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.
- Full-duplex vs. half-duplex - Both walkie-talkies and CB
radios are half-duplex 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
full-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 1,664
channels or more!
- Range - A walkie-talkie can transmit about 1 mile (1.6 km)
using a 0.25-watt transmitter. A CB radio, because it has much higher
power, can transmit about 5 miles (8 km) 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.
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In half-duplex radio, both transmitters use the
same frequency. Only one party can talk at a time.
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In full-duplex radio, the two transmitters use
different frequencies, so both parties can talk at the same time.
Cell phones are full-duplex.
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In the next section, you'll get a good look inside a digital cell
phone.
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