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, and microwave ovens among others.
Key Concepts in Radio
These are some 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.
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. Demodulators are usually part of radio receivers.
Uses of Radio Technology
Telecommunications
The main use of radio technology is the conveying of information wirelessly, over long distances. This can take the form of a broadcast, where a transmitter radiates a modulated signal over a large area to be accessible by users with a suitable receiver, or access can be restricted by encrypting the signal, scrambling (special types of modulation that requires special equipment to decode), or focusing the radio waves into narrow beams for point to point communications, such as in microwave links.
Radio Control
Unmanned equipment or vehicles can be controlled by sending commands via radio signals.
Navigation
A directional antenna system is able to determine the direction from which a radio signal is coming from, this allows the creation of navigation beacons that allow vehicles such as boats or planes to estimate their position and heading even with no visibility.
Radar
The detection of objects by radio waves being reflected off their surfaces. Using directional antenna systems that send pulses of radio waves in narrow beams allows to sense the direction of objects while the delay of the reflected signal from the transmitted one allows the calculation of the distance to them.
This technology has been of great military use since the second world war, typically operating in the microwave range of the electromagnetic spectrum. Other uses include weather radar, which detects reflections from masses of water vapor in the atmosphere, traffic radar used to measure the speed of road vehicles, and astronomical radar used to detect objects in outer space, as could be done by the defunct Arecibo telescope.
Microwave ovens
Various materials can absorb radio waves (mainly microwaves) converting this energy into heat. This can be used to heat and cook food in a microwave oven, as well as other uses for high temperature chemistry and industrial processes.
Microwave heating was an accidental discovery during works on radar technology.
Radio Astronomy
The detection of radio waves produced naturally by astronomical objects, allowing their detection and study.
Wireless Power Transfer
It is possible, although extremely inefficient and impractical, to power devices remotely and wirelessly using powerful radio transmitters, as pioneered by Nikola Tesla.
Wireless power systems are inextricably subject to the inverse square law, which reduces the power output over distance for any given antenna system, as well as inherent energy waste from waves radiating in directions where they are not captured by any device making use of them.