1

INDUSTRIAL TRAINING PROJECT

On

Direct-To-Home Satellite Broadcasting

Submitted to

AIR & Doordarshan

UNDER GUIDANCE OF:

Dr. Rakesh Sharma

Asst. Dir.( Engg.)

AIR & Doordarshan

FACULTY GUIDES: SUBMITTED BY:

Sachin Rajput Kumar Deepak

(Lecturer) A2305108122

Paurush Bhulania ` B.Tech (ECE)

(Lecturer) ASET

AMITY SCHOOL OF ENGINEERING AND TECHNOLOGY

AMITY UNIVERSITY, NOIDA, UTTAR PRADESH

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ACKNOWLEDGEMENT

At the outset of this project I would like to place my sincere thanks to everybody who has

helped me directly or indirectly,in completing my industrial training of its kind successfully. I

would like to express my gratefulness to Mr. Rakesh Sharma ( Assistant Director engg.) for

providing me with a golden opportunity to undergo Industrial training in AIR &

Doordarshan. He not only provided me with the correct guidance at every stage but also gave

a great moral support and encouragement. His suggestions were of immense help and this

project would not have been a reality without his inspiring all-round help including the

special attention paid by him to the editing of the project.

In addition to this I would like to express my gratitude towards my parents, who

provided a sound environment for my working and encouraged me towards my work, and

friends, who were very innovative and creative in their suggestions and ideas.

I would also like to thank Amity School of Engineering and Technology, Amity

University for including this industrial training in our curriculum. It will definitely help me in

shaping my professional life.

At the end I am thankful to the Almighty who was always with me all the time as a

guiding force.

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CERTIFICATE

This is to certify that Mr.Kumar Deepak, student of B.Tech. in Electronics and

Communication Engineering has carried out the work presented in the project report of

the summer internship entitled “Direct-To-Home Satellite Broadcasting” as a part of

programme of Bachelor of Technology in Electronics and Communication Engineering

from STI(T) AIR & Doordarshan, Kingsway Camp,New Delhi, under my supervision.

……………………………… …………………………..

Mr. Sachin Rajput Mr. Paurush Bhulania

Lecturer Lecturer

Department of ECE Department of ECE

ASET, Noida ASET, Noida

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ABSTRACT

DTH is a new technology and it has matured to its full potential in other parts of the

world. There are many application has been found everyday for exploitation of

benefits of DTH?

The word ‘DTH’ is synonymous with transmission of digital video channel to home

subscriber’s using a small dish antenna. The DTH utilizes a technology which enables a

home to receive high speed internet broadband access data communication, voice over

internet protocol (IP) telephony and much more using an open standard Digital Video

Broadcasting (DVB) technology. The video channels are received with a suitable set top box.

Capable of demodulating Motion Picture Engineering Group (MPEG-2) standard videos. It is

for the return channel required for other services such as voice over internet protocol and

broadband access data communications, that a return channel is also required for the home

terminal. The return channel via the satellite is called RCS and is an open standard.

Hardware compatible with DVB-RCS technology are readily available in the market in both

Ku-band and C-band. DVB-RCS is an international open standard for multimedia satellite

network where the return data rates in access of 2 Mbps are possible using low cost user

terminals. The forward ink is usually at 40 Mbps.

Today, most satellite TV customers in developed television markets get their programming

through a direct broadcast satellite (DBS) provider, such as DISH TV or DTH platform. 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 the customer’s television

in a form that approximates the competition from Cable TV. Unlike earlier programming, the

provider’s broