Transmitter station
Encyclopedia
Transmitter station refers to terrestrial infrastructure for transmitting radio frequency
signals. The station maybe used for, wireless communication, broadcasting
, microwave link, mobile telephone etc.
consideration. In case of microwave link chains, stations should be in observable ranges of each other. (see Earth bulge
) Computer programmes for the terrain profile and abacs are used in addition to on site observations. Avoidance of industrial noise is also taken into consideration. Another parameter may be the government regulations concerning public health requiring a minimum distance to human habitation. The distance depends on the power
and the frequency
of the transmitting signal. Low power stations may be in cities; higher power stations are always in rural areas. Most of the stations (especially high frequency stations) are at high altitudes. So, both the minimum distance regulations and the line of sight creteria are met.
They all have masts or towers
to install antenna
systems. In most cases the mast is a passive structure to support the antennas. But in low frequency stations (such as AM radio
) the mast itself may be the active antenna element. In such cases, the mast is isolated from the ground.(See Monopole antenna
). If the mast itself is an active antenna element the ground can be covered by a mesh of wires or metal elements to create a reflecting ground. Most of the stations also have facility to receive microwave signals from a microwave link or a telecommunications satellite, (TVRO or RRO).
Most stations use mains electricity; but they also have standby generators or solar energy panels in case of failure.
If the voltage of the mains fluctuates, a high power voltage regulator
may be used.
for personal safety against electrical shocks. On the masts and roofs, lightning rod
s should be used. In most cases, it is desirable to connect the rods to each other to form a simple Faraday cage
. But in high altitude stations, the ground is usually rocky and finding an appropriate point for the grounding bus may be impossible. In such cases, very long grounding connectors may be used to find a good ground at lower altitudes.
equipment. But in older stations and stations which require continuous attendance, operation personnel may be employed. In such stations, personnel work on shifts and transportation may also be a parameter of station design. In such cases, accommodation, catering and health problems also play a part in station management. Especially in high altitude stations, snowmobile
s must be used during winter.
radio transmitters are high-power equipment. Because of the relatively low frequency they use, they don't need to be located in high places. They may broadcast in LW
(long wave), MW (medium wave) or SW
(short wave). Since SW stations are assigned for very long distance communication (via reflections from atmospheric layers) they are usually employed for multi-language international services and there may be many SW transmitters in the same station.
TV and FM
(frequency modulated ) radio transmitter stations as well as transposer
stations are almost always built on top of hills. A single station may have many transmitters both for TV and FM . In rare cases each transmitter has an antenna system. But in stations where many transmitters are used, this is not always possible, so the outputs of transmitters transmitting in the same frequency band are combined by a diplexer
and applied to a single antenna system. (i.e. VHF 1
, VHF 2, VHF 3
, UHF). If two or more antenna systems have to be used, higher frequency antennas are mounted higher on the antenna mast. (The sequence of antenna systems on a typical TV-FM station may be from bottom to top; VHF-2, VHF-3 and UHF.)
Microwave stations are also high altitude stations. Although high altitude is desirable also in GSM, the operators may use low power intracity stations for areas of high population density.
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
signals. The station maybe used for, wireless communication, broadcasting
Broadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
, microwave link, mobile telephone etc.
Choice of location
Location may be chosen to fit the coverage area and in most cases line of sightLine-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
consideration. In case of microwave link chains, stations should be in observable ranges of each other. (see Earth bulge
Earth bulge
Earth bulge is a term used in telecommunications. It refers to the circular segment of earth profile which blocks off long distance communications.- Distance to horizon :...
) Computer programmes for the terrain profile and abacs are used in addition to on site observations. Avoidance of industrial noise is also taken into consideration. Another parameter may be the government regulations concerning public health requiring a minimum distance to human habitation. The distance depends on the power
Effective radiated power
In radio telecommunications, effective radiated power or equivalent radiated power is a standardized theoretical measurement of radio frequency energy using the SI unit watts, and is determined by subtracting system losses and adding system gains...
and the frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
of the transmitting signal. Low power stations may be in cities; higher power stations are always in rural areas. Most of the stations (especially high frequency stations) are at high altitudes. So, both the minimum distance regulations and the line of sight creteria are met.
Buildings and antenna masts
Stations may be housed in several buildings or a single building. In some cases the station is nothing but a small container.They all have masts or towers
Radio masts and towers
Radio masts and towers are, typically, tall structures designed to support antennas for telecommunications and broadcasting, including television. They are among the tallest man-made structures...
to install antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
systems. In most cases the mast is a passive structure to support the antennas. But in low frequency stations (such as AM radio
AM broadcasting
AM broadcasting is the process of radio broadcasting using amplitude modulation. AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is carried out in the medium wave band world wide, and on long wave and short wave...
