Polarization is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. A simple example of a polarized transverse wave is vibrations traveling along a taut string. Depending on how the string is plucked, the vibrations can be in a vertical direction, horizontal direction, or at any angle perpendicular to the string. In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the displacement of the particles in the oscillation is always in the direction of propagation, so these waves do not exhibit polarization. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, transverse sound waves in solids. In some types of transverse waves, the wave displacement is limited to a single direction, so these do not exhibit polarization. An electromagnetic wave such as light consists of a coupled oscillating electric field and magnetic field which are always perpendicular.
In linear polarization, the fields oscillate in a single direction. In circular or elliptical polarization, the fields rotate at a constant rate in a plane as the wave travels; the rotation can have two possible directions. Light or other electromagnetic radiation from many sources, such as the sun and incandescent lamps, consists of short wave trains with an equal mixture of polarizations. Polarized light can be produced by passing unpolarized light through a polarizer, which allows waves of only one polarization to pass through; the most common optical materials are isotropic and do not affect the polarization of light passing through them. Some of these are used to make polarizing filters. Light is partially polarized when it reflects from a surface. According to quantum mechanics, electromagnetic waves can be viewed as streams of particles called photons; when viewed in this way, the polarization of an electromagnetic wave is determined by a quantum mechanical property of photons called their spin.
A photon has one of two possible spins: it can either spin in a right hand sense or a left hand sense about its direction of travel. Circularly polarized electromagnetic waves are composed of photons with only one type of spin, either right- or left-hand. Linearly polarized waves consist of photons that are in a superposition of right and left circularly polarized states, with equal amplitude and phases synchronized to give oscillation in a plane. Polarization is an important parameter in areas of science dealing with transverse waves, such as optics, seismology and microwaves. Impacted are technologies such as lasers and optical fiber telecommunications, radar. Most sources of light are classified as incoherent and unpolarized because they consist of a random mixture of waves having different spatial characteristics, frequencies and polarization states. However, for understanding electromagnetic waves and polarization in particular, it is easiest to just consider coherent plane waves. Characterizing an optical system in relation to a plane wave with those given parameters can be used to predict its response to a more general case, since a wave with any specified spatial structure can be decomposed into a combination of plane waves.
And incoherent states can be modeled stochastically as a weighted combination of such uncorrelated waves with some distribution of frequencies and polarizations. Electromagnetic waves, traveling in free space or another homogeneous isotropic non-attenuating medium, are properly described as transverse waves, meaning that a plane wave's electric field vector E and magnetic field H are in directions perpendicular to the direction of wave propagation. By convention, the "polarization" direction of an electromagnetic wave is given by its electric field vector. Considering a monochromatic plane wave of optical frequency f, let us take the direction of propagation as the z axis. Being a transverse wave the E and H fields must contain components only in the x and y directions whereas Ez = Hz = 0. Using complex notation, the instantaneous physical electric and magnetic fields are given by the real parts of the complex quantities occurring in the following equations; as a function of time t and spatial position z these complex fields can be written as: E → =
A Yagi–Uda antenna known as a Yagi antenna, is a directional antenna consisting of multiple parallel elements in a line half-wave dipoles made of metal rods. Yagi–Uda antennas consist of a single driven element connected to the transmitter or receiver with a transmission line, additional "parasitic elements" which are not connected to the transmitter or receiver: a so-called reflector and one or more directors, it was invented in 1926 by Shintaro Uda of Tohoku Imperial University and Hidetsugu Yagi. The reflector element is longer than the driven dipole, whereas the directors are a little shorter; the parasitic elements absorb and reradiate the radio waves from the driven element with a different phase, modifying the dipole's radiation pattern. The waves from the multiple elements superpose and interfere to enhance radiation in a single direction, achieving a substantial increase in the antenna's gain compared to a simple dipole. Called a "beam antenna", or "parasitic array", the Yagi is widely used as a high-gain antenna on the HF, VHF and UHF bands.
It has moderate to high gain which depends on the number of elements used limited to about 20 dBi, linear polarization, unidirectional beam pattern with high front-to-back ratio of up to 20 db. and is lightweight and simple to construct. The bandwidth of a Yagi antenna, the frequency range over which it has high gain, is narrow, a few percent of the center frequency, decreases with increasing gain, so it is used in fixed-frequency applications; the largest and best-known use is as rooftop terrestrial television antennas, but it is used for point-to-point fixed communication links, in radar antennas, for long distance shortwave communication by shortwave broadcasting stations and radio amateurs. The antenna was invented in 1926 by Shintaro Uda of Tohoku Imperial University, with a lesser role played by his colleague Hidetsugu Yagi; however the "Yagi" name has become more familiar with the name of Uda omitted. This appears to have been due to Yagi filing a patent on the idea in Japan without Uda's name in it, transferring the patent to the Marconi Company in the UK.
