AIM: - to Study the Block Diagram of DTH Receiver

Expt. No. 3 DIRECT TO HOME RECEIVER

AIM: - To study the Block diagram of DTH Receiver.

THEORY:-

The block diagram of a Dish antenna receiver is shown is Fig. 1.

It consists of following stages :

(1) Dish antenna and LNB ( Low Noise Band Converter ) section:-

A satellite antenna intercepts the extremely weak microwave transmission signal from a targeted satellite and reflects the signals to its focal point, where the feed horn is placed. The feed horn collects microwave signals reflected from the antenna surface and ignores noise and other signals coming from off-axis directions. Then LNB amplifies the signal received through feed horn and converts its frequency from 11.7 to 12.2 GHz to 1.450 to 0.950 GHz. Thus it down converts frequency. It also converts microwave signals into electrical signals.

(2) Tuner section:-

The down converted signal from LNB is given to Tuner of Receiver amplifier through co-axial low loss cable.

The received signal is amplified by the R.F. Amplifier and further converted in the mixer amplifier stage to yield the intermediate picture and sound I.F. signals (Composite I.F. Signal) by heterodyning with local Oscillator frequency. Tuner also incorporates Video IF amplifier and detector. The output of Tuner is the MPEG Baseband signal which consists of Video signal and Sound signal in compressed form.

BLOCK DIAGRAM OF SATELLITE RECEIVER

Figure-1

(3) MPEG DECODER:-

The output of DTH Tuner, the MPEG Baseband signal, is applied to MPEG decoder consisting of IC MB86H25 which encodes audio and Video signal.

(4) VIDEO AMPLIFIER:-

The base band signal is applied to video amplifier consisting of IC NE562. This section amplifies Video signal and final amplified signal is given to the R.F. modulator and Video Out Socket.

(5) SOUND I.F. AND AUDIO AMPLIFIER:-

The base band signal is applied to sound IF and Audio amplifier subsystem IC NE564. This I.C. amplifies and detect the sound I.F. Then IC 741 is used for further amplification of obtained audio. The final amplified signal is given to the R.F. modulator and Audio Out Socket.

(6) R.F. Modulator section:-

This section is based on IC 1374 or 1473. It modulates Audio and Video signals obtained from above sections

and concerts into R.F signal for Channel-2. This R.F. output is then connected to the antenna input of T.V.

receiver.

(7) Power supply section:-

R.P.S. stage provides the different DC voltages required for various stages of receiver viz. +3.3V, +5.0V, +12V, +22V and +30V.

Theory of DTH Receiver.

DIRECT-TO-HOME (DTH) / DIRECT BROADCAST SATELLITE (DBS)

(Direct Broadcast Satellite) A one-way TV broadcast service from a communications satellite to a small round or oval dish antenna no larger than 20" in diameter. Using a highly compressed digital signal in the 11-15GHz Ku-band, DBS offers every household in the country a service similar to cable TV. Prior to DBS, costly equipment and very large dishes were required, and tuning stations was complicated because content was available on multiple satellites.

DirecTV and USSB

Although DBS service existed in other countries, the first DBS in the U.S. was launched in 1994 by Hughes Electronics (DIRECTV) and Hubbard Broadcasting (USSB). DIRECTV and USSB were offered in 1994 using the DSS standard with equipment made by RCA and other manufacturers.

PrimeStar and EchoStar

Soon after, PrimeStar introduced a DBS service that included installation of its own equipment that was leased with the content. In 1995, EchoStar launched its first satellite and offers the Digital Sky Highway (DISH) network.

USSB and Primestar Became DIRECTV

Hughes acquired USSB and Primestar in 1998 and 1999, respectively and officially renamed its satellite fleet DIRECTV. In 2003, a proposed merger between DIRECTV and EchoStar never came to fruition.

Direct broadcast satellite (DBS) is a term used to refer to satellite television broadcasts intended for home reception, also referred to as direct-to-home signals. It covers both analog and digital television and radio reception, and is often extended to other services provided by modern digital television systems, including video-on-demand and interactive features. A "DBS service" usually refers to either a commercial service, or a group of free channels available from one orbital position targeting one country.

Terminology confusion

In certain regions of the world, especially in North America, DBS is used to refer to providers of subscription satellite packages, and has become applied to the entire equipment chain involved. With modern satellite providers in the United States using high power Ku-band transmissions using circular polarization, which result in small dishes, and digital compression (hence bringing in an alternative term, Digital Satellite System, itself likely connected to the proprietary encoding system used by DirecTV, Digital Satellite Service), DBS is often misused to refer to these. DBS systems are often driven by pay television providers, which drives further confusion. Additionally, in some areas it is used to refer to specific segments of the Ku-band, normally 12.2 to 12.7 GHz, as this bandwidth is often referred to as DBS or one of its synonyms. In comparison, European "Ku band" DBS systems can drop as low as 10.7 GHz, which is in fact in the X band.

