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100-1458: Telecommunications Tower may refer to: Telecommunications tower , a mast or tower built primarily to hold telecommunications antennas Telecommunications Tower (Montevideo) , or Antel tower, in Uruguay Telecommunication Tower of US-Forces Heidelberg, in Germany Telecom Telecommunication Tower Heidelberg , in Germany Bungsberg telecommunications tower , in Germany Lohmar-Birk telecommunications tower , in Germany See also [ edit ] All pages with titles containing Telecommunications Tower Telekom Tower , in Kuala Lumpur, Malaysia Montjuïc Communications Tower , in Spain Liberation Tower (Kuwait) , originally intended to be named The Kuwait Telecommunications Tower Pasilan linkkitorni , or Yle Transmission Tower, in Finland Topics referred to by

200-431: 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 the vertical monopole or Marconi antenna , which was initially a wire suspended from a tall wooden pole. He found that

300-569: 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

400-420: A loading coil , at the feedpoint in series with the antenna, with inductive reactance equal to the antenna's capacitive reactance at the operating frequency, will cancel the capacitance of the antenna, so the combination of the antenna and coil will be resonant at the operating frequency. Since adding inductance is equivalent to increasing the electrical length, this technique is called electrically lengthening

500-467: A circuit. Ordinary lumped element electric circuits only work well for alternating currents at frequencies for which the circuit is electrically small (electrical length much less than one). For frequencies high enough that the wavelength approaches the size of the circuit (the electrical length approaches one) the lumped element model on which circuit theory is based becomes inaccurate, and transmission line techniques must be used. Electrical length

600-771: A conductor with a physical length of l {\displaystyle l} at a given frequency f {\displaystyle f} is the number of wavelengths or fractions of a wavelength of the wave along the conductor; in other words the conductor's length measured in wavelengths Electrical length G = l f v p = l λ = Physical length Wavelength {\displaystyle \quad {\text{Electrical length}}\,G={lf \over v_{p}}={l \over \lambda }={{\text{Physical length}} \over {\text{Wavelength}}}\quad } The phase velocity v p {\displaystyle v_{p}} at which electrical signals travel along

700-399: A conductor, it is often the phase shift ϕ {\displaystyle \phi } , the difference in phase of the sinusoidal wave between the two ends of the conductor, that is of importance. The length of a sinusoidal wave is commonly expressed as an angle, in units of degrees (with 360° in a wavelength) or radians (with 2π radians in a wavelength). So alternately

800-478: 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,

900-647: 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

1000-473: 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 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

1100-400: A monopole longer than a quarter wavelength but shorter than a half wavelength, will have inductive reactance . This can be cancelled by adding a capacitor of equal but opposite reactance at the feed point to make the antenna resonant. This is called electrically shortening the antenna. Two antennas that are similar (scaled copies of each other), fed with different frequencies, will have

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1200-507: 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

1300-418: A radiation resistance of less than one ohm, making it very hard to drive. A second disadvantage is that since the capacitive reactance of the antenna and inductive reactance of the required loading coil do not decrease, the Q factor of the antenna increases; it acts electrically like a high Q tuned circuit . As a result, the bandwidth of the antenna decreases with the square of electrical length, reducing

1400-407: A reactance. Adding an equal but opposite type of reactance in series with the feedline will cancel the antenna's reactance; the combination of the antenna and reactance will act as a series resonant circuit , so at its operating frequency its input impedance will be purely resistive, allowing it to be fed power efficiently at a low SWR without reflections. In a common application, an antenna which

1500-401: A sine wave there, decreasing faster toward the ends. When approximated as a sine wave, the current does not quite go to zero at the ends; the nodes of the current standing wave, instead of being at the ends of the element, occur somewhat beyond the ends. Thus the electrical length of the antenna is longer than its physical length. The electrical length of an antenna element also depends on

1600-434: A specific frequency or narrow band of frequencies. It is determined by the construction of the cable, so different cables of the same length operating at the same frequency can have different electrical lengths. A conductor is called electrically long if it has an electrical length much greater than one; that is it is much longer than the wavelength of the alternating current passing through it, and electrically short if it

1700-574: A subscript 0) Thus a physical length l {\displaystyle l} of a radio wave in space or air has an electrical length of In the SI system of units, empty space has a permittivity of ϵ 0 = {\displaystyle \epsilon _{\text{0}}=} 8.854×10 F/m (farads per metre) and a magnetic permeability of μ 0 = {\displaystyle \mu _{\text{0}}=} 1.257×10 H/m (henries per meter). These universal constants determine

