1.
Parabolic antenna
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A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is called a dish antenna or parabolic dish. The main advantage of an antenna is that it has high directivity. It functions similarly to a searchlight or flashlight reflector to direct the waves in a narrow beam. Parabolic antennas have some of the highest gains, that is, they can produce the narrowest beamwidths and they are also used in radio telescopes. The other large use of antennas is for radar antennas, in which there is a need to transmit a narrow beam of radio waves to locate objects like ships, airplanes. With the advent of satellite television receivers, parabolic antennas have become a common feature of the landscapes of modern countries. The parabolic antenna was invented by German physicist Heinrich Hertz during his discovery of radio waves in 1887 and he used cylindrical parabolic reflectors with spark-excited dipole antennas at their focus for both transmitting and receiving during his historic experiments. Conversely, a plane wave parallel to the axis will be focused to a point at the focal point. A typical parabolic antenna consists of a parabolic reflector with a small feed antenna suspended in front of the reflector at its focus. The reflector is a surface formed into a paraboloid of revolution. In a transmitting antenna, radio frequency current from a transmitter is supplied through a transmission line cable to the feed antenna, the radio waves are emitted back toward the dish by the feed antenna and reflect off the dish into a parallel beam. The reflector can be of metal, metal screen, or wire grill construction. Large dishes often require a supporting structure behind them to provide the required stiffness. A reflector made of a grill of parallel wires or bars oriented in one direction acts as a polarizing filter as well as a reflector and it only reflects linearly polarized radio waves, with the electric field parallel to the grill elements. This type is used in radar antennas. Combined with a linearly polarized feed horn, it helps filter out noise in the receiver, the feed antenna at the reflectors focus is typically a low-gain type such as a half-wave dipole or more often a small horn antenna called a feed horn. The feed antenna is connected to the associated radio-frequency transmitting or receiving equipment by means of a cable transmission line or waveguide
2.
Satellite dish
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A satellite dish is a dish-shaped type of parabolic antenna designed to receive electromagnetic signals from satellites, which transmit data transmissions or broadcasts, such as satellite television. The parabolic shape of a dish reflects the signal to the focal point. Mounted on brackets at the focal point is a device called a feedhorn. This feedhorn is essentially the front-end of a waveguide that gathers the signals at or near the focal point, the LNB converts the signals from electromagnetic or radio waves to electrical signals and shifts the signals from the downlinked C-band and/or Ku-band to the L-band range. Direct broadcast satellite dishes use an LNBF, which integrates the feedhorn with the LNB, the theoretical gain of a dish increases as the frequency increases. The actual gain depends on factors including surface finish, accuracy of shape. A typical value for a consumer type 60 cm satellite dish at 11.75 GHz is 37.50 dB, with lower frequencies, C-band for example, dish designers have a wider choice of materials. The large size of dish required for lower frequencies led to the dishes being constructed from metal mesh on a metal framework, at higher frequencies, mesh type designs are rarer though some designs have used a solid dish with perforations. A common misconception is that the LNBF, the device at the front of the dish, modern dishes intended for home television use are generally 43 cm to 80 cm in diameter, and are fixed in one position, for Ku-band reception from one orbital position. Prior to the existence of direct broadcast satellite services, home users would generally have a motorised C-band dish of up to 3 m in diameter for reception of channels from different satellites. Overly small dishes can still cause problems, however, including rain fade, in Europe, the frequencies used by DBS services are 10. 7–12.75 GHz on two polarisations H and V. This range is divided into a low band with 10. 7–11.7 GHz, and this results in two frequency bands, each with a bandwidth of about 1 GHz, each with two possible polarizations. In the LNB they become down converted to 950–2150 MHz, which is the range allocated for the satellite service on the coaxial cable between LNBF and receiver. Lower frequencies are allocated to cable and terrestrial TV, FM radio, in a single receiver residential installation there is a single coaxial cable running from the receiver set-top box in the building to the LNB on the dish. The DC electric power for the LNB is provided through the coaxial cable conductors that carry the signal to the receiver. In addition, control signals are transmitted from the receiver to the LNB through the cable. The receiver uses different power supply voltages to select antenna polarization, a satellite finder may aid in aiming. A dish that is mounted on a pole and driven by a motor or a servo can be controlled and rotated to face any satellite position in the sky
3.
