Direct Broadcasting Satellites - Online Article

Direct Broadcast Satellite (DBS) refers to satellite television (TV) systems in which the subscribers, or end users, receive signals directly from geostationary satellite. Signals are broadcast in digital format at microwave frequencies. DBS is the descendant of direct-to-home (DTH) satellite services.

A DBS subscriber installation consists of a dish antenna two to three feet (60 to 90centimeters) in diameter, a conventional TV set, a signal converter placed next to the TV set, and a length of co-axial cable between the dish and the converter. The dish intercepts microwave signals directly from the satellite. The converter produces output that can be viewed on the TV receiver.

The first satellite television signal was relayed from Europe to the Telstar satellite over North America in 1962. The first geosynchronous communication satellite, Syncom2 was launched in 1963. The world's first commercial communication satellite,called Intelsat I (nicknamed EarlyBird), was launched into synchronous orbit on April 6, 1965. The first national network of satellite television, called Orbita, was created in Soviet Union in 1967, and was based on the principle of using the highly elliptical Molniya satellite for re-broadcasting and delivering of TV signal to ground downlink stations. The first domestic North American satellite to carry television was Canada’s geostationary Anik 1, which was launched in 1972 . ATS-6, the world's first experimental educational and Direct Broadcast Satellite, was launched in 1974. The first Soviet geostationary satellite to carry Direct-To-Home television, called Ekran, was launched in 1976.

Satellites used for television signals are generally in either naturally highly elliptical (with inclination of +/-63.4 degrees and orbital period of about 12 hours) or geostationary orbit 37,000km (22,300 miles) above the earth’s equator.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink satellite dishes are very large, as much as 9 to 12 meters (30to 40 feet) in diameter. The increased diameter results in more accurate aiming and increased signal strength at the satellite. The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted with in a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite. The transponder 'retransmits' the signals back to Earth but at a different frequency band (a process known as translation, used to avoid interference with the uplink signal), typically in the C-band (4–8 GHz) or Ku-band (12–18 GHz) or both. The leg of the signal path from the satellite to the receiving Earth station is called the downlink.

A typical satellite has up to 32 transponders for Ku-band and up to 24 for a C-band only satellite, or more for hybrid satellites. Typical transponders each have a bandwidth between 27 MHz and 50 MHz. Each geo-stationary C-band satellite needs to be spaced 2 degrees from the next satellite (to avoid interference). For Ku the spacing can be 1 degree. This means that there is an upper limit of 360/2 =180 geostationary C-band satellites and 360/1 = 360 geostationary Ku-bandsatellites. C-band transmission is susceptible to terrestrial interference while Ku- band transmission is affected by rain (as water is an excellent absorber of microwaves at this particular frequency).

The downlinked satellite signal, quite weak after traveling the great distance (see inverse-square law), is collected by a parabolic receiving dish, which reflects the weak signal to the dish’s focal point. Mounted on brackets at the dish's focal point is a device called a feedhorn. This feedhorn is essentially the flared front-end of a section of wave guide that gathers the signals at or near the focal point and 'conducts' them to aprobe or pickup connected to a low-noise block down converter or LNB. The LNB amplifies the relatively weak signals, filters the block of frequencies in which the satellite TV signals are transmitted, and converts the block off requencies to a lower frequency range in the L-band range. The evolution of LNBs was one of necessity and invention.

The original C-Band satellite TV systems used aLow Noise Amplifier connected to the feedhorn at the focal point of the dish.The amplified signal was then fed via very expensive 50 Ohm impedance coaxial cable to an indoor receiver or in other designs fed to a down converter (a mixer and a voltage tuned oscillator with some filter circuitry) for down conversion to an intermediate frequency. The channel selection was controlled, typically by a voltage tuned oscillator with the tuning voltage being fed via a separate cable to the headend. But this simple design evolved.

Designs for microstrip based converters for Amateur Radio frequencies were adapted for the 4 GHz C-Band. Central to these designs was concept of block down conversion of a rangeof frequencies to a lower, and technologically more easily handled block of frequencies (intermediate frequency).

