Radio

Radio is the technology of using radio waves to carry information, such as sound and images, by systematically modulating properties of electromagnetic energy waves transmitted through space, such as their amplitude, frequency, phase, or pulse width. When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form.

Radio systems need a transmitter to modulate (change) some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation (which can be frequency modulation or phase modulation). Radio systems also need an antenna to convert electric currents into radio waves, and radio waves into an electric current. An antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual frequencies to be selected. The electromagnetic wave is intercepted by a tuned receiving antenna. A radio receiver receives its input from an antenna and converts it into a form that is usable for the consumer, such as sound, pictures, digital data, measurement values, navigational positions, etc.[1] Radio frequencies occupy the range from a 30 Hz to 300 GHz, although commercially important uses of radio use only a small part of this spectrum.[2]

A radio communication system requires a transmitter and a receiver, each having an antenna and appropriate terminal equipment such as a microphone at the transmitter and a loudspeaker at the receiver in the case of a voice-communication system.[3]

Alexandra Palace mast
The Alexandra Palace, here: mast of the broadcasting station
The PVR
Classic radio receiver dial

Etymology

The term "radio" is derived from the Latin word "radius", meaning "spoke of a wheel, beam of light, ray". It was first applied to communications in 1881 when, at the suggestion of French scientist Ernest Mercadier, Alexander Graham Bell adopted "radiophone" (meaning "radiated sound") as an alternate name for his photophone optical transmission system.[4] However, this invention would not be widely adopted.

Following Heinrich Hertz's establishment of the existence of electromagnetic radiation in the late 1880s, a variety of terms were initially used for the phenomenon, with early descriptions of the radiation itself including "Hertzian waves", "electric waves", and "ether waves", while phrases describing its use in communications included "spark telegraphy", "space telegraphy", "aerography" and, eventually and most commonly, "wireless telegraphy". However, "wireless" included a broad variety of related electronic technologies, including electrostatic induction, electromagnetic induction and aquatic and earth conduction, so there was a need for a more precise term referring exclusively to electromagnetic radiation.

The first use of radio- in conjunction with electromagnetic radiation appears to have been by French physicist Édouard Branly, who in 1890 developed a version of a coherer receiver he called a radio-conducteur.[5] The radio- prefix was later used to form additional descriptive compound and hyphenated words, especially in Europe. For example, in early 1898 the British publication The Practical Engineer included a reference to "the radiotelegraph" and "radiotelegraphy",[6] while the French text of both the 1903 and 1906 Berlin Radiotelegraphic Conventions includes the phrases radiotélégraphique and radiotélégrammes.

The use of "radio" as a standalone word dates back to at least December 30, 1904, when instructions issued by the British Post Office for transmitting telegrams specified that "The word 'Radio'... is sent in the Service Instructions".[7] This practice was universally adopted, and the word "radio" introduced internationally, by the 1906 Berlin Radiotelegraphic Convention, which included a Service Regulation specifying that "Radiotelegrams shall show in the preamble that the service is 'Radio'".

The switch to "radio" in place of "wireless" took place slowly and unevenly in the English-speaking world. Lee de Forest helped popularize the new word in the United States—in early 1907 he founded the DeForest Radio Telephone Company, and his letter in the June 22, 1907 Electrical World about the need for legal restrictions warned that "Radio chaos will certainly be the result until such stringent regulation is enforced".[8] The United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms "wireless telegraph" and "wireless telegram", by 1912 it began to promote the use of "radio" instead. The term started to become preferred by the general public in the 1920s with the introduction of broadcasting. ("Broadcasting" is based upon an agricultural term meaning roughly "scattering seeds widely".) British Commonwealth countries continued to commonly use the term "wireless" until the mid-20th century, though the magazine of the British Broadcasting Corporation in the UK has been called Radio Times since its founding in the early 1920s.

In recent years the more general term "wireless" has gained renewed popularity, even for devices using electromagnetic radiation, through the rapid growth of short-range computer networking, e.g., Wireless Local Area Network (WLAN), Wi-Fi, and Bluetooth, as well as mobile telephony, e.g., GSM and UMTS cell phones. Today, the term "radio" specifies the transceiver device or chip, whereas "wireless" refers to the lack of physical connections; thus equipment employs embedded radio transceivers, but operates as wireless devices over wireless sensor networks.

Processes

Signal processing system
Radio communication. Information such as sound is converted by a transducer such as a microphone to an electrical signal, which modulates a radio wave sent from a transmitter. A receiver intercepts the radio wave and extracts the information-bearing electronic signal, which is converted back using another transducer such as a speaker.

Radio systems used for communication have the elements listed below. With more than 100 years of development, each process is implemented using a number of different methods which have become specialised for different communication purposes.

Transmitter and modulation

Each system contains a transmitter. This consists of a source of electrical energy, producing alternating current of a desired frequency of oscillation. The transmitter contains a system to modulate (change) some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle properties such as amplitude, frequency, phase, or combinations of these properties. The transmitter sends the modulated electrical energy to a tuned resonant antenna; this structure converts the rapidly changing alternating current into an electromagnetic wave that can move through free space (sometimes with a particular polarization).

Amfm3-en-de
An audio signal (top) may be carried by an AM or FM radio wave.

Amplitude modulation of a carrier wave works by varying the strength of the transmitted signal in proportion to the information being sent. For example, changes in the signal strength can be used to reflect the sounds to be reproduced by a speaker, or to specify the light intensity of television pixels. It was the method used for the first audio radio transmissions, and remains in use today. "AM" is often used to refer to the medium wave broadcast band (see AM radio), but it is used in various radiotelephone services such as the Citizens Band, amateur radio and especially in aviation, due to its ability to be received under very weak signal conditions and its immunity to capture effect, allowing more than one signal to be heard simultaneously.

Frequency modulation varies the frequency of the carrier. The instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. FM has the "capture effect" whereby a receiver only receives the strongest signal, even when others are present. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency (VHF) radio frequencies for high-fidelity broadcasts of music and speech (see FM broadcasting). Analog TV sound is also broadcast using FM.

Angle modulation alters the instantaneous phase of the carrier wave to transmit a signal. It may be either FM or phase modulation (PM).

Antenna

Antenna
Rooftop television antennas. Yagi-Uda antennas like these six are widely used at VHF and UHF frequencies.

An antenna (or aerial) is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter supplies an electric current oscillating at radio frequency (i.e. high frequency AC) to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified. Some antennas can be used for both transmitting and receiving, even simultaneously, depending on the connected equipment.

Propagation

Once generated, electromagnetic waves travel through space either directly, or have their path altered by reflection, refraction or diffraction. The intensity of the waves diminishes due to geometric dispersion (the inverse-square law); some energy may also be absorbed by the intervening medium in some cases. Noise will generally alter the desired signal; this electromagnetic interference comes from natural sources, as well as from artificial sources such as other transmitters and accidental radiators. Noise is also produced at every step due to the inherent properties of the devices used. If the magnitude of the noise is large enough, the desired signal will no longer be discernible; the signal-to-noise ratio is the fundamental limit to the range of radio communications.

