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Radio masts and towers are, typically, tall structures designed to support Antenna s (also known as aerials in the UK) for Telecommunication s and Broadcasting , including Television . They are among the tallest man-made structures. Similar structures include Electricity Pylon s and towers for Wind Turbine s. Masts are sometimes named after the broadcasting organisations that use them, or after a nearby city or town. The Warsaw Radio Mast (Warszawa radio maszt) was the world's tallest supported structure on land, but it collapsed in 1991, leaving the KVLY/KTHI-TV Mast as the tallest. In the case of a Mast Radiator or radiating tower, the whole mast or tower is itself the transmitting antenna. MAST OR TOWER? The terms "mast" and "tower" are often used interchangeably. However:
(This article reflects the engineers' distinction between the two.) Masts tend to be cheaper to build, but because they require an extended area surrounding them to accommodate stay blocks, towers are more commonly used in cities where land is in short supply. There are a few borderline designs which are partly free-standing and partly guyed. For example:
MATERIALS Steel lattice The steel lattice is the most widespread form of construction. It provides great strength, low wind resistance and economy in the use of materials. Such structures are usually triangular or square in cross-section. When built as a stayed mast, usually the whole mast is parallel-sided. One exception is the Blaw-Knox type. When built as a tower, the structure may be parallel-sided or taper over part or all of its height. When constructed of several sections which taper exponentially with height, in the manner of the Eiffel Tower , the tower is said to be an Eiffelized one. The Crystal Palace tower in London is an example. Tubular steel Some masts are constructed out of steel tubes. In the UK, these were the subject of Collapses at the Emley Moor and Waltham TV stations in the 1960s. Reinforced concrete 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 is to be occupied by people. 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 Tower s. Concrete towers can form prestigious landmarks, such as the CN Tower in Toronto. As well as accommodating technical staff, these buildings may have public areas such as observation decks or restaurants. The Stuttgart TV Tower was the first tower in the world to be built in reinforced concrete. It was designed in 1956 by the local civil engineer, Fritz Leonhardt . Fibreglass Fibreglass poles are occasionally used for low-power non-directional beacons or medium-wave broadcast transmitters. Wood There are fewer wooden towers now than in the past. Many were built in the UK during World War II because of a shortage of steel. In Germany before World War II wooden towers were used at nearly all mediumwave transmission sites. These towers have been demolished, except for the Transmitter Gliwice . Ferryside Relay is an example of a TV relay transmitter using a wooden pole. OTHER TYPES OF ANTENNA SUPPORTS AND STRUCTURES Poles 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 Monopole s. Buildings In some cases, it is possible to install transmitting antennas on the roofs of tall buildings. In North America, for instance, there are transmitting antennas on the , particularly for portable radio services and low-power FM radio stations. Disguised cell-sites style mast in Durham , England , stands out as a feature in the street.]] Many people view bare cell phone towers as ugly and an intrusion into their neighbourhoods. Even though people increasingly depend upon cellular communications, they hate the bare towers popping up across scenic views. Many companies offer to 'hide' cellphone towers as trees, church towers, flag poles, water tanks, etc.http://www.ece.uncc.edu/research/clean_room/engr1202/celltowers.html There are many providers that offer these services as part of the normal tower installation and maintenance service. These are generally called "stealth towers" or "stealth installations". The level of detail and realism achieved by disguised cell phone towers is remarkably high; for example, such towers disguised as trees are nearly indistinguishable from the real thing, even for local wildlife (who additionally benefit from the faux florahttp://waynesword.palomar.edu/faketree.htm) Such towers also have the added advantage of being able to be placed in , and also 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.http://www.lightwatcher.com/culturejam/stealth_towers.html Mast radiators A mast radiator is a radio tower or mast in which the whole structure works as an antenna. It is used frequently as a transmitting antenna for Long or Medium Wave broadcasting. Structurally, the only difference is that a mast radiator may be supported on an insulator at its base. In the case of a tower, there will be one insulator supporting each leg. Technical details are outside the scope of this article and can be found on the Mast Radiator page. Telescopic, pump-up and tiltover towers 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. Telescopic masts consist of two or more concentric sections and come in two principal types:
Balloons and kites A tethered Balloon or 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 Martà broadcast a television program to Cuba by means of such a balloon. A captive balloon was also used for the British GQV experimental transmitter in 2003. Other special structures For two . The same technique was also used for the Criggion VLF Transmitter . 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 powerlines of the 10 kV level and are installed on similar pylons. DESIGN FEATURES Economic and aesthetic considerations
Masts for HF/shortwave antennas For transmissions in the Shortwave range, there is little to be gained by raising the antenna more than a few Wavelength s above ground level. Shortwave transmitters rarely use masts taller than about 100 metres. Access for riggers Because masts, towers and the antennas mounted on them require maintenance, access to 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. Aircraft warning lamps Taller structures are often equipped with Aircraft Warning Lamps , usually red in colour, to warn pilots of the structure's existence. In the past, ruggedized and under-run filament lamps were used to maximise the bulb life. Nowadays such lamps tend to use LED arrays. Wind-induced oscillations One problem with radio masts 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 a guyed radio mast is installed. The most well-known such construction is the Gerbrandy Tower in Lopik (the Netherlands ). Further towers of this building method can be found near Smilde (the Netherlands) and Waldenburg (Baden-Wuerttemberg, Germany ). CATASTROPHIC COLLAPSES Arranged by date Masts and towers can collapse due to natural disasters, such as storms and fires; from engineering defects; and from accidents or sabotage. Here is a list of such incidents by date: Arranged by height This table is arranged by height: SEE ALSO
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