Horn antenna
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A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies and their advantages are moderate directivity, low standing wave ratio, broad bandwidth, and simple construction and adjustment. One of the first horn antennas was constructed in 1897 by Indian radio researcher Jagadish Chandra Bose in his experiments with microwaves. In the 1930s the first experimental research and theoretical analysis of horns as antennas was done, the development of radar in World War 2 stimulated horn research to design feed horns for radar antennas. The corrugated horn invented by Kay in 1962 has become used as a feed horn for microwave antennas such as satellite dishes. An advantage of horn antennas is that since they have no resonant elements, they can operate over a range of frequencies. The usable bandwidth of horn antennas is typically of the order of 10,1, the input impedance is slowly varying over this wide frequency range, allowing low voltage standing wave ratio over the bandwidth. The gain of horn antennas ranges up to 25 dBi, with 10 -20 dBi being typical, a horn antenna is used to transmit radio waves from a waveguide out into space, or collect radio waves into a waveguide for reception. It typically consists of a length of rectangular or cylindrical metal tube, closed at one end. The radio waves are usually introduced into the waveguide by a cable attached to the side. The waves then radiate out the end in a narrow beam. In some equipment the radio waves are conducted between the transmitter or receiver and the antenna by a waveguide, in case the horn is attached to the end of the waveguide. In outdoor horns, such as the horns of satellite dishes. A horn antenna serves the function for electromagnetic waves that an acoustical horn does for sound waves in a musical instrument such as a trumpet. It provides a transition structure to match the impedance of a tube to the impedance of free space. This is similar to the reflection at a transmission line or a boundary between optical mediums with a low and high index of refraction, like at a glass surface. The reflected waves cause standing waves in the waveguide, increasing the SWR, wasting energy, in addition, the small aperture of the waveguide causes significant diffraction of the waves issuing from it, resulting in a wide radiation pattern without much directivity. To improve these characteristics, the ends of the waveguide are flared out to form a horn
4.
Radio receiver
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In radio communications, a radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna, the antenna intercepts radio waves and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The information produced by the receiver may be in the form of sound, a radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar form of radio receiver is a broadcast receiver, often just called a radio, the sound is produced either by a loudspeaker in the radio or an earphone which plugs into a jack on the radio. The radio requires electric power, provided either by batteries inside the radio or a cord which plugs into an electric outlet. All radios have a control to adjust the loudness of the audio. The frequency of radio stations is usually listed prominently in their advertising, in order to select a particular station to receive, the radio is adjusted to the frequency of the desired transmitter. In some radios this is done by the user turning a tuning knob until the station is heard in the radios loudspeaker. In most countries radio broadcasting is permitted using two different methods of modulation, that is, methods of adding the signal to the radio wave, AM and FM. In amplitude modulation the strength of the signal is varied by the audio signal. AM broadcasting is permitted on AM broadcast bands between 148 and 283 kHz in the low range and 526 and 1706 kHz in the medium frequency range of the radio spectrum. In frequency modulation the frequency of the signal is varied slightly by the audio signal. FM broadcasting is permitted in the FM broadcast bands between about 65 and 108 MHz in the high frequency range. The exact frequency ranges vary somewhat in different countries, radios sold in each receive the correct frequency range for that country. Most broadcast radios, called AM/FM radios, can receive both AM and FM bands, and have a switch to select which band to receive. Limited AM broadcasting is permitted in parts of the high frequency band called the shortwave band. Shortwave listening requires a receiver that can receive these bands, called a shortwave receiver, at these frequencies, radio waves transmitted into the sky can reflect from a layer in the atmosphere called the ionosphere, returning to earth at transcontinental distances. So shortwaves are used for long distance international broadcasting, often by governmental public service broadcasting organizations like the BBC, due to their lower frequency, AM radio stations can often be received at longer distances than FM stations, at hundreds of miles
5.
