Radio masts and towers are typically tall structures designed to support antennas for telecommunications and broadcasting , including television . There are two main types: guyed and self-supporting structures. They are among the tallest human-made structures. Masts are often named after the broadcasting organizations that originally built them or currently use them.
122-621: A mast radiator or radiating tower is one in which the metal mast or tower itself is energized and functions as the transmitting antenna. The terms "mast" and "tower" are often used interchangeably. However, in structural engineering terms, a tower is a self-supporting or cantilevered structure, while a mast is held up by stays or guy-wires . There are a few borderline designs that are partly free-standing and partly guyed, called additionally guyed towers . Examples: The first experiments in radio communication were conducted by Guglielmo Marconi beginning in 1894. In 1895–1896 he invented
244-425: A grounding (Earthing) system under the antenna to make contact with the soil to collect the return current. One side of the feedline from the helix house is attached to the mast, and the other side to the ground system. The ground system is in series with the antenna and carries the full antenna current, so for efficiency its resistance must be kept low, under two ohms, so it consists of a network of cables buried in
366-568: A kite can serve as a temporary support. It can carry an antenna or a wire (for VLF, LW or MW) up to an appropriate height. Such an arrangement is used occasionally by military agencies or radio amateurs. The American broadcasters TV Martí broadcast a television program to Cuba by means of such a balloon. In 2013, interest began in using unmanned aerial vehicles (drones) for telecom purposes. For two VLF transmitters wire antennas spun across deep valleys are used. The wires are supported by small masts or towers or rock anchors. The same technique
488-620: A better radiation pattern. It was found that reducing the height of the monopole mast from 225 electrical degrees to 190 degrees could eliminate the high angle radio waves that caused fading. Sectional masts were also developed in this era. Multipath fading In radio communication , multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting , ionospheric reflection and refraction , and reflection from water bodies and terrestrial objects such as mountains and buildings. When
610-465: A capacitive top-load. In a second paper the same year he showed that the amount of power radiated horizontally in ground waves reached a maximum at a mast height of 5 / 8 wavelength . By 1930 the expense of the T-antenna led broadcasters to adopt the mast radiator antenna, in which the metal structure of the mast itself functions as the antenna. One of the first types used
732-402: A concrete base, relieving bending moments on the structure. The first, a 200-meter (665 ft) half-wave mast was installed at radio station WABC's 50 kW Wayne, New Jersey transmitter in 1931. Radial wire ground systems were also introduced during this era. During the 1930s the broadcast industry recognized the problem of multipath fading , that at night high angle waves reflected from
854-440: A delay. In radar processing, multipath causes ghost targets to appear, deceiving the radar receiver . These ghosts are particularly bothersome since they move and behave like the normal targets (which they echo), and so the receiver has difficulty in isolating the correct target echo. These problems can be minimized by incorporating a ground map of the radar's surroundings and eliminating all echoes which appear to originate below
976-476: A fraction of the weight (70% less) which has allowed monopoles and towers to be built in locations that were too expensive or difficult to access with the heavy lifting equipment that is needed for a steel structure. Overall a carbon fiber structure is 40 - 50% faster to be erected compared to traditional building materials. As of 2022, wood, previously an uncommon material for telecommunications tower construction, has started to become increasingly common. In 2022,
1098-418: A greater number of shorter radials. The metal support under the mast insulator is bonded to the ground system with conductive metal straps so no voltage appears across the concrete pad supporting the mast, as concrete has poor dielectric qualities. For masts near a half-wavelength high (180 electrical degrees) the mast has a voltage maximum ( antinode ) near its base, which results in strong electric fields in
1220-647: A guyed radio mast is installed. One example is the Gerbrandy Tower in Lopik , Netherlands. Further towers of this building method can be found near Smilde , Netherlands and the Fernsehturm in Waldenburg , Germany. Radio, television and cell towers have been documented to pose a hazard to birds. Reports have been issued documenting known bird fatalities and calling for research to find ways to minimize
1342-405: A half wavelength (180 electrical degrees) the radiation pattern of the antenna has a single lobe with a maximum in horizontal directions. At heights above a half wavelength the pattern splits and has a second lobe directed into the sky at an angle of about 60°. The reason horizontal radiation is maximum at 0.625 λ {\displaystyle \lambda } is that at slightly above
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#17327730994021464-420: A half wavelength, the opposite phase radiation from the two lobes interferes destructively and cancels at high elevation angles, causing most of the power to be emitted in horizontal directions. Heights above 0.625 λ {\displaystyle \lambda } are not generally used because above this the power radiated in horizontal directions decreases rapidly due to increasing power wasted into
1586-408: A hazard to aircraft. Aviation regulations require masts to be painted in alternating strips of international orange and white paint, and have aircraft warning lights along their length, to make them more visible to aircraft. Regulations require flashing lights at the top, and (depending on height) at several points along the length of the tower. The high radio frequency voltage on the mast poses
1708-421: A height of 225 electrical degrees, about 5 / 8 or 0.625 of a wavelength (this is an approximation valid for a typical finite thickness mast; for an infinitely thin mast the maximum occurs at 2 λ / π {\displaystyle 2\lambda /\pi } = 0.637 λ {\displaystyle \lambda } ) As shown in the diagram, at heights below