Resonance

Electrical resonance of tuned circuits in radios allow individual stations to be selected. A resonant circuit will respond strongly to a particular frequency, and much less so to differing frequencies. This allows the radio receiver to discriminate between multiple signals differing in frequency.

Receiver and demodulation

The electromagnetic wave is intercepted by a tuned receiving antenna; this structure captures some of the energy of the wave and returns it to the form of oscillating electrical currents. At the receiver, these currents are demodulated, which is conversion to a usable signal form by a detector sub-system. The receiver is "tuned" to respond preferentially to the desired signals, and reject undesired signals.

Early radio systems relied entirely on the energy collected by an antenna to produce signals for the operator. Radio became more useful after the invention of electronic devices such as the vacuum tube and later the transistor, which made it possible to amplify weak signals. Today radio systems are used for applications from walkie-talkie children's toys to the control of space vehicles, as well as for broadcasting, and many other applications.

A radio receiver receives its input from an antenna, uses electronic filters to separate a wanted radio signal from all other signals picked up by this antenna, amplifies it to a level suitable for further processing, and finally converts through demodulation and decoding the signal into a form usable for the consumer, such as sound, pictures, digital data, measurement values, navigational positions, etc.[9]

Frequency band

Light comparison
Name Frequency (Hz) (Wavelength) Photon energy (eV)
Gamma ray > 30 EHz (0.01 nm) 124 keV – 300+ GeV
X-Ray

30 EHz - 30 PHz (0.01 nm - 10 nm)

124 eV – 120 keV
Ultraviolet

30 PHz - 750 THz (10 nm - 400 nm)

3.1 eV – 124 eV
Visible

750 THz - 428.5 THz (400 nm - 700 nm)

1.7 eV – 3.1 eV
Infrared

428.5 THz - 300 GHz (700 nm - 1 mm)

1.24 meV – 1.7 eV
Microwave

300 GHz - 300 MHz (1 mm - 1 m)

1.24 µeV – 1.24 meV
Radio

300 MHz - 3 kHz (1 m - 100 km)

12.4 feV – 1.24 µeV

Radio frequencies occupy the range from a 30 Hz to 300 GHz, although commercially important uses of radio use only a small part of this spectrum.[10] Other types of electromagnetic radiation, with frequencies above the RF range, are infrared, visible light, ultraviolet, X-rays and gamma rays. Since the energy of an individual photon of radio frequency is too low to remove an electron from an atom, radio waves are classified as non-ionizing radiation.

Communication

A radio communication system sends signals by radio.[11] Types of radio communication systems deployed depend on technology, standards, regulations, radio spectrum allocation, user requirements, service positioning, and investment.[12]

The radio equipment involved in communication systems includes a transmitter and a receiver, each having an antenna and appropriate terminal equipment such as a microphone at the transmitter and a loudspeaker at the receiver in the case of a voice-communication system.[13] The power consumed in a transmitting station varies depending on the distance of communication and the transmission conditions. The power received at the receiving station is usually only a tiny fraction of the transmitter's output, since communication depends on receiving the information, not the energy, that was transmitted.

Classical radio communications systems use frequency-division multiplexing (FDM) as a strategy to split up and share the available radio-frequency bandwidth for use by different parties' communications concurrently. Modern radio communication systems include those that divide up a radio-frequency band by time-division multiplexing (TDM) and code-division multiplexing (CDM) as alternatives to the classical FDM strategy. These systems offer different tradeoffs in supporting multiple users, beyond the FDM strategy that was ideal for broadcast radio but less so for applications such as mobile telephony.

A radio communication system may send information only one way. For example, in broadcasting a single transmitter sends signals to many receivers. Two stations may take turns sending and receiving, using a single radio frequency; this is called "simplex." By using two radio frequencies, two stations may continuously and concurrently send and receive signals – this is called " duplex" operation.

History

In 1864 James Clerk Maxwell showed mathematically that electromagnetic waves could propagate through free space.[14] The effects of electromagnetic waves (then-unexplained "action at a distance" sparking behavior) were actually observed before and after Maxwell's work by many inventors and experimenters including George Adams (1780–1784), Luigi Galvani (1791), Peter Samuel Munk (1835), Joseph Henry (1842), Samuel Alfred Varley (1852), Edwin Houston, Elihu Thomson, Thomas Edison (1875) and David Edward Hughes (1878).[15][16][17][18] Edison gave the effect the name "etheric force"[19] and Hughes detected a spark impulse up to 500 yards (460 m) with a portable receiver, but none could identify what caused the phenomenon and it was usually written off as electromagnetic induction.[20] In 1886 Heinrich Rudolf Hertz noticed the same sparking phenomenon and, in published experiments (1887–1888), was able to demonstrate the existence of electromagnetic waves in an experiment confirming Maxwell's theory of electromagnetism.

The discovery of these "Hertzian waves" (radio waves) prompted many experiments by physicists. An August 1894 lecture by the British physicist Oliver Lodge, where he transmitted and received "Hertzian waves" at distances up to 50 meters, was followed up the same year with experiments by Bengali physicist Jagadish Chandra Bose in extremely high frequency radio microwave optics and a year later with the construction of a radio based lightning detector by Russian physicist Alexander Stepanovich Popov. Starting in late 1894, Guglielmo Marconi began pursuing the idea of building a wireless telegraphy system based on Hertzian waves (radio). Marconi gained a patent on the system in 1896 and developed it into a commercial communication system over the next few years.[21]

Early 20th century radio systems transmitted messages by continuous wave code only. Early attempts at developing a system of amplitude modulation for voice and music were demonstrated in 1900 and 1906, but had little success. World War I accelerated the development of radio for military communications, and in this era the first vacuum tubes were applied to radio transmitters and receivers. Electronic amplification was a key development in changing radio from an experimental practice by experts into a home appliance. After the war, commercial radio broadcasting began in the 1920s and became an important mass medium for entertainment and news. David Sarnoff, an early exponent of broadcast radio,[22] persuaded the Radio Corporation of America to begin an AM broadcasting service which rapidly grew in popularity. World War II again accelerated development of radio for the wartime purposes of aircraft and land communication, radio navigation and radar.[23] After the war, the experiments in television that had been interrupted were resumed, and it also became an important home entertainment broadcast medium. Stereo FM broadcasting of radio was taking place from the 1930s onwards in the United States and displaced AM as the dominant commercial standard by the 1960s, and by the 1970s in the United Kingdom.[24]

Uses

Early uses were maritime, for sending telegraphic messages using Morse code between ships and land. The earliest users included the Japanese Navy scouting the Russian fleet during the Battle of Tsushima in 1905. One of the most memorable uses of marine telegraphy was during the sinking of the RMS Titanic in 1912, including communications between operators on the sinking ship and nearby vessels, and communications to shore stations listing the survivors.

Radio was used to pass on orders and communications between armies and navies on both sides in World War I; Germany used radio communications for diplomatic messages once it discovered that its submarine cables had been tapped by the British. The United States passed on President Woodrow Wilson's Fourteen Points to Germany via radio during the war. Broadcasting began from San Jose, California in 1909,[25] and became feasible in the 1920s, with the widespread introduction of radio receivers, particularly in Europe and the United States. Besides broadcasting, point-to-point broadcasting, including telephone messages and relays of radio programs, became widespread in the 1920s and 1930s. Another important application of radio, in the years just before and during World War II, was its development and active use for detecting and locating aircraft and ships by the use of radar (RAdio Detection And Ranging).

Today, radio takes many forms, including wireless networks and mobile communications of all types, as well as radio broadcasting. Before the advent of television, commercial radio broadcasts included not only news and music, but dramas, comedies, variety shows, and many other forms of entertainment (the era from the late 1920s to the mid-1950s is commonly called radio's "Golden Age"). Radio was unique among methods of dramatic presentation in that it used only sound. For more, see radio programming.

Audio

One-way

Bakelite radio
Bakelite radio at the Bakelite Museum, Orchard Mill, Williton, Somerset, UK.
Fisher 500 radio
A Fisher 500 AM/FM hi-fi receiver from 1959.

AM radio uses amplitude modulation, in which the amplitude of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone, while the transmitted frequency remains unchanged. Transmissions are affected by static and interference because lightning and other sources of radio emissions on the same frequency add their amplitudes to the original transmitted amplitude.

In the early part of the 20th century, American AM radio stations broadcast with powers as high as 500 kW, and some could be heard worldwide; these stations' transmitters were commandeered for military use by the US Government during World War II. Currently, the maximum broadcast power for a civilian AM radio station in the United States and Canada is 50 kW, and the majority of stations that emit signals this powerful were grandfathered in (see List of 50 kW AM radio stations in the United States). In 1986 KTNN received the last granted 50,000-watt class A license. These 50 kW stations are generally called "clear channel" stations (not to be confused with Clear Channel Communications), because within North America each of these stations has exclusive use of its broadcast frequency throughout part or all of the broadcast day.

Bush house
Bush House, old home of the BBC World Service.

FM broadcast radio sends music and voice with less noise than AM radio. It is often mistakenly thought that FM is higher fidelity than AM, but that is not true. AM is capable of the same audio bandwidth that FM employs. AM receivers typically use narrower filters in the receiver to recover the signal with less noise. AM stereo receivers can reproduce the same audio bandwidth that FM does due to the wider filter used in an AM stereo receiver, but today, AM radios limit the audio bandpass to 3–5 kHz. In frequency modulation, amplitude variation at the microphone causes the transmitter frequency to fluctuate. Because the audio signal modulates the frequency and not the amplitude, an FM signal is not subject to static and interference in the same way as AM signals. Due to its need for a wider bandwidth, FM is transmitted in the Very High Frequency (VHF, 30 MHz to 300 MHz) radio spectrum.

VHF radio waves act more like light, traveling in straight lines; hence the reception range is generally limited to about 50–200 miles (80–322 km). During unusual upper atmospheric conditions, FM signals are occasionally reflected back towards the Earth by the ionosphere, resulting in long distance FM reception. FM receivers are subject to the capture effect, which causes the radio to only receive the strongest signal when multiple signals appear on the same frequency. FM receivers are relatively immune to lightning and spark interference.

High power is useful in penetrating buildings, diffracting around hills, and refracting in the dense atmosphere near the horizon for some distance beyond the horizon. Consequently, 100,000-watt FM stations can regularly be heard up to 100 miles (160 km) away, and farther, 150 miles (240 km), if there are no competing signals. A few old, "grandfathered" stations do not conform to these power rules. WBCT-FM (93.7) in Grand Rapids, Michigan, US, runs 320,000 watts ERP, and can increase to 500,000 watts ERP by the terms of its original license. Such a huge power level does not usually help to increase range as much as one might expect, because VHF frequencies travel in nearly straight lines over the horizon and off into space.[26]

FM subcarrier services are secondary signals transmitted in a "piggyback" fashion along with the main program. Special receivers are required to utilize these services. Analog channels may contain alternative programming, such as reading services for the blind, background music or stereo sound signals. In some extremely crowded metropolitan areas, the sub-channel program might be an alternate foreign-language radio program for various ethnic groups. Sub-carriers can also transmit digital data, such as station identification, the current song's name, web addresses, or stock quotes. In some countries, FM radios automatically re-tune themselves to the same channel in a different district by using sub-bands.

Two-way

Aviation voice radios use Aircraft band VHF AM. AM is used so that multiple stations on the same channel can be received. (Use of FM would result in stronger stations blocking out reception of weaker stations due to FM's capture effect). Aircraft fly high enough that their transmitters can be received hundreds of miles away, even though they are using VHF.

Degen de1103
Degen DE1103, an advanced world mini-receiver with single sideband modulation and dual conversion

Marine voice radios can use single sideband voice (SSB) in the shortwave High Frequency (HF—3 MHz to 30 MHz) radio spectrum for very long ranges or Marine VHF radio / narrowband FM in the VHF spectrum for much shorter ranges. Narrowband FM sacrifices fidelity to make more channels available within the radio spectrum, by using a smaller range of radio frequencies, usually with five kHz of deviation, versus the 75 kHz used by commercial FM broadcasts, and 25 kHz used for TV sound.

Government, police, fire and commercial voice services also use narrowband FM on special frequencies. Early police radios used AM receivers to receive one-way dispatches. Civil and military HF (high frequency) voice services use shortwave radio to contact ships at sea, aircraft and isolated settlements. Most use single sideband voice (SSB), which uses less bandwidth than AM.[27] On an AM radio SSB sounds like ducks quacking, or the adults in a Charlie Brown cartoon. Viewed as a graph of frequency versus power, an AM signal shows power where the frequencies of the voice add and subtract with the main radio frequency. SSB cuts the bandwidth in half by suppressing the carrier and one of the sidebands. This also makes the transmitter about three times more powerful, because it doesn't need to transmit the unused carrier and sideband.

TETRA, Terrestrial Trunked Radio is a digital cell phone system for military, police and ambulances. Commercial services such as XM, WorldSpace and Sirius offer encrypted digital satellite radio.

Telephony

Mobile phones transmit to a local cell site (transmitter/receiver) that ultimately connects to the public switched telephone network (PSTN) through an optic fiber or microwave radio and other network elements. When the mobile phone nears the edge of the cell site's radio coverage area, the central computer switches the phone to a new cell. Cell phones originally used FM, but now most use either GSM or CDMA digital modulation schemes.[28] Satellite phones use satellites rather than cell towers to communicate.

Video

Analog television sends the picture as AM and the sound as AM or FM, with the sound carrier a fixed frequency (4.5 MHz in the NTSC system) away from the video carrier. Analog television also uses a vestigial sideband on the video carrier to reduce the bandwidth required.

Digital television uses 8VSB modulation in North America (under the ATSC digital television standard), and COFDM modulation elsewhere in the world (using the DVB-T standard). A Reed–Solomon error correction code adds redundant correction codes and allows reliable reception during moderate data loss. Although many current and future codecs can be sent in the MPEG transport stream container format, as of 2006 most systems use a standard-definition format almost identical to DVD: MPEG-2 video in Anamorphic widescreen and MPEG layer 2 (MP2) audio. High-definition television is possible simply by using a higher-resolution picture, but H.264/AVC is being considered as a replacement video codec in some regions for its improved compression. With the compression and improved modulation involved, a single "channel" can contain a high-definition program and several standard-definition programs.

