Cage aerial

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A cage antenna (British cage aerial) is a radio antenna that consists of the top portion of a tower or mast and of several parallel wires, which are radially arranged around the lower part of the mast. One advantage of the cage aerial is that the supporting tower can be grounded, allowing it to be used for other radio services, such as a support for VHF or UHF antennas. A grounded tower also simplifies the installation of aircraft warning lamps. Cage aerials have been built in different variants for broadcasting stations in the longwave and mediumwave bands.

Longwave radio broadcast band

In radio, longwave, long wave or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with wavelengths longer than what was originally called the medium-wave broadcasting band. The term is historic, dating from the early 20th century, when the radio spectrum was considered to consist of longwave (LW), medium-wave (MW), and short-wave (SW) radio bands. Most modern radio systems and devices use wavelengths which would then have been considered 'ultra-short'.

The cage is electrically one-quarter of the operating wavelength. It is connected to the mast at its upper end. That way it isolates the lower part of the mast (λ/4 stub) and makes the upper part of the mast the radiator. Very often the typical height of such an antenna is no problem as the height of the mast is selected for the TV or FM antennas on top.

Example: At 1000 kHz the wavelength is 300 m. Therefore, the minimum length of the cage antenna is a bit more than 150 m; 75 m for the radiator, 75 m for the cage and a few metres to make the lower end of the cage inaccessible from the ground, as the lower end of the cage carries a very high RF voltage. This type of antenna is known in America as a "folded unipole", which has been extensively studied by John H. Mullaney.

Folded unipole antenna

The folded unipole antenna is a type of monopole antenna; it consists of a vertical metal rod or mast mounted over a conductive surface called a ground plane. The mast is surrounded by a "skirt" of vertical wires electrically attached to the top of the mast. The skirt wires are connected by a metal ring at the bottom and the feed line is connected between the bottom of the wires and ground.


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Medium wave

Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. For Europe the MW band ranges from 526.5 kHz to 1606.5 kHz, using channels spaced every 9 kHz, and in North America an extended MW broadcast band ranges from 525 kHz to 1705 kHz, using 10 kHz spaced channels. The term is a historic one, dating from the early 20th century, when the radio spectrum was divided on the basis of the wavelength of the waves into long wave (LW), medium wave, and short wave (SW) radio bands.

Low frequency or LF is the ITU designation for radio frequencies (RF) in the range of 30 kilohertz (kHz) to 300 kHz. As its wavelengths range from ten kilometres to one kilometre, respectively, it is also known as the kilometre band or kilometre wave.

Warsaw radio mast tower

The Warsaw Radio Mast was the world's tallest structure from 1974 until its collapse on 8 August 1991. It was the second tallest structure ever built, being surpassed as tallest by the Burj Khalifa, completed in 2010.

Whip antenna

A whip antenna is an antenna consisting of a straight flexible wire or rod. The bottom end of the whip is connected to the radio receiver or transmitter. The antenna is designed to be flexible so that it does not break easily, and the name is derived from the whip-like motion that it exhibits when disturbed. Whip antennas for portable radios are often made of a series of interlocking telescoping metal tubes, so they can be retracted when not in use. Longer ones, made for mounting on vehicles and structures, are made of a flexible fiberglass rod around a wire core and can be up to 35 ft long. The length of the whip antenna is determined by the wavelength of the radio waves it is used with. The most common type is the quarter-wave whip, which is approximately one-quarter of a wavelength long. Whips are the most common type of monopole antenna, and are used in the higher frequency HF, VHF and UHF radio bands. They are widely used as the antennas for hand-held radios, cordless phones, walkie-talkies, FM radios, boom boxes, and Wi-Fi enabled devices, and are attached to vehicles as the antennas for car radios and two-way radios for wheeled vehicles and for aircraft. Larger versions mounted on roofs and radio masts are used as base station antennas for police, fire, ambulance, taxi, and other vehicle dispatchers.

Gerbrandy Tower

The Gerbrandy Tower is a tower in IJsselstein, the Netherlands. It was built in 1961.

Guyed mast tall thin vertical structure that receives support from guy lines

A guyed mast is a tall thin vertical structure that depends on guy lines for stability. The mast itself has the compressive strength to support its own weight, but does not have the shear strength to stand unsupported, and requires guy lines to resist lateral forces such as wind loads and keep it upright. Guy lines are diagonal tensioned cables attached to the ground, usually spaced at equal angles about the structure's base.

A guy-wire, guy-line, or guy-rope, also known as simply a guy, is a tensioned cable designed to add stability to a free-standing structure. They are used commonly in ship masts, radio masts, wind turbines, utility poles, fire service extension ladders used in church raises and tents. A thin vertical mast supported by guy wires is called a guyed mast. Structures that support antennas are frequently of a lattice construction and are called "towers". One end of the guy is attached to the structure, and the other is anchored to the ground at some distance from the mast or tower base. The tension in the diagonal guy-wire, combined with the compression and buckling strength of the structure, allows the structure to withstand lateral loads such as wind or the weight of cantilevered structures. They are installed radially, usually at equal angles about the structure, in trios and quads. As the tower leans a bit due to the wind force, the increased guy tension is resolved into a compression force in the tower or mast and a lateral force that resists the wind load. For example, antenna masts are often held up by three guy-wires at 120° angles. Structures with predictable lateral loads, such as electrical utility poles, may require only a single guy-wire to offset the lateral pull of the electrical wires, at a spot where the wires change direction.

