Radio

From Wikipedia, the free encyclopedia

For other uses, see Radio (disambiguation).

Radio is  the wireless transmission of signals, by modulation of electromagnetic waves with frequencies below those of visible light.

Contents 1 Means of communication radio/TV 2 History and  invention 2.1 Invention 2.2 Brief history 3 Uses of radio 3.1 Audio 3.2 Telephony 3.3 Video 3.4 Navigation 3.5 Radar 3.6 Emergency services 3.7 Data (digital radio) 3.8 Heating 3.9 Mechanical force 3.10 Amateur radio service 3.11 Unlicensed radio services 3.12 Radio control (RC) 3.13 Other 4 See also 5 References 6 Further reading 6.1 Primary sources 7 External links

[edit] Means of communication radio/TV

Radio waves are  a form of electromagnetic radiation, created whenever a charged object (in normal radio transmission, an  electron) accelerates with a frequency that lies in the radio frequency (RF) portion of the electromagnetic spectrum. In radio, this acceleration is  caused by an  alternating current in an  antenna. Radio frequencies occupy the range from a few tens of hertz to three hundred gigahertz, although commercially important uses of radio use only a small part of this spectrum.^[1]

ELF - SLF - ULF/VF - VLF - LF/LW - MW - HF/SW - VHF - UHF - SHF - EHF Electromagnetic radio spectrum

Other types of electromagnetic radiation, with frequencies above the RF range, are  microwave, 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.

Electromagnetic radiation travels (propagates) by means of oscillating electromagnetic fields that pass through the air and  the vacuum of space. it  does not require a medium of transport (such as the aether). When radio waves pass an  electrical conductor, the oscillating electric or  magnetic field (depending on the shape of the conductor) induces an  alternating current and  voltage in the conductor. This can be transformed into audio or  other signals that carry information. The word 'radio' is  used to describe this phenomenon, and  television, radio, and  cell phone transmissions are  all classed as radio frequency emissions.

[ and  invention">edit] History and  invention

Originally, radio technology was called 'wireless telegraphy', which was shortened to 'wireless'. The prefix radio- in the sense of wireless transmission was first recorded in the word radioconductor, coined by the French physicist Edouard Branly in 1897 and  based on the verb to radiate. 'Radio' as a noun is  said to have  been coined by advertising expert Waldo Warren (White 1944). The word appears in a 1907 article by Lee de Forest, was adopted by the United States Navy in 1912 and  became common by the time of the first commercial broadcasts in the United States in the 1920s. (The noun 'broadcasting' itself came from an  agricultural term, meaning 'scattering seeds'.) The American term was then adopted by other languages in Europe and  Asia, although British Commonwealth countries retained the term 'wireless' until the mid-20th century. In Chinese, the term 'wireless' is  the basis for the term 'radio wave' although the term for the device that listens to radio waves is  literally 'device for receiving sounds'.

In recent years the term 'wireless' has gained renewed popularity through the rapid growth of short range networking, e.g. WLAN ('Wireless Local Area Network'), WiFi ('Wireless Fidelity'), Bluetooth as well as mobile telephony, e.g. GSM and  UMTS. Today, the term 'radio' often refers to the actual transceiver device or  chip, whereas 'wireless' refers to the system and/or method used for radio communication. Hence one talks about radio transceivers and  Radio Frequency Identification (RFID), but about wireless devices and  wireless sensor networks.

[edit] Invention

The identity of the original inventor of radio, at the time called wireless telegraphy, is  contentious. The controversy over who invented the radio, with the benefit of hindsight, can be broken down as follows:

• Alexander Stepanovich Popov, in 1894, built his first radio receiver, which contained a coherer. Further refined as a lightning detector, he presented it  to the Russian Physical and  Chemical Society on May 7, 1895.

• Nikola Tesla developed means to reliably produce radio frequencies, publicly demonstrated the principles of radio, and  transmitted long-distance signals. He holds the US patent for the invention of the radio, as defined as "wireless transmission of data."
• Guglielmo Marconi was an  early radio experimenter and  founded the first commercial organization devoted to the development and  use of radio.
• Reginald Fessenden _[1] and  Lee de Forest invented amplitude-modulated (AM) radio, so that more  than one station can send signals (as opposed to spark-gap radio, where one transmitter covers the entire bandwidth of the spectrum).
• Edwin H. Armstrong invented frequency-modulated (FM) radio, so that an  audio signal can avoid "static," that is, interference from electrical equipment and  atmospherics.
• Between 1893 and  1894, Roberto Landell de Moura, a Brazilian priest and  scientist, conducted experiments. He did not publicize his achievement until 1900 but later obtained Brazilian and  American patents.

Early radios ran the entire power of the transmitter through a carbon microphone. While some early radios used some type of amplification through electric current or  battery, until the mid 1920s the most common type of receiver was the crystal set. In the 1920s, amplifying vacuum tube radio receivers and  transmitters came into use.

[edit] Brief history

In 1893, in St. Louis, Missouri, Tesla made devices for his experiments with electricity. Addressing the Franklin Institute in Philadelphia and  the National Electric Light Association, he described and  demonstrated in detail the principles of his work. [2] The descriptions contained all the elements that were later incorporated into radio systems before the development of the vacuum tube. He initially experimented with magnetic receivers, unlike the coherers (detecting devices consisting of tubes filled with iron filings which had been invented by Temistocle Calzecchi-Onesti at Fermo in Italy in 1884) used by Guglielmo Marconi and  other early experimenters. [3]. Tesla is  usually considered the first to apply the mechanism of electrical conduction to wireless practices.

In 1896, Marconi was awarded the British patent 12039, Improvements in transmitting electrical impulses and  signals and  in apparatus there-for, for radio. In 1897 he established the world's first radio station on the Isle of Wight, England. Marconi opened the world's first "wireless" factory in Hall Street, Chelmsford, England in 1898, employing around 50 people. Around 1900, Tesla opened the Wardenclyffe Tower facility and  advertised services. By 1903, the tower structure neared completion. Various theories exist on how Tesla intended to achieve the goals of this wireless system (reportedly, a 200 kW system). Tesla claimed that Wardenclyffe, as part of a world system of transmitters, would have  allowed secure multichannel transceiving of information, universal navigation, time synchronization, and  a global location system.

The next great invention was the vacuum tube detector, invented by a team of Westinghouse engineers. On Christmas Eve, 1906, Reginald Fessenden used a synchronous rotary-spark transmitter for the first radio program broadcast, from Brant Rock, Massachusetts. Ships at sea heard a broadcast that included Fessenden playing O Holy Night on the violin and  reading a passage from the Bible. The first radio news program was broadcast August 31, 1920 by station 8MK in Detroit, Michigan. The first college radio station, 2ADD, renamed WRUC in 1940, began broadcasting October 14, 1920 from Union College, Schenectady, New York. The first regular entertainment broadcasts commenced in 1922 from the Marconi Research Centre at Writtle, near Chelmsford, England.

One of the first developments in the early 20th century (1900-1959) was that aircraft used commercial am  radio stations for navigation. This continued until the early 1960s when VOR systems finally became widespread (though am  stations are  still marked on U.S. aviation charts). In the early 1930s, single sideband and  frequency modulation were invented by amateur radio operators. By the end of the decade, they were established commercial modes. Radio was used to transmit pictures visible as television as early as the 1920s. Standard analog transmissions started in North America and  Europe in the 1940s. In 1954, Regency introduced a pocket transistor radio, the TR-1, powered by a "standard 22.5 V Battery".

In 1960, Sony introduced its first transistorized radio, small enough to fit in a vest pocket, and  able to be powered by a small battery. it  was durable, because there were no tubes to burn out. Over the next 20 years, transistors replaced tubes almost completely except for very high-power uses. In 1963 color television was commercially transmitted, and  the first (radio) communication satellite, TELSTAR, was launched. In the late 1960s, the U.S. long-distance telephone network began to convert to a digital network, employing digital radios for many of its links. In the 1970s, LORAN became the premier radio navigation system. Soon, the U.S. Navy experimented with satellite navigation, culminating in the invention and  launch of the GPS constellation in 1987. In the early 1990s, amateur radio experimenters began to use personal computers with audio cards to process radio signals. In 1994, the U.S. Army and  DARPA launched an  aggressive, successful project to construct a software radio that could become a different radio on the fly by changing software. Digital transmissions began to be applied to broadcasting in the late 1990s.

[edit] Uses of radio

Many of radio's 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 its submarine cables were cut by the British. The United States passed on President Woodrow Wilson's Fourteen Points to Germany via radio during the war.

Broadcasting began to become 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 use of radio in the pre-war years was the development of detecting and  locating aircraft and  ships by the use of radar (RAdio Detection And Ranging).

Today, radio takes many forms, including wireless networks, mobile communications of all types, as well as radio broadcasting. Read more  about radio's history.

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. Radio was unique among dramatic presentation that it  used only sound. For more, see radio programming.