Yagi antennas were first used during World War II in radar systems by the Japanese, British and US. After the war they saw extensive development as home television antennas; the Yagi–Uda antenna consists of a number of parallel thin rod elements in a line half-wave long supported on a perpendicular crossbar or "boom" along their centers. There is a single driven element driven in the center, a variable number of parasitic elements, a single reflector on one side and optionally one or more directors on the other side; the parasitic elements are not electrically connected to the transmitter or receiver, serve as passive radiators, reradiating the radio waves to modify the radiation pattern. Typical spacings between elements vary from about 1⁄10 to ¼ of a wavelength, depending on the specific design; the directors are shorter than the driven element, while the reflector are longer. The radiation pattern is unidirectional, with the main lobe along the axis perpendicular to the elements in the plane of the elements, off the end with the directors.
Conveniently, the dipole parasitic elements have a node at their centre, so they can be attached to a conductive metal support at that point without need of insulation, without disturbing their electrical operation. They are bolted or welded to the antenna's central support boom; the driven element is fed at centre so its two halves must be insulated where the boom supports them. The gain increases with the number of parasitic elements used. Only one reflector is used since the improvement of gain with additional reflectors is negligible, but Yagis have been built with up to 30–40 directors; the bandwidth of the antenna is the frequency range between the frequencies at which the gain drops 3 dB below its maximum. The Yagi–Uda array in its basic form has narrow bandwidth, 2–3 percent of the centre frequency. There is a tradeoff between gain and bandwidth, with the bandwidth narrowing as more elements are used. For applications that require wider bandwidths, such as terrestrial television, Yagi–Uda antennas feature trigonal reflectors, larger diameter conductors, in order to cover the relevant portions of the VHF and UHF bands.
Wider bandwidth can be achieved by the use of "traps", as described below. Yagi–Uda antennas used for amateur radio are sometimes designed to operate on multiple bands; these elaborate designs create electrical breaks along each element at which point a parallel LC circuit is inserted. This so-called trap has the effect of truncating the element at the higher frequency band, making it a half wavelength in length. At the lower frequency, the entire element is close to half-wave resonance, implementing a different Yagi–Uda antenna. Using a second set of traps, a "triband" antenna can be resonant at three different bands. Given the associated costs of erecting an antenna and rotor system above a tower, the combination of antennas for three amateur bands in one unit is a practical solution; the use of traps is not without disadvantages, however, as they reduce the bandwidth of the antenna on the individual bands and reduce the antenna's electrical efficiency and subject the antenna to additional mechanical considerations.
Consider a Yagi–Uda consisting of a reflect
The United States of America known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico; the State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean; the U. S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The diverse geography and wildlife of the United States make it one of the world's 17 megadiverse countries.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century; the United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies following the French and Indian War led to the American Revolution, which began in 1775, the subsequent Declaration of Independence in 1776; the war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties; the United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery.
By the end of the century, the United States had extended into the Pacific Ocean, its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power; the United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U. S. Moon landing; the end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower. The United States is the world's oldest surviving federation, it is a representative democracy.
The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, other international organizations. The United States is a developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for a quarter of global GDP; the U. S. economy is post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U. S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country. Despite wide income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, human development, per capita GDP, worker productivity.
The United States is the foremost military power in the world, making up a third of global military spending, is a leading political and scientific force internationally. In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci; the first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq. to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort; the first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776. The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the'United States of America'".
The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence; this draft of the document did not surface unti
Height above average terrain
Height above average terrain, or effective height above average terrain, is a measure of how high an antenna site is above the surrounding landscape. HAAT is used extensively in FM radio and television, as it is more important than effective radiated power in determining the range of broadcasts. For international coordination, it is measured in meters by the Federal Communications Commission in the United States, as Canada and Mexico have extensive border zones where stations can be received on either side of the international boundaries. Stations that want to increase above a certain HAAT must reduce their power accordingly, based on the maximum distance their station class is allowed to cover; the FCC procedure to calculate HAAT is: from the proposed or actual antenna site, either 12 or 16 radials were drawn, points at 2, 4, 6, 8, 10 miles radius along each radial were used. The entire radial graph could be rotated to achieve the best effect for the station; the altitude of the antenna site, minus the average altitude of all the specified points, is the HAAT.
