Radio

A variety of radio antennas on Sandia Peak near Albuquerque, New Mexico, US
Radio communication. Information such as sound is converted by a transducer such as a microphone to an electrical signal, which modulates a radio wave produced by the transmitter. A receiver intercepts the radio wave and extracts the information-bearing modulation signal, which is converted back to a human usable form with another transducer such as a loudspeaker.
Comparison of AM and FM modulated radio waves
Frequency spectrum of a typical modulated AM or FM radio signal. It consists of a component C at the carrier wave frequency f_c with the information (modulation) contained in two narrow bands of frequencies called sidebands (SB) just above and below the carrier frequency.
Satellite television dish on a residence
Satellite phones, showing the large antennas needed to communicate with the satellite
Firefighter using walkie-talkie
VHF marine radio on a ship
Parabolic antennas of microwave relay links on tower in Australia
RFID tag from a DVD
Satellite Communications Center Dubna in Russia
Communications satellite belonging to Azerbaijan
Military air traffic controller on US Navy aircraft carrier monitors aircraft on radar screen
ASR-8 airport surveillance radar antenna. It rotates once every 4.8 seconds. The rectangular antenna on top is the secondary radar.
Rotating marine radar antenna on a ship
A personal navigation assistant GPS receiver in a car, which can give driving directions to a destination.
EPIRB emergency locator beacon on a ship
Wildlife officer tracking radio-tagged mountain lion
US Air Force MQ-1 Predator drone flown remotely by a pilot on the ground
Remote keyless entry fob for a car
Quadcopter, a popular remote-controlled toy

Technology of signaling and communicating using radio waves.

- Radio
A variety of radio antennas on Sandia Peak near Albuquerque, New Mexico, US

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Wireless network

Computer network that uses wireless data connections between network nodes.

Computer network that uses wireless data connections between network nodes.

Wireless icon
Computers are very often connected to networks using wireless links, e.g. WLANs
Wireless LANs are often used for connecting to local resources and to the Internet
Example of frequency reuse factor or pattern 1/4
In a hidden node problem Station A can communicate with Station B. Station C can also communicate with Station B. However, Stations A and C cannot communicate with each other, but their signals can interfere at B.
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Understanding of SISO, SIMO, MISO and MIMO. Using multiple antennas and transmitting in different frequency channels can reduce fading, and can greatly increase the system capacity.

Admin telecommunications networks are generally implemented and administered using radio communication.

US Air Force MQ-1 Predator drone flown remotely by a pilot on the ground

Radio control

US Air Force MQ-1 Predator drone flown remotely by a pilot on the ground
Quadcopter, a popular radio-controlled toy
In 1898, Tesla demonstrated a radio-controlled boat ( —Method of an Apparatus for Controlling Mechanism of Moving Vehicle or Vehicles).
The Telekino, invented by Leonardo Torres y Quevedo in 1903, which executed commands transmitted by electromagnetic waves.
Radio control gear invented by John Hays Hammond, Jr. installed in the battleship USS Iowa (1922)
A boy runs his radio controlled boat in Ystad's marina 2019.
This radio controlled airplane is carrying a scale model of Lockheed Martin X-33 and is taking part in NASA research.

Radio control (often abbreviated to RC) is the use of control signals transmitted by radio to remotely control a device.

Categorization for signal modulation based on data and carrier types

Modulation

Process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted.

Process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted.

Categorization for signal modulation based on data and carrier types
A low-frequency message signal (top) may be carried by an AM or FM radio wave.
Waterfall plot of a 146.52 MHz radio carrier, with amplitude modulation by a 1,000 Hz sinusoid. Two strong sidebands at + and - 1 kHz from the carrier frequency are shown.
A carrier, frequency modulated by a 1,000 Hz sinusoid. The modulation index has been adjusted to around 2.4, so the carrier frequency has small amplitude. Several strong sidebands are apparent; in principle an infinite number are produced in FM but the higher-order sidebands are of negligible magnitude.
Schematic of 4 baud, 8 bit/s data link containing arbitrarily chosen values

In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver.

Long wave radio broadcasting station, Motala, Sweden

Radio broadcasting

Transmission of audio , sometimes with related metadata, by radio waves to radio receivers belonging to a public audience.

Transmission of audio , sometimes with related metadata, by radio waves to radio receivers belonging to a public audience.

