Naval Radio Transmitter Facility Grindavik (NRTF Grindavik) is a transmission facility of the US Navy at Grindavík , Iceland, maintained by the N62 Division. It is active on shortwave and longwave under the callsign TFK on 37.5 kHz.
127-534: NRTF Grindavik originally had two towers for its longwave service – the west tower with a height of 243.8 metres (800 ft) and the east tower with a height of 182.9 metres (600 ft) – which were, when built, the tallest man-made objects in Iceland. In 1983, the east tower was replaced by a new tower of the same height. The west tower was replaced by a new 304.8-metre (1,000 ft) guyed mast and 2,500-square-foot (230 m) helix house , now
254-452: A ground plane to approximate the effect of being mounted on the Earth's surface. More complex antennas increase the directivity of the antenna. Additional elements in the antenna structure, which need not be directly connected to the receiver or transmitter, increase its directionality. Antenna "gain" describes the concentration of radiated power into a particular solid angle of space. "Gain"
381-569: 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
508-426: A "broadside array" (directional normal to a line connecting the elements) or as an "end-fire array" (directional along the line connecting the elements). Antenna arrays may employ any basic (omnidirectional or weakly directional) antenna type, such as dipole, loop or slot antennas. These elements are often identical. Log-periodic and frequency-independent antennas employ self-similarity in order to be operational over
635-405: A boom; the boom is only for support and not involved electrically. Only one of the elements is electrically connected to the transmitter or receiver, while the remaining elements are passive. The Yagi produces a fairly large gain (depending on the number of passive elements) and is widely used as a directional antenna with an antenna rotor to control the direction of its beam. It suffers from having
762-405: A current of 1 Ampere will require 63 Volts, and the antenna will radiate 63 Watts (ignoring losses) of radio frequency power. Now consider the case when the antenna is fed a signal with a wavelength of 1.25 m; in this case the current induced by the signal would arrive at the antenna's feedpoint out-of-phase with the signal, causing the net current to drop while the voltage remains
889-463: A current will reflect when there are changes in the electrical properties of the material. In order to efficiently transfer the received signal into the transmission line, it is important that the transmission line has the same impedance as its connection point on the antenna, otherwise some of the signal will be reflected backwards into the body of the antenna; likewise part of the transmitter's signal power will be reflected back to transmitter, if there
1016-495: A fashion are known to be harmonically operated . Resonant antennas usually use a linear conductor (or element ), or pair of such elements, each of which is about a quarter of the wavelength in length (an odd multiple of quarter wavelengths will also be resonant). Antennas that are required to be small compared to the wavelength sacrifice efficiency and cannot be very directional. Since wavelengths are so small at higher frequencies ( UHF , microwaves ) trading off performance to obtain
1143-400: A feed-point impedance that matches that of a transmission line; a matching network between antenna terminals and the transmission line will improve power transfer to the antenna. A non-adjustable matching network will most likely place further limits the usable bandwidth of the antenna system. It may be desirable to use tubular elements, instead of thin wires, to make an antenna; these will allow
1270-436: A flux of 1 pW / m (10 Watts per square meter) and an antenna has an effective area of 12 m , then the antenna would deliver 12 pW of RF power to the receiver (30 microvolts RMS at 75 ohms). Since the receiving antenna is not equally sensitive to signals received from all directions, the effective area is a function of the direction to the source. Due to reciprocity (discussed above)
1397-478: 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,
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#17327981062631524-403: A greater bandwidth. Or, several thin wires can be grouped in a cage to simulate a thicker element. This widens the bandwidth of the resonance. Amateur radio antennas that operate at several frequency bands which are widely separated from each other may connect elements resonant at those different frequencies in parallel. Most of the transmitter's power will flow into the resonant element while
1651-647: 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
1778-500: A half wavelength . The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of electromagnetic waves predicted by the 1867 electromagnetic theory of James Clerk Maxwell . Hertz placed dipole antennas at the focal point of parabolic reflectors for both transmitting and receiving. Starting in 1895, Guglielmo Marconi began development of antennas practical for long-distance, wireless telegraphy, for which he received
1905-450: A long Beverage antenna can have significant directivity. For non directional portable use, a short vertical antenna or small loop antenna works well, with the main design challenge being that of impedance matching . With a vertical antenna a loading coil at the base of the antenna may be employed to cancel the reactive component of impedance ; small loop antennas are tuned with parallel capacitors for this purpose. An antenna lead-in
2032-473: 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
2159-455: 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