Navigation

All satellite navigation systems use satellites with precision clocks. The satellite transmits its position, and the time of the transmission. The receiver listens to four satellites, and can figure its position as being on a line that is tangent to a spherical shell around each satellite, determined by the time-of-flight of the radio signals from the satellite. A computer in the receiver does the math.

Radio direction-finding is the oldest form of radio navigation. Before 1960 navigators used movable loop antennas to locate commercial AM stations near cities. In some cases they used marine radiolocation beacons, which share a range of frequencies just above AM radio with amateur radio operators. LORAN systems also used time-of-flight radio signals, but from radio stations on the ground.

Very High Frequency Omnidirectional Range (VOR), systems (used by aircraft), have an antenna array that transmits two signals simultaneously. A directional signal rotates like a lighthouse at a fixed rate. When the directional signal is facing north, an omnidirectional signal pulses. By measuring the difference in phase of these two signals, an aircraft can determine its bearing or radial from the station, thus establishing a line of position. An aircraft can get readings from two VORs and locate its position at the intersection of the two radials, known as a "fix."

When the VOR station is collocated with DME (Distance Measuring Equipment), the aircraft can determine its bearing and range from the station, thus providing a fix from only one ground station. Such stations are called VOR/DMEs. The military operates a similar system of navaids, called TACANs, which are often built into VOR stations. Such stations are called VORTACs. Because TACANs include distance measuring equipment, VOR/DME and VORTAC stations are identical in navigation potential to civil aircraft.

Radar

Radar (Radio Detection And Ranging) detects objects at a distance by bouncing radio waves off them. The delay caused by the echo measures the distance. The direction of the beam determines the direction of the reflection. The polarization and frequency of the return can sense the type of surface. Navigational radars scan a wide area two to four times per minute. They use very short waves that reflect from earth and stone. They are common on commercial ships and long-distance commercial aircraft.

General purpose radars generally use navigational radar frequencies, but modulate and polarize the pulse so the receiver can determine the type of surface of the reflector. The best general-purpose radars distinguish the rain of heavy storms, as well as land and vehicles. Some can superimpose sonar data and map data from GPS position.

Search radars scan a wide area with pulses of short radio waves. They usually scan the area two to four times a minute. Sometimes search radars use the Doppler effect to separate moving vehicles from clutter. Targeting radars use the same principle as search radar but scan a much smaller area far more often, usually several times a second or more. Weather radars resemble search radars, but use radio waves with circular polarization and a wavelength to reflect from water droplets. Some weather radar use the Doppler effect to measure wind speeds.

Data (digital radio)

Radio DAB
2008 Pure One Classic digital radio

Most new radio systems are digital, including Digital TV, satellite radio, and Digital Audio Broadcasting. The oldest form of digital broadcast was spark gap telegraphy, used by pioneers such Popov[29] or Marconi. By pressing the key, the operator could send messages in Morse code by energizing a rotating commutating spark gap. The rotating commutator produced a tone in the receiver, where a simple spark gap would produce a hiss, indistinguishable from static. Spark-gap transmitters are now illegal, because their transmissions span several hundred megahertz. This is very wasteful of both radio frequencies and power.

The next advance was continuous wave telegraphy, or CW (Continuous Wave), in which a pure radio frequency, produced by a vacuum tube electronic oscillator was switched on and off by a key. A receiver with a local oscillator would "heterodyne" with the pure radio frequency, creating a whistle-like audio tone. CW uses less than 100 Hz of bandwidth. CW is still used, these days primarily by amateur radio operators (hams). Strictly, on-off keying of a carrier should be known as "Interrupted Continuous Wave" or ICW or on-off keying (OOK).

Radioteletype equipment usually operates on short-wave (HF) and is much loved by the military because they create written information without a skilled operator. They send a bit as one of two tones using frequency-shift keying. Groups of five or seven bits become a character printed by a teleprinter. From about 1925 to 1975, radioteletype was how most commercial messages were sent to less developed countries. These are still used by the military and weather services.

Aircraft use a 1200 Baud radioteletype service over VHF to send their ID, altitude and position, and get gate and connecting-flight data. Microwave dishes on satellites, telephone exchanges and TV stations usually use quadrature amplitude modulation (QAM). QAM sends data by changing both the phase and the amplitude of the radio signal. Engineers like QAM because it packs the most bits into a radio signal when given an exclusive (non-shared) fixed narrowband frequency range. Usually the bits are sent in "frames" that repeat. A special bit pattern is used to locate the beginning of a frame.

GPS Receivers
Modern GPS receivers.

Communication systems that limit themselves to a fixed narrowband frequency range are vulnerable to jamming. A variety of jamming-resistant spread spectrum techniques were initially developed for military use, most famously for Global Positioning System satellite transmissions. Commercial use of spread spectrum began in the 1980s. Bluetooth, most cell phones, and the 802.11b version of Wi-Fi each use various forms of spread spectrum.

Systems that need reliability, or that share their frequency with other services, may use "coded orthogonal frequency-division multiplexing" or COFDM. COFDM breaks a digital signal into as many as several hundred slower subchannels. The digital signal is often sent as QAM on the subchannels. Modern COFDM systems use a small computer to make and decode the signal with digital signal processing, which is more flexible and far less expensive than older systems that implemented separate electronic channels.

COFDM resists fading and ghosting because the narrow-channel QAM signals can be sent slowly. An adaptive system, or one that sends error-correction codes can also resist interference, because most interference can affect only a few of the QAM channels. COFDM is used for Wi-Fi, some cell phones, Digital Radio Mondiale, Eureka 147, and many other local area network, digital TV and radio standards.

Heating

Radio-frequency energy generated for heating of objects is generally not intended to radiate outside of the generating equipment, to prevent interference with other radio signals. Microwave ovens use intense radio waves to heat food. Diathermy equipment is used in surgery for sealing of blood vessels.

Amateur radio service

NX1Z Radio
Amateur radio station with multiple receivers and transceivers

Amateur radio, also known as "ham radio", is a hobby in which enthusiasts are licensed to communicate on a number of bands in the radio frequency spectrum non-commercially and for their own experiments. They may also provide emergency and service assistance in unexpected circumstances. This contribution has been very beneficial in saving lives in many instances.[30]

Radio amateurs use a variety of modes, including efficient ones like Morse code and experimental ones like Low-Frequency Experimental Radio. Several forms of radio were pioneered by radio amateurs and later became commercially important, including FM, single-sideband (SSB), AM, digital packet radio and satellite repeaters. Some amateur frequencies may be disrupted illegally by power-line internet service.

Unlicensed radio services

Unlicensed, government-authorized personal radio services such as Citizens' band radio in Australia, most of the Americas, and Europe, and Family Radio Service and Multi-Use Radio Service in North America exist to provide simple, usually short range communication for individuals and small groups, without the overhead of licensing. Similar services exist in other parts of the world. These radio services involve the use of handheld units.

Wi-Fi also operates in unlicensed radio bands and is very widely used to network computers.