The advantages of using an LNB are that cheaper cable could be used to connect the indoor receiver with the satellite TV dish and LNB, and that the technology for handling the signal at L-Band and UHF was far cheaper than that for handling the signal at C-Band frequencies. The shift to cheaper technology from the 50 Ohm impedance cable and N-Connectors of the early C-Band systems to the cheaper 75 Ohm technology and F-Connectors allowed the early satellite TV receivers to use, what were in reality, modified UHF TV tuners which selected the satellite television channel for down conversion to another lower intermediate frequency centered on70 MHz where it was demodulated. This shift allowed the satellite television DTH industry to change from being a largely hobbyist one where receivers were built in low numbers and complete systems were expensive (costing thousands of Dollars) to a far more commercial one of mass production. Direct broadcast satellite dishes are fitted with an LNBF, which integrates the feedhorn with the LNB.

The satellite receiver demodulates and converts the signals to the desired form (outputs for television, audio, data, etc.). Sometimes, the receiver includes the capability to unscramble or decrypt; the receiver is then called an Integrated receiver/decoder or IRD. The cable connecting the receiver tothe LNBF or LNB must be of the low loss type RG-6, quad shield RG-6 orRG-11, etc. It cannot be standard RG-59.

Analog television distributed via satellite is usually sent scrambled or unscrambled in NTSC, PAL, or SECAM television broadcast standards. The analog signal is frequency modulated and is converted from an FM signal to what is referred to as baseband. This baseband comprises the video signal and the audio subcarrier(s). The audio subcarrier is further demodulated to provide araw audio signal. If the signal is a digitized television signal or multiplex of signals, it is typically QPSK.

In general, digital television, including that transmitted via satellites, are generally based on open standards such as MPEG and DVB-S.

The IEEE C band is a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 4 to 8 GHz.

It was the first frequency band allocated for commercial ground-to-satellite communications. A typical C band satellite uses 3.7–4.2 GHz for downlink, and 5.925–6.425 GHz for uplink. C band is primarily used for open satellite communications, whether for full-time satellite TV networks or raw satellite feeds, although subscription programming also exists. This use contrasts with directbroadcast satellite, whichis a completely closed system used to deliver subscription programming to small satellite dishes connected to proprietary receiving equipment.

C band is highly associated with TVRO satellite reception systems, commonly called "big dish" systems since small receiving antennas are not optimal for C-band systems. Typical antenna sizes on C-band capable systems ranges from 7.5 to 12 feet (2.5 to 3.5 meters) on consumer satellite dishes, although larger ones also can be used. The NATO C band is that portion of the electromagnetic spectrum between 500 MHz and 1000 MHz.

The Ku band (pronounced "kay-yoo") is a portion of the electromagnetic spectrum in the microwave range of frequencies. This symbol refers to "K-under" — in other words, the band directly below the K-band. In radar applications, it ranges from 12 to 18 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard 521-2002.

Ku band is primarily used for satellite communications, most notably NASA's Tracking Data Relay Satellite used for both space shuttles, and ISS communications. Ku band satellites are also used for backhauls and particularly for satellite from remote locations back to a television network's studio for editing and broadcasting. The band is split into multiple segments that vary by geographical region by the International Telecommunication Union (ITU). NBC was the first television network to uplink amajority of its affiliate feeds via Ku band in 1983.

A communications satellite’s channels are called transponders, because each is a separate transceiver or repeater. With digital video data compression and multiplexing, several video and audio channels may travel through a single transponder on a single wide band carrier. Original analog video only has one channel per transponder, with subcarriers for audio and automatic transmission identification service ATIS. Non-multiplexed radio stations can also travel in single channel per carrier (SCPC) mode, with multiple carriers (analog or digital) per transponder. This allows each station to transmit directly to the satellite, rather than paying for a whole transponder, or using landlines to send it to an earth station for multiplexing with other stations.