There are  a number of uses of radio:

[edit] Audio

AM broadcast radio sends music and  voice in the Medium Frequency (MF—0.300 MHz to 3 MHz) radio spectrum. 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 that are  transmitting at the same frequency add their amplitudes to the original transmitted amplitude.

FM broadcast radio sends music and  voice with higher fidelity than am  radio. In frequency modulation, amplitude variation at the microphone cause 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. FM is  transmitted in the Very High Frequency (VHF—30 MHz to 300 MHz) radio spectrum. VHF radio waves act more  like light, travelling in straight lines, hence the reception range is  generally limited to about 50-100 miles. 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.

FM Subcarrier services are  secondary signals transmitted "piggyback" 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 subchannel program might be an  alternate foreign language radio program for various ethnic groups. Subcarriers 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 retune themselves to the same channel in a different district by using sub-bands.

Aviation voice radios use 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 (kilometres) away, even though they are  using VHF.

Marine voice radios can use am  in the shortwave High Frequency (HF—3 MHz to 30 MHz) radio spectrum for very long ranges or  narrowband FM in the VHF spectrum for much shorter ranges. Government, police, fire and  commercial voice services use narrowband FM on special frequencies. Fidelity is  sacrificed to use a smaller range of radio frequencies, usually five kHz of deviation, rather than the 75 kHz used by FM broadcasts and  25 kHz used by TV sound.

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. On an  AM radio SSB sounds like ducks quacking. 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  (usually) lower sideband. 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.

[edit] 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 various digital modulation schemes. Satellite phones come in two types: INMARSAT and  Iridium. Both types provide world-wide coverage. INMARSAT uses geosynchronous satellites, with aimed high-gain antennas on the vehicles. Iridium uses 66 Low Earth Orbit satellites as the cells.

[edit] Video

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

Digital television uses quadrature amplitude modulation. 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-2 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.

[edit] 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. 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.

[edit] Radar

Radar (Radio Detection and  Ranging) detects things 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 to measure wind speeds.

[edit] Emergency services

Emergency Position-Indicating Radio Beacons (EPIRBs), Emergency Locating Transmitters (ELTs) or  Personal Locator Beacons (PLBs) are  small radio transmitters that satellites can use to locate a person or  vehicle needing rescue. Their purpose is  to help rescue people in the first day, when survival is  most likely. There are  several types, with widely-varying performance.

[edit] Data (digital radio)

Most new radio systems are  digital, see also: Digital TV, Satellite Radio, Digital Audio Broadcasting. The oldest form of digital broadcast was spark gap telegraphy, used by pioneers such as 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.

Radio teletypes usually operate on short-wave (HF) and  are much loved by the military because they create written information without a skilled operator. They send a bit as one of two tones. Groups of five or  seven bits become a character printed by a teletype. From about 1925 to 1975, radio teletype 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. Usually the bits are  sent in "frames" that repeat. A special bit pattern is  used to locate the beginning of a frame.

Systems that need reliability, or  that share their frequency with other services, may use "corrected 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 WiFi, some cell phones, Digital Radio Mondiale, Eureka 147, and  many other local area network, digital TV and  radio standards.

[edit] 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. (Note: it  is a common misconception that the radio waves are  tuned to the resonant frequency of water molecules. The microwave frequencies used are  actually about a factor of ten below the resonant frequency.) Diathermy equipment is  used in surgery for sealing of blood vessels. Induction furnaces are  used for melting metal for casting.

[edit] Mechanical force

Tractor beams can use radio waves which exert small electrostatic and  magnetic forces. These are  enough to perform station-keeping in microgravity environments. Conceptually, spacecraft propulsion: Radiation pressure from intense radio waves has been proposed as a propulsion method for an  interstellar probe called Starwisp. Since the waves are  long, the probe could be a very light metal mesh, and  thus achieve higher accelerations than if it  were a solar sail.

[edit] Amateur radio service

Amateur radio is  a hobby in which enthusiasts purchase or  build their own equipment and  use radio for their own enjoyment. They may also provide an  emergency and  public-service radio service. This has been of great use, saving lives in many instances. Radio amateurs are  licensed to use frequencies in a large number of narrow bands throughout the radio spectrum. They use all forms of encoding, including obsolete and  experimental ones. 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.

[edit] Unlicensed radio services

Personal radio services such as Citizens' Band Radio, Family Radio Service, Multi-Use Radio Service and  others exist in North America 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.

[edit] Radio control (RC)

Radio remote control use of 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  aeroplanes. Large industrial remote-controlled equipment such as cranes and  switching locomotives now usually use digital radio techniques to ensure safety and  reliability.