Free radio stations, sometimes called pirate radio or "clandestine" stations, are unauthorized, unlicensed, illegal broadcasting stations. These are often low power transmitters operated on sporadic schedules by hobbyists, community activists, or political and cultural dissidents. Some pirate stations operating offshore in parts of Europe and the United Kingdom more closely resembled legal stations, maintaining regular schedules, using high power, and selling commercial advertising time.[31][32]

Radio control (RC)

Radio remote controls use radio waves to transmit control data to a remote object as in some early forms of guided missile, some early TV remotes and a range of model boats, cars and airplanes. Large industrial remote-controlled equipment such as cranes and switching locomotives now usually use digital radio techniques to ensure safety and reliability.

In Madison Square Garden, at the Electrical Exhibition of 1898, Nikola Tesla successfully demonstrated a radio-controlled boat.[33] He was awarded U.S. patent No. 613,809 for a "Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles."[34]

See also

References

  1. ^ "Radio-Electronics, Radio Receiver Technology". Radio-electronics.com. Retrieved 2014-08-02.
  2. ^ The Electromagnetic Spectrum, University of Tennessee, Dept. of Physics and Astronomy
  3. ^ R.K. Puri (2004). Solid State Physics and Electronics. S. Chand. ISBN 978-81-219-1475-8.
  4. ^ "Production of Sound by Radiant Energy" by Alexander Graham Bell, Popular Science Monthly, July 1881, pp. 329–30: "[W]e have named the apparatus for the production and reproduction of sound in this way the "photophone", because an ordinary beam of light contains the rays which are operative. To avoid in future any misunderstandings upon this point, we have decided to adopt the term "radiophone", proposed by M. Mercadier, as a general term signifying the production of sound by any form of radiant energy..."
  5. ^ "The Genesis of Wireless Telegraphy" by A. Frederick Collins, Electrical World and Engineer, May 10, 1902, p. 811.
  6. ^ "Wireless Telegraphy", The Practical Engineer, February 25, 1898, p. 174. "Dr. O. J. Lodge, who preceded Marconi in making experiments in what may be called "ray" telegraphy or radiotelegraphy by a year or two, has devised a new method of sending and receiving the messages. The reader will understand that in the radiotelegraph electric waves forming the signals of the message start from the sending instrument and travel in all directions like rays of light from a lamp, only they are invisible."
  7. ^ "Wireless Telegraphy", The Electrical Review (London), January 20, 1905, p. 108, quoting from the British Post Office's December 30, 1904 Post Office Circular.
  8. ^ "Interference with Wireless Messages", Electrical World, June 22, 1907, p. 1270.
  9. ^ "Radio Receiver Technology". Radio-electronics.com. Retrieved 2014-08-02.
  10. ^ The Electromagnetic Spectrum, University of Tennessee, Dept. of Physics and Astronomy
  11. ^ Clint Smith, Curt Gervelis (2003). Wireless Network Performance Handbook. McGraw-Hill Professional. ISBN 978-0-07-140655-0.
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  13. ^ R.K. Puri (2004). Solid State Physics and Electronics. S. Chand. ISBN 978-81-219-1475-8.
  14. ^ web.pdx.edu/~bseipel/Lecture%20notes%206-%20203%20EMwaves.pdf
  15. ^ Mallik, M.C. (1988). "EM Wave Detectors". IETE Technical Review. 5 (8): 329–31. doi:10.1080/02564602.1988.11438340.
  16. ^ T. K. Sarkar, Robert Mailloux, Arthur A. Oliner, M. Salazar-Palma, Dipak L. Sengupta , History of Wireless, John Wiley & Sons – 2006, pp. 258–61
  17. ^ Christopher H. Sterling, Encyclopedia of Radio 3 – Volume, Routledge – 2004, p. 831
  18. ^ Anand Kumar Sethi, The Business of Electronics: A Concise History, Palgrave Macmillan – 2013, p. 22
  19. ^ ieeeghn.org, IEEE Global History Network, Etheric Force
  20. ^ W. Bernard Carlson, Innovation as a Social Process: Elihu Thomson and the Rise of General Electric, Cambridge University Press – 2003, pp. 57–58
  21. ^ "U.S. Supreme Court". Retrieved 2012-04-23.
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  24. ^ Théberge, P., Devine, K. & Everrett, T. (2015). Living Stereo: Histories and Cultures of Multichannel Sound. New York: Bloomsbury Publishing USA.
  25. ^ "The History Of KQW Radio – KCBS". Bayarearadio.org. Retrieved 2009-07-22.
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  27. ^ "Audio example of SSB". Retrieved 2014-08-02.
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  29. ^ Electronics World, Volume 64, Ziff-Davis Publishing Company – 1960, p. 78
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  32. ^ Rebel Radio: The Full Story of British Pirate Radio by John Hind, Stephen Mosco. Pluto Press, 1985. ISBN 0-7453-0055-3, 978-0-7453-0055-9
  33. ^ "Tesla – Master of Lightning: Remote Control". PBS. Retrieved 2009-07-22.
  34. ^ "Tesla – Master of Lightning: Selected Tesla Patents". PBS. Retrieved 2009-07-22.
Alex Jones

Alexander Emric (or Emerick) Jones (born February 11, 1974) is an American radio show host and far right conspiracy theorist. He hosts The Alex Jones Show from Austin, Texas, which airs on the Genesis Communications Network across the United States and online. Jones runs a website, Infowars.com, devoted to conspiracy theories and fake news, and the websites NewsWars and PrisonPlanet.

Born in Dallas, Texas, Jones began his career in the 1990s running a live public-access cable television program, later switching to radio. He has been the center of many controversies, including his promotion of Sandy Hook Elementary School shooting conspiracy theories, and his aggressive opposition to gun control in a debate with Piers Morgan. Jones has accused the US government of planning the Oklahoma City bombing, the September 11 attacks, and falsifying some details regarding the Moon landing. He has claimed that several governments and big businesses have colluded to create a "New World Order" through "manufactured economic crises, sophisticated surveillance tech and—above all—inside-job terror attacks that fuel exploitable hysteria".Jones has described himself as a conservative, paleoconservative and libertarian, terms he uses interchangeably. Others describe him as conservative, right-wing, alt-right, and far-right. New York magazine has described Jones as "America's leading conspiracy theorist", and the Southern Poverty Law Center describes him as "the most prolific conspiracy theorist in contemporary America". Asked about such labels, Jones said he is "proud to be listed as a thought criminal against Big Brother".

Australian Broadcasting Corporation

The Australian Broadcasting Corporation (ABC) is Australia's national broadcaster founded in 1929. It is currently principally funded by direct grants from the Australian government, but is expressly independent of government and partisan politics. The ABC plays a leading role in journalistic independence and is fundamental in the history of broadcasting in Australia.

Modelled on the BBC in the United Kingdom, it was originally financed by consumer licence fees on broadcasting receivers. Licence fees were abolished in 1973 and replaced principally by direct government grants, as well as revenue from commercial activities related to its core broadcasting mission.

The ABC now provides television, radio, online and mobile services throughout metropolitan and regional Australia and overseas through ABC Australia and Radio Australia. The ABC headquarters is in Ultimo, an inner-city suburb of Sydney, New South Wales.