2286-484: A new and improved helix house RF copper shielding design and installation method. All successes in the program improved on former designs and were partially influential in the previously-mentioned awards. The N62 Division is divided into three subdivision: N62A, Antenna Maintenance; N62B, longwave equipment and Integrated Submarine Automated Broadcast Processing System (ISABPS) Maintenance; and N62C, shortwave equipment and Ancillary Equipment Maintenance. In 2006, Grindavik
2413-421: A particular direction ( directional , or high-gain, or "beam" antennas). An antenna may include components not connected to the transmitter, parabolic reflectors , horns , or parasitic elements , which serve to direct the radio waves into a beam or other desired radiation pattern . Strong directivity and good efficiency when transmitting are hard to achieve with antennas with dimensions that are much smaller than
2540-497: A pole. In Italian a tent pole is known as l'antenna centrale , and the pole with the wire was simply called l'antenna . Until then wireless radiating transmitting and receiving elements were known simply as "terminals". Because of his prominence, Marconi's use of the word antenna spread among wireless researchers and enthusiasts, and later to the general public. Antenna may refer broadly to an entire assembly including support structure, enclosure (if any), etc., in addition to
2667-427: A proper resonant antenna at the trap frequency. At substantially higher or lower frequencies the trap allows the full length of the broken element to be employed, but with a resonant frequency shifted by the net reactance added by the trap. The bandwidth characteristics of a resonant antenna element can be characterized according to its Q where the resistance involved is the radiation resistance , which represents
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#17327981062632794-516: A pure resistance. Sometimes the resulting (lower) electrical resonant frequency of such a system (antenna plus matching network) is described using the concept of electrical length , so an antenna used at a lower frequency than its resonant frequency is called an electrically short antenna For example, at 30 MHz (10 m wavelength) a true resonant 1 / 4 wave monopole would be almost 2.5 meters long, and using an antenna only 1.5 meters tall would require
2921-440: A radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified . Antennas are essential components of all radio equipment. An antenna is an array of conductors ( elements ), electrically connected to the receiver or transmitter. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally ( omnidirectional antennas ), or preferentially in
3048-504: A rather limited bandwidth, restricting its use to certain applications. Rather than using one driven antenna element along with passive radiators, one can build an array antenna in which multiple elements are all driven by the transmitter through a system of power splitters and transmission lines in relative phases so as to concentrate the RF power in a single direction. What's more, a phased array can be made "steerable", that is, by changing
3175-443: A signal into the transmission line only when the source signal's frequency is close to that of the design frequency of the antenna, or one of the resonant multiples. This makes resonant antenna designs inherently narrow-band: Only useful for a small range of frequencies centered around the resonance(s). It is possible to use simple impedance matching techniques to allow the use of monopole or dipole antennas substantially shorter than
3302-440: A smaller physical size is usually not required. The quarter-wave elements imitate a series-resonant electrical element due to the standing wave present along the conductor. At the resonant frequency, the standing wave has a current peak and voltage node (minimum) at the feed. In electrical terms, this means that at that position, the element has minimum impedance magnitude , generating the maximum current for minimum voltage. This
3429-498: A standard resistive impedance needed for its optimum operation. The feed point location(s) is selected, and antenna elements electrically similar to tuner components may be incorporated in the antenna structure itself, to improve the match . It is a fundamental property of antennas that most of the electrical characteristics of an antenna, such as those described in the next section (e.g. gain , radiation pattern , impedance , bandwidth , resonant frequency and polarization ), are
3556-477: A total 360 degree phase change, returning it to the original signal. The current in the element thus adds to the current being created from the source at that instant. This process creates a standing wave in the conductor, with the maximum current at the feed. The ordinary half-wave dipole is probably the most widely used antenna design. This consists of two 1 / 4 wavelength elements arranged end-to-end, and lying along essentially
3683-403: 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
3810-585: 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
3937-473: A wide range of bandwidths . The most familiar example is the log-periodic dipole array which can be seen as a number (typically 10 to 20) of connected dipole elements with progressive lengths in an endfire array making it rather directional; it finds use especially as a rooftop antenna for television reception. On the other hand, a Yagi–Uda antenna (or simply "Yagi"), with a somewhat similar appearance, has only one dipole element with an electrical connection;
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4064-488: 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
4191-434: Is a change in electrical impedance where the feedline joins the antenna. This leads to the concept of impedance matching , the design of the overall system of antenna and transmission line so the impedance is as close as possible, thereby reducing these losses. Impedance matching is accomplished by a circuit called an antenna tuner or impedance matching network between the transmitter and antenna. The impedance match between