) the mast itself may be the active antenna element. In such cases, the mast is isolated from the ground.(See Monopole antenna
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 voltage is taken,...
). If the mast itself is an active antenna element the ground can be covered by a mesh of wires or metal elements to create a reflecting ground. Most of the stations also have facility to receive microwave signals from a microwave link or a telecommunications satellite, (TVRO or RRO).
Most stations use mains electricity; but they also have standby generators or solar energy panels in case of failure.
If the voltage of the mains fluctuates, a high power voltage regulator
Voltage regulator
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components...
may be used.
Grounding
Like all industrial sites, the buildings, the antenna masts, the generators, and the transmitting equipment of the stations should be groundedGround (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
for personal safety against electrical shocks. On the masts and roofs, lightning rod
Lightning rod
A lightning rod or lightning conductor is a metal rod or conductor mounted on top of a building and electrically connected to the ground through a wire, to protect the building in the event of lightning...
s should be used. In most cases, it is desirable to connect the rods to each other to form a simple Faraday cage
Faraday cage
A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks out external static and non-static electric fields...
. But in high altitude stations, the ground is usually rocky and finding an appropriate point for the grounding bus may be impossible. In such cases, very long grounding connectors may be used to find a good ground at lower altitudes.
Exploitation
Transmitters may be operated by government (civil or military) or private industry. At the present stage of technical development most of stations are unattended and controlled by remote controlRemote control
A remote control is a component of an electronics device, most commonly a television set, used for operating the television device wirelessly from a short line-of-sight distance.The remote control is usually contracted to remote...
equipment. But in older stations and stations which require continuous attendance, operation personnel may be employed. In such stations, personnel work on shifts and transportation may also be a parameter of station design. In such cases, accommodation, catering and health problems also play a part in station management. Especially in high altitude stations, snowmobile
Snowmobile
A snowmobile, also known in some places as a snowmachine, or sled,is a land vehicle for winter travel on snow. Designed to be operated on snow and ice, they require no road or trail. Design variations enable some machines to operate in deep snow or forests; most are used on open terrain, including...
s must be used during winter.
Transmitting equipment
Most AMAM broadcasting
AM broadcasting is the process of radio broadcasting using amplitude modulation. AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is carried out in the medium wave band world wide, and on long wave and short wave...
radio transmitters are high-power equipment. Because of the relatively low frequency they use, they don't need to be located in high places. They may broadcast in LW
LW
- Entertainment :* LightWave 3D Software* Life's Work, a 1990s American situation comedy* Lethal Weapon, a 1987 film* LimeWire* Long wave* Lovewrecked- Services :* Luftwaffe* Lutheran Worship* Lw, the former symbol of lawrencium, now Lr....
(long wave), MW (medium wave) or SW
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
(short wave). Since SW stations are assigned for very long distance communication (via reflections from atmospheric layers) they are usually employed for multi-language international services and there may be many SW transmitters in the same station.
TV and FM
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
(frequency modulated ) radio transmitter stations as well as transposer
Transposer
In broadcasting, a transposer is a device in the service area of a transmitter which rebroadcasts signals to the receivers which can’t properly receive the signals of the transmitter because of a physical obstruction . A transposer receives the signals of the transmitter and rebroadcasts the...
stations are almost always built on top of hills. A single station may have many transmitters both for TV and FM . In rare cases each transmitter has an antenna system. But in stations where many transmitters are used, this is not always possible, so the outputs of transmitters transmitting in the same frequency band are combined by a diplexer
Diplexer
A diplexer is a passive device that implements frequency domain multiplexing. Two ports are multiplexed onto a third port . The signals on ports L and H occupy disjoint frequency bands...
and applied to a single antenna system. (i.e. VHF 1
Band I
Band I is the name of a radio frequency range within the very high frequency part of the electromagnetic spectrum.Band I ranges from 47 to 88 MHz, and it is primarily used for radio and television broadcasting....
, VHF 2, VHF 3
Band III
Band III is the name of a radio frequency range within the very high frequency part of the electromagnetic spectrum.Band III ranges from 174 to 230 MHz, and it is primarily used for radio and television broadcasting...
, UHF). If two or more antenna systems have to be used, higher frequency antennas are mounted higher on the antenna mast. (The sequence of antenna systems on a typical TV-FM station may be from bottom to top; VHF-2, VHF-3 and UHF.)
Microwave stations are also high altitude stations. Although high altitude is desirable also in GSM, the operators may use low power intracity stations for areas of high population density.