Adding to the naming complexity, the ITU's original frequency allocation plan for Europe, the Soviet Union and Northern Africa from 1977 introduced a concept of extremely high power spot-beam broadcasting (see Ekran satellite) which they termed DBS, although only a handful of the participating countries even went as far as to launch satellites under this plan, even fewer operated anything resembling a DBS service.

Commercial DBS services

The first commercial DBS service, Sky Television plc (now BSkyB), was launched in 1989. Sky TV started as a four-channel free-to-air analogue service on the Astra 1A satellite, serving the United Kingdom and Republic of Ireland. By 1991, Sky had changed to a conditional access pay model, and launched a digital service, Sky Digital, in 1998, with analogue transmission ceasing in 2001. Since the DBS nomenclature is rarely used in the UK or Ireland, the popularity of Sky's service has caused the terms "minidish" and "digibox" to be applied to products other than Sky's hardware. BSkyB is controlled by News Corporation.

PrimeStar began transmitting an analog service to North America in 1991, and was joined by DirecTV Group's DirecTV, in 1994. At the time, DirecTV's introduction was the most successful consumer electronics debut in American history. Although PrimeStar transitioned to a digital system in 1994, it was ultimately unable to compete with DirecTV, which required a smaller satellite dish and could deliver more programming. DirecTV eventually purchased PrimeStar in 1999 and migrated all PrimeStar subscribers to DirecTV equipment. In 2003, News Corporation purchased a controlling interest in DirecTV's parent company, Hughes Electronics, and renamed the company DirecTV Group.

In 1996, EchoStar's Dish Network went online in the United States and, as DirecTV's primary competitor, achieved similar success. AlphaStar also launched but soon went under.

Dominion Video Satellite Inc.'s Sky Angel also went online in the United States in 1996 with its DBS service geared toward the faith and family market. It has since grown from six to 36 TV and radio channels of family entertainment, Christian-inspirational programming and 24-hour news. Dominion, under its former corporate name Video Satellite Systems Inc., was actually the second from among the first nine companies to apply to the FCC for a high-power DBS license in 1981 and is the sole surviving DBS pioneer from that first round of forward-thinking applicants. Sky Angel, although a separate and independent DBS service, uses the satellites, transmission facilities, & receiving equipment used for Dish Network through an agreement with Echostar. Because of this, Sky Angel subscribers also have the option of subscribing to Dish Network's channels as well.

In 2003, EchoStar attempted to purchase DirecTV, but the U.S. Department of Justice denied the purchase based on anti-competitive concerns.

Free DBS services

Germany is likely the leader in free-to-air DBS, with approximately 40 analogue and 100 digital channels broadcast from the SES Astra 1 position at 19.2E. These are not marketed as a DBS service, but are received in approximately 12 million homes, as well as in any home using the German commercial DBS system, Premiere.

The United Kingdom has approximately 90 free-to-air digital channels, for which a promotional and marketing plan is being devised by the BBC and ITV, to be sold as "Freesat". It is intended to provide a multi-channel service for areas which cannot receive Freeview, and eventually replace their network of UHF repeaters in these areas

India's national broadcaster, Doordarshan, promotes a free-to-air DBS package as "DD Direct Plus", which is provided as in-fill for the country's terrestrial transmission network.

While originally launched as backhaul for their digital terrestrial television service, a large number of French channels are free-to-air on 5W, and have recently been announced as being official in-fill for the DTT network.

In North America (USA, Canada and Mexico) there are over 80 FTA digital channels available on Intelsat Americas 5, the majority of them are ethnic or religious. Other popular FTA satellites include AMC-4, AMC-6, Galaxy 10R and SatMex 5. A company called GloryStar promotes FTA religious broadcasters on IA-5 and AMC-4.

Conceptually, satellite television is a lot like broadcast television. It's a wireless system for delivering television programming directly to a viewer's house. Both broadcast television and satellite stations transmit programming via a radio signal (see How Radio Works for information about radio broadcasting).

Broadcast stations use a powerful antenna to transmit radio waves to the surrounding area. Viewers can pick up the signal with a much smaller antenna. The main limitation of broadcast television is range. The radio signals used to broadcast television shoot out from the broadcast antenna in a straight line. In order to receive these signals, you have to be in the direct "line of sight" of the antenna. Small obstacles like trees or small buildings aren't a problem; but a big obstacle, such as the Earth, will reflect these radio waves.

If the Earth were perfectly flat, you could pick up broadcast television thousands of miles from the source. But because the planet is curved, it eventually breaks the signal's line of site. The other problem with broadcast television is that the signal is often distorted even in the viewing area. To get a perfectly clear signal like you find on cable, you have to be pretty close to the broadcast antenna without too many obstacles in the way.

The Satellite TV Solution

Satellite television solves the problems of range and distortion by transmitting broadcast signals from satellites orbiting the Earth. Since satellites are high in the sky, there are a lot more customers in the line of site. Satellite television systems transmit and receive radio signals using specialized antennas called satellite dishes.