4318-417: Is a component which due to its shape and position functions to selectively delay or advance portions of the electromagnetic wavefront passing through it. The refractor alters the spatial characteristics of the wave on one side relative to the other side. It can, for instance, bring the wave to a focus or alter the wave front in other ways, generally in order to maximize the directivity of the antenna system. This
4445-490: Is a consequence of the reciprocity theorem of electromagnetics. Therefore, in discussions of antenna properties no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient. A necessary condition for the aforementioned reciprocity property is that the materials in the antenna and transmission medium are linear and reciprocal. Reciprocal (or bilateral ) means that
4572-410: Is adjusted according to the receiver tuning. On the other hand, log-periodic antennas are not resonant at any single frequency but can (in principle) be built to attain similar characteristics (including feedpoint impedance) over any frequency range. These are therefore commonly used (in the form of directional log-periodic dipole arrays ) as television antennas. Gain is a parameter which measures
4699-407: Is connected to a transmission line . The conductor, or element , is aligned with the electrical field of the desired signal, normally meaning it is perpendicular to the line from the antenna to the source (or receiver in the case of a broadcast antenna). The radio signal's electrical component induces a voltage in the conductor. This causes an electrical current to begin flowing in the direction of
4826-458: 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
4953-438: Is equal to 1. Therefore, the effective area A eff in terms of the gain G in a given direction is given by: For an antenna with an efficiency of less than 100%, both the effective area and gain are reduced by that same amount. Therefore, the above relationship between gain and effective area still holds. These are thus two different ways of expressing the same quantity. A eff is especially convenient when computing
5080-420: 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
5207-465: Is its radiation pattern . The frequency range or bandwidth over which an antenna functions well can be very wide (as in a log-periodic antenna) or narrow (as in a small loop antenna); outside this range the antenna impedance becomes a poor match to the transmission line and transmitter (or receiver). Use of the antenna well away from its design frequency affects its radiation pattern , reducing its directive gain. Generally an antenna will not have
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5334-578: 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
5461-412: Is perhaps an unfortunately chosen term, by comparison with amplifier "gain" which implies a net increase in power. In contrast, for antenna "gain", the power increased in the desired direction is at the expense of power reduced in undesired directions. Unlike amplifiers, antennas are electrically " passive " devices which conserve total power, and there is no increase in total power above that delivered from
5588-434: Is redirected toward the desired direction, increasing the antenna's gain by a factor of at least 2. Likewise, a corner reflector can insure that all of the antenna's power is concentrated in only one quadrant of space (or less) with a consequent increase in gain. Practically speaking, the reflector need not be a solid metal sheet, but can consist of a curtain of rods aligned with the antenna's polarization; this greatly reduces
5715-619: 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
5842-418: Is the transmission line , or feed line , which connects the antenna to a transmitter or receiver. The " antenna feed " may refer to all components connecting the antenna to the transmitter or receiver, such as an impedance matching network in addition to the transmission line. In a so-called "aperture antenna", such as a horn or parabolic dish, the "feed" may also refer to a basic radiating antenna embedded in
5969-404: Is the basis for most antenna designs, is a balanced component, with equal but opposite voltages and currents applied at its two terminals. The vertical antenna is a monopole antenna, not balanced with respect to ground. The ground (or any large conductive surface) plays the role of the second conductor of a monopole. Since monopole antennas rely on a conductive surface, they may be mounted with
6096-494: 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
6223-410: Is the ideal situation, because it produces the maximum output for the minimum input, producing the highest possible efficiency. Contrary to an ideal (lossless) series-resonant circuit, a finite resistance remains (corresponding to the relatively small voltage at the feed-point) due to the antenna's resistance to radiating , as well as any conventional electrical losses from producing heat. Recall that
6350-405: Is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver . In transmission , a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception , an antenna intercepts some of the power of
6477-412: 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
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#17327981062636604-416: Is the radio equivalent of an optical lens . An antenna coupling network is a passive network (generally a combination of inductive and capacitive circuit elements) used for impedance matching in between the antenna and the transmitter or receiver. This may be used to minimize losses on the feed line, by reducing transmission line's standing wave ratio , and to present the transmitter or receiver with