1800-403: 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

1900-585: 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

2000-606: A transmission line of a given length l {\displaystyle l} than in the same length of wave in free space, so the electrical length of a transmission line is longer than the electrical length of a wave of the same frequency in free space G = l λ = l κ λ 0 = l f κ c {\displaystyle \;G={l \over \lambda }={l \over \kappa \lambda _{\text{0}}}={lf \over \kappa c}\;} Ordinary electrical cable suffices to carry alternating current when

2100-419: A transmission line or other cable depends on the construction of the line. Therefore, the wavelength λ {\displaystyle \lambda } corresponding to a given frequency varies in different types of lines, thus at a given frequency different conductors of the same physical length can have different electrical lengths. In radio frequency applications, when a delay is introduced due to

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2200-404: A transmission line, in which the fields are mainly confined to the vicinity of the conductors. Near the ends of the antenna elements the electric field is not perpendicular to the conductor axis as in a transmission line but spreads out in a fan shape (fringing field). As a result, the end sections of the antenna have increased capacitance, storing more charge, so the current waveform departs from

2300-425: A transmission line, is its length in wavelengths of the current on the antenna at the operating frequency. An antenna's resonant frequency , radiation pattern , and driving point impedance depend not on its physical length but on its electrical length. A thin antenna element is resonant at frequencies at which the standing current wave has a node (zero) at the ends (and in monopoles an antinode (maximum) at

2400-449: A vacuum an electromagnetic wave ( radio wave ) travels at the speed of light v p = c = {\displaystyle v_{p}=c=} 2.9979×10 meters per second, and very close to this speed in air, so the free space wavelength of the wave is λ 0 = c / f {\displaystyle \lambda _{\text{0}}=c/f} . (in this article free space variables are distinguished by

2500-405: A wire or cable at a particular phase velocity v p {\displaystyle v_{p}} . It takes time for later portions of the wave to reach a given point on the conductor so the spatial distribution of current and voltage along the conductor at any time is a moving sine wave . After a time equal to the period T {\displaystyle T} a complete cycle of

2600-488: 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

2700-438: Is electrically short , shorter than its fundamental resonant length, a monopole antenna with an electrical length shorter than a quarter-wavelength ( λ / 4 {\displaystyle \lambda /4} ), or a dipole antenna shorter than a half-wavelength ( λ / 2 {\displaystyle \lambda /2} ) will have capacitive reactance . Adding an inductor (coil of wire), called

2800-430: Is a quarter wavelength ( λ / 4 , ϕ = 90 ∘ or π / 2 radians {\displaystyle \lambda /4,\phi =90^{\circ }\;{\text{or}}\;\pi /2\;{\text{radians}}} ) or a multiple of it. Resonant frequency is important because at frequencies at which the antenna is resonant the input impedance it presents to its feedline

2900-458: 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

3000-411: Is defined for conductors carrying alternating current (AC) at a single frequency or narrow band of frequencies. An alternating electric current of a single frequency f {\displaystyle f} is an oscillating sine wave which repeats with a period of T = 1 / f {\displaystyle T=1/f} . This current flows through a given conductor such as

3100-446: Is different from Wikidata All article disambiguation pages All disambiguation pages Telecommunications tower 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

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3200-553: Is divided into three regimes or fields of study depending on the electrical length of the apparatus, that is the physical length l {\displaystyle l} of the apparatus compared to the wavelength λ = c / f {\displaystyle \lambda =c/f} of the waves: Completely different apparatus is used to conduct and process electromagnetic waves in these different wavelength ranges Historically, electric circuit theory and optics developed as separate branches of physics until at

3300-409: Is inconvenient or impossible to use an antenna of resonant length. An antenna of nonresonant length at the operating frequency can be made resonant by adding a reactance , a capacitance or inductance , either in the antenna itself or in a matching network between the antenna and its feedline . A nonresonant antenna appears at its feedpoint electrically equivalent to a resistance in series with

3400-561: Is much shorter than a wavelength. Electrical lengthening and electrical shortening means adding reactance ( capacitance or inductance ) to an antenna or conductor to increase or decrease the electrical length, usually for the purpose of making it resonant at a different resonant frequency . This concept is used throughout electronics , and particularly in radio frequency circuit design, transmission line and antenna theory and design. Electrical length determines when wave effects ( phase shift along conductors) become important in

