Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Transmitter shopping experience:

1. Compare - without doubt the biggest advantage that the Transmitter offers shoppers today is the ability to compare thousands of Transmitter at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about

3. Testimonials - don't know anybody that has bought a Transmitter? Wrong! If the Transmitter is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Transmitter then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Transmitter? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Transmitter and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Transmitter wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Transmitter then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Transmitter site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Transmitter, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Transmitter, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

transmitter, LondonA transmitter (sometimes abbreviated XMTR) is an Electronics machine which with the aid of an antenna (electronics) propagates an electromagnetic radiation Signalling (telecommunication) such as radio, television, or other telecommunications.

A transmitter usually has a electronic power supply, an electronic oscillator, a modulator, and amplifiers for Sound (AF) and radio frequency (RF). The modulator is the device which piggybacks (or modulates) the signal information onto the carrier wave radio frequency, which is then broadcast. Sometimes a device (for example, a cell phone) contains both a transmitter and a radio receiver, with the combined unit referred to as a transceiver - see also Radio transmitter design.

More generally and in communications and information processing, a "transmitter" is any object (signal (information theory)) which sender information to an observer (receiver). When used in this more general sense, vocal cords may also be considered an example of a "transmitter".

In industrial process control a "transmitter" is any device which converts measurements from a sensor into a signal to be received, usually sent via wires, by some display or control device located a distance away. Typically in process control applications the "transmitter" will output a 4-20 Ampere current loop or digital protocol to represent a measured variable within a range. For example, a pressure transmitter might use 4 mA as a representation for 50 Pounds_per_square_inch#Psig of pressure and 20 mA as 1000 psig of pressure and any value in between proportionately ranged between 50 and 1000 psig. Older technology transmitters used pneumatic pressure typically ranged between 3 to 15 psig (20 to 100 pascal_(unit)) to represent a process variable.

History In the early days of radio engineering, radio frequency energy was generated using arcs or Alexanderson alternator (of which a rare example survives at the Grimeton VLF transmitter transmitter in Grimeton, Sweden). In the 1920s electronic transmitters, based on vacuum tubes, began to be used.

Cooling of final stages Low-power transmitters do not require special cooling equipment. Modern transmitters can be incredibly efficient, with efficiencies exceeding 98 percent. However, a broadcast transmitter with a megawatt power stage transferring 98% of that into the antenna can also be viewed as a 20 kilowatt electric heater.

For medium-power transmitters, up to a few hundred watts, air cooling with fans is used. At power levels over a few kilowatts, the output stage is cooled by a forced liquid cooling system analogous to an automobile cooling system. Since the coolant directly touches the high-voltage anodes of the vacuum tubes, only distilled, deionised water or a special dielectric coolant can be used in the cooling circuit. This high-purity coolant is in turn cooled by a heat exchanger, where the second cooling circuit can use water of ordinary quality because it is not in contact with energized parts. Very-high-power tubes of small physical size may use evaporative cooling by water in contact with the anode. The production of steam allows a high heat flow in a small space.

Power supply Transmitters are sometimes fed from a higher voltage level of the power supply grid than necessary in order to improve security of supply. For example, the Longwave transmitter Allouis, Warsaw Radio Mast and Transmitter Roumoules transmitters are fed from the high-voltage network (110 kV in Alouis and Konstantynow, 150 kV in Roumoules) even though a power supply from the medium-voltage level of the power grid (about 20 kV) would be able to deliver enough power.http://perso.orange.fr/monte-carlo-radiodiffusion/anglais/olan.htmhttp://perso.orange.fr/tvignaud/am/allouis/allouis4.htm

Protection equipment The high voltages used in high power transmitters (up to 40 kV) require extensive protection equipment. Also, transmitters are exposed to damage from lightning. Transmitters may be damaged if operated without an antenna, so protection circuits must detect the loss of the antenna and switch off the transmitter immediately. Tube-based transmitters must have power applied in the proper sequence, with the filament voltage applied before the anode voltage, otherwise the tubes can be damaged. The output stage must be monitored for VSWR, which indicate that generated power is not being radiated but instead is being reflected back into the transmitter.

