Radio
"Radio" refers to a family of technologies that make the use of electromagnetic waves in the radio frequency range, for purposes related to wireless telecommunications and other uses such as direction finding for navigation, radar, .
Key Concepts in Radio
These are most of the main general concepts required to understand radio technology at large.
Radio waves are electromagnetic waves, with frequencies below roughly 300 GHz in the electromagnetic spectrum (or wavelengths larger than 1 millimeter). These waves are produced by the motion of electric charges, and they propagate at the speed of light through air, vacuum and other mediums to a case dependent degree.
Radio waves can be modified at their origin to imprint information on them (a process called modulation) and convey it wiressly over long distances.
Radio signals are characterized by parameters such as their carrier frequency (the frequency of the unmodulated signal), their bandwidth (the size of the span of frequencies contained in the signal when modulated) and the type of modulation used in them.
Radio Transmitter
A device used to produce high frequency (radio frequency) alternating current, which is fed into an antenna for the emission of radio waves. The transmitter is powered by electricity and usually serves the additional role of modulating the RF signal to carry information, such as a sound signal, analog television, digital data or other.
Transmitter types and construction vary greatly depending on their frequency of operation, type of modulation, power output, and the technology used in its construction.
Radio Receiver
A device that takes the radio frequency signal captured by an antenna and extracts useful information modulated into said signal. A radio receiver usually performs the task of amplifying the incoming signals, filtering them so that only one frequency is selected (and the specific transmission on that frequency), and extracting the information being conveyed (demodulating).
Radio Antenna
A device used to convert radio-frequency electrical energy into electromagnetic waves that propagate through open space, and viceversa. Antennas are used both by transmitters and receivers, and can be of a variety of types depending on their purpose and mode of operation.
Antennas are usually built by the strategic arrangement of electrical conductors (cables) and optionally reflectors such as parabollic dishes or metal bars. They work by spatially arranging the conductors so that the magnetic and electric fields produced by RF electricity flowing through them interact in the right way required to form the electromagnetic waves. The same process works in the opposite direction, efficiently capturing radio waves and producing an electrical RF signal that can be processed by a radio receiver.
Modulation
The process of altering one or more parameters of a radio frequency carrier signal to convey information. There are many types of modulation used for different purposes, the most widely known being Amplitude Modulation (AM) and frequency modulation (FM) used for commercial radio broadcasts. The process of doing this modification to the carrier signal is called Modulation, and the system in charge of doing this is called a modulator (usually part of a transmitter), while the reverse process to retrieve the information is called demodulation, and is carried by a system called a demodulator, or detector in older literature.