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Cell Phones and CBs A good way to understand the sophistication of a cell phone is to compare it to a CB radio or a walkie-talkie Simplex vs Duplex Both walkie-talkies and CB radios are simplex devices That is two people communicating on a CB radio use the same frequency so only one person can talk at a time A cell phone is a duplex device That means that you use one frequency for talking and a second separate frequency for listening Both people on the call can talk at once Channels A walkie-talkie typically has one channel and a CB radio has 40 channels A typical cell phone can communicate on 1664 channels or more Range A walkie-talkie can transmit about one mile using a 025 watt transmitter A CB radio because it has much higher power can transmit about five miles using a 5 watt transmitter Cell phones operate within cells and they can switch cells as they move around Cells give cell phones incredible range Someone using a cell phone can drive hundreds of miles and maintain a conversation the entire time because of the cellular approach In 1983 the analog cell phone standard called AMPS Advanced Mobile Phone System was approved by the FCC and first used in Chicago AMPS uses a range of frequencies between 824 MHz and 894 MHz for analog cell phones In order to encourage competition and keep prices low the U S government required the presence of two carriers in every market known as A and B carriers One of the carriers was normally the local exchange carrier LEC a fancy way of saying the local phone company Digital cell phones use the same radio technology as analog phones but in a different way Analog systems do not fully utilize the signal between the phone and the cellular network Analog signals cannot be compressed and manipulated as easily as a true digital
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