This can create some unusual cases in mountainous regions—it is possible to have a negative number for HAAT. The FCC has divided the Contiguous United States into three zones for the determination of spacing between FM and TV stations using the same frequencies. FM and TV stations are assigned maximum ERP and HAAT values, depending on their assigned zones, to prevent co-channel interference; the FCC regulations for ERP and HAAT are listed under Title 47, Part 73 of the Code of Federal Regulations. Maximum HAAT: 150 metres Maximum ERP: 50 kilowatts Minimum co-channel separation: 241 km Maximum HAAT: 600 metres Maximum ERP: 100 kilowatts Minimum co-channel separation: 290 km. In all zones, maximum ERP for analog TV transmitters is. In addition, Zone I-A consists of all of California south of 40° north latitude, Puerto Rico and the U. S. Virgin Islands. Zones I and I-A have the most "grandfathered" overpowered stations, which are allowed the same extended coverage areas that they had before the zones were established.
One of the most powerful of these stations is WBCT in Grand Rapids, which operates at 320,000 watts and 238 meters HAAT. Zone III consists of all of Florida and the areas of Alabama, Louisiana and Texas within 241.4 kilometers of the Gulf of Mexico. Zone II is all the rest of the Continental United States and Hawaii. Above mean sea level Above ground level Canadian Radio-television and Telecommunications Commission List of broadcast station classes United States Federal Communications Commission 47 CFR Part 73 Index FCC: Mass Media Calculated Contours FCC: HAAT Calculator "Superpower" Grandfathered FM stations
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: electromagnetic radiation, such as radio waves, infrared, visible light, ultraviolet, x-rays, gamma radiation particle radiation, such as alpha radiation, beta radiation, neutron radiation acoustic radiation, such as ultrasound and seismic waves gravitational radiation, radiation that takes the form of gravitational waves, or ripples in the curvature of spacetime. Radiation is categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, enough to ionize atoms and molecules, break chemical bonds; this is an important distinction due to the large difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, photons, respectively.
Other sources include X-rays from medical radiography examinations and muons, positrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere. Gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum; the word "ionize" refers to the breaking of one or more electrons away from an atom, an action that requires the high energies that these electromagnetic waves supply. Further down the spectrum, the non-ionizing lower energies of the lower ultraviolet spectrum cannot ionize atoms, but can disrupt the inter-atomic bonds which form molecules, thereby breaking down molecules rather than atoms; the waves of longer wavelength than UV in visible light and microwave frequencies cannot break bonds but can cause vibrations in the bonds which are sensed as heat. Radio wavelengths and below are not regarded as harmful to biological systems; these are not sharp delineations of the energies.
The word radiation arises from the phenomenon of waves radiating from a source. This aspect leads to a system of measurements and physical units that are applicable to all types of radiation; because such radiation expands as it passes through space, as its energy is conserved, the intensity of all types of radiation from a point source follows an inverse-square law in relation to the distance from its source. Like any ideal law, the inverse-square law approximates a measured radiation intensity to the extent that the source approximates a geometric point. Radiation with sufficiently high energy can ionize atoms. Ionization occurs when an electron is stripped from an electron shell of the atom, which leaves the atom with a net positive charge; because living cells and, more the DNA in those cells can be damaged by this ionization, exposure to ionizing radiation is considered to increase the risk of cancer. Thus "ionizing radiation" is somewhat artificially separated from particle radiation and electromagnetic radiation due to its great potential for biological damage.
While an individual cell is made of trillions of atoms, only a small fraction of those will be ionized at low to moderate radiation powers. The probability of ionizing radiation causing cancer is dependent upon the absorbed dose of the radiation, is a function of the damaging tendency of the type of radiation and the sensitivity of the irradiated organism or tissue. If the source of the ionizing radiation is a radioactive material or a nuclear process such as fission or fusion, there is particle radiation to consider. Particle radiation is subatomic particle accelerated to relativistic speeds by nuclear reactions; because of their momenta they are quite capable of knocking out electrons and ionizing materials, but since most have an electrical charge, they don't have the penetrating power of ionizing radiation. The exception is neutron particles. There are several different kinds of these particles, but the majority are alpha particles, beta particles and protons. Speaking and particles with energies above about 10 electron volts are ionizing.