1830-492: A higher conductivity medium, copper, in the parts of the ground carrying high current density, to reduce power losses. A standard widely used ground system acceptable to the US Federal Communications Commission (FCC) is 120 equally-spaced radial ground wires extending out one quarter of a wavelength (.25 λ {\displaystyle \lambda } , 90 electrical degrees) from
1952-506: A length of a half wavelength, so a mast around that length had an input resistance that was much higher than the ground resistance, reducing the fraction of transmitter power that was lost in the ground system, eliminating the need for a capacitive topload. In a second paper the same year he showed that the amount of power radiated horizontally in ground waves reached a maximum at a mast height of 0.625 λ {\displaystyle \lambda } (225 electrical degrees). By 1930
2074-418: A little less than a multiple of a quarter wavelength, 1 4 λ , 1 2 λ , 3 4 λ {\displaystyle {1 \over 4}\lambda ,{1 \over 2}\lambda ,{3 \over 4}\lambda } ...(G = 90°, 180°, 270°...) the mast is resonant ; at these heights the antenna presents a pure resistance to the feedline , simplifying impedance matching
2196-429: A map of signal strength produced by actual commercially available masts over the actual terrain. This is compared with the audience population distribution to find the best design. A second design goal that affects height is to reduce multipath fading in the reception area. Some of the radio energy radiated at an angle into the sky is reflected by layers of charged particles in the ionosphere and returns to Earth in
2318-457: A problem for powering the warning lights: the power cable which runs down the mast from the lights to connect to the mains power line is at the high RF potential of the mast. Without protective equipment it would conduct radio frequency (RF) current to the AC power wiring ground, short-circuiting the mast. To prevent this a protective isolator is installed in the lighting power cable at the base of
2440-520: A small reduction in horizontal gain. The optimum height is around 190 electrical degrees or 0.53 λ {\displaystyle \lambda } , so this is another common height for masts. A type of mast with improved anti-fading performance is the sectionalized mast, also called an anti-fading mast. In a sectionalized mast, insulators in the vertical support members divide the mast into two vertically stacked conductive sections, which are fed in phase by separate feedlines. This increases
2562-517: A stationary receiver's output to indicate as if it were randomly jumping about or creeping. When the unit is moving the jumping or creeping may be hidden, but it still degrades the displayed accuracy of location and speed. Multipath propagation is similar in power line communication and in telephone local loops . In either case, impedance mismatch causes signal reflection . High-speed power line communication systems usually employ multi-carrier modulations (such as OFDM or wavelet OFDM) to avoid
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#17327730994022684-402: A tower doubling as a flagpole attracted controversy in 2004 in relation to the U.S. presidential campaign of that year , and highlighted the sentiment that such disguises serve more to allow the installation of such towers in subterfuge, away from public scrutiny, rather than to serve towards the beautification of the landscape. A mast radiator or mast antenna is a radio tower or mast in which
2806-585: 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
2928-486: A wood telecommunications tower – the first of its kind in Italy – replaced a previously-existing steel structure to blend in with its wooded surroundings. One of the most commonly cited reasons telecom companies opt for wood is because it is the only material in the industry that is climate positive . For this reason, some utility pole distributors started to offer wood towers to meet the growing demands of 5G infrastructure. In
3050-458: Is currently the tallest guyed tubular mast in the world after the Belmont transmitting station was reduced in height in 2010. Reinforced concrete towers are relatively expensive to build but provide a high degree of mechanical rigidity in strong winds. This can be important when antennas with narrow beamwidths are used, such as those used for microwave point-to-point links, and when the structure
3172-429: Is in the low frequency band, due to the increasing inefficiency of masts shorter than a quarter wavelength. As frequency decreases the wavelength increases, requiring a taller antenna to make a given fraction of a wavelength. Construction costs and land area required increase with height, putting a practical limit on mast height. Masts over 300 m (980 feet) are prohibitively expensive and very few have been built;
3294-700: Is no chance that high voltage will be present on the mast when personnel are working on it. A tall radio mast is a convenient structure to mount other wireless antennas on, so many radio stations lease space on their towers to other radio services for their antennas. These are called colocated antennas . Types of antenna often mounted on mast radiators are: fiberglass whip antennas for land mobile radio systems for taxi and delivery services, dish antennas for microwave relay links carrying commercial telecommunications and internet data, FM radio broadcasting antennas consisting of collinear bays of twisted dipole elements, and cellular base station antennas. As long as
3416-578: Is not an essential feature. A special form of the radio tower is the telescopic mast . These can be erected very quickly. Telescopic masts are used predominantly in setting up temporary radio links for reporting on major news events, and for temporary communications in emergencies. They are also used in tactical military networks. They can save money by needing to withstand high winds only when raised, and as such are widely used in amateur radio . Telescopic masts consist of two or more concentric sections and come in two principal types: A tethered balloon or
3538-407: Is often located in a building a short distance away from the mast, so its sensitive electronics and operating personnel will not be exposed to the strong radio waves at the base of the mast. Alternatively it is sometimes located at the base of the mast, with the transmitter room surrounded by a Faraday shield of copper screen to keep radio waves out. The current from the transmitter is delivered to
3660-419: Is simply bolted or brazed to the tower. The actual transmitter is usually located in a separate building, which supplies RF power to the tuning hut via a transmission line . To keep it upright the mast has tensioned guy wires attached, usually in sets of 3 at 120° angles, which are anchored to the ground usually with concrete anchors . Multiple sets of guys (from 2 to 5) at different levels are used to make