Lightning protection is required between the transmitter and antenna. This consists of spark gaps and gas-filled surge arresters to limit the voltage that appears on the transmitter terminals. The control instrument that measures the voltage standing-wave ratio switches the transmitter off briefly if a higher voltage standing-wave ratio is detected after a lightning strike, as the reflections are probably due to lightning damage. If this does not succeed after several attempts, the antenna may be damaged and the transmitter should remain switched off. In some transmitting plants UV detectors are fitted in critical places, to switch off the transmitter if an electric arc is detected. The operating voltages, modulation factor, frequency and other transmitter parameters are monitored for protection and diagnostic purposes, and may be displayed locally and/or at a remote control room.

Building A transmitter site will have a control building to shelter the transmitter components and control devices. This is usually a purely functional building, which may contain apparatus for both radio and television transmitters. To reduce transmission line loss the transmitter building is usually immediately adjacent to the antenna for VHF and Ultra high frequency sites, but for lower frequencies it may be desirable to have a distance of a few score or several hundred metres between the building and the antenna. Some transmitting towers have enclosures built into the tower to house radio relay link transmitters or other, relatively low-power transmitters.

Legal and regulatory aspects Since radio waves go over borders, international agreements control radio transmissions. In European countries like Germany often the national Post Office is the regulating authority. In the United States broadcast and industrial transmitters are regulated by the Federal Communications Commission (FCC). In Canada technical aspects of broadcast and radio transmitters are controlled by Industry Canada, but broadcast content is regulated separately by the Canadian Radio-television and Telecommunications Commission (CRTC). In Australia transmitters, spectrum, and content are controlled by the Australian Communications and Media Authority (ACMA). The International Telecommunication Union (ITU) helps managing the radio-frequency spectrum internationally.

Planning As in any costly project, the planning of a high power transmitter site requires great care. This begins with the location. A minimum distance, which depends on the transmitter frequency, transmitter power, and the design of the transmitting antennas, is required to protect people from the radio frequency energy. Antenna towers are often very tall and therefore flight paths must be evaluated. Sufficient electric power must be available for high power transmitters. Transmitters for long and medium wave require good grounding and soil of high electrical conductivity. Locations at the sea or in river valleys are ideal, but the flood danger must be considered. Transmitters for Ultra high frequency are best on high mountains to improve the range (see radio propagation). The antenna pattern must be considered because it is costly to change the pattern of a long-wave or medium-wave antenna.

Transmitting antennas for long and medium wave are usually implemented as a mast radiator. Similar antennas with smaller dimensions are used also for short wave transmitters, if these send in the round spray enterprise. For arranging radiation at free standing steel towers fastened planar arrays are used. Radio towers for UHF and TV transmitter can be implemented in principle as grounded constructions. Towers may be steel lattice masts or reinforced concrete towers with antennas mounted at the top. Some transmitting towers for UHF have high-altitude operating rooms and/or facilities such as restaurants and observation platforms, which are accessible by elevator. Such towers are usually called TV tower. For microwaves one uses frequently parabolic antennas. These can be set up for applications of radio relay links on transmitting towers for FM to special platforms. For the program passing on of television satellites and the funkkontakt to space vehicles large parabolic antennas with diameters of 3 to 100 meters are necessary. These plants, which can be used if necessary also as radio telescope, are established on free standing constructions, whereby there are also numerous special designs, like the radio telescope in Arecibo.

Just as important as the planning of the construction and location of the transmitter is how its output fits in with existing transmissions. Two transmitters cannot broadcast on the same frequency in the same area as this would cause co-channel interference. For a good example of how the channel planners have dovetailed different transmitters' outputs see Crystal Palace UHF TV channel allocations. This reference also provides a good example of a grouped transmitter, in this case an A group. That is, all of its output is within the bottom third of the UK UHF television broadcast band. The other two groups (B and C/D) utilise the middle and top third of the band, see graph. By replicating this grouping across the country (using different groups for adjacent transmitters), co-channel interference can be minimised, and in addition, those in marginal reception areas can use more efficient grouped receiving antennas. Unfortunately, in the UK, this carefully planned system has had to be compromised with the advent of digital broadcasting which (during the changeover period at least) requires yet more channel space, and consequently the additional digital broadcast channels cannot always be fitted within the transmitter's existing group. Thus many UK transmitters have become "wideband" with the consequent need for replacement of receiving antennas (see external links). Once the Digital Switch Over (DSO) occurs the plan is that most transmitters will revert to their original groups, source Ofcom July 2007.