Particle radiation from radioactive material or cosmic rays invariably carries enough energy to be ionizing. Most ionizing radiation originates from radioactive materials and space, as such is present in the environment, since most rocks and soil have small concentrations of radioactive materials. Since this radiation is invisible and not directly detectable by human senses, instruments such as Geiger counters are required to detect its presence. In some cases, it may lead to secondary emission of visible light upon its interaction with matter, as in the case of Cherenkov radiation and radio-luminescence. Ionizing radiation has many practical uses in medicine and construction, but presents a health hazard if used improperly. Exposure to radiation causes damage to living tissue.
In the field of antenna design the term radiation pattern refers to the directional dependence of the strength of the radio waves from the antenna or other source. In the fields of fiber optics and integrated optics, the term radiation pattern may be used as a synonym for the near-field pattern or Fresnel pattern; this refers to the positional dependence of the electromagnetic field in the near-field, or Fresnel region of the source. The near-field pattern is most defined over a plane placed in front of the source, or over a cylindrical or spherical surface enclosing it; the far-field pattern of an antenna may be determined experimentally at an antenna range, or alternatively, the near-field pattern may be found using a near-field scanner, the radiation pattern deduced from it by computation. The far-field radiation pattern can be calculated from the antenna shape by computer programs such as NEC. Other software, like HFSS can compute the near field; the far field radiation pattern may be represented graphically as a plot of one of a number of related variables, including.
Only the relative amplitude is plotted, normalized either to the amplitude on the antenna boresight, or to the total radiated power. The plotted quantity may be shown on a linear scale, or in dB; the plot is represented as a three-dimensional graph, or as separate graphs in the vertical plane and horizontal plane. This is known as a polar diagram, it is a fundamental property of antennas that the receiving pattern of an antenna when used for receiving is identical to the far-field radiation pattern of the antenna when used for transmitting. This is proved below. Therefore, in discussions of radiation patterns the antenna can be viewed as either transmitting or receiving, whichever is more convenient. Note however that this applies only to the passive antenna elements. Active antennas that include amplifiers or other components are no longer reciprocal devices. Since electromagnetic radiation is dipole radiation, it is not possible to build an antenna that radiates coherently in all directions, although such a hypothetical isotropic antenna is used as a reference to calculate antenna gain.
The simplest antennas and dipole antennas, consist of one or two straight metal rods along a common axis. These axially symmetric antennas have radiation patterns with a similar symmetry, called omnidirectional patterns; this illustrates the general principle that if the shape of an antenna is symmetrical, its radiation pattern will have the same symmetry. In most antennas, the radiation from the different parts of the antenna interferes at some angles; this results in zero radiation at certain angles where the radio waves from the different parts arrive out of phase, local maxima of radiation at other angles where the radio waves arrive in phase. Therefore, the radiation plot of most antennas shows a pattern of maxima called "lobes" at various angles, separated by "nulls" at which the radiation goes to zero; the larger the antenna is compared to a wavelength, the more lobes there will be. In a directive antenna in which the objective is to direct the radio waves in one particular direction, the lobe in that direction is larger than the others.
The axis of maximum radiation, passing through the center of the main lobe, is called the "beam axis" or boresight axis". In some antennas, such as split-beam antennas, there may exist more than one major lobe. A minor lobe is any lobe except a major lobe; the other lobes, representing unwanted radiation in other directions, are called "side lobes". The side lobe in the opposite direction from the main lobe is called the "back lobe". Minor lobes represent radiation in undesired directions, so in directional antennas a design goal is to reduce the minor lobes. Side lobes are the largest of the minor lobes; the level of minor lobes is expressed as a ratio of the power density in the lobe in question to that of the major lobe. This ratio is termed the side lobe ratio or side lobe level. Side lobe levels of −20 dB or greater are not desirable in many applications. Attainment of a side lobe level smaller than −30 dB requires careful design and construction. In most radar systems, for example, low side lobe ratios are important to minimize false target indications through the side lobes.