3782-618: Is still in use. Disguised cell sites sometimes can be introduced into environments that require a low-impact visual outcome, by being made to look like trees, chimneys or other common structures. Many people view bare cellphone towers as ugly and an intrusion into their neighbourhoods. Even though people increasingly depend upon cellular communications, they are opposed to the bare towers spoiling otherwise scenic views. Many companies offer to 'hide' cellphone towers in, or as, trees, church towers, flag poles, water tanks and other features. There are many providers that offer these services as part of
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3904-441: Is that the capacitive reactance of the mast is high, requiring a large loading coil in the antenna tuner to tune it out and make the mast resonant. The high reactance vs the low resistance give the antenna a high Q factor ; the antenna and coil act as a high Q tuned circuit , reducing the usable bandwidth of the antenna. At lower frequencies mast radiators are replaced by more elaborate capacitively toploaded antennas such as
4026-441: Is that the components of the wave remain coherent throughout the whole extent of their travel. The interference will arise owing to the two (or more) components of the wave having, in general, travelled a different length (as measured by optical path length – geometric length and refraction (differing optical speed)), and thus arriving at the detector out of phase with each other. The signal due to indirect paths interferes with
4148-494: Is the danger of wind-induced oscillations. This is particularly a concern with steel tube construction. One can reduce this by building cylindrical shock-mounts into the construction. One finds such shock-mounts, which look like cylinders thicker than the mast, for example, at the radio masts of DHO38 in Saterland . There are also constructions, which consist of a free-standing tower, usually from reinforced concrete , onto which
4270-412: Is the most widespread form of construction. 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
4392-425: Is time varying, and as such we have Very often, just one parameter is used to denote the severity of multipath conditions: it is called the multipath time , T M {\displaystyle T_{M}} , and it is defined as the time delay existing between the first and the last received impulses In practical conditions and measurement, the multipath time is computed by considering as last impulse
4514-509: Is to be occupied by people. In the 1950s, AT&T built numerous concrete towers, more resembling silos than towers, for its first transcontinental microwave route. In Germany and the Netherlands most towers constructed for point-to-point microwave links are built of reinforced concrete , while in the UK most are lattice towers . Concrete towers can form prestigious landmarks, such as
4636-489: Is to increase the number of ground wires near the mast and bury them very shallowly in a surface layer of asphalt pavement, which has low dielectric losses. Base-fed mast radiators have a high voltage on the base of the mast, which can deliver a dangerous electric shock to a grounded person touching it. The potential on the mast is typically several thousand volts with respect to the ground. Electrical codes require such exposed high voltage equipment to be fenced off from
4758-539: The CN Tower in Toronto , Canada. In addition to accommodating technical staff, these buildings may have public areas such as observation decks or restaurants. The Katanga TV tower near Jabalpur , Madhya Pradesh, in central India hosts a high-power transmitter for the public broadcasters Doordarshan and Prasar Bharati . The Stuttgart TV tower was the first tower in the world to be built in reinforced concrete. It
4880-421: The T antenna or umbrella antenna which can have higher efficiency. In circumstances in which short masts must be used, a capacitive topload (also known as top hat or capacitance hat ) is sometimes added at the top of the mast to increase the radiated power. This is a round screen of horizontal wires extending radially from the top of the antenna. It acts as a capacitor plate; the increased current in
5002-422: The complex amplitude (i.e., magnitude and phase) of the generic received pulse. As a consequence, y ( t ) {\displaystyle y(t)} also represents the impulse response function h ( t ) {\displaystyle h(t)} of the equivalent multipath model. More in general, in presence of time variation of the geometrical reflection conditions, this impulse response
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5124-407: The gain of even a short antenna is very close to that of a quarter-wave antenna. However they cannot be driven efficiently due to their low radiation resistance . The radiation resistance of the antenna, the electrical resistance which represents power radiated as radio waves, which is around 25–37 ohms at one-quarter wavelength, decreases below one-quarter wavelength with the square of
5246-622: The intersymbol interference that multipath propagation would cause. The ITU-T G.hn standard provides a way to create a high-speed (up to 1 gigabit per second) local area network using existing home wiring ( power lines , phone lines, and coaxial cables ). G.hn uses OFDM with a cyclic prefix to avoid ISI. Because multipath propagation behaves differently in each kind of wire, G.hn uses different OFDM parameters (OFDM symbol duration, guard interval duration) for each media. DSL modems also use orthogonal frequency-division multiplexing to communicate with their DSLAM despite multipath. In this case
5368-538: The ionosphere interfered with the ground waves, causing an annular region of poor reception at a certain distance from the antenna. It was found that the diamond shape of the Blaw-Knox tower had an unfavorable current distribution which increased the power emitted at high angles. By the 1940s the AM broadcast industry had abandoned the Blaw-Knox design for the narrow, uniform cross section lattice mast used today, which had
5490-411: The longwave band, which limited the vertical height of the radiator to much less than a quarter wavelength, so the antenna was electrically short and had low radiation resistance from 5 to 30 ohms. Therefore, most transmitters used capacitively toploaded antennas like the umbrella antenna or inverted L and T antenna to increase the power radiated. During this era, the operation of antennas
