Radio
Radio Radio technology provides a means of instant communication with moving vehicles such as taxicabs or service trucks. Police and fire departments use two-way radios to get information to and from officers in squad cars and on motorcycles. Observers in airplanes can report traffic violations, accidents, and traffic jams by radio to police officers on the ground. Many people in the medical profession use beepers. They are portable electronic devices used to page the person who carries it. The device is activated when it receives a special radio signal. 4. Though local telephone communication is carried by electrical signals in coaxial cable systems, long-distance calls are often made with radio signals. In cellular mobile telephones, voice signals are sent across town or over long distances by high-frequency radio signals called microwaves. Land-based microwave relay stations and communication satellites orbiting the Earth receive and transmit...