[edit] Other

Energy autarkic radio technology consists of a small radio transmitter powered by environmental energy (push of a button, temperature differences, light, vibrations, etc.). A number of schemes have  been proposed for Wireless energy transfer. Various plans included transmitting power using microwaves, and  the technique has been demonstrated. (See Microwave power transmission). These schemes include, for example, solar power stations in orbit beaming energy down to terrestrial users. [monica]

[edit] See also

• Satellite radio
• Invention of radio
• Radio propagation and  ionosphere
• Radio programming
• Old-time radio
• Music radio
• Pirate radio
• Radio commercial
• International broadcasting
• Amateur radio
• Hospital radio
• Army No. 11 Wireless Set
• Shortwave
• Mediumwave
• Longwave
• Near Vertical Incidence Skywave
• Transistor radio
• Crystal radio receiver
• Software radio
• Internet radio
• Types of radio emissions
• Dead air
• Radio astronomy
• Tuner (radio)
• Long-distance FM reception (FM DX)
• VFO
• Hertz
• Radio software
• Lists
  • Radio network
  • List of radio stations
  • List of Internet stations
  • List of radio broadcasters who also do podcasting

[edit] References

1. ^ The Electromagnetic Spectrum, University of Tennessee, Dept. of Physics and  Astronomy

• A História da Rádio em Datas (1819-1997) (in Portuguese) - notes on etymology
• Leigh White, Buck Fuller and  the Dymaxion World (refers to Waldo Warren as the inventor of the word radio), in: The Saturday Evening Post, 14 October 1944, cited in: Joachim Krausse and  Claude Lichtenstein (eds.), Your Private Sky, Lars Müller Publishers, Baden/Switzerland, 1999, page 132. ISBN 3-907044-88-6
• L. de Forest, article in Electrical World 22 June 1270/1 (1907), early use of word "radio".

[edit] Further reading

• Aitkin Hugh G. J. The Continuous Wave: Technology and  the American Radio, 1900-1932 (Princeton University Press, 1985).
• Briggs Asa. The History of Broadcasting in the United Kingdom (Oxford University Press, 1961).
• Ewbank Henry and  Lawton Sherman P. Broadcasting: Radio and  Television (Harper & Brothers, 1952).
• Maclaurin W. Rupert. Invention and  Innovation in the Radio Industry (The Macmillan Company, 1949).
• Ray William B. FCC: The Ups and  Downs of Radio-TV Regulation (Iowa State University Press, 1990).
• Scannell, Paddy, and  Cardiff, David. A Social History of British Broadcasting, Volume One, 1922-1939 (Basil Blackwell, 1991).
• Schwoch James. The American Radio Industry and  Its Latin American Activities, 1900-1939 (University of Illinois Press, 1990).
• Sterling Christopher H. Electronic Media, A Guide to Trends in Broadcasting and  Newer Technologies 1920-1983 (Praeger, 1984).
• White Llewellyn. The American Radio (University of Chicago Press, 1947).

[edit] Primary sources

• De Forest, Lee. Father of Radio: The Autobiography of Lee de Forest (1950).

[edit] External links

Wikimedia Commons has media related to: Radio

• TFMX radio

• FMSCAN type in your city and  you'll get a complete FM/AM frequency list
• FMLIST FM transmitter database for Europe, North America and  some other regions
• Radio Frequency Chart
• Horzepa, Stan, "Surfin': Who Invented Radio?". Arrl.org. 10 October 2003.
• IAteacher: Interactive Explanation of Radio Receiver Construction
• U.S. Supreme Court, "Marconi Wireless Telegraph co. of America v. United States". 320 U.S. 1. Nos. 369, 373. Argued 9 April-12, 1943. Decided 21 June 1943.
• Radio Locator: Find a radio station in your area
• 'A Day In Radio' from The University of Virginia's Department of American Studies
• Steven Schoenherr's History of Radio
• The Broadcast Archive - Radio History on the Web!
• George H. Clark Radioana Collection, ca. 1880 - 1950 - Archives Center, National Museum of American History, Smithsonian Institution
• A gallery of Antiques from the 1920s to the 1960s
• The 1950s-2000s Week-By-Week - Includes detailed information on pop radio through the decades. Follows the am  top-40 wars, FM stereo Rock, syndication, FM top-40, DJ's and  trends.
• TVRadioWorld
• United States Early Radio History
• Dates in Radio history
• Open Directory Project - Radio
• Books about Radios and  RF field; schematics for radio transmitters and  receivers