6731-511: 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
6858-448: The 1 / 4 or 1 / 2 wave , respectively, at which they are resonant. As these antennas are made shorter (for a given frequency) their impedance becomes dominated by a series capacitive (negative) reactance; by adding an appropriate size " loading coil " – a series inductance with equal and opposite (positive) reactance – the antenna's capacitive reactance may be cancelled leaving only
6985-539: 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
7112-405: The lens antenna . The antenna's power gain (or simply "gain") also takes into account the antenna's efficiency, and is often the primary figure of merit. Antennas are characterized by a number of performance measures which a user would be concerned with in selecting or designing an antenna for a particular application. A plot of the directional characteristics in the space surrounding the antenna
7239-403: The resonance principle. This relies on the behaviour of moving electrons, which reflect off surfaces where the dielectric constant changes, in a fashion similar to the way light reflects when optical properties change. In these designs, the reflective surface is created by the end of a conductor, normally a thin metal wire or rod, which in the simplest case has a feed point at one end where it
7366-435: 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
7493-596: 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
7620-425: 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
7747-509: The 1909 Nobel Prize in physics . The words antenna and aerial are used interchangeably. Occasionally the equivalent term "aerial" is used to specifically mean an elevated horizontal wire antenna. The origin of the word antenna relative to wireless apparatus is attributed to Italian radio pioneer Guglielmo Marconi . In the summer of 1895, Marconi began testing his wireless system outdoors on his father's estate near Bologna and soon began to experiment with long wire "aerials" suspended from
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#17327981062637874-411: 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
8001-638: 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
8128-523: 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
8255-418: 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
8382-624: The actions necessary to procure such a coil, while the COMSTA CO, CAPT Ralph L Spaulding, a graduate of the Naval Post Graduate School in Communications Engineering, designed a temporary coil with the appropriate characteristics, and the crew at Grindavik built it. The completed coil was about 6 ft long and 2 ft in diameter, with dry walnut lumber used to make the coil form. The completed coil
8509-418: The actual RF current-carrying components. A receiving antenna may include not only the passive metal receiving elements, but also an integrated preamplifier or mixer , especially at and above microwave frequencies. Antennas are required by any radio receiver or transmitter to couple its electrical connection to the electromagnetic field. Radio waves are electromagnetic waves which carry signals through
8636-467: The addition of a loading coil. Then it may be said that the coil has lengthened the antenna to achieve an electrical length of 2.5 meters. However, the resulting resistive impedance achieved will be quite a bit lower than that of a true 1 / 4 wave (resonant) monopole, often requiring further impedance matching (a transformer) to the desired transmission line. For ever shorter antennas (requiring greater "electrical lengthening")
8763-551: The air (or through space) at the speed of light with almost no transmission loss . Antennas can be classified as omnidirectional , radiating energy approximately equally in all horizontal directions, or directional , where radio waves are concentrated in some direction(s). A so-called beam antenna is unidirectional, designed for maximum response in the direction of the other station, whereas many other antennas are intended to accommodate stations in various directions but are not truly omnidirectional. Since antennas obey reciprocity
8890-402: The antenna consisting of a thin conductor. Antennas for use over much broader frequency ranges are achieved using further techniques. Adjustment of a matching network can, in principle, allow for any antenna to be matched at any frequency. Thus the small loop antenna built into most AM broadcast (medium wave) receivers has a very narrow bandwidth, but is tuned using a parallel capacitance which
9017-474: The antenna to the power radiated by a half-wave dipole antenna I dipole {\displaystyle I_{\text{dipole}}} ; these units are called decibels-dipole (dBd) Since the gain of a half-wave dipole is 2.15 dBi and the logarithm of a product is additive, the gain in dBi is just 2.15 decibels greater than the gain in dBd High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully at
9144-432: The areas around were placed under a state of emergency and evacuated due to the threat of a volcanic eruption. Radio tower 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
9271-402: The broadcasting organizations that originally built them or currently use them. 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
9398-427: The broadside direction. If higher gain is needed one cannot simply make the antenna larger. Due to the constraint on the effective area of a receiving antenna detailed below , one sees that for an already-efficient antenna design, the only way to increase gain (effective area) is by reducing the antenna's gain in another direction. If a half-wave dipole is not connected to an external circuit but rather shorted out at
9525-574: 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
9652-524: 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