5612-435: The shortwave range, there is little to be gained by raising the antenna more than a half to three quarters of a wavelength above ground level, and at lower frequencies and longer wavelengths, the height becomes infeasibly great (greater than 85 metres (279 ft)). Shortwave transmitters rarely use masts taller than about 100 metres. Because masts, towers and the antennas mounted on them require maintenance, access to
5734-493: The vertical monopole or Marconi antenna , which was initially a wire suspended from a tall wooden pole. He found that the higher the antenna was suspended, the further he could transmit, the first recognition of the need for height in antennas. Radio began to be used commercially for radiotelegraphic communication around 1900. The first 20 years of commercial radio were dominated by radiotelegraph stations, transmitting over long distances by using very long wavelengths in
5856-445: The very low frequency band – such long waves that they are nearly unused at present. Because the extreme wavelengths were one to several kilometers long, even the tallest feasible antennas by comparison were still too short, electrically , and consequently had inherently very low radiation resistance (only 5~25 Ohms). In any antenna, low radiation resistance leads to excessive power losses in its surrounding ground system , since
5978-595: The visual horizon . The only way to cover larger areas is to raise the antenna high enough so it has a line-of-sight path to them. Until 8 August 1991, the Warsaw radio mast was the world's tallest supported structure on land; its collapse left the KVLY / KTHI-TV mast as the tallest. There are over 50 radio structures in the United States that are 600 m ( 1 968.5 ft ) or taller. The steel lattice
6100-425: The whole structure is an antenna. Mast antennas are the transmitting antennas typical for long or medium wave broadcasting. Structurally, the only difference is that some mast radiators require the mast base to be insulated from the ground. In the case of an insulated tower, there will usually be one insulator supporting each leg. Some mast antenna designs do not require insulation, however, so base insulation
6222-441: The 1930s it was found that the diamond shape of the Blaw-Knox tower had an unfavorable current distribution which increased the power emitted at high angles, causing multipath fading in the listening area. By the 1940s the AM broadcast industry had abandoned the Blaw-Knox design for the narrow, uniform cross section lattice mast used today, which had a better radiation pattern. The rise of FM radio and television broadcasting in
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#17327730994026344-542: The 1930s, is commonly used for transmitting antennas operating at low frequencies , in the LF and MF bands, in particular those used for AM radio broadcasting stations. The conductive steel mast is electrically connected to the transmitter . Its base is usually mounted on a nonconductive support to insulate it from the ground. A mast radiator is a form of monopole antenna . Most mast radiators are built as guyed masts . Steel lattice masts of triangular cross-section are
6466-531: The 1940s–1950s created a need for even taller masts. The earlier AM broadcasting used LF and MF bands, where radio waves propagate as ground waves which follow the contour of the Earth. The ground-hugging waves allowed the signals to travel beyond the horizon, out to hundreds of kilometers. However the newer FM and TV transmitters used the VHF band, in which radio waves travel by line-of-sight , so they are limited by
6588-638: The 1960s. In Germany the Bielstein transmitter collapsed in 1985. Tubular masts were not built in all countries. In Germany, France, UK, Czech Republic, Slovakia, Japan and the Soviet Union, many tubular guyed masts were built, while there are nearly none in Poland or North America. Several tubular guyed masts were built in cities in Russia and Ukraine. These masts featured horizontal crossbars running from
6710-450: The MF and LF bands. They also can radiate enough power at higher elevation angles for skywave (skip) radio transmission. Most radio stations use single masts. Multiple masts fed with radio current at different phases can be used to construct directional antennas , which radiate more power in specific directions than others. The transmitter which generates the radio frequency current
6832-417: The United States, for example, wood utility pole distributor Bell Lumber & Pole began developing products for the telecommunications industry . Shorter masts may consist of a self-supporting or guyed wooden pole, similar to a telegraph pole. Sometimes self-supporting tubular galvanized steel poles are used: these may be termed monopoles. In some cases, it is possible to install transmitting antennas on
6954-435: The amount of power it radiates at different elevation angles, is determined by its height h {\displaystyle h} compared to the wavelength λ = c / f {\displaystyle \lambda =c/f} of the radio waves, equal to the speed of light c {\displaystyle c} divided by the frequency f {\displaystyle f} . The height of
7076-405: The antenna in which reception may be inadequate, sometimes called a "zone of silence", fading wall or mush zone . However multipath fading only becomes significant if the signal strength of the skywave is within about 50% (3 dB) of the ground wave. By reducing the height of a monopole slightly the power radiated in the second lobe can be reduced enough to eliminate multipath fading, with only
7198-448: The antenna. Masts shorter than 0.17 λ {\displaystyle \lambda } (60 electrical degrees) are seldom used. At this height, the radiation resistance is about 10 ohms, so the typical resistance of a buried ground system, 2 ohms, is about 20% of the radiation resistance, so below this height over 20% of the transmitter power is wasted in the ground system. A second problem with electrically short masts
7320-414: The bottom for stability, narrowing to a slender mast. The advantage of this construction is the elimination of guy lines and thus reduction in land area required. These towers can have a triangular or a square cross section, with each leg supported on an insulator. A disadvantage is the wide base of the tower distorts the vertical current pattern on the tower, reducing the radiation resistance and therefore
7442-573: The buildings collapsed, several local TV and radio stations were knocked off the air until backup transmitters could be put into service. Such facilities also exist in Europe , particularly for portable radio services and low-power FM radio stations. In London , the BBC erected in 1936 a mast for broadcasting early television on one of the towers of a Victorian building, the Alexandra Palace . It