BBC

The British Broadcasting Corporation (BBC) is a British public service broadcaster. Its headquarters are at Broadcasting House in Westminster, London, and it is the world's oldest national broadcasting organisation and the largest broadcaster in the world by number of employees. It employs over 20,950 staff in total, 16,672 of whom are in public sector broadcasting. The total number of staff is 35,402 when part-time, flexible, and fixed-contract staff are included.The BBC is established under a Royal Charter and operates under its Agreement with the Secretary of State for Digital, Culture, Media and Sport. Its work is funded principally by an annual television licence fee which is charged to all British households, companies, and organisations using any type of equipment to receive or record live television broadcasts and iPlayer catch-up. The fee is set by the British Government, agreed by Parliament, and used to fund the BBC's radio, TV, and online services covering the nations and regions of the UK. Since 1 April 2014, it has also funded the BBC World Service (launched in 1932 as the BBC Empire Service), which broadcasts in 28 languages and provides comprehensive TV, radio, and online services in Arabic and Persian.

Around a quarter of BBC revenues come from its commercial arm BBC Studios Ltd (formerly BBC Worldwide), which sells BBC programmes and services internationally and also distributes the BBC's international 24-hour English-language news services BBC World News, and from BBC.com, provided by BBC Global News Ltd.

From its inception, through the Second World War (where its broadcasts helped to unite the nation), to the 21st century, the BBC has played a prominent role in British culture. It is also known colloquially as "The Beeb", "Auntie", or a combination of both (as "Auntie Beeb" or "Auntie B").

BBC Radio 1

BBC Radio 1 is a British radio station operated by the British Broadcasting Corporation which also broadcasts internationally, specialising in modern popular music and current chart hits throughout the day. Radio 1 provides alternative genres after 7 pm, including electronica, dance, hip hop, rock and indie. The choice of music and presenting style is entirely that of programme hosts, however those who present in the daytime have to rotate a number of songs a specific number of times (8, 13 or 15) per week. It was launched in 1967 to meet the demand for music generated by pirate radio stations, when the average age of the UK population was 27. The BBC claim that they target the 15–29 age group, and the average age of its UK audience since 2009 is 30. BBC Radio 1 started 24-hour broadcasting on 1 May 1991.

CBS

CBS (an initialism of the network's former name, the Columbia Broadcasting System) is an American English language commercial broadcast television and radio network that is a flagship property of CBS Corporation. The company is headquartered at the CBS Building in New York City with major production facilities and operations in New York City (at the CBS Broadcast Center) and Los Angeles (at CBS Television City and the CBS Studio Center).

CBS is sometimes referred to as the Eye Network, in reference to the company's iconic symbol, in use since 1951. It has also been called the "Tiffany Network", alluding to the perceived high quality of CBS programming during the tenure of William S. Paley. It can also refer to some of CBS's first demonstrations of color television, which were held in a former Tiffany & Co. building in New York City in 1950.The network has its origins in United Independent Broadcasters Inc., a collection of 16 radio stations that was purchased by Paley in 1928 and renamed the Columbia Broadcasting System. Under Paley's guidance, CBS would first become one of the largest radio networks in the United States, and eventually one of the Big Three American broadcast television networks. In 1974, CBS dropped its former full name and became known simply as CBS, Inc. The Westinghouse Electric Corporation acquired the network in 1995, renamed its corporate entity to the current CBS Broadcasting, Inc. in 1997, and eventually adopted the name of the company it had acquired to become CBS Corporation. In 2000, CBS came under the control of Viacom, which was formed as a spin-off of CBS in 1971. In late 2005, Viacom split itself into two separate companies and re-established CBS Corporation – through the spin-off of its broadcast television, radio, and select cable television and non-broadcasting assets – with the CBS television network at its core. CBS Corporation is controlled by Sumner Redstone through National Amusements, which also controls the current Viacom.

CBS formerly operated the CBS Radio network until 2017, when it merged its radio division with Entercom. Prior to then, CBS Radio mainly provided news and features content for its portfolio owned-and-operated radio stations in large and mid-sized markets, and affiliated radio stations in various other markets. While CBS Corporation owns a 72% stake in Entercom, it no longer owns or operates any radio stations directly, though CBS still provides radio news broadcasts to its radio affiliates and the new owners of its former radio stations. The television network has more than 240 owned-and-operated and affiliated television stations throughout the United States. The company ranked 197th on the 2018 Fortune 500 of the largest United States corporations by revenue.

Canadian Broadcasting Corporation

The Canadian Broadcasting Corporation (French: Société Radio-Canada), branded as CBC/Radio-Canada, is a Canadian federal Crown corporation that serves as the national public broadcaster for both radio and television. The English- and French-language service units of the corporation are commonly known as CBC and Radio-Canada respectively, and both short-form names are also commonly used in the applicable language to refer to the corporation as a whole.

Although some local stations in Canada predate CBC's founding, CBC is the oldest existing broadcasting network in Canada, first established in its present form on November 2, 1936. Radio services include CBC Radio One, CBC Music, Ici Radio-Canada Première, Ici Musique and the international radio service Radio Canada International. Television operations include CBC Television, Ici Radio-Canada Télé, CBC News Network, Ici RDI, Ici Explora, Documentary Channel (part ownership), and Ici ARTV. The CBC operates services for the Canadian Arctic under the names CBC North and Radio-Canada Nord. The CBC also operates digital services including CBC.ca/Ici.Radio-Canada.ca, CBC Radio 3, CBC Music/ICI.mu and Ici.TOU.TV, and owns 20.2% of satellite radio broadcaster Sirius XM Canada, which carries several CBC-produced audio channels.

CBC/Radio-Canada offers programming in English, French and eight aboriginal languages on its domestic radio service, and in five languages on its web-based international radio service, Radio Canada International (RCI). However, budget cuts in the early 2010s have contributed to the corporation reducing its service via the airwaves, discontinuing RCI's shortwave broadcasts as well as terrestrial television broadcasts in all communities served by network-owned rebroadcast transmitters, including communities not subject to Canada's over-the-air digital television transition.

CBC's federal funding is supplemented by revenue from commercial advertising on its television broadcasts. The radio service employed commercials from its inception to 1974, but since its primary radio networks have been commercial-free. In 2013, CBC's secondary radio networks, CBC Music and Ici Musique, introduced limited advertising of up to four minutes an hour, but this was discontinued in 2016.

Howard Stern

Howard Allan Stern (born January 12, 1954) is an American radio and television personality, producer, author, actor, and photographer. He is best known for his radio show The Howard Stern Show, which gained popularity when it was nationally syndicated on terrestrial radio from 1986 to 2005. Stern has broadcast on Sirius XM Radio since 2006.

Stern landed his first radio jobs while at Boston University. From 1976 to 1982, Stern developed his on-air personality through morning positions at WRNW in Briarcliff Manor, New York, WCCC in Hartford, Connecticut, WWWW in Detroit, Michigan, and WWDC in Washington, D.C. Stern worked afternoons at WNBC in New York City from 1982 until his firing in 1985. In 1985, he began a 20-year run at WXRK in New York City; his morning show entered syndication in 1986 and aired in 60 markets and attracted 20 million listeners at its peak. Stern won numerous industry awards, including Billboard’s Nationally Syndicated Air Personality of the Year eight consecutive times, and is the first to have the number one morning show in New York City and Los Angeles simultaneously. He became the most fined radio host when the Federal Communications Commission issued fines totaling $2.5 million to station owners for content it deemed indecent. Stern became one of the highest paid radio figures after signing a five-year deal with Sirius in 2004 worth $500 million. In recent years, Stern's photography has been featured in Hamptons and WHIRL magazines. From 2012 to 2015, he served as a judge on America's Got Talent.