The advantage of satellite TV over cable TV is that it offers you even more choices...up to 300 channels! With satellite TV, you can pick which company you want to subscribe with and what package of channels to buy. This is different from cable television, where you are forced to purchase whatever system your region offers and pay whatever price it offer. DBS systems can be installed rapidly, even in areas without a well developed communications infrastructure, although some uplink path will be needed, perhaps through the public switched telephone system. This makes DBS ideal for establishing communications in support of emergency response activities, and the system is particularly effective at distributing critical information to the field.
 

Network affiliates provided on the DBS services cannot be received by the majority of U.S. households. For those who can receive them, it is usually not their local affiliate. Because of the broadcast frequencies used by the DBS providers, outages can occur as a result of severe thunderstorms in all DBS systems. The satellites are focused to send more power to rainier areas to help minimize this problem, but it does exist.

There are occasional visible digital artifacts which some viewers find objectionable. Some claim this is very distracting while others hardly notice it. It appears to be quite subjective. Nevertheless digital artifacts are a part of the DBS services.

India's national broadcaster, Doordarshan, promotes a free-to-air DBS package as "DD DirectPlus", which is provided as in-fill for the country's terrestrial transmission network. In India there are more than 300 TV Channels are operating. India has the indigenously built INSAT series satellites from Indian Space Research Organisation (ISRO) along with some private operators. INSAT 4A, INSAT-2E, INSAT-3C and INSAT-3E carry multiple channels for Indian television viewers.1. Netherlands-based SES Global-owned NSS 6, Thaicom-2 and Telstar 10 are the other major private satellites over India. Notable service providers offering a bouquet of multiple channels are state-owned Doordarshan, News Corporation owned STAR TV, Sony owned Sony Entertainment Television, Sun Network and ZeeTV, DD Direct Plus, DishTV and Tata Sky are the three major commercial service providers of Satellite Television in India.

Direct Broadcast Satellite (DBS) refers to satellite television (TV) systems in which the subscribers, or end users, receive signals directly from geostationary satellite. Signals are broadcast in digital format at microwave frequencies. DBS is the descendant of direct-to-home (DTH) satellite services.

A DBS subscriber installation consists of a dish antenna two to three feet (60 to 90centimeters) in diameter, a conventional TV set, a signal converter placed next to the TV set, and a length of co-axial cable between the dish and the converter. The dish intercepts microwave signals directly from the satellite. The converter produces output that can be viewed on the TV receiver.

The first satellite television signal was relayed from Europe to the Telstar satellite over North America in 1962. The first geosynchronous communication satellite, Syncom2 was launched in 1963. The world's first commercial communication satellite,called Intelsat I (nicknamed EarlyBird), was launched into synchronous orbit on April 6, 1965. The first national network of satellite television, called Orbita, was created in Soviet Union in 1967, and was based on the principle of using the highly elliptical Molniya satellite for re-broadcasting and delivering of TV signal to ground downlink stations. The first domestic North American satellite to carry television was Canada’s geostationary Anik 1, which was launched in 1972 . ATS-6, the world's first experimental educational and Direct Broadcast Satellite, was launched in 1974. The first Soviet geostationary satellite to carry Direct-To-Home television, called Ekran, was launched in 1976.

Satellites used for television signals are generally in either naturally highly elliptical (with inclination of +/-63.4 degrees and orbital period of about 12 hours) or geostationary orbit 37,000km (22,300 miles) above the earth’s equator.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility. Uplink satellite dishes are very large, as much as 9 to 12 meters (30to 40 feet) in diameter. The increased diameter results in more accurate aiming and increased signal strength at the satellite. The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted with in a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite. The transponder 'retransmits' the signals back to Earth but at a different frequency band (a process known as translation, used to avoid interference with the uplink signal), typically in the C-band (4–8 GHz) or Ku-band (12–18 GHz) or both. The leg of the signal path from the satellite to the receiving Earth station is called the downlink.