3500-578: 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

3600-427: Is purely resistive . If the resistance of the antenna is matched to the characteristic resistance of the feedline, it absorbs all the power supplied to it, while at other frequencies it has reactance and reflects some power back down the line toward the transmitter, causing standing waves (high SWR ) on the feedline. Since only a portion of the power is radiated this causes inefficiency, and can possibly overheat

3700-619: 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

3800-494: 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

3900-412: 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

4000-511: 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

4100-546: Is used instead. A transmission line is a specialized cable designed for carrying electric current of radio frequency . The distinguishing feature of a transmission line is that it is constructed to have a constant characteristic impedance along its length and through connectors and switches, to prevent reflections. This also means AC current travels at a constant phase velocity along its length, while in ordinary cable phase velocity may vary. The velocity factor κ {\displaystyle \kappa } depends on

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4200-539: 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

4300-426: The aperture scales with the square of the wavelength. An electrically short conductor, much shorter than one wavelength, makes an inefficient radiator of electromagnetic waves . As the length of an antenna is made shorter than its fundamental resonant length (a half-wavelength for a dipole antenna and a quarter-wavelength for a monopole), the radiation resistance the antenna presents to the feedline decreases with

4400-399: The data rate that can be transmitted. At VLF frequencies even the huge toploaded wire antennas that must be used have bandwidths of only ~10 hertz, limiting the data rate that can be transmitted. The field of electromagnetics is the study of electric fields , magnetic fields , electric charge , electric currents and electromagnetic waves . Classic electromagnetism is based on

4500-453: The dielectric constant of the substrate board increases the electrical length of the antenna. Proximity to the Earth or a ground plane , a dielectric coating on the conductor, nearby grounded towers, metal structural members, guy lines and the capacitance of insulators supporting the antenna also increase the electrical length. These factors, called "end effects", cause the electrical length of an antenna element to be somewhat longer than

4600-445: The lumped element circuit model is only valid for alternating current when the circuit is electrically small , much smaller than a wavelength. When the electrical length approaches or is greater than one, a conductor will have significant reactance , inductance or capacitance , depending on its length. So simple circuit theory is inadequate and transmission line techniques (the distributed-element model ) must be used. In

4700-435: 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

4800-596: 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

4900-407: The wavelength of alternating current at a given frequency traveling through the conductor. In other words, it is the length of the conductor measured in wavelengths. It can alternately be expressed as an angle , in radians or degrees , equal to the phase shift the alternating current experiences traveling through the conductor. Electrical length is defined for a conductor operating at

5000-425: 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

5100-411: 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 the first he derived the radiation resistance of a vertical conductor over a ground plane . He found that

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5200-638: 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

5300-523: 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 the 1940s–1950s created

5400-418: 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

5500-443: The antenna conductors, reflecting from the ends. If the antenna rods are not too thick (have a large enough length to diameter ratio), the current along them is close to a sine wave, so the concept of electrical length also applies to these. The current is in the form of two oppositely directed sinusoidal traveling waves which reflect from the ends, which interfere to form standing waves . The electrical length of an antenna, like

5600-445: The antenna. This is the usual technique for matching an electrically short transmitting antenna to its feedline, so it can be fed power efficiently. However, an electrically short antenna that has been loaded in this way still has the same radiation pattern ; it does not radiate as much power, and therefore has lower gain than a full-sized antenna. Conversely, an antenna longer than resonant length at its operating frequency, such as

5700-416: The behavior of the antenna must be calculated by electromagnetic simulation computer programs like NEC . As with a transmission line, an antenna's electrical length is increased by anything that adds shunt capacitance or series inductance to it, such as the presence of high permittivity dielectric material around it. In microstrip antennas which are fabricated as metal strips on printed circuit boards ,

5800-574: 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

5900-574: The cable is electrically short ; the electrical length of the cable is small compared to one, that is when the physical length of the cable is small compared to a wavelength, say l < λ / 10 {\displaystyle l<\lambda /10} . As frequency gets high enough that the length of the cable becomes a significant fraction of a wavelength, l > λ / 10 {\displaystyle l>\lambda /10} , ordinary wires and cables become poor conductors of AC. Impedance discontinuities at

6000-408: The cable, which reduces the velocity factor below unity. If there is a material with high magnetic permeability ( μ {\displaystyle \mu } ) in the line such as steel or ferrite which increases the distributed inductance L {\displaystyle L} , it can also reduce κ {\displaystyle \kappa } , but this is almost never