The television satellites are all in geosynchronous orbit, meaning that they stay in one place in the sky relative to the Earth. Each satellite is launched into space at about 7,000 mph (11,000 kph), reaching approximately 22,200 miles (35,700 km) above the Earth. At this speed and altitude, the satellite will revolve around the planet once every 24 hours -- the same period of time it takes the Earth to make one full rotation. In other words, the satellite keeps pace with our moving planet exactly. This way, you only have to direct the dish at the satellite once, and from then on it picks up the signal without adjustment, at least when everything works right. (See How Satellites Work for more information on satellite orbits.)

At the core, this is all there is to satellite television. But as we'll see in the next section, there are several important steps between the original programming source and your television.

The Overall System, Components and Programming

Early satellite TV viewers were explorers of sorts. They used their expensive dishes to discover unique programming that wasn't necessarily intended for mass audiences. The dish and receiving equipment gave viewers the tools to pick up foreign stations, live feeds between different broadcast stations, NASA activities and a lot of other stuff transmitted using satellites.

Some satellite owners still seek out this sort of programming on their own, but today, most satellite TV customers get their programming through a direct broadcast satellite (DBS) provider, such as DirecTV or the Dish Network. The provider selects programs and broadcasts them to subscribers as a set package. Basically, the provider's goal is to bring dozens or even hundreds of channels to your television in a form that approximates the competition, cable TV. Unlike earlier programming, the provider's broadcast is completely digital, which means it has much better picture and sound quality (see How Digital Television Works for details). Early satellite television was broadcast in C-band radio -- radio in the 3.4-gigahertz (GHz) to 7-GHz frequency range. Digital broadcast satellite transmits programming in the Ku frequency range (12 GHz to 14 GHz ).

The Components

There are five major components involved in a direct to home (DTH) satellite system: the programming source, the broadcast center, the satellite, the satellite dish and the receiver.

• Programming sources are simply the channels that provide programming for broadcast. The provider doesn't create original programming itself; it pays other companies (HBO, for example, or ESPN) for the right to broadcast their content via satellite. In this way, the provider is kind of like a broker between you and the actual programming sources. (Cable television companies work on the same principle.)
• The broadcast center is the central hub of the system. At the broadcast center, the television provider receives signals from various programming sources and beams a broadcast signal to satellites in geostationary orbit.
• The satellites receive the signals from the broadcast station and rebroadcast them to the ground.
• The viewer's dish picks up the signal from the satellite (or multiple satellites in the same part of the sky) and passes it on to the receiver in the viewer's house.
• The receiver processes the signal and passes it on to a standard television.

The Programming

Satellite TV providers get programming from two major sources: national turnaround channels (such as HBO, ESPN and CNN) and various local channels . Most of the turnaround channels also provide programming for cable television, and the local channels typically broadcast their programming over the airwaves.

Turnaround channels usually have a distribution center that beams their programming to a geostationary satellite. The broadcast center uses large satellite dishes to pick up these analog and digital signals from several sources.

Most local stations don't transmit their programming to satellites, so the provider has to get it another way. If the provider includes local programming in a particular area, it will have a small local facility consisting of a few racks of communications equipment. The equipment receives local signals directly from the broadcaster through fiber-optic cable or an antenna and then transmits them to the central broadcast center.

The broadcast center converts all of this programming into a high-quality, uncompressed digital stream. At this point, the stream contains a vast quantity of data -- about 270 megabits per second (Mbps) for each channel. In order to transmit the signal from there, the broadcast center has to compress it. Otherwise, it would be too big for the satellite to handle. In the next section, we'll find out how the signal is compressed.

The Dish and the Receiver

A satellite dish is just a special kind of antenna designed to focus on a specific broadcast source. The standard dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller sends it through the horn, and the dish focuses the signal into a relatively narrow beam.

The dish on the receiving end can't transmit information; it can only receive it. The receiving dish works in the exact opposite way of the transmitter. When a beam hits the curved dish, the parabola shape reflects the radio signal inward onto a particular point, just like a concave mirror focuses light onto a particular point.

In this case, the point is the dish's feed horn, which passes the signal on to the receiving equipment. In an ideal setup, there aren't any major obstacles between the satellite and the dish, so the dish receives a clear signal.

In some systems, the dish needs to pick up signals from two or more satellites at the same time. The satellites may be close enough together that a regular dish with a single horn can pick up signals from both. This compromises quality somewhat, because the dish isn't aimed directly at one or more of the satellites. A new dish design uses two or more horns to pick up different satellite signals. As the beams from different satellites hit the curved dish, they reflect at different angles so that one beam hits one of the horns and another beam hits a different horn.

The central element in the feed horn is the low noise blockdown converter, or LNB. The LNB amplifies the radio signal bouncing off the dish and filters out the noise (radio signals not carrying programming). The LNB passes the amplified, filtered signal to the satellite receiver inside the viewer's house.