A typical satellite has up to 32 transponders for Ku-band and up to 24 for a C-band only satellite, or more for hybrid satellites. Typical transponders each have a bandwidth between 27 MHz and 50 MHz. Each geo-stationary C-band satellite needs to be spaced 2 degrees from the next satellite (to avoid interference). For Ku the spacing can be 1 degree. This means that there is an upper limit of 360/2 =180 geostationary C-band satellites and 360/1 = 360 geostationary Ku-bandsatellites. C-band transmission is susceptible to terrestrial interference while Ku- band transmission is affected by rain (as water is an excellent absorber of microwaves at this particular frequency).

The downlinked satellite signal, quite weak after traveling the great distance (see inverse-square law), is collected by a parabolic receiving dish, which reflects the weak signal to the dish’s focal point. Mounted on brackets at the dish's focal point is a device called a feedhorn. This feedhorn is essentially the flared front-end of a section of wave guide that gathers the signals at or near the focal point and 'conducts' them to aprobe or pickup connected to a low-noise block down converter or LNB. The LNB amplifies the relatively weak signals, filters the block of frequencies in which the satellite TV signals are transmitted, and converts the block off requencies to a lower frequency range in the L-band range. The evolution of LNBs was one of necessity and invention.

The original C-Band satellite TV systems used aLow Noise Amplifier connected to the feedhorn at the focal point of the dish.The amplified signal was then fed via very expensive 50 Ohm impedance coaxial cable to an indoor receiver or in other designs fed to a down converter (a mixer and a voltage tuned oscillator with some filter circuitry) for down conversion to an intermediate frequency. The channel selection was controlled, typically by a voltage tuned oscillator with the tuning voltage being fed via a separate cable to the headend. But this simple design evolved.

Designs for microstrip based converters for Amateur Radio frequencies were adapted for the 4 GHz C-Band. Central to these designs was concept of block down conversion of a rangeof frequencies to a lower, and technologically more easily handled block of frequencies (intermediate frequency).

The advantages of using an LNB are that cheaper cable could be used to connect the indoor receiver with the satellite TV dish and LNB, and that the technology for handling the signal at L-Band and UHF was far cheaper than that for handling the signal at C-Band frequencies. The shift to cheaper technology from the 50 Ohm impedance cable and N-Connectors of the early C-Band systems to the cheaper 75 Ohm technology and F-Connectors allowed the early satellite TV receivers to use, what were in reality, modified UHF TV tuners which selected the satellite television channel for down conversion to another lower intermediate frequency centered on70 MHz where it was demodulated. This shift allowed the satellite television DTH industry to change from being a largely hobbyist one where receivers were built in low numbers and complete systems were expensive (costing thousands of Dollars) to a far more commercial one of mass production. Direct broadcast satellite dishes are fitted with an LNBF, which integrates the feedhorn with the LNB.

The satellite receiver demodulates and converts the signals to the desired form (outputs for television, audio, data, etc.). Sometimes, the receiver includes the capability to unscramble or decrypt; the receiver is then called an Integrated receiver/decoder or IRD. The cable connecting the receiver tothe LNBF or LNB must be of the low loss type RG-6, quad shield RG-6 orRG-11, etc. It cannot be standard RG-59.

Analog television distributed via satellite is usually sent scrambled or unscrambled in NTSC, PAL, or SECAM television broadcast standards. The analog signal is frequency modulated and is converted from an FM signal to what is referred to as baseband. This baseband comprises the video signal and the audio subcarrier(s). The audio subcarrier is further demodulated to provide araw audio signal. If the signal is a digitized television signal or multiplex of signals, it is typically QPSK.

In general, digital television, including that transmitted via satellites, are generally based on open standards such as MPEG and DVB-S.

The IEEE C band is a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 4 to 8 GHz.