For a complete proof, see the reciprocity article. Here, we present a common simple proof limited to the approximation of two antennas separated by a large distance compared to the size of the antenna, in a homogeneous medium; the first antenna is the test antenna. The second antenna is a reference antenna; each antenna is alternately connected to a transmitter having a particular source impedance, a receiver having the same input impedance. It is assumed that the two antennas are sufficiently far apart that the properties of the transmitting antenna are not affected by the load placed upon it by the receiving antenna; the amount of power transferred from the transmitter to the receiver c
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 digital audio. The earliest radio stations did not carry audio. For audio broadcasts to be possible, electronic detection and amplification devices had to be incorporated; the thermionic valve was invented in 1904 by the English physicist John Ambrose Fleming. He developed a device he called an "oscillation valve"; the heated filament, or cathode, was capable of thermionic emission of electrons that would flow to the plate when it was at a higher voltage. Electrons, could not pass in the reverse direction because the plate was not heated and thus not capable of thermionic emission of electrons. Known as the Fleming valve, it could be used as a rectifier of alternating current and as a radio wave detector; this improved the crystal set which rectified the radio signal using an early solid-state diode based on a crystal and a so-called cat's whisker.
However, what was still required was an amplifier. The triode was patented on March 4, 1906, by the Austrian Robert von Lieben independent from that, on October 25, 1906, Lee De Forest patented his three-element Audion, it wasn't put to practical use until 1912 when its amplifying ability became recognized by researchers. By about 1920, valve technology had matured to the point where radio broadcasting was becoming viable. However, an early audio transmission that could be termed a broadcast may have occurred on Christmas Eve in 1906 by Reginald Fessenden, although this is disputed. While many early experimenters attempted to create systems similar to radiotelephone devices by which only two parties were meant to communicate, there were others who intended to transmit to larger audiences. Charles Herrold started broadcasting in California in 1909 and was carrying audio by the next year.. In The Hague, the Netherlands, PCGG started broadcasting on November 6, 1919, making it, arguably the first commercial broadcasting station.
In 1916, Frank Conrad, an electrical engineer employed at the Westinghouse Electric Corporation, began broadcasting from his Wilkinsburg, Pennsylvania garage with the call letters 8XK. The station was moved to the top of the Westinghouse factory building in East Pittsburgh, Pennsylvania. Westinghouse relaunched the station as KDKA on November 2, 1920, as the first commercially licensed radio station in America; the commercial broadcasting designation came from the type of broadcast license. The first licensed broadcast in the United States came from KDKA itself: the results of the Harding/Cox Presidential Election; the Montreal station that became CFCF began broadcast programming on May 20, 1920, the Detroit station that became WWJ began program broadcasts beginning on August 20, 1920, although neither held a license at the time. In 1920, wireless broadcasts for entertainment began in the UK from the Marconi Research Centre 2MT at Writtle near Chelmsford, England. A famous broadcast from Marconi's New Street Works factory in Chelmsford was made by the famous soprano Dame Nellie Melba on 15 June 1920, where she sang two arias and her famous trill.
She was the first artist of international renown to participate in direct radio broadcasts. The 2MT station began to broadcast regular entertainment in 1922; the BBC was amalgamated in 1922 and received a Royal Charter in 1926, making it the first national broadcaster in the world, followed by Czech Radio and other European broadcasters in 1923. Radio Argentina began scheduled transmissions from the Teatro Coliseo in Buenos Aires on August 27, 1920, making its own priority claim; the station got its license on November 19, 1923. The delay was due to the lack of official Argentine licensing procedures before that date; this station continued regular broadcasting of entertainment and cultural fare for several decades. Radio in education soon followed and colleges across the U. S. began adding radio broadcasting courses to their curricula. Curry College in Milton, Massachusetts introduced one of the first broadcasting majors in 1932 when the college teamed up with WLOE in Boston to have students broadcast programs.
Broadcasting service is – according to Article 1.38 of the International Telecommunication Union´s Radio Regulations – defined as «A radiocommunication service in which the transmission are intended for direct reception by the general public. This service may include sound transmissions, television transmissions or other types of transmission.» Definitions identical to those contained in the Annexes to the Constitution and Convention of the International Telecommunication Union are marked "" or "" respectively. A radio broadcasting station is associated with wireless transmission, though in practice broadcasting transmission take place using both wires and radio waves; the point of this is that anyone with the appropriate receiving technology can receive the broadcast. In line to ITU Radio Regulations each broadcasting station shall be classified by the service in which it operates permanently or temporarily. Broadcasting by radio takes several forms; these include FM stations. There are several subtypes, namely commercial broadcasting, non-commercial educational public broadcasting and non-profit varieties as well as community radio, student-run campus radio stations, and