Blaw-Knox tower

The Blaw-Knox company was a manufacturer of steel structures and construction equipment based in Pittsburgh, Pennsylvania. The company is today best known for its radio towers, most of which were constructed during the 1930s in the United States. Although Blaw-Knox built many kinds of towers, the term Blaw-Knox tower usually refers to the company's unusual "diamond cantilever" design, which is stabilized by guy wires attached only at the vertical center of the mast, where its cross-section is widest. A 1942 advertisement claims that 70% of all radio towers in the US at the time were built by Blaw-Knox.

Antenna height considerations

The Aspects for Antenna heights considerations are depending upon the wave range and economical reasons.

Radio masts and towers tall structure designed to support antennas

Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. There are two main types: guyed and self-supporting structures. They are among the tallest human-made structures. Masts are often named after the broadcasting organizations that originally built them or currently use them.

Mast radiator

A mast radiator is a radio mast or tower in which the entire structure functions as an antenna. This design, first used in radiotelegraphy stations in the early 1900s, is commonly used for transmitting antennas operating at low frequencies, in the VLF, LF and MF ranges, in particular those used for AM broadcasting. The metal mast is electrically connected to the transmitter. Its base is usually mounted on a nonconductive support to insulate it from the ground. A mast radiator is a form of monopole antenna.

T-antenna

A T-antenna, T-aerial, flat-top antenna, or top-hat antenna is a capacitively loaded monopole wire radio antenna used in the VLF, LF, MF and shortwave bands. T-antennas are widely used as transmitting antennas for amateur radio stations, long wave and medium wave broadcasting stations. They are also used as receiving antennas for shortwave listening.

Monopole antenna

A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the lower end of the monopole and the ground plane. One side of the antenna feedline is attached to the lower end of the monopole, and the other side is attached to the ground plane, which is often the Earth. This contrasts with a dipole antenna which consists of two identical rod conductors, with the signal from the transmitter applied between the two halves of the antenna.

Partially guyed tower tower structure

A partially guyed tower is a tower structure which consists of a free-standing basement, in most cases of concrete or of lattice steel with a guyed mast on the top. The anchor basements of the guyed mast can be on the top of the tower or on the ground.

Umbrella antenna

An umbrella antenna is a top-loaded electrically lengthened monopole antenna, consisting in most cases of a mast fed at the ground end, to which a number of radial wires are connected at the top, sloping downwards. They are used as transmitting antennas below 1 MHz, in the LF and particularly the VLF bands, at frequencies sufficiently low that it is impractical or infeasible to build a full size quarter-wave monopole antenna.

Golm transmitter was a medium wave broadcasting facility on the area of a former Reichsarbeitsdienst officer candidate school at Kuhforter Damm in Golm near Potsdam. It entered service in 1948 as the central broadcast transmitter for Brandenburg state. Until 1979 it used a wooden lattice tower of 98 m (322 ft) height with a horizontal wooden cross on its top as its antenna support. The ends of the beams of this cross were connected with wires. From the centre of each of these horizontal wires, a vertical wire was run down to the antenna tuner which was located in a building under the feet of the tower construction. The antenna of Golm transmitter consisted therefore of 4 T-antennas connected in parallel, forming an omnidirectional antenna with a natural wavelength of 528 m. The transmitter was built from second-hand parts obtained by dismantling a site in Reichenbach, Upper Lusatia. Test transmissions were undertaken on 16 April 1948, and from 1 May 1948 the facility operated on 564 kHz.

A shortwave broadband antenna is a radio antenna, that without adjustment, can be used for transmission of a shortwave radio channel chosen from greater part of the shortwave radio spectrum. Some shortwave broadband antennas can even be used on the whole shortwave radio spectrum (1.6-30 MHz) which consist of the upper part of medium frequency (1.6-3 MHz) and the whole of high frequency (3-30 MHz). A true shortwave broadband antenna will work continuously across most of, if not all of the shortwave spectrum with good radiation efficiency and minimal compromise of the radiation pattern.

Counterpoise (ground system)

In electronics and radio communication a counterpoise is a network of suspended horizontal wires or cables, used as a substitute for an earth (ground) connection in a radio antenna system. It is used with radio transmitters or receivers when a normal earth ground cannot be used because of high soil resistance or when an antenna is mounted above ground level, for example, on a building. It usually consists of a single wire or network of horizontal wires, parallel to the ground, suspended above the ground under the antenna, connected to the receiver or transmitter's "ground" wire. The counterpoise functions as one plate of a large capacitor, with the conductive layers of the earth acting as the other plate.

In radio systems, many different antenna types are used with specialized properties for particular applications. Antennas can be classified in various ways. The list below groups together antennas under common operating principles, following the way antennas are classified in many engineering textbooks.