It was the first frequency band allocated for commercial ground-to-satellite communications. A typical C band satellite uses 3.7–4.2 GHz for downlink, and 5.925–6.425 GHz for uplink. C band is primarily used for open satellite communications, whether for full-time satellite TV networks or raw satellite feeds, although subscription programming also exists. This use contrasts with directbroadcast satellite, whichis a completely closed system used to deliver subscription programming to small satellite dishes connected to proprietary receiving equipment.

C band is highly associated with TVRO satellite reception systems, commonly called "big dish" systems since small receiving antennas are not optimal for C-band systems. Typical antenna sizes on C-band capable systems ranges from 7.5 to 12 feet (2.5 to 3.5 meters) on consumer satellite dishes, although larger ones also can be used. The NATO C band is that portion of the electromagnetic spectrum between 500 MHz and 1000 MHz.

The Ku band (pronounced "kay-yoo") is a portion of the electromagnetic spectrum in the microwave range of frequencies. This symbol refers to "K-under" — in other words, the band directly below the K-band. In radar applications, it ranges from 12 to 18 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard 521-2002.

Ku band is primarily used for satellite communications, most notably NASA's Tracking Data Relay Satellite used for both space shuttles, and ISS communications. Ku band satellites are also used for backhauls and particularly for satellite from remote locations back to a television network's studio for editing and broadcasting. The band is split into multiple segments that vary by geographical region by the International Telecommunication Union (ITU). NBC was the first television network to uplink amajority of its affiliate feeds via Ku band in 1983.

A communications satellite’s channels are called transponders, because each is a separate transceiver or repeater. With digital video data compression and multiplexing, several video and audio channels may travel through a single transponder on a single wide band carrier. Original analog video only has one channel per transponder, with subcarriers for audio and automatic transmission identification service ATIS. Non-multiplexed radio stations can also travel in single channel per carrier (SCPC) mode, with multiple carriers (analog or digital) per transponder. This allows each station to transmit directly to the satellite, rather than paying for a whole transponder, or using landlines to send it to an earth station for multiplexing with other stations.

The advantage of satellite TV over cable TV is that it offers you even more choices...up to 300 channels! With satellite TV, you can pick which company you want to subscribe with and what package of channels to buy. This is different from cable television, where you are forced to purchase whatever system your region offers and pay whatever price it offer. DBS systems can be installed rapidly, even in areas without a well developed communications infrastructure, although some uplink path will be needed, perhaps through the public switched telephone system. This makes DBS ideal for establishing communications in support of emergency response activities, and the system is particularly effective at distributing critical information to the field.
 

Network affiliates provided on the DBS services cannot be received by the majority of U.S. households. For those who can receive them, it is usually not their local affiliate. Because of the broadcast frequencies used by the DBS providers, outages can occur as a result of severe thunderstorms in all DBS systems. The satellites are focused to send more power to rainier areas to help minimize this problem, but it does exist.

There are occasional visible digital artifacts which some viewers find objectionable. Some claim this is very distracting while others hardly notice it. It appears to be quite subjective. Nevertheless digital artifacts are a part of the DBS services.

India's national broadcaster, Doordarshan, promotes a free-to-air DBS package as "DD DirectPlus", which is provided as in-fill for the country's terrestrial transmission network. In India there are more than 300 TV Channels are operating. India has the indigenously built INSAT series satellites from Indian Space Research Organisation (ISRO) along with some private operators. INSAT 4A, INSAT-2E, INSAT-3C and INSAT-3E carry multiple channels for Indian television viewers.1. Netherlands-based SES Global-owned NSS 6, Thaicom-2 and Telstar 10 are the other major private satellites over India. Notable service providers offering a bouquet of multiple channels are state-owned Doordarshan, News Corporation owned STAR TV, Sony owned Sony Entertainment Television, Sun Network and ZeeTV, DD Direct Plus, DishTV and Tata Sky are the three major commercial service providers of Satellite Television in India.

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Comments

Manvendra Rana on 2009-03-05 21:56:50 wrote,

Minblowing yaar... What an article on DBSTV. A must read content

Nishant Mishra on 2009-03-06 20:53:36 wrote,

beautifully written..hats off mate!!!!