Radio

Radio is the transmission or reception of electromagnetic radiation in the radio frequency range from one place to another without wires. Only a transmitter and a receiver need to be used for the propagation and interception of the radio waves. These waves carry information-bearing signals that may be encoded directly on the wave by periodically interrupting its transmission like a telegraph on the carrier frequency by a process called MODULATION, e.g., amplitude modulation (AM) or frequency modulation (FM).

These sounds are converted into electrical signals by making use of a microphone, amplified, and used to modulate a carrier wave that has been generated by a transmitter. The modulated carrier is also amplified and is then applied to an antenna that converts the electrical signals to electromagnetic waves that travel into space at the speed of light. Part of this radiation is intercepted by receiving antennas and are converted back into electrical signals, they are then fed to a receiver.  

Once the basic signals have been separated from the carrier wave, they are fed  to a loudspeaker or cathode-ray tube, where they are converted into sound and visual images, respectively. Some celestial bodies and interstellar gases emit relatively strong radio waves that are observed with radio telescopes composed of very sensitive receivers and large directional antennas. Long-range radio signals enable communications between astronauts and ground-based controllers and carry information from space probes as they travel to and encounter distant planets. The invention of the TRANSISTOR and other microelectronic devices led to the development of portable transmitters and receivers. Military applications of radio include the proximity fuse and various types of reconnaissance satellites. Special receivers to determine once position may use radio signals sent by navigation satellites. Vehicles also use Citizens band (CB) radios, operating at frequencies near 27 megahertz for communication.

Citizen Band Radio

Citizens band radio is a method of short-distance communication used by private citizens. It operates on the citizens band (CB), a group of radio frequencies that many nations reserve for private use.  

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