6100-674: The case. If all the space around the transmission line conductors containing the near fields was filled with a material of permittivity ϵ {\displaystyle \epsilon } and permeability μ {\displaystyle \mu } , the phase velocity on the line would be v p = 1 ϵ μ {\displaystyle \;\;v_{p}={1 \over {\sqrt {\epsilon \mu }}}\;}    The effective permittivity ϵ {\displaystyle \epsilon } and permeability μ {\displaystyle \mu } per unit length of

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6200-524: 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

6300-489: The details of construction, and is different for each type of transmission line. However the approximate velocity factor for the major types of transmission lines is given in the table. Electrical length is widely used with a graphical aid called the Smith chart to solve transmission line calculations. A Smith chart has a scale around the circumference of the circular chart graduated in wavelengths and degrees, which represents

6400-598: The effective proportion of space around the line occupied by dielectric. In most transmission lines there are no materials with high magnetic permeability, so μ = μ 0 {\displaystyle \mu =\mu _{\text{0}}} and μ r = 1 {\displaystyle \mu _{\text{r}}=1} and so κ = 1 ϵ eff {\displaystyle \;\;\kappa ={1 \over {\sqrt {\epsilon _{\text{eff}}}}}\;} (no magnetic materials)     Since

6500-407: The electrical length can be expressed as an angle which is the phase shift of the wave between the ends of the conductor The electrical length of a conductor determines when wave effects (phase shift along the conductor) are important. If the electrical length G {\displaystyle G} is much less than one, that is the physical length of a conductor is much shorter than

6600-443: The electrical length of the transmission line from the point of measurement to the source or load. The equation for the voltage as a function of time along a transmission line with a matched load , so there is no reflected power, is where In a matched transmission line, the current is in phase with the voltage, and their ratio is the characteristic impedance Z 0 {\displaystyle Z_{\text{0}}} of

6700-516: The electromagnetic waves travel slower in the line than in free space, the wavelength of the wave in the transmission line λ {\displaystyle \lambda } is shorter than the free space wavelength by the factor kappa: λ = v p / f = κ c / f = κ λ 0 {\displaystyle \lambda =v_{\text{p}}/f=\kappa c/f=\kappa \lambda _{\text{0}}} . Therefore, more wavelengths fit in

6800-418: 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 the low-resistance antenna cannot effectively compete for power with

6900-451: The ground plane). A dipole antenna is resonant at frequencies at which its electrical length is a half wavelength ( λ / 2 , ϕ = 180 ∘ or π radians {\displaystyle \lambda /2,\phi =180^{\circ }\;{\text{or}}\;\pi \;{\text{radians}}} ) or a multiple of it. A monopole antenna is resonant at frequencies at which its electrical length

7000-412: 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. Electrical length In electrical engineering , electrical length is a dimensionless parameter equal to the physical length of an electrical conductor such as a cable or wire, divided by

7100-486: 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 the possibility of using single vertical masts without top loading. The antenna used for broadcasting through

7200-470: 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 the very low frequency band – such long waves that they are nearly unused at present. Because

7300-445: The length of the same wave in free space. In other words, the physical length of the antenna at resonance will be somewhat shorter than the resonant length in free space (one-half wavelength for a dipole, one-quarter wavelength for a monopole). As a rough generalization, for a typical dipole antenna , the physical resonant length is about 5% shorter than the free space resonant length. In many circumstances for practical reasons it

7400-406: The length-to-diameter ratio of the conductor. As the ratio of the diameter to wavelength increases, the capacitance increases, so the node occurs farther beyond the end, and the electrical length of the element increases. When the elements get too thick, the current waveform becomes significantly different from a sine wave, so the entire concept of electrical length is no longer applicable, and

7500-444: The line An important class of radio antenna is the thin element antenna in which the radiating elements are conductive wires or rods. These include monopole antennas and dipole antennas , as well as antennas based on them such as the whip antenna , T antenna , mast radiator , Yagi , log periodic , and turnstile antennas . These are resonant antennas, in which the radio frequency electric currents travel back and forth in

7600-530: The line are frequently given as dimensionless constants; relative permittivity : ϵ r {\displaystyle \epsilon _{\text{r}}} and relative permeability : μ r {\displaystyle \mu _{\text{r}}} equal to the ratio of these parameters compared to the universal constants ϵ 0 {\displaystyle \epsilon _{\text{0}}} and μ 0 {\displaystyle \mu _{\text{0}}} so

7700-428: The line or transmitter. Therefore, transmitting antennas are usually designed to be resonant at the transmitting frequency; and if they cannot be made the right length they are electrically lengthened or shortened to be resonant (see below). A thin-element antenna can be thought of as a transmission line with the conductors separated, so the near-field electric and magnetic fields extend further into space than in