Further complication arises when adjacent transmitters have to transmit on the same frequency and under these circumstances the broadcast radiation patterns are attenuated in the relevant direction(s). A good example of this is Waltham transmitting station which broadcasts digital MUXES 5 & 6 on the same frequencies as Sandy Heath, another transmitter 50 miles SSE of it. Thus Waltham's transmitter array does not broadcast these two channels in the direction of Sandy Heath and vice versa. All of the above provides a perfect case study in transmission frequency planning.

Transmitters in culture Some cities in Europe, like Mühlacker, Ismaning, Langenberg, Kalundborg, Hoerby and Allouis became famous as sites of powerful transmitters. Some Radio masts and towers like the radio tower Berlin or the TV tower Stuttgart became landmarks of cities. Many transmitting plants have very high radio towers that are masterpieces of engineering.

Having the tallest building in the world, the nation, the state/province/prefecture, city, etc., has often been considered something to brag about. Often, builders of high-rise buildings have used transmitter antennas to lay claim to having the tallest building. A historic example was the "tallest building" feud between the Chrysler Building and the Empire State Building in New York City.

Some towers have an observation deck accessible to tourists. An example is the Ostankino Tower in Moscow, which was completed in 1967 on the 50th anniversary of the October Revolution to demonstrate the technical abilities of the Soviet Union. As very tall radio towers of any construction type are prominent landmarks, requiring careful planning and construction, and high-power transmitters especially in the long- and mediumwave ranges can be received over long distances, such facilities were often mentioned in propaganda. Other examples were the Deutschlandsender Herzberg/Elster and the Warsaw Radio Mast.

Records





Broadcasting In broadcasting, the part which contains the oscillator, modulator, and sometimes audio processor, is called the exciter. Confusingly, the high-power amplifier which the exciter then feeds into is often called the "transmitter" by broadcast engineers. The final output is given as transmitter power output (TPO), although this is not what most stations are rated by.

Effective radiated power (ERP) is used when calculation station coverage, even for most non-broadcast stations. It is the TPO, minus any attenuation (electronics) or radiated loss in the line to the antenna, multiplied by the gain (magnification) which the antenna provides toward the horizon. This is important, because the electric utility billing for the transmitter would be enormous otherwise, as would the cost of a transmitter. For most large stations in the VHF- and UHF-range, the transmitter power is no more than 20% of the ERP.For VLF, LF, MF and HF the ERP is typically not determined separately. In most cases the transmission power found in lists of transmitters is the value for the output of the transmitter. This is only correct for omnidirectional aerials with a length of a quarter wavelength or shorter.For other aerial types there are gain factors, which can reach values until 50 for shortwave directional beams in the direction of maximum beam intensity.Since some authors take account of gain factors of aerials of transmitters for frequencies below 30 MHz and others not, there are often discrepancies of the values of transmitted powers.

Where a particular service needs to have wide coverage, this is usually achieved by using multiple transmitters at different locations. Usually, these transmitters will operate at different frequencies to avoid interference where coverage overlaps. Examples include national broadcasting networks and cellular networks. In the latter, frequency switching is automatically done by the receiver as necessary, in the former, manual retuning is more common (though the Radio Data System is an example of automatic frequency switching in broadcast networks). Another system for extending coverage using multiple transmitters is quasi-synchronous transmission, but this is rarely used nowadays.

Main and relay (repeater) transmitters Transmitting stations are usually either classified as main stations or relay stations (also known as Radio repeater or Broadcast translator).

Main stations are defined as those that generate their own modulated output signal from a baseband (unmodulated) input. Usually main stations operate at high power and cover large areas.

Relay stations take an already modulated input signal (usually by direct reception of a parent station (off-air)) and simply shift (translate) its frequency before rebroadcasting. Usually relay stations operate at medium or low power, and are used to fill in pockets of poor reception within, or at the fringe of, the service area of a parent main station.

Note that a main station may also take its input signal directly off-air from another station, however this signal would be fully demodulated to baseband first, processed, and then remodulated for transmission.

References

See also

External links

transmitter, LondonA transmitter (sometimes abbreviated XMTR) is an Electronics machine which with the aid of an antenna (electronics) propagates an electromagnetic radiation Signalling (telecommunication) such as radio, television, or other telecommunications.