9779-470: The degree of directivity of the antenna's radiation pattern . A high-gain antenna will radiate most of its power in a particular direction, while a low-gain antenna will radiate over a wide angle. The antenna gain , or power gain of an antenna is defined as the ratio of the intensity (power per unit surface area) I {\displaystyle I} radiated by the antenna in the direction of its maximum output, at an arbitrary distance, divided by
9906-557: The design operating frequency, f o , and antennas are normally designed to be this size. However, feeding that element with 3 f o (whose wavelength is 1 / 3 that of f o ) will also lead to a standing wave pattern. Thus, an antenna element is also resonant when its length is 3 / 4 of a wavelength. This is true for all odd multiples of 1 / 4 wavelength. This allows some flexibility of design in terms of antenna lengths and feed points. Antennas used in such
10033-427: The emission of energy from the resonant antenna to free space. The Q of a narrow band antenna can be as high as 15. On the other hand, the reactance at the same off-resonant frequency of one using thick elements is much less, consequently resulting in a Q as low as 5. These two antennas may perform equivalently at the resonant frequency, but the second antenna will perform over a bandwidth 3 times as wide as
10160-418: The entire system of reflecting elements (normally at the focus of the parabolic dish or at the throat of a horn) which could be considered the one active element in that antenna system. A microwave antenna may also be fed directly from a waveguide in place of a (conductive) transmission line . An antenna counterpoise , or ground plane , is a structure of conductive material which improves or substitutes for
10287-418: 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
10414-526: The feedline and antenna is measured by a parameter called the standing wave ratio (SWR) on the feedline. Consider a half-wave dipole designed to work with signals with wavelength 1 m, meaning the antenna would be approximately 50 cm from tip to tip. If the element has a length-to-diameter ratio of 1000, it will have an inherent impedance of about 63 ohms resistive. Using the appropriate transmission wire or balun, we match that resistance to ensure minimum signal reflection. Feeding that antenna with
10541-430: The feedpoint, then it becomes a resonant half-wave element which efficiently produces a standing wave in response to an impinging radio wave. Because there is no load to absorb that power, it retransmits all of that power, possibly with a phase shift which is critically dependent on the element's exact length. Thus such a conductor can be arranged in order to transmit a second copy of a transmitter's signal in order to affect
10668-446: The gain of an antenna used for transmitting must be proportional to its effective area when used for receiving. Consider an antenna with no loss , that is, one whose electrical efficiency is 100%. It can be shown that its effective area averaged over all directions must be equal to λ /4π , the wavelength squared divided by 4π . Gain is defined such that the average gain over all directions for an antenna with 100% electrical efficiency
10795-439: The geometrical divergence of the transmitted wave. For a given incoming flux, the power acquired by a receiving antenna is proportional to its effective area . This parameter compares the amount of power captured by a receiving antenna in comparison to the flux of an incoming wave (measured in terms of the signal's power density in watts per square metre). A half-wave dipole has an effective area of about 0.13 λ seen from
10922-474: The ground. It may be connected to or insulated from the natural ground. In a monopole antenna, this aids in the function of the natural ground, particularly where variations (or limitations) of the characteristics of the natural ground interfere with its proper function. Such a structure is normally connected to the return connection of an unbalanced transmission line such as the shield of a coaxial cable . An electromagnetic wave refractor in some aperture antennas
11049-493: 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. Antenna (radio) In radio engineering , an antenna ( American English ) or aerial ( British English ) is an electronic device that converts an alternating electric current into radio waves (transmitting), or radio waves into an electric current (receiving). It
11176-486: 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
11303-470: 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
11430-413: The increase in signal power due to an amplifying device placed at the front-end of the system, such as a low-noise amplifier . The effective area or effective aperture of a receiving antenna expresses the portion of the power of a passing electromagnetic wave which the antenna delivers to its terminals, expressed in terms of an equivalent area. For instance, if a radio wave passing a given location has
11557-405: The intensity I iso {\displaystyle I_{\text{iso}}} radiated at the same distance by a hypothetical isotropic antenna which radiates equal power in all directions. This dimensionless ratio is usually expressed logarithmically in decibels , these units are called decibels-isotropic (dBi) A second unit used to measure gain is the ratio of the power radiated by
11684-417: The loading coil, relative to the decreased radiation resistance, entail a reduced electrical efficiency , which can be of great concern for a transmitting antenna, but bandwidth is the major factor that sets the size of antennas at 1 MHz and lower frequencies. The radiant flux as a function of the distance from the transmitting antenna varies according to the inverse-square law , since that describes