Long wave radio broadcasting station, Motala, Sweden
Slovak Radio Building, Bratislava, Slovakia (architects: Štefan Svetko, Štefan Ďurkovič and Barnabáš Kissling, 1967–1983)
Broadcasting tower in Trondheim, Norway
Advertisement placed in the November 5, 1919 Nieuwe Rotterdamsche Courant announcing PCGG's debut broadcast scheduled for the next evening.
Use of a sound broadcasting station
Transmission diagram of sound broadcasting (AM and FM)
AM broadcasting stations in 2006
FM radio broadcast stations in 2006
Worldwide presence of Radio Maria broadcasters.

The earliest radio stations were radiotelegraphy systems and did not carry audio.

DVOR (Doppler VOR) ground station, collocated with DME.

VHF omnidirectional range

Type of short-range radio navigation system for aircraft, enabling aircraft with a receiving unit to determine its position and stay on course by receiving radio signals transmitted by a network of fixed ground radio beacons.

Type of short-range radio navigation system for aircraft, enabling aircraft with a receiving unit to determine its position and stay on course by receiving radio signals transmitted by a network of fixed ground radio beacons.

DVOR (Doppler VOR) ground station, collocated with DME.
On-board VOR display with CDI
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D-VORTAC TGO (TANGO) Germany
The Avenal VORTAC (at 35.646999,-119.978996) shown on a sectional aeronautical chart. Notice the light blue Victor Airways radiating from the VORTAC. (click to enlarge)
VORTAC located on Upper Table Rock in Jackson County, Oregon
Conventional VOR
red(F3-) green(F3) blue(F3+)
black(A3-) grey(A3) white(A3+)
Doppler VOR
red(F3-) green(F3) blue(F3+)
black(A3-) grey(A3) white(A3+)
USB transmitter offset is exaggerated
LSB transmitter is not shown
A mechanical cockpit VOR indicator
Oceanside VORTAC in California
On the course deviation indicator the radial is selected, and together the needle and TO/FR flag show the aircraft's position.
Aircraft in NW quadrant with VOR indicator shading heading from 360 to 090 degrees

Each station broadcasts a VHF radio composite signal including the mentioned navigation and reference signal, station's identifier and voice, if so equipped.

Comparison of frequency band designations

Radio spectrum

Part of the electromagnetic spectrum with frequencies from 0 Hz to 3,000 GHz .

Part of the electromagnetic spectrum with frequencies from 0 Hz to 3,000 GHz .

Comparison of frequency band designations

To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).

Example of omnidirectional antenna; a whip antenna on a walkie-talkie

Omnidirectional antenna

Example of omnidirectional antenna; a whip antenna on a walkie-talkie
Radiation pattern of a 3λ/2 monopole antenna. Although the radiation of an omnidirectional antenna is symmetrical in azimuthal directions, it may vary in a complicated way with elevation angle, having lobes and nulls at different angles.
Vertical polarized VHF-UHF biconical antenna 170–1100 MHz with omnidirectional H-plane pattern

In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis (elevation angle), declining to zero on the axis.

An undamped spring–mass system is an oscillatory system

Radio frequency

Oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz to around 300 GHz.

Oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz to around 300 GHz.

An undamped spring–mass system is an oscillatory system

Energy from RF currents in conductors can radiate into space as electromagnetic waves (radio waves). This is the basis of radio technology.

A portable battery-powered AM/FM broadcast receiver, used to listen to audio broadcast by local radio stations.