A transmitter usually has a electronic power supply, an electronic oscillator, a modulator, and amplifiers for Sound (AF) and radio frequency (RF). The modulator is the device which piggybacks (or modulates) the signal information onto the carrier wave radio frequency, which is then broadcast. Sometimes a device (for example, a cell phone) contains both a transmitter and a radio receiver, with the combined unit referred to as a transceiver - see also Radio transmitter design.

More generally and in communications and information processing, a "transmitter" is any object (signal (information theory)) which sender information to an observer (receiver). When used in this more general sense, vocal cords may also be considered an example of a "transmitter".

In industrial process control a "transmitter" is any device which converts measurements from a sensor into a signal to be received, usually sent via wires, by some display or control device located a distance away. Typically in process control applications the "transmitter" will output a 4-20 Ampere current loop or digital protocol to represent a measured variable within a range. For example, a pressure transmitter might use 4 mA as a representation for 50 Pounds_per_square_inch#Psig of pressure and 20 mA as 1000 psig of pressure and any value in between proportionately ranged between 50 and 1000 psig. Older technology transmitters used pneumatic pressure typically ranged between 3 to 15 psig (20 to 100 pascal_(unit)) to represent a process variable.

History In the early days of radio engineering, radio frequency energy was generated using arcs or Alexanderson alternator (of which a rare example survives at the Grimeton VLF transmitter transmitter in Grimeton, Sweden). In the 1920s electronic transmitters, based on vacuum tubes, began to be used.

Cooling of final stages Low-power transmitters do not require special cooling equipment. Modern transmitters can be incredibly efficient, with efficiencies exceeding 98 percent. However, a broadcast transmitter with a megawatt power stage transferring 98% of that into the antenna can also be viewed as a 20 kilowatt electric heater.

For medium-power transmitters, up to a few hundred watts, air cooling with fans is used. At power levels over a few kilowatts, the output stage is cooled by a forced liquid cooling system analogous to an automobile cooling system. Since the coolant directly touches the high-voltage anodes of the vacuum tubes, only distilled, deionised water or a special dielectric coolant can be used in the cooling circuit. This high-purity coolant is in turn cooled by a heat exchanger, where the second cooling circuit can use water of ordinary quality because it is not in contact with energized parts. Very-high-power tubes of small physical size may use evaporative cooling by water in contact with the anode. The production of steam allows a high heat flow in a small space.

Power supply Transmitters are sometimes fed from a higher voltage level of the power supply grid than necessary in order to improve security of supply. For example, the Longwave transmitter Allouis, Warsaw Radio Mast and Transmitter Roumoules transmitters are fed from the high-voltage network (110 kV in Alouis and Konstantynow, 150 kV in Roumoules) even though a power supply from the medium-voltage level of the power grid (about 20 kV) would be able to deliver enough power.http://perso.orange.fr/monte-carlo-radiodiffusion/anglais/olan.htmhttp://perso.orange.fr/tvignaud/am/allouis/allouis4.htm

Protection equipment The high voltages used in high power transmitters (up to 40 kV) require extensive protection equipment. Also, transmitters are exposed to damage from lightning. Transmitters may be damaged if operated without an antenna, so protection circuits must detect the loss of the antenna and switch off the transmitter immediately. Tube-based transmitters must have power applied in the proper sequence, with the filament voltage applied before the anode voltage, otherwise the tubes can be damaged. The output stage must be monitored for VSWR, which indicate that generated power is not being radiated but instead is being reflected back into the transmitter.

Lightning protection is required between the transmitter and antenna. This consists of spark gaps and gas-filled surge arresters to limit the voltage that appears on the transmitter terminals. The control instrument that measures the voltage standing-wave ratio switches the transmitter off briefly if a higher voltage standing-wave ratio is detected after a lightning strike, as the reflections are probably due to lightning damage. If this does not succeed after several attempts, the antenna may be damaged and the transmitter should remain switched off. In some transmitting plants UV detectors are fitted in critical places, to switch off the transmitter if an electric arc is detected. The operating voltages, modulation factor, frequency and other transmitter parameters are monitored for protection and diagnostic purposes, and may be displayed locally and/or at a remote control room.