Stern has been described as the "King of All Media" since 1992 for his successes outside radio. He hosted and produced numerous late night television shows, pay-per-view events, and home videos. His two books, Private Parts (1993) and Miss America (1995), entered The New York Times Best Seller list at number one and sold over one million copies. The former was made into a biographical comedy film in 1997 that had Stern and his radio show staff star as themselves. It topped the US box office in its opening week and grossed $41.2 million domestically. Stern performs on its soundtrack, which charted the Billboard 200 at number one and was certified platinum for one million copies sold. Stern's third book, Howard Stern Comes Again, will be released in May 2019.

Korean Broadcasting System

Korean Broadcasting System (KBS) (Hangul: 한국방송공사; Hanja: 韓國放送公社; RR: Han-guk Bangsong Gongsa; MR: Han'guk Pangsong Kongsa) is the national public broadcaster of South Korea. It was founded in 1927, and operates radio, television, and online services, being one of the biggest South Korean television networks.

Mobile phone

A mobile phone, cell phone, cellphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone that can make and receive calls over a radio frequency link while the user is moving within a telephone service area. The radio frequency link establishes a connection to the switching systems of a mobile phone operator, which provides access to the public switched telephone network (PSTN). Modern mobile telephone services use a cellular network architecture, and, therefore, mobile telephones are called cellular telephones or cell phones, in North America. In addition to telephony, 2000s-era mobile phones support a variety of other services, such as text messaging, MMS, email, Internet access, short-range wireless communications (infrared, Bluetooth), business applications, video games, and digital photography. Mobile phones offering only those capabilities are known as feature phones; mobile phones which offer greatly advanced computing capabilities are referred to as smartphones.

The first handheld mobile phone was demonstrated by John F. Mitchell and Martin Cooper of Motorola in 1973, using a handset weighing c. 2 kilograms (4.4 lbs). In 1979, Nippon Telegraph and Telephone (NTT) launched the world's first cellular network in Japan. In 1983, the DynaTAC 8000x was the first commercially available handheld mobile phone. From 1983 to 2014, worldwide mobile phone subscriptions grew to over seven billion—enough to provide one for every person on Earth. In first quarter of 2016, the top smartphone developers worldwide were Samsung, Apple, and Huawei, and smartphone sales represented 78 percent of total mobile phone sales. For feature phones (or "dumbphones") as of 2016, the largest were Samsung, Nokia, and Alcatel.

Morse code

Morse code is a character encoding scheme used in telecommunication that encodes text characters as standardized sequences of two different signal durations called dots and dashes or dits and dahs. Morse code is named for Samuel F. B. Morse, an inventor of the telegraph.

The International Morse Code encodes the ISO basic Latin alphabet, some extra Latin letters, the Arabic numerals and a small set of punctuation and procedural signals (prosigns). Each Morse code symbol is formed by a sequence of dots and dashes. The dot duration is the basic unit of time measurement in Morse code transmission. The duration of a dash is three times the duration of a dot. Each dot or dash within a character is followed by period of signal absence, called a space, equal to the dot duration. The letters of a word are separated by a space of duration equal to three dots, and the words are separated by a space equal to seven dots. To increase the efficiency of encoding, Morse code was designed so that the length of each symbol is approximately inverse to the frequency of occurrence in text of the English language character that it represents. Thus the most common letter in English, the letter "E", has the shortest code: a single dot. Because the Morse code elements are specified by proportion rather than specific time durations, the code is usually transmitted at the highest rate that the receiver is capable of decoding. The Morse code transmission rate (speed) is specified in groups per minute, commonly referred to as words per minute.Morse code is usually transmitted by on-off keying of an information carrying medium such as electric current, radio waves, visible light or sound waves. The current or wave is present during time period of the dot or dash and absent during the time between dots and dashes.Morse code can be memorized, and Morse code signalling in a form perceptible to the human senses, such as sound waves or visible light, can be directly interpreted by persons trained in the skill.Because many non-English natural languages use other than the 26 Roman letters, Morse alphabets have been developed for those languages.

In an emergency, Morse code can be generated by improvised methods such as turning a light on and off, tapping on an object or sounding a horn or whistle, making it one of the simplest and most versatile methods of telecommunication. The most common distress signal is SOS – three dots, three dashes, and three dots – internationally recognized by treaty.

NATO phonetic alphabet

The NATO phonetic alphabet, officially denoted as the International Radiotelephony Spelling Alphabet, and also commonly known as the ICAO phonetic alphabet, and in a variation also known officially as the ITU phonetic alphabet and figure code, is the most widely used radiotelephone spelling alphabet. Although often called "phonetic alphabets", spelling alphabets are unrelated to phonetic transcription systems such as the International Phonetic Alphabet. Instead, the International Civil Aviation Organization (ICAO) alphabet assigned codewords acrophonically to the letters of the English alphabet, so that critical combinations of letters and numbers are most likely to be pronounced and understood by those who exchange voice messages by radio or telephone, regardless of language differences or the quality of the communication channel.The 26 code words in the NATO phonetic alphabet are assigned to the 26 letters of the English alphabet in alphabetical order as follows: Alfa, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu.Strict adherence to the prescribed spelling words is required in order to avoid the problems of confusion that the spelling alphabet is designed to overcome. As noted in a 1955 NATO memo:

It is known that [the ICAO spelling alphabet] has been prepared only after the most exhaustive tests on a scientific basis by several nations. One of the firmest conclusions reached was that it was not practical to make an isolated change to clear confusion between one pair of letters. To change one word involves reconsideration of the whole alphabet to ensure that the change proposed to clear one confusion does not itself introduce others.

The same memo notes a potential confusion between ZERO and SIERRA is overcome when following the procedures in ACP 125, which specify the use of the procedure word FIGURES in many instances in which digits need to be read.

NPR

National Public Radio (NPR, stylized as npr) is an American privately and publicly funded non-profit membership media organization based in Washington, D.C. NPR differs from other non-profit membership media organizations, such as AP, in that it was established by an act of Congress and most of its member stations are owned by government entities (often public universities). It serves as a national syndicator to a network of over 1,000 public radio stations in the United States.NPR produces and distributes news and cultural programming. Individual public radio stations are not required to broadcast all NPR programs; most broadcast a mix of NPR programs, content from American Public Media, Public Radio International, Public Radio Exchange and WNYC Studios, and locally produced programs. The organisation's flagship shows are two drive-time news broadcasts, Morning Edition and the afternoon All Things Considered; both are carried by most NPR member stations, and are among the most popular radio programs in the country. As of March 2018, the drive time programs attract an audience of 14.9 million and 14.7 million respectively.NPR manages the Public Radio Satellite System, which distributes NPR programs and other programming from independent producers and networks such as American Public Media and Public Radio International. Its content is also available on-demand online, on mobile networks, and, in many cases, as podcasts.