7800-453: The line. In cables and transmission lines an electrical signal travels at a rate determined by the effective shunt capacitance C {\displaystyle C} and series inductance L {\displaystyle L} per unit length of the transmission line Some transmission lines consist only of bare metal conductors, if they are far away from other high permittivity materials their signals propagate at very close to

7900-593: 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;

8000-529: 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

8100-502: The phase velocity is So the velocity factor of the line is In many lines, for example twin lead , only a fraction of the space surrounding the line containing the fields is occupied by a solid dielectric. With only part of the electromagnetic field effected by the dielectric, there is less reduction of the wave velocity. In this case an effective permittivity ϵ eff {\displaystyle \epsilon _{\text{eff}}} can be calculated which if it filled all

8200-450: 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 a capacitive top-load. In a second paper the same year he showed that the amount of power radiated horizontally in ground waves reached

8300-406: The ratio of signal velocity in the line to the speed of light. Most transmission lines contain a dielectric material (insulator) filling some or all of the space in between the conductors. The permittivity ϵ {\displaystyle \epsilon } or dielectric constant of that material increases the distributed capacitance C {\displaystyle C} in

8400-541: 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

8500-423: The same radiation resistance and radiation pattern and fed with equal power will radiate the same power density in any direction if they have the same electrical length at the operating frequency; that is, if their lengths are in the same proportion as the wavelengths. This means the length of antenna required for a given antenna gain scales with the wavelength (inversely with the frequency), or equivalently

8600-445: The same term [REDACTED] This disambiguation page lists articles associated with the title Telecommunications Tower . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Telecommunications_Tower&oldid=1205602143 " Category : Disambiguation pages Hidden categories: Short description

8700-494: 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

8800-416: The solution of Maxwell's equations . These equations are mathematically difficult to solve in all generality, so approximate methods have been developed that apply to situations in which the electrical length of the apparatus is very short ( G ≪ 1 {\displaystyle G\ll 1} ) or very long ( G ≫ 1 {\displaystyle G\gg 1} ). Electromagnetics

8900-404: The source, load, connectors and switches begin to reflect the electromagnetic current waves back toward the source, creating bottlenecks so not all the power reaches the load. Ordinary wires act as antennas, radiating the power into space as radio waves, and in radio receivers can also pick up radio frequency interference (RFI). To mitigate these problems, at these frequencies transmission line

9000-411: The space around the line would give the same phase velocity. This is computed as a weighted average of the relative permittivity of free space, unity, and that of the dielectric: ϵ eff = ( 1 − F ) + F ϵ r {\displaystyle \epsilon _{\text{eff}}=(1-F)+F\epsilon _{\text{r}}} where the fill factor F expresses

9100-410: The speed of light In an electrical cable, for a cycle of the alternating current to move a given distance along the line, it takes time to charge the capacitance between the conductors, and the rate of change of the current is slowed by the series inductance of the wires. This determines the phase velocity v p {\displaystyle v_{p}} at which the wave moves along

9200-412: The speed of light, c {\displaystyle c} . In most transmission lines the material construction of the line slows the velocity of the signal so it travels at a reduced phase velocity where κ {\displaystyle \kappa } (kappa) is a dimensionless number between 0 and 1 called the velocity factor (VF), characteristic of the type of line, equal to

9300-536: The square of the electrical length, that is the ratio of physical length to wavelength, ( l / λ ) 2 {\displaystyle (l/\lambda )^{2}} . As a result, other resistances in the antenna, the ohmic resistance of metal antenna elements, the ground system if present, and the loading coil, dissipate an increasing fraction of transmitter power as heat. A monopole antenna with an electrical length below .05 λ {\displaystyle \lambda } or 18° has

9400-554: 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

9500-403: The wave has passed a given point and the wave repeats; during this time a point of constant phase on the wave has traveled a distance of so λ {\displaystyle \lambda } (Greek lambda ) is the wavelength of the wave along the conductor, the distance between successive crests of the wave. The electrical length G {\displaystyle G} of

9600-485: The wavelength, say less than one tenth of the wavelength ( l < λ / 10 {\displaystyle l<\lambda /10} ) it is called electrically short . In this case the voltage and current are approximately constant along the conductor, so it acts as a simple connector which transfers alternating current with negligible phase shift. In circuit theory the connecting wires between components are usually assumed to be electrically short, so

9700-404: 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

9800-425: 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

9900-405: 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

10000-410: 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 the 1930s it was found that the diamond shape of

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