Parabolic reflector
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A parabolic reflector is a reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a paraboloid, that is. The parabolic reflector transforms an incoming plane wave traveling along the axis into a spherical wave converging toward the focus, conversely, a spherical wave generated by a point source placed in the focus is reflected into a plane wave propagating as a collimated beam along the axis. Parabolic reflectors are used to collect energy from a distant source, since the principles of reflection are reversible, parabolic reflectors can also be used to focus radiation from an isotropic source into a narrow beam. In optics, parabolic mirrors are used to light in reflecting telescopes and solar furnaces, and project a beam of light in flashlights, searchlights, stage spotlights. In acoustics, parabolic microphones are used to record faraway sounds such as calls, in sports reporting. Strictly, the shape of the reflector is called a paraboloid. A parabola is the two-dimensional figure, however, in informal language, the word parabola and its associated adjective parabolic are often used in place of paraboloid and paraboloidal. Correspondingly, the dimensions of a symmetrical paraboloidal dish are related by the equation,4 F D = R2, where F is the length, D is the depth of the dish. All units must be the same, if two of these three quantities are known, this equation can be used to calculate the third. A more complex calculation is needed to find the diameter of the dish measured along its surface. This is sometimes called the diameter, and equals the diameter of a flat, circular sheet of material, usually metal. Two intermediate results are useful in the calculation, P =2 F and Q = P2 + R2, where F, D, and R are defined as above. The diameter of the dish, measured along the surface, is given by, R Q P + P ln . The volume of the dish, the amount of liquid it could hold if the rim were horizontal and the vertex at the bottom, is given by 12 π R2 D, where the symbols are defined as above. This can be compared with the formulae for the volumes of a cylinder, a hemisphere (23 π R2 D, {\displaystyle \scriptstyle, and a cone. π R2 is the area of the dish, the area enclosed by the rim. The area of the surface of the dish can be found using the area formula for a surface of revolution which gives A = π R6 D2
6.
Microwave
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Microwaves are a form of electromagnetic radiation with wavelengths ranging from one meter to one millimeter, with frequencies between 300 MHz and 300 GHz. Different sources define different frequency ranges as microwaves, the broad definition includes both UHF and EHF bands. A more common definition in radio engineering is the range between 1 and 100 GHz, in all cases, microwaves include the entire SHF band at minimum. Frequencies in the range are often referred to by their IEEE radar band designations, S, C, X, Ku, K, or Ka band. The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range and it indicates that microwaves are small, compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. The boundaries between far infrared, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. At the high end of the band they are absorbed by gases in the atmosphere, microwaves are extremely widely used in modern technology. Although at the low end of the band they can pass through building walls enough for useful reception, therefore on the surface of the Earth microwave communication links are limited by the visual horizon to about 30 -40 miles. Microwaves are absorbed by moisture in the atmosphere, and the attenuation increases with frequency, beginning at about 40 GHz, atmospheric gases also begin to absorb microwaves, so above this frequency microwave transmission is limited to a few kilometers. A spectral band structure causes absorption peaks at specific frequencies, in a microwave beam directed at an angle into the sky, a small amount of the power will be randomly scattered as the beam passes through the troposphere. A sensitive receiver beyond the horizon with a high gain antenna focused on that area of the troposphere can pick up the signal. This technique has been used at frequencies between 0.45 and 5 GHz in tropospheric scatter communication systems to communicate beyond the horizon and their short wavelength allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter. Therefore beams of microwaves are used for point-to-point communication links, an advantage of narrow beams is that they allow frequency reuse by nearby transmitters. Parabolic antennas are the most widely used directive antennas at microwave frequencies, flat microstrip antennas are being increasingly used in consumer devices. Where omnidirectional antennas are required, for example in wireless devices and Wifi routers for wireless LANs, small monopoles, dipole, or patch antennas are used. Due to the high cost and maintenance requirements of waveguide runs, the term microwave also has a more technical meaning in electromagnetics and circuit theory. As a consequence, practical microwave circuits tend to away from the discrete resistors, capacitors. Open-wire and coaxial transmission lines used at lower frequencies are replaced by waveguides and stripline, high-power microwave sources use specialized vacuum tubes to generate microwaves
7.
Polarization (waves)
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Polarization is a parameter applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave the direction of the oscillation is transverse to the direction of motion of the wave, a simple example of a polarized transverse wave is vibrations traveling along a taut string for example in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a direction, horizontal direction. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, in some types of transverse waves the wave displacement is limited to a single direction, so these also dont exhibit polarization. For example, in waves in liquids the wave displacement of the particles is always in a vertical plane. 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. Polarized light can be produced by passing unpolarized light through a polarizing filter, some of these are used to make polarizing filters. Light is also partially polarized when it reflects from a surface, according to quantum mechanics, electromagnetic waves consist of particles called photons. When viewed in this way, the polarization of a wave is determined by a quantum mechanical property of photons called their spin. A photon has one of two 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 one type of spin. Linearly polarized waves consist of numbers of right and left hand spinning photons. Polarization is an important parameter in areas of science dealing with transverse waves, such as optics, seismology, radio, especially impacted are technologies such as lasers, wireless and optical fiber telecommunications, and radar. And incoherent states can be modeled stochastically as a combination of such uncorrelated waves with some distribution of frequencies, phases. Considering a monochromatic 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 then contain components only in the x and y directions whereas Ez=Hz=0. Using complex notation, we understand the instantaneous electric and magnetic fields to be given by the real parts of the complex quantities occurring in the following equations. Here ex, ey, hx, and hy are complex numbers, in the second more compact form, as these equations are customarily expressed, these factors are described using the wavenumber k =2 π n / λ and angular frequency ω =2 π f
8.