Podcast

A podcast or generically netcast, is an episodic series of digital audio or video files which a user can download in order to listen to. It is often available for subscription, so that new episodes are automatically downloaded via web syndication to the user's own local computer, mobile application, or portable media player.The word was originally suggested by Ben Hammersley as a portmanteau of "iPod" (a brand of media player) and "broadcast".The files distributed are in audio format, but may sometimes include other file formats such as PDF or EPUB. Videos which are shared following a podcast model are sometimes called video podcasts or vodcasts.

The generator of a podcast maintains a central list of the files on a server as a web feed that can be accessed through the Internet. The listener or viewer uses special client application software on a computer or media player, known as a podcatcher, which accesses this web feed, checks it for updates, and downloads any new files in the series. This process can be automated to download new files automatically, which may seem to users as though new episodes are broadcast or "pushed" to them. Files are stored locally on the user's device, ready for offline use. There are many different mobile applications available for people to use to subscribe and to listen to podcasts. Many of these applications allow users to download podcasts or to stream them on demand as an alternative to downloading. Many podcast players (apps as well as dedicated devices) allow listeners to skip around the podcast and control the playback speed.

Some have labeled podcasting as a converged medium bringing together audio, the web, and portable media players, as well as a disruptive technology that has caused some individuals in the radio business to reconsider established practices and preconceptions about audiences, consumption, production, and distribution.

Podcasts are usually free of charge to listeners and can often be created for little to no cost, which sets them apart from the traditional model of "gate-kept" media and production tools. Podcast creators can monetize their podcasts by allowing companies to purchase ad time, as well as via sites such as Patreon, which provides special extras and content to listeners for a fee. Podcasting is very much a horizontal media form – producers are consumers, consumers may become producers, and both can engage in conversations with each other.

Radar

Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver and processor to determine properties of the object(s). Radio waves (pulsed or continuous) from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed.

Radar was developed secretly for military use by several nations in the period before and during World War II. A key development was the cavity magnetron in the UK, which allowed the creation of relatively small systems with sub-meter resolution. The term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging The term radar has since entered English and other languages as a common noun, losing all capitalization.

The modern uses of radar are highly diverse, including air and terrestrial traffic control, radar astronomy, air-defense systems, antimissile systems, marine radars to locate landmarks and other ships, aircraft anticollision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring, altimetry and flight control systems, guided missile target locating systems, ground-penetrating radar for geological observations, and range-controlled radar for public health surveillance. High tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from very high noise levels. Radar is a key technology that the self-driving systems are mainly designed to use, along with sonar and other sensors.Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "lidar", which uses predominantly infrared light from lasers rather than radio waves. With the emergence of driverless vehicles, Radar is expected to assist the automated platform to monitor its environment, thus preventing unwanted incidents.

Radio broadcasting

Radio broadcasting is transmission by radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both.

The signal types can be either analog audio or digital audio.

Ryan Seacrest

Ryan John Seacrest (born December 24, 1974) is an American radio personality, television host, and producer. Seacrest is known for hosting the competition show American Idol, the syndicated countdown program American Top 40, and iHeartMedia's KIIS-FM morning radio show On Air with Ryan Seacrest.In 2006 Seacrest became co-host and executive producer of Dick Clark's New Year's Rockin' Eve. Seacrest remained a co-host and executive producer following Clark's death in 2012.He began co-hosting Live with Kelly and Ryan on a permanent basis May 1, 2017.Seacrest received Emmy Award nominations for American Idol from 2004 to 2013, and again in 2016. He won an Emmy for producing Jamie Oliver's Food Revolution in 2010 and was nominated again in 2012. In 2018, Seacrest received nominations for Live with Kelly and Ryan in Outstanding Talk Show Entertainment as well as Outstanding Entertainment Talk Show Host.

Single (music)

In the music industry, a single is a type of release, typically a song recording of fewer tracks than an LP record or an album. This can be released for sale to the public in a variety of different formats. In most cases, a single is a song that is released separately from an album, although it usually also appears on an album. Typically, these are the songs from albums that are released separately for promotional uses such as digital download or commercial radio airplay and are expected to be the most popular. In other cases a recording released as a single may not appear on an album.

Despite being referred to as a single, singles can include up to as many as three tracks. The biggest digital music distributor, iTunes Store, accepts as many as three tracks less than ten minutes each as a single, as does popular music player Spotify. Any more than three tracks on a musical release or thirty minutes in total running time is either an extended play (EP) or, if over six tracks long, an album.

Telecommunication

Telecommunication is the transmission of signs, signals, messages, words, writings, images and sounds or information of any nature by wire, radio, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology. It is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are often divided into communication channels which afford the advantages of multiplexing. Since the Latin term communicatio is considered the social process of information exchange, the term telecommunications is often used in its plural form because it involves many different technologies.Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs. Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, and loud whistles. 20th- and 21st-century technologies for long-distance communication usually involve electrical and electromagnetic technologies, such as telegraph, telephone, and teleprinter, networks, radio, microwave transmission, fiber optics, and communications satellites.

A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909, and other notable pioneering inventors and developers in the field of electrical and electronic telecommunications. These included Charles Wheatstone and Samuel Morse (inventors of the telegraph), Alexander Graham Bell (inventor of the telephone), Edwin Armstrong and Lee de Forest (inventors of radio), as well as Vladimir K. Zworykin, John Logie Baird and Philo Farnsworth (some of the inventors of television).

The Hitchhiker's Guide to the Galaxy

The Hitchhiker's Guide to the Galaxy (sometimes referred to as HG2G, HHGTTG or H2G2) is a comedy science fiction series created by Douglas Adams. Originally a radio comedy broadcast on BBC Radio 4 in 1978, it was later adapted to other formats, including stage shows, novels, comic books, a 1981 TV series, a 1984 video game, and 2005 feature film.

A prominent series in British popular culture, The Hitchhiker's Guide to the Galaxy has become an international multi-media phenomenon; the novels are the most widely distributed, having been translated into more than 30 languages by 2005. In 2017, BBC Radio 4 announced a 40th-anniversary celebration with Dirk Maggs, one of the original producers, in charge. This sixth series of the sci-fi spoof has been based on Eoin Colfer's book And Another Thing, with additional unpublished material by Douglas Adams. The first of six new episodes was broadcast on 8 March 2018.The broad narrative of Hitchhiker follows the misadventures of the last surviving man, Arthur Dent, following the demolition of the planet Earth by a Vogon constructor fleet to make way for a hyperspace bypass. Dent is rescued from Earth's destruction by Ford Prefect, a human-like alien writer for the eccentric, electronic travel guide The Hitchhiker's Guide to the Galaxy, by hitchhiking onto a passing Vogon spacecraft. Following his rescue, Dent explores the galaxy with Prefect and encounters Trillian, another human who had been taken from Earth prior to its destruction by the President of the Galaxy, the two-headed Zaphod Beeblebrox, and the depressed Marvin, the Paranoid Android. Certain narrative details were changed between the various adaptations.

Transmission methods
Notable signals
Other writing systems
in Morse code
History
Pioneers
Transmission
media
Network topology
and switching
Multiplexing
Networks
Terrestrial
Satellite
Codecs
Subcarrier signals
Media
Ideology
Deception
Philosophers
Counterculture
In academia
Issues
Synonyms

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