio use the similar frequency, so only a single person can talk at one time. A cell phone is a full-duplex device. The meaning of this is that you use one frequency for talking and a second, other frequency for listening. Both persons on the call can talk at one time.

• Channels:

A walkie-talkie usually comprises one channel and a CB radio or Citizens' Band radio has 40 channels. A general cell phone can communicate on 1,664 channels or many more!

• Range:

A walkie-talkie can send out about 1 mile (1.6km) by using a 0.25watt transmitter. A CB radio, since it has very much greater power, can send out approximately 5 miles (8km) by using a 5 watt transmitter. Cell phones operate in cells. Cells provide cell phones unbelievable range. A person that using a cell phone can drive hundreds of miles and keep a conversation the full time due to the cellular approach.

In half-duplex radio, both transmitters use similar frequency, only one person can talk at a time.

In full duplex radio, the two transmitters employ dissimilar frequencies, thus both persons can talk at similar, time. Cell phones are full-duplex.

In a general analog cell-phone system in the United States (US), the cell-phone carrier receives approximately 800 frequencies to use beyond the city. The carrier divides the city into cells. Every cell is usually sized approximately 10 square miles (26 square Kilometres). Cells are generally thought of as several small hexagons on a big hexagonal grid.

Every cell has a base station which contains a tower and a small building consisting of the radio equipment.

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