Radio masts and towers
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Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. There are two types, guyed and self supporting structures. They are among the tallest man-made structures, masts are often named after the broadcasting organizations that originally built them or currently use them. In the case of a mast radiator or radiating tower, the whole mast or tower is itself the transmitting antenna, the terms mast and tower are often used interchangeably. However, in engineering terms, a tower is a self-supporting or cantilevered structure. Broadcast engineers in the UK use the same terminology, in US broadcast engineering, a tower is an antenna structure attached to the ground, whereas a mast is a vertical antenna support mounted on some other structure. Masts tend to be cheaper to build but require an extended area surrounding them to accommodate the guy wires, Towers are more commonly used in cities where land is in short supply. There are a few designs that are partly free-standing and partly guyed, called additionally guyed towers. For example, The Gerbrandy tower consists of a tower with a guyed mast on top. The few remaining Blaw-Knox towers do the opposite, they have a lower section surmounted by a freestanding part. Until August 8,1991, the Warsaw radio mast was the worlds tallest supported structure on land, there are over 50 radio structures in the United States that are 600 m or taller. The steel lattice is the most widespread form of construction and it provides great strength, low weight and wind resistance, and economy in the use of materials. Lattices of triangular cross-section are most common, and square lattices are also widely used, guyed masts are often used, the supporting guy lines carry lateral forces such as wind loads, allowing the mast to be very narrow and simply constructed. When built as a tower, the structure may be parallel-sided or taper over part or all of its height, when constructed of several sections which taper exponentially with height, in the manner of the Eiffel Tower, the tower is said to be an Eiffelized one. The Crystal Palace tower in London is an example, guyed masts are sometimes also constructed out of steel tubes. This construction type has the advantage that cables and other components can be protected from weather inside the tube and these masts are mainly used for FM-/TV-broadcasting, but sometimes also as mast radiator. The big mast of Mühlacker transmitting station is an example of this. A disadvantage of this mast type is that it is more affected by winds than masts with open bodies
9.
Tripod
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A tripod is a portable three-legged frame, used as a platform for supporting the weight and maintaining the stability of some other object. A tripod provides stability against downward forces and horizontal forces and movements about horizontal axes, the positioning of the three legs away from the vertical centre allows the tripod better leverage for resisting lateral forces. The earliest attested form of the word is the Mycenaean Greek
10.
Coaxial cable
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Coaxial cable, or coax, is a type of cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an outer sheath or jacket. The term coaxial comes from the conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers with their antennas, computer network connections, digital audio and this allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides protection of the signal from external electromagnetic interference, the cable is protected by an outer insulating jacket. Normally, the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor, the advantage of coaxial design is that electric and magnetic fields are restricted to the dielectric with little leakage outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable, larger diameter cables and cables with multiple shields have less leakage. Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, the characteristic impedance of the cable is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. A controlled cable characteristic impedance is important because the source and load impedance should be matched to ensure maximum power transfer, other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality. Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, the inner conductor might be solid or stranded, stranded is more flexible. To get better performance, the inner conductor may be silver-plated. Copper-plated steel wire is used as an inner conductor for cable used in the cable TV industry. The insulator surrounding the conductor may be solid plastic, a foam plastic. The properties of control some electrical properties of the cable. A common choice is a solid polyethylene insulator, used in lower-loss cables, solid Teflon is also used as an insulator. Some coaxial lines use air and have spacers to keep the conductor from touching the shield. Many conventional coaxial cables use braided copper wire forming the shield and this allows the cable to be flexible, but it also means there are gaps in the shield layer, and the inner dimension of the shield varies slightly because the braid cannot be flat
11.