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#17327730994027564-524: The central mast structure to the guys and were built in the 1960s. The crossbars of these masts are equipped with a gangway that holds smaller antennas, though their main purpose is oscillation damping. The design designation of these masts is 30107 KM and they are exclusively used for FM and TV and are between 150–200-metre (490–660 ft) tall with one exception. The exception being the mast in Vinnytsia which has height of 354 m (1161 ft) and
7686-469: The colocated antennas do not operate at frequencies anywhere near the transmitting frequency of the mast, it is usually possible to isolate them electrically from the voltage on the mast. The transmission lines feeding RF power to the colocated antennas pose much the same problem as the aircraft lighting power lines: they have to pass down the tower and across the base insulator and connect to low voltage equipment, so without isolation devices, they will carry
7808-403: The construction cost of a single mast antenna, far more land area, and parasitic currents in the masts distorted the radiation pattern. Two historic papers published in 1924 by Stuart Ballantine led to the development of the mast radiator. One derived the radiation resistance of a vertical monopole antenna over a ground plane. He found that the radiation resistance increased to a maximum at
7930-404: The disadvantages of the T antenna led broadcasters to adopt the mast radiator antenna. One of the first types used was the diamond cantilever or Blaw-Knox tower . This had a diamond ( rhombohedral ) shape which made it rigid, so only one set of guy lines was needed, at its wide waist. The pointed lower end of the antenna ended in a large ceramic insulator in the form of a ball-and-socket joint on
8052-591: The distance (in Hz) between two consecutive valleys (or two consecutive peaks), is roughly inversely proportional to the multipath time. The so-called coherence bandwidth is thus defined as For example, with a multipath time of 3 μs (corresponding to a 1 km of added on-air travel for the last received impulse), there is a coherence bandwidth of about 330 kHz. [REDACTED] This article incorporates public domain material from Federal Standard 1037C . General Services Administration . Archived from
8174-415: The earth above the ground wires near the mast where the displacement current enters the ground. This can cause significant dielectric power losses in the earth. To reduce this loss these antennas often use a conductive copper ground screen around the mast connected to the buried ground wires, either lying on the ground or elevated a few feet, to shield the ground from the electric field. Another solution
8296-400: The earth. Since for an omnidirectional antenna the Earth currents travel radially toward the ground point from all directions, the grounding system usually consists of a radial pattern of buried cables extending outward from the base of the mast in all directions, connected together to the ground lead at a terminal next to the base. The transmitter power lost in the ground resistance, and so
8418-404: The efficiency of the antenna, depends on the soil conductivity. This varies widely; marshy ground or ponds, particularly salt water, provide the lowest resistance ground. The RF current density in the earth, and thus the power loss per square meter, increases the closer one gets to the ground terminal at the base of the mast, so the radial ground system can be thought of as replacing the soil with
8540-426: The equivalent of 15-30 degrees of added electrical height. For mast radiators the earth under the mast is part of the antenna; the current fed to the mast passes through the air into the ground under the antenna as displacement current (oscillating electric field). The ground also serves as a ground plane to reflect the radio waves. The antenna is fed power between the bottom of the mast and ground so it requires
8662-420: The feedline to the antenna. At other lengths the antenna has capacitive reactance or inductive reactance . However masts of these lengths can be fed efficiently by cancelling the reactance of the antenna with a conjugate reactance in the matching network in the helix house. Due to the finite thickness of the mast, resistance, and other factors the actual antenna current on the mast differs significantly from
8784-421: The first he derived the radiation resistance of a vertical conductor over a ground plane . He found that the radiation resistance increased to a maximum at a length of 1 / 2 wavelength , so a mast around that length had an input resistance that was much higher than the ground resistance, reducing the fraction of transmitter power that was lost in the ground system without assistance from
8906-489: The first large mast radiators was the experimental tubular 130-meter (420 ft) mast erected in 1906 by Reginald Fessenden for his spark gap transmitter at Brant Rock, Massachusetts with which he made the first two-way transatlantic transmission, communicating with an identical antenna in Machrihanish , Scotland. However, during the radiotelegraphy era before 1920 most long-distance radio stations transmitted in
9028-413: The first one which allows receiving a determined amount of the total transmitted power (scaled by the atmospheric and propagation losses), e.g. 99%. Keeping our aim at linear, time invariant systems, we can also characterize the multipath phenomenon by the channel transfer function H ( f ) {\displaystyle H(f)} , which is defined as the continuous time Fourier transform of
9150-504: The ground or above a certain height (altitude). In digital radio communications (such as GSM ) multipath can cause errors and affect the quality of communications. The errors are due to intersymbol interference (ISI). Equalizers are often used to correct the ISI. Alternatively, techniques such as orthogonal frequency division modulation and rake receivers may be used. In a Global Positioning System receiver , multipath effects can cause
9272-417: The hazard that communications towers can pose to birds. There have also been instances of rare birds nesting in cell towers and thereby preventing repair work due to legislation intended to protect them. Mast radiator A mast radiator (or radiating tower ) is a radio mast or tower in which the metal structure itself is energized and functions as an antenna . This design, first used widely in
9394-481: The high mast voltage and can short circuit the mast to ground. The transmission lines are isolated by low pass filter inductors consisting of helixes of coaxial cable wound on a nonconductive form. The vertical or monopole antenna was invented and patented by radio entrepreneur Guglielmo Marconi in 1896 during his development of the first practical radio transmitters and receivers . He initially used horizontal dipole antennas invented by Heinrich Hertz , but