11811-435: The log-periodic principle it obtains the unique property of maintaining its performance characteristics (gain and impedance) over a very large bandwidth. When a radio wave hits a large conducting sheet it is reflected (with the phase of the electric field reversed) just as a mirror reflects light. Placing such a reflector behind an otherwise non-directional antenna will insure that the power that would have gone in its direction
11938-553: The material has the same response to an electric current or magnetic field in one direction, as it has to the field or current in the opposite direction. Most materials used in antennas meet these conditions, but some microwave antennas use high-tech components such as isolators and circulators , made of nonreciprocal materials such as ferrite . These can be used to give the antenna a different behavior on receiving than it has on transmitting, which can be useful in applications like radar . The majority of antenna designs are based on
12065-593: 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;
12192-653: The other parasitic elements interact with the electromagnetic field in order to realize a highly directional antenna but with a narrow bandwidth. Even greater directionality can be obtained using aperture antennas such as the parabolic reflector or horn antenna . Since high directivity in an antenna depends on it being large compared to the wavelength, highly directional antennas (thus with high antenna gain ) become more practical at higher frequencies ( UHF and above). At low frequencies (such as AM broadcast ), arrays of vertical towers are used to achieve directionality and they will occupy large areas of land. For reception,
12319-409: The other antenna. An example of a high-gain antenna is a parabolic dish such as a satellite television antenna. Low-gain antennas have shorter range, but the orientation of the antenna is relatively unimportant. An example of a low-gain antenna is the whip antenna found on portable radios and cordless phones . Antenna gain should not be confused with amplifier gain , a separate parameter measuring
12446-464: The other side connected to ground or an equivalent ground plane (or counterpoise ). Monopoles, which are one-half the size of a dipole, are common for long-wavelength radio signals where a dipole would be impractically large. Another common design is the folded dipole which consists of two (or more) half-wave dipoles placed side by side and connected at their ends but only one of which is driven. The standing wave forms with this desired pattern at
12573-401: The others present a high impedance. Another solution uses traps , parallel resonant circuits which are strategically placed in breaks created in long antenna elements. When used at the trap's particular resonant frequency the trap presents a very high impedance (parallel resonance) effectively truncating the element at the location of the trap; if positioned correctly, the truncated element makes
12700-529: 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
12827-465: The phases applied to each element the radiation pattern can be shifted without physically moving the antenna elements. Another common array antenna is the log-periodic dipole array which has an appearance similar to the Yagi (with a number of parallel elements along a boom) but is totally dissimilar in operation as all elements are connected electrically to the adjacent element with a phase reversal; using
12954-399: The power source (the transmitter), only improved distribution of that fixed total. A phased array consists of two or more simple antennas which are connected together through an electrical network. This often involves a number of parallel dipole antennas with a certain spacing. Depending on the relative phase introduced by the network, the same combination of dipole antennas can operate as
13081-488: The power that would be received by an antenna of a specified gain, as illustrated by the above example. The radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles in the far field. It is typically represented by a three-dimensional graph, or polar plots of the horizontal and vertical cross sections. The pattern of an ideal isotropic antenna , which radiates equally in all directions, would look like
13208-444: The radiation pattern (and feedpoint impedance) of the element electrically connected to the transmitter. Antenna elements used in this way are known as passive radiators . A Yagi–Uda array uses passive elements to greatly increase gain in one direction (at the expense of other directions). A number of parallel approximately half-wave elements (of very specific lengths) are situated parallel to each other, at specific positions, along
13335-450: 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
13462-421: The radiation resistance plummets (approximately according to the square of the antenna length), so that the mismatch due to a net reactance away from the electrical resonance worsens. Or one could as well say that the equivalent resonant circuit of the antenna system has a higher Q factor and thus a reduced bandwidth, which can even become inadequate for the transmitted signal's spectrum. Resistive losses due to
13589-441: The reflector's weight and wind load . Specular reflection of radio waves is also employed in a parabolic reflector antenna, in which a curved reflecting surface effects focussing of an incoming wave toward a so-called feed antenna ; this results in an antenna system with an effective area comparable to the size of the reflector itself. Other concepts from geometrical optics are also employed in antenna technology, such as with
13716-541: 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