Low-noise block downconverter
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A low-noise block downconverter is the receiving device mounted on satellite dishes used for satellite TV reception, which collects the radio waves from the dish. Also called a block, low-noise converter, or even low-noise downconverter. The LNB is a combination of low-noise amplifier, frequency mixer, local oscillator and it receives the microwave signal from the satellite collected by the dish, amplifies it, and downconverts the block of frequencies to a lower block of intermediate frequencies. The LNB is usually a box suspended on one or more short booms, or feed arms, in front of the dish reflector. The microwave signal from the dish is picked up by a feedhorn on the LNB and is fed to a section of waveguide. One or more pins, or probes, protrude into the waveguide at right angles to the axis and act as antennas. The lower frequency IF output signal emerges from a socket on the box to which the cable connects. The LNB gets its power from the receiver or set-top box and this phantom power travels to the LNB, opposite to the signals from the LNB. A corresponding component, called a block upconverter, is used at the earth station dish to convert the band of television channels to the microwave uplink frequency. The signal received by the LNB is extremely weak and it has to be amplified before downconversion, the low noise amplifier section of the LNB amplifies this weak signal while adding the minimum possible amount of noise to the signal. The low-noise quality of an LNB is expressed as the noise figure and this is the signal to noise ratio at the input divided by the signal to noise ratio at the output. It is typically expressed as a decibels value, the ideal LNB, effectively a perfect amplifier, would have a noise figure of 0 dB and would not add any noise to the signal. Every LNB off the line has a different noise figure because of manufacturing tolerances. Satellites use comparatively high radio frequencies to transmit their TV signals, as microwave satellite signals do not easily pass through walls, roofs, or even glass windows, it is preferable for satellite antennas to be mounted outdoors. The purpose of the LNB is to use the principle to take a block of relatively high frequencies. These lower frequencies travel through cables with much less attenuation, so there is much more signal left at the receiver end of the cable. It is also easier and cheaper to design electronic circuits to operate at these lower frequencies. The local oscillator frequency determines what block of incoming frequencies is downconverted to the expected by the receiver
12.
History of broadcasting
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The first broadcasting of a radio transmission consisted of Morse code was made from a temporary station set up by Guglielmo Marconi in 1895. This followed on from pioneering work in the field by Alessandro Volta, André-Marie Ampère, Georg Ohm, James Clerk Maxwell, the broadcasting of music and talk via radio started experimentally around 1905-1906, and commercially around 1920 to 1923. VHF stations started 30 to 35 years later, when people started broadcasting television the first movie that was shown was Batman curse of the green pearl it was 10 minutes long. In Britain this system was known as Electrophone, and was available as early as 1895 or 1899, in Hungary, it was called Telefon Hírmondó, and in France, Théâtrophone ). The Wikipedia Telefon Hírmondó page includes a 1907 program guide which looks similar to the types of schedules used by many broadcasting stations some 20 or 30 years later. By the 1950s, virtually every country had a broadcasting system, today, most countries have evolved into a dual system, including the UK. By 1955, practically every family in North America and Western Europe, a dramatic change came in the 1960s with the introduction of small inexpensive portable transistor radio, the greatly expanded ownership and usage. Access became practically universal across the world, Australia developed its own system, through its own engineers, manufacturers, retailers, newspapers, entertainment services, and news agencies. The government set up the first radio system, and business interests marginalized the hobbyists, the Labor Party was especially interested in radio because it allowed them to bypass the newspapers, which were mostly controlled by the opposition. Both parties agreed on the need for a system, and in 1932 set up the Australian Broadcasting Commission. The first commercial broadcasters, originally known as B class stations, were on the air as early as 1925, the number of stations remained relatively dormant throughout World War II and in the post-war era. The broadcasting system was deregulated in 1992, except that there were limits on foreign ownership. By 2000,99 percent of Australians owned at least one television set, Australian radio hams can be traced to the early 1900s. The 1905 Wireless Telegraphy Act whilst acknowledging the existence of wireless telgraphy, in 1906, the first official Morse code transmission in Australia was by the Marconi Company between Queenscliff, Victoria and Devonport, Tasmania. The first broadcast of music was made during a demonstration on 13 August 1919 by Ernest Fisk of AWA – Amalgamated Wireless, a number of amateurs commenced broadcasting music in 1920 and 1921. 2CM was run by Charles MacLuran who started the station in 1921 with regular Sunday evening broadcasts from the Wentworth Hotel, 2CM is often regarded as Australias first, regular, non-official station. It was not until November 1923 when the government finally gave its approval for a number of officially recognised medium wave stations, all stations operated under a unique Sealed Set system under which each set was sealed to the frequency of one station. Part of the price of the set went to the government via the Postmaster-Generals Department, apart from extremely limited advertising, this was the broadcasters only source of income