9516-399: The ideal sine wave assumed above, and as shown by the graph, resonant lengths of a typical tower are closer to 80°, 140°, and 240°. Ground waves travel horizontally away from the antenna just above the ground, therefore the goal of most mast designs is to radiate a maximum amount of power in horizontal directions. An ideal monopole antenna radiates maximum power in horizontal directions at
9638-519: The impulse response h ( t ) {\displaystyle h(t)} where the last right-hand term of the previous equation is easily obtained by remembering that the Fourier transform of a Dirac pulse is a complex exponential function, an eigenfunction of every linear system. The obtained channel transfer characteristic has a typical appearance of a sequence of peaks and valleys (also called notches ); it can be shown that, on average,
9760-600: The light takes 3 μs to cross a 1 km span). Thus, the received signal will be expressed by where N {\displaystyle N} is the number of received impulses (equivalent to the number of electromagnetic paths, and possibly very large), τ n {\displaystyle \tau _{n}} is the time delay of the generic n t h {\displaystyle n^{th}} impulse, and ρ n e j ϕ n {\displaystyle \rho _{n}e^{j\phi _{n}}} represent
9882-438: The lightning arrester should go directly to a metal ground stake by the shortest path. The top of the mast should have a lightning rod to protect the top aircraft warning light. The mast should also have a DC path to ground, so that static electric charges on the mast can drain off. Also at the base is a grounding switch, which is used to connect the mast to the ground system during maintenance operations to ensure that there
10004-443: The low-resistance antenna cannot effectively compete for power with the high-resistance earth. To partially compensate, radiotelegraph stations used huge capacitively top-loaded flattop antennas consisting of horizontal wires strung between multiple 100–300 meters (330–980 ft) steel towers to increase efficiency. AM radio broadcasting began around 1920. The allocation of the medium wave frequencies for broadcasting raised
10126-404: The mast is usually mounted on a thick ceramic insulator , which has the compressive strength to support the tower's weight and the dielectric strength to withstand the high voltage applied by the transmitter. The RF power to drive the antenna is supplied by a impedance matching network , usually housed in an antenna tuning hut near the base of the mast, and the cable supplying the current
10248-467: The mast is usually specified in fractions of the wavelength, or in " electrical degrees " where each degree equals λ / 360 {\displaystyle \lambda /360} meters. The current distribution on the mast determines the radiation pattern . The radio frequency current flows up the mast and reflects from the top, and the direct and reflected current interfere , creating an approximately sinusoidal standing wave on
10370-451: The mast required to charge and discharge the topload capacitance each RF cycle increases the radiated power. Since the topload acts electrically like an additional length of mast, this is called " electrically lengthening " the antenna. Another way to construct a capacity hat is to use sections of the top guy wire set, by inserting the strain insulators in the guy line a short distance from the mast. Capacity hats are structurally limited to
10492-452: The mast through a feedline , a specialized cable ( transmission line ) for carrying radio frequency current. At LF and MF frequencies foam insulated coaxial cable is usually used. The feedline is connected to an antenna tuning unit ( impedance matching network ) at the base of the mast, to match the transmission line to the mast. This may be located in a waterproof box or a small shed called an antenna tuning hut (helix house) next to
10614-460: The mast which blocks the RF current while letting the low frequency 50 or 60 Hz AC power pass through up the mast. Several types of isolator devices have been used: At its base, the mast should have a lightning arrester consisting of a ball or horn spark gap between the mast and the ground terminal, so that current from a lightning strike to the mast will be conducted to ground. The conductor from
10736-403: The mast with a node (point of zero current) at the top and a maxima one quarter wavelength down where i ( y ) {\displaystyle i(y)} is the current at a height of y {\displaystyle y} electrical degrees above the ground, and I max {\displaystyle I_{\text{max}}} is the maximum current. At heights of
10858-619: The mast, disturbing the radiation pattern of the antenna. To prevent this, additional strain insulators are inserted at intervals in the guy cables to divide the line into nonresonant lengths: Usually segments should be limited to a maximum of one-eighth to one-tenth wavelength ( 1 8 λ ∼ 1 10 λ {\displaystyle \ {\tfrac {\ 1\ }{8}}\lambda \sim {\tfrac {1}{\ 10\ }}\lambda \ } ). Mast radiators can also be built as free-standing lattice towers , wide at
10980-472: The mast. No. 10 gauge soft-drawn copper wire is typically used, buried 10 to 25 cm (4 to 10 inches) deep. For AM broadcast band masts this requires a circular land area extending from the mast 47–136 m (154–446 feet). This is usually planted with grass, which is kept mowed short as tall grass can increase power loss in certain circumstances. If the land area around the mast is too limited for such long radials, they can in many cases be replaced by
11102-462: The mast. The antenna tuning circuit matches the characteristic impedance of the feedline to the impedance of the antenna (given by the graph below), and includes a reactance , usually a loading coil , to tune out the reactance of the antenna, to make it resonant at the operating frequency. Without the antenna tuner the impedance mismatch between the antenna and feedline would cause a condition called standing waves (high SWR ), in which some of
11224-402: The most common type. Square lattice masts and tubular masts are also sometimes used. To ensure that the tower is a continuous conductor, the tower's structural sections are electrically bonded at the joints by short copper jumpers which are soldered to each side or "fusion" (arc) welds across the mating flanges. Base-fed masts, the most common type, must be insulated from the ground. At its base,