Building A transmitter site will have a control building to shelter the transmitter components and control devices. This is usually a purely functional building, which may contain apparatus for both radio and television transmitters. To reduce transmission line loss the transmitter building is usually immediately adjacent to the antenna for VHF and Ultra high frequency sites, but for lower frequencies it may be desirable to have a distance of a few score or several hundred metres between the building and the antenna. Some transmitting towers have enclosures built into the tower to house radio relay link transmitters or other, relatively low-power transmitters.

Legal and regulatory aspects Since radio waves go over borders, international agreements control radio transmissions. In European countries like Germany often the national Post Office is the regulating authority. In the United States broadcast and industrial transmitters are regulated by the Federal Communications Commission (FCC). In Canada technical aspects of broadcast and radio transmitters are controlled by Industry Canada, but broadcast content is regulated separately by the Canadian Radio-television and Telecommunications Commission (CRTC). In Australia transmitters, spectrum, and content are controlled by the Australian Communications and Media Authority (ACMA). The International Telecommunication Union (ITU) helps managing the radio-frequency spectrum internationally.

Planning As in any costly project, the planning of a high power transmitter site requires great care. This begins with the location. A minimum distance, which depends on the transmitter frequency, transmitter power, and the design of the transmitting antennas, is required to protect people from the radio frequency energy. Antenna towers are often very tall and therefore flight paths must be evaluated. Sufficient electric power must be available for high power transmitters. Transmitters for long and medium wave require good grounding and soil of high electrical conductivity. Locations at the sea or in river valleys are ideal, but the flood danger must be considered. Transmitters for Ultra high frequency are best on high mountains to improve the range (see radio propagation). The antenna pattern must be considered because it is costly to change the pattern of a long-wave or medium-wave antenna.

Transmitting antennas for long and medium wave are usually implemented as a mast radiator. Similar antennas with smaller dimensions are used also for short wave transmitters, if these send in the round spray enterprise. For arranging radiation at free standing steel towers fastened planar arrays are used. Radio towers for UHF and TV transmitter can be implemented in principle as grounded constructions. Towers may be steel lattice masts or reinforced concrete towers with antennas mounted at the top. Some transmitting towers for UHF have high-altitude operating rooms and/or facilities such as restaurants and observation platforms, which are accessible by elevator. Such towers are usually called TV tower. For microwaves one uses frequently parabolic antennas. These can be set up for applications of radio relay links on transmitting towers for FM to special platforms. For the program passing on of television satellites and the funkkontakt to space vehicles large parabolic antennas with diameters of 3 to 100 meters are necessary. These plants, which can be used if necessary also as radio telescope, are established on free standing constructions, whereby there are also numerous special designs, like the radio telescope in Arecibo.

Just as important as the planning of the construction and location of the transmitter is how its output fits in with existing transmissions. Two transmitters cannot broadcast on the same frequency in the same area as this would cause co-channel interference. For a good example of how the channel planners have dovetailed different transmitters' outputs see Crystal Palace UHF TV channel allocations. This reference also provides a good example of a grouped transmitter, in this case an A group. That is, all of its output is within the bottom third of the UK UHF television broadcast band. The other two groups (B and C/D) utilise the middle and top third of the band, see graph. By replicating this grouping across the country (using different groups for adjacent transmitters), co-channel interference can be minimised, and in addition, those in marginal reception areas can use more efficient grouped receiving antennas. Unfortunately, in the UK, this carefully planned system has had to be compromised with the advent of digital broadcasting which (during the changeover period at least) requires yet more channel space, and consequently the additional digital broadcast channels cannot always be fitted within the transmitter's existing group. Thus many UK transmitters have become "wideband" with the consequent need for replacement of receiving antennas (see external links). Once the Digital Switch Over (DSO) occurs the plan is that most transmitters will revert to their original groups, source Ofcom July 2007.

Further complication arises when adjacent transmitters have to transmit on the same frequency and under these circumstances the broadcast radiation patterns are attenuated in the relevant direction(s). A good example of this is Waltham transmitting station which broadcasts digital MUXES 5 & 6 on the same frequencies as Sandy Heath, another transmitter 50 miles SSE of it. Thus Waltham's transmitter array does not broadcast these two channels in the direction of Sandy Heath and vice versa. All of the above provides a perfect case study in transmission frequency planning.

Transmitters in culture Some cities in Europe, like Mühlacker, Ismaning, Langenberg, Kalundborg, Hoerby and Allouis became famous as sites of powerful transmitters. Some Radio masts and towers like the radio tower Berlin or the TV tower Stuttgart became landmarks of cities. Many transmitting plants have very high radio towers that are masterpieces of engineering.