Radio receiver

A portable battery-powered AM/FM broadcast receiver, used to listen to audio broadcast by local radio stations.
A modern communications receiver, used in two-way radio communication stations to talk with remote locations by shortwave radio.
Girl listening to vacuum tube radio in the 1940s. During the golden age of radio, 1925–1955, families gathered to listen to the home radio receiver in the evening
A bedside clock radio that combines a radio receiver with an alarm clock
Symbol for an antenna
Symbol for a bandpass filter used in block diagrams of radio receivers
Symbol for an amplifier
Symbol for a demodulator
Envelope detector circuit
How an envelope detector works
Block diagram of a tuned radio frequency receiver. To achieve enough selectivity to reject stations on adjacent frequencies, multiple cascaded bandpass filter stages had to be used. The dotted line indicates that the bandpass filters must be tuned together.
Block diagram of a superheterodyne receiver. The dotted line indicates that the RF filter and local oscillator must be tuned in tandem.
Block diagram of a dual-conversion superheterodyne receiver
Guglielmo Marconi, who built the first radio receivers, with his early spark transmitter (right) and coherer receiver (left) from the 1890s. The receiver records the Morse code on paper tape
Generic block diagram of an unamplified radio receiver from the wireless telegraphy era
Example of transatlantic radiotelegraph message recorded on paper tape by a siphon recorder at RCA's New York receiving center in 1920. The translation of the Morse code is given below the tape.
Coherer from 1904 as developed by Marconi.
Experiment to use human brain as a radio wave detector, 1902
Magnetic detector
Electrolytic detector
A galena cat's whisker detector from a 1920s crystal radio
Marconi's inductively coupled coherer receiver from his controversial April 1900 "four circuit" patent no. 7,777.
Radio receiver with Poulsen "tikker" consisting of a commutator disk turned by a motor to interrupt the carrier.
Fessenden's heterodyne radio receiver circuit
Unlike today, when almost all radios use a variation of the superheterodyne design, during the 1920s vacuum tube radios used a variety of competing circuits.
During the "Golden Age of Radio" (1920 to 1950), families gathered to listen to the home radio in the evening, such as this Zenith console model 12-S-568 from 1938, a 12-tube superheterodyne with pushbutton tuning and 12-inch cone speaker.
De Forest's first commercial Audion receiver, the RJ6 which came out in 1914. The Audion tube was always mounted upside down, with its delicate filament loop hanging down, so it did not sag and touch the other electrodes in the tube.
Block diagram of regenerative receiver
Circuit of single tube Armstrong regenerative receiver
Armstrong presenting his superregenerative receiver, June 28, 1922, Columbia University
Hazeltine's prototype Neutrodyne receiver, presented at a March 2, 1923 meeting of the Radio Society of America at Columbia University.
Block diagram of simple single tube reflex receiver
The first superheterodyne receiver built at Armstrong's Signal Corps laboratory in Paris during World War I. It is constructed in two sections, the mixer and local oscillator (left) and three IF amplification stages and a detector stage (right). The intermediate frequency was 75 kHz.
A Zenith transistor based portable radio receiver
A modern smartphone has several RF CMOS digital radio transmitters and receivers to connect to different devices, including a cellular receiver, wireless modem, Bluetooth modem, and GPS receiver.

In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form.

Guglielmo Marconi

Italian inventor and electrical engineer, known for his creation of a practical radio wave-based wireless telegraph system.

Italian inventor and electrical engineer, known for his creation of a practical radio wave-based wireless telegraph system.

Marconi's first transmitter incorporating a monopole antenna. It consisted of an elevated copper sheet (top) connected to a Righi spark gap (left) powered by an induction coil (center) with a telegraph key (right) to switch it on and off to spell out text messages in Morse code.
British Post Office engineers inspect Marconi's radio equipment during a demonstration on Flat Holm Island, 13 May 1897. The transmitter is at centre, the coherer receiver below it, and the pole supporting the wire antenna is visible at top.
Plaque on the outside of the BT Centre commemorates Marconi's first public transmission of wireless signals.
SS Ponce entering New York Harbor 1899, by Milton J. Burns
Marconi watching associates raising the kite (a "Levitor" by B.F.S. Baden-Powell ) used to lift the antenna at St. John's, Newfoundland, December 1901
Magnetic detector by Marconi used during the experimental campaign aboard a ship in summer 1902, exhibited at the Museo Nazionale Scienza e Tecnologia Leonardo da Vinci of Milan.
Marconi demonstrating apparatus he used in his first long-distance radio transmissions in the 1890s. The transmitter is at right, the receiver with paper tape recorder at left.
Marconi caricatured by Leslie Ward for Vanity Fair, 1905
Villa Marconi, with Marconi's tomb in foreground.
American electrical engineer Alfred Norton Goldsmith and Marconi on 26 June 1922.
Guglielmo and Beatrice Marconi c. 1910
Memorial plaque in the Basilica Santa Croce, Florence. Italy
Guglielmo Marconi Memorial in Washington, D.C.
Bronze statue of Guglielmo Marconi, sculpted by Saleppichi Giancarlo erected 1975 Philadelphia, Pennsylvania

Marconi's experimental apparatus proved to be the first engineering-complete, commercially successful radio transmission system.