11346-591: The normal tower installation and maintenance service. These are generally called "stealth towers" or "stealth installations", or simply concealed cell sites . The level of detail and realism achieved by disguised cellphone towers is remarkably high; for example, such towers disguised as trees are nearly indistinguishable from the real thing. Such towers can be placed unobtrusively in national parks and other such protected places, such as towers disguised as cacti in United States' Coronado National Forest . Even when disguised, however, such towers can create controversy;
11468-529: The past, ruggedized and under-run filament lamps were used to maximize the bulb life. Alternatively, neon lamps were used. Nowadays such lamps tend to use LED arrays. Height requirements vary across states and countries, and may include additional rules such as requiring a white flashing strobe in the daytime and pulsating red fixtures at night. Structures over a certain height may also be required to be painted with contrasting color schemes such as white and orange or white and red to make them more visible against
11590-406: The possibility of using single vertical masts without top loading. The antenna used for broadcasting through the 1920s was the T-antenna , which consisted of two masts with loading wires on top, strung between them, requiring twice the construction costs and land area of a single mast. In 1924 Stuart Ballantine published two historic papers which led to the development of the single mast antenna. In
11712-448: The power emitted at low elevation angles. In the medium frequency (MF) and low frequency (LF) bands AM radio stations cover their listening area using ground waves , vertically polarized radio waves which travel close to the ground surface, following the contour of the terrain. Mast radiators make good ground wave antennas, and are the main type of transmitting antennas used by AM radio stations, as well as other radio services in
11834-424: The proportion of power radiated in horizontal directions and allows the mast to be taller than 0.625 λ {\displaystyle \lambda } without excessive high angle radiation. Practical sectionals with heights of 120 over 120 degrees, 180 over 120 degrees and 180 over 180 degrees are presently in operation with good results. The lower limit to the frequency at which mast radiators can be used
11956-451: The public, so the mast and antenna tuning hut are surrounded by a locked fence. Usually a chain-link fence is used, but sometimes wooden fences are used to prevent currents induced in a metallic fence from distorting the radiation pattern of the antenna. An alternate design is to mount the mast on top of the antenna tuning hut, out of the reach of the public, eliminating the need for a fence. Antenna masts are tall enough that they can be
12078-704: The radiated power, so guyed masts are preferred. A country's national radio ministry usually has regulatory authority over the design and operation of radio masts, in addition to local building codes which cover structural design. In the US this is the Federal Communications Commission (FCC). Plans for a mast must be approved by regulators before building. A single mast radiator is an omnidirectional antenna which radiates equal radio wave power in all horizontal directions. Mast radiators radiate vertically polarized radio waves, with most of
12200-492: The radio power is reflected back down the feedline toward the transmitter, resulting in inefficiency and possibly overheating the transmitter. From the antenna tuner a short feedline is bolted or brazed to the mast. There are several ways of feeding a mast radiator: Government regulations usually require the power fed to the antenna to be monitored at the antenna base, so the antenna tuning hut also includes an antenna current sampling circuit, which sends its measurements back to
12322-402: The ratio of mast height to wavelength. Other electrical resistances in the antenna system, the ohmic resistance of the mast and the buried ground system, are in series with the radiation resistance, and the transmitter power divides proportionally between them. As the radiation resistance decreases more of the transmitter power is dissipated as heat in these resistances, reducing the efficiency of
12444-409: The received signal at any point on the ground is determined by two factors, the power radiated by the antenna in that direction and the path attenuation between the transmitting antenna and the receiver, which depends on ground conductivity . The design process of an actual radio mast usually involves doing a survey of soil conductivity, then using an antenna simulation computer program to calculate
12566-406: The receiver, due to the presence of the multiple electromagnetic paths, more than one pulse will be received, and each one of them will arrive at different times. In fact, since the electromagnetic signals travel at the speed of light , and since every path has a geometrical length possibly different from that of the other ones, there are different air travelling times (consider that, in free space ,
12688-414: The reception area. This is called the skywave . At certain distances from the antenna these radio waves are out of phase with the ground waves, and the two radio waves interfere destructively and partly or completely cancel each other, reducing the signal strength. This is called fading . At night when ionospheric reflection is strongest, this results in an annular region of low signal strength around
12810-434: The reflections may be caused by mixed wire gauges , but those from bridge taps are usually more intense and complex. Where OFDM training is unsatisfactory, bridge taps may be removed. The mathematical model of the multipath can be presented using the method of the impulse response used for studying linear systems . Suppose you want to transmit a single, ideal Dirac pulse of electromagnetic power at time 0, i.e. At
12932-438: The required signal in amplitude as well as phase which is called multipath fading. In analog facsimile and television transmission , multipath causes jitter and ghosting, seen as a faded duplicate image to the right of the main image. Ghosts occur when transmissions bounce off a mountain or other large object, while also arriving at the antenna by a shorter, direct route, with the receiver picking up two signals separated by
13054-541: The roofs of tall buildings. In North America , for instance, there are transmitting antennas on the Empire State Building , the Willis Tower , Prudential Tower , 4 Times Square , and One World Trade Center . The North Tower of the original World Trade Center also had a 110-metre (360 ft) telecommunications antenna atop its roof, constructed in 1978–1979, and began transmission in 1980. When