Having the tallest building in the world, the nation, the state/province/prefecture, city, etc., has often been considered something to brag about. Often, builders of high-rise buildings have used transmitter antennas to lay claim to having the tallest building. A historic example was the "tallest building" feud between the Chrysler Building and the Empire State Building in New York City.

Some towers have an observation deck accessible to tourists. An example is the Ostankino Tower in Moscow, which was completed in 1967 on the 50th anniversary of the October Revolution to demonstrate the technical abilities of the Soviet Union. As very tall radio towers of any construction type are prominent landmarks, requiring careful planning and construction, and high-power transmitters especially in the long- and mediumwave ranges can be received over long distances, such facilities were often mentioned in propaganda. Other examples were the Deutschlandsender Herzberg/Elster and the Warsaw Radio Mast.

Records





Broadcasting In broadcasting, the part which contains the oscillator, modulator, and sometimes audio processor, is called the exciter. Confusingly, the high-power amplifier which the exciter then feeds into is often called the "transmitter" by broadcast engineers. The final output is given as transmitter power output (TPO), although this is not what most stations are rated by.

Effective radiated power (ERP) is used when calculation station coverage, even for most non-broadcast stations. It is the TPO, minus any attenuation (electronics) or radiated loss in the line to the antenna, multiplied by the gain (magnification) which the antenna provides toward the horizon. This is important, because the electric utility billing for the transmitter would be enormous otherwise, as would the cost of a transmitter. For most large stations in the VHF- and UHF-range, the transmitter power is no more than 20% of the ERP.For VLF, LF, MF and HF the ERP is typically not determined separately. In most cases the transmission power found in lists of transmitters is the value for the output of the transmitter. This is only correct for omnidirectional aerials with a length of a quarter wavelength or shorter.For other aerial types there are gain factors, which can reach values until 50 for shortwave directional beams in the direction of maximum beam intensity.Since some authors take account of gain factors of aerials of transmitters for frequencies below 30 MHz and others not, there are often discrepancies of the values of transmitted powers.

Where a particular service needs to have wide coverage, this is usually achieved by using multiple transmitters at different locations. Usually, these transmitters will operate at different frequencies to avoid interference where coverage overlaps. Examples include national broadcasting networks and cellular networks. In the latter, frequency switching is automatically done by the receiver as necessary, in the former, manual retuning is more common (though the Radio Data System is an example of automatic frequency switching in broadcast networks). Another system for extending coverage using multiple transmitters is quasi-synchronous transmission, but this is rarely used nowadays.

Main and relay (repeater) transmitters Transmitting stations are usually either classified as main stations or relay stations (also known as Radio repeater or Broadcast translator).

Main stations are defined as those that generate their own modulated output signal from a baseband (unmodulated) input. Usually main stations operate at high power and cover large areas.

Relay stations take an already modulated input signal (usually by direct reception of a parent station (off-air)) and simply shift (translate) its frequency before rebroadcasting. Usually relay stations operate at medium or low power, and are used to fill in pockets of poor reception within, or at the fringe of, the service area of a parent main station.

Note that a main station may also take its input signal directly off-air from another station, however this signal would be fully demodulated to baseband first, processed, and then remodulated for transmission.

References

See also

External links



Transmitter - Wikipedia, the free encyclopedia
For biologic transmitters, see transmitter substance. A transmitter is an electronic device which, usually with the aid of an antenna, propagates an electromagnetic signal such as ...

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iTrip, i Trip & FM Transmitter Reviews, Comparisons and Accessories for all iPod and MP3 Players from The iTrip Store UK

Definition: transmitter from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.

AM Transmitter
AM Transmitter ... Notes: Please read the disclaimer on this site before making any transmitter circuit.

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VHF 405 line TV transmissions ceased in the UK in January 1985: The Death of 405-line Television in the UK

Fm Transmitter,Griffin Itrip,LCD Screen Wireless Fm Transmitter USB ...
Fm Transmitter: Techfocus offers Graffin Itrip, Wireless Fm Transmitter, LCD Screen Fm Transmitter, USB Port Fm Transmitter. Get the best Mp3 FM Transmitter, Mini Fm Transmitter ...

 

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