13843-411: The same radiation pattern applies to transmission as well as reception of radio waves. A hypothetical antenna that radiates equally in all directions (vertical as well as all horizontal angles) is called an isotropic radiator ; however, these cannot exist in practice nor would they be particularly desired. For most terrestrial communications, rather, there is an advantage in reducing radiation toward
13970-458: The same axis (or collinear ), each feeding one side of a two-conductor transmission wire. The physical arrangement of the two elements places them 180 degrees out of phase, which means that at any given instant one of the elements is driving current into the transmission line while the other is pulling it out. The monopole antenna is essentially one half of the half-wave dipole, a single 1 / 4 wavelength element with
14097-425: The same whether the antenna is transmitting or receiving . For example, the "receiving pattern" (sensitivity to incoming signals as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator, even though the current and voltage distributions on the antenna itself are different for receiving and sending. This
14224-432: The same. Electrically this appears to be a very high impedance. The antenna and transmission line no longer have the same impedance, and the signal will be reflected back into the antenna, reducing output. This could be addressed by changing the matching system between the antenna and transmission line, but that solution only works well at the new design frequency. The result is that the resonant antenna will efficiently feed
14351-540: The second tallest structure in Iceland , after the Hellissandur longwave radio mast . Before all these improvements were made, in about 1976, the station was tasked to operate its 600 feet (180 m) tower on a very low frequency, much lower than any frequency on which it had ever before been operated. There was some concern about running the shorter tower on such a low frequency, but the 800 feet (240 m) tower
14478-469: The signal's instantaneous field. When the resulting current reaches the end of the conductor, it reflects, which is equivalent to a 180 degree change in phase. If the conductor is 1 / 4 of a wavelength long, current from the feed point will undergo 90 degree phase change by the time it reaches the end of the conductor, reflect through 180 degrees, and then another 90 degrees as it travels back. That means it has undergone
14605-472: The sky or ground in favor of horizontal direction(s). A dipole antenna oriented horizontally sends no energy in the direction of the conductor – this is called the antenna null – but is usable in most other directions. A number of such dipole elements can be combined into an antenna array such as the Yagi–Uda in order to favor a single horizontal direction, thus termed a beam antenna. The dipole antenna, which
14732-494: 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
14859-554: 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
14986-404: 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
15113-405: Was a runner up in the same category in 1997. The new taller antenna and helix house were structurally designed by Donald W. Anderson, PE who additionally managed the design and construction programs while employed at Naval Facilities Engineering Command (NAVFAC), Atlantic. The final design incorporated many new and improved items which required integrated electronic and structural designs, including
15240-428: Was already tasked with a higher priority mission. When the 600 feet (180 m) tower and its helix house were tuned to the desired frequency and the transmitter power output was increased to the required level, the biggest coil in the helix house arced internally and destroyed itself. A limited number of replacement coils were available in the supply system and were, in turn, installed and similarly destroyed. The problem
15367-425: 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
15494-405: 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
15621-484: Was listed as transmitting AFRTS on 7590 kHz and 9980 kHz USB. In the 2014 edition of Radio Navigational Aids, Publication No. 117, NRTF Grindavik was listed as broadcasting NAVTEX on 490 kHz and 518 kHz using callsign TFK. In November 2019, the installation formally had a Director appointed to head it, as U.S. Naval Computer and Telecommunications Area Masters Station Atlantic Detachment Grindavik, Iceland (NCTAMS LANT DET GRINDAVIK IC). In November 2023, Grindavik and
15748-410: 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
15875-430: Was set on a wooden chair in the helix house, connected to the original chain of coils (needed to make minor changes in inductance to tune the antenna), and the output port of the helix house. This arrangement worked well, except that an occasional arc between the output port and the copper coated internal wall of the helix house would trip the transmitter off the air. The new coil was received and installed sometime later. It
16002-566: Was significantly larger than the wooden coil, designed to just fit through the helix house door. This configuration worked for some time, until an arc occurred at the large feed-through insulator at the output port and destroyed the insulator. This put the antenna down until significant helix house modifications could be made. NRTF Grindavik was the 1999 winner of the Defense Information Systems Agency (DISA) Outstanding Transmission Facility Award (Category II), and
16129-439: Was that the low frequency and the corresponding high reactance needed to resonate the antenna resulted in an abnormally high voltage at the output of the helix house, causing the last and largest coil to arc internally and destroy itself. The solution to the problem was to design and install a different final coil in the helix house with the inductance and physical shape needed to supply the needed reactance without arcing. HQ started
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