13176-400: The same signal is received over more than one path, it can create interference and phase shifting of the signal. Destructive interference causes fading ; this may cause a radio signal to become too weak in certain areas to be received adequately. For this reason, this effect is also known as multipath interference or multipath distortion . Where the magnitudes of the signals arriving by
13298-438: The sky in the second lobe. For medium wave AM broadcast band masts 0.625 λ {\displaystyle \lambda } would be a height of 117–341 m (384–1,119 feet), and taller for longwave masts. The high construction costs of such tall masts mean frequently shorter masts are used. The above gives the radiation pattern of a perfectly conducting mast over perfectly conducting ground. The actual strength of
13420-494: The sky. In some countries where light pollution is a concern, tower heights may be restricted so as to reduce or eliminate the need for aircraft warning lights. For example, in the United States the 1996 Telecommunications Act allows local jurisdictions to set maximum heights for towers, such as limiting tower height to below 200 feet (61 m) and therefore not requiring aircraft illumination under US Federal Communications Commission (FCC) rules. One problem with radio masts
13542-593: The tallest masts in the world are around 600 m (2,000 feet). Another constraint in some areas is height restrictions on structures; near airports aviation authorities may limit the maximum height of masts. These constraints often require a mast be used that is shorter than the ideal height. Antennas significantly shorter than the fundamental resonant length of one-quarter of the wavelength (0.25 λ {\displaystyle \lambda } , 90 electrical degrees) are called electrically short antennas. Electrically short antennas are efficient radiators ;
13664-437: The tower rigid against buckling. The guy lines have strain insulators inserted, usually at the top near the attachment point to the mast, to insulate the conductive cable from the mast, preventing the high voltage on the tower from reaching the ground. Even though they are insulated from the mast the conductive guy cables can act electrically as resonant antennas ( parasitic elements ), absorbing and reradiating radio waves from
13786-400: The transmitter control room. The hut also usually contains the power supply for the aircraft warning lights. The ideal height of a mast radiator depends on transmission frequency f {\displaystyle f} , the geographical distribution of the listening audience, and terrain. An unsectionalized mast radiator is a monopole antenna , and its vertical radiation pattern ,
13908-554: The tube and consequently the structure may look cleaner. These masts are mainly used for FM-/TV-broadcasting, but sometimes also as mast radiator. The big mast of Mühlacker transmitting station is a good example of this. A disadvantage of this mast type is that it is much more affected by winds than masts with open bodies. Several tubular guyed masts have collapsed. In the UK, the Emley Moor and Waltham TV stations masts collapsed in
14030-399: The underlying physics. Multipath interference is a phenomenon in the physics of waves whereby a wave from a source travels to a detector via two or more paths and the two (or more) components of the wave interfere constructively or destructively. Multipath interference is a common cause of " ghosting " in analog television broadcasts and of fading of radio waves . The condition necessary
14152-603: The various paths have a distribution known as the Rayleigh distribution , this is known as Rayleigh fading . Where one component (often, but not necessarily, a line of sight component) dominates, a Rician distribution provides a more accurate model, and this is known as Rician fading . Where two components dominate, the behavior is best modeled with the two-wave with diffuse power (TWDP) distribution. All of these descriptions are commonly used and accepted and lead to results. However, they are generic and abstract/hide/approximate
14274-404: The whole of the structure is necessary. Small structures are typically accessed with a ladder . Larger structures, which tend to require more frequent maintenance, may have stairs and sometimes a lift, also called a service elevator. Tall structures in excess of certain legislated heights are often equipped with aircraft warning lamps , usually red, to warn pilots of the structure's existence. In
14396-425: Was also used at Criggion radio station . For ELF transmitters ground dipole antennas are used. Such structures require no tall masts. They consist of two electrodes buried deep in the ground at least a few dozen kilometres apart. From the transmitter building to the electrodes, overhead feeder lines run. These lines look like power lines of the 10 kV level, and are installed on similar pylons. For transmissions in
14518-405: Was designed in 1956 by the local civil engineer Fritz Leonhardt . Fiberglass poles are occasionally used for low-power non-directional beacons or medium-wave broadcast transmitters. Carbon fibre monopoles and towers have traditionally been too expensive but recent developments in the way the carbon fibre tow is spun have resulted in solutions that offer strengths exceeding steel (10 times) for
14640-431: Was little understood, and designs were based on trial and error and half-understood rules of thumb. The beginning of AM radio broadcasting in 1920 and the allocation of medium wave frequencies to broadcasting stations sparked an increase in interest in medium wave antennas. The flattop or T-antenna was used as the main broadcasting antenna through the 1920s. It had the disadvantage that it required two masts, twice
14762-429: Was not able to communicate further than a few miles. He discovered by experiment that if he connected one terminal of his transmitter and receiver to a vertical wire suspended overhead, and the other terminal to a metal plate buried in the Earth, he could transmit for longer distances. Marconi's antennas, as well as most other vertical antennas through the 1920s, were constructed of wires suspended by wooden masts. One of
14884-502: Was the diamond cantilever or Blaw-Knox tower . This had a diamond ( rhombohedral ) shape which made it rigid, so only one set of guy lines was needed, at its wide waist. The pointed lower end of the antenna ended in a large ceramic insulator in the form of a ball-and-socket joint on a concrete base, relieving bending moments on the structure. The first, a 665 foot (203 m) half-wave mast was installed at radio station WABC 's 50 kW transmitter at Wayne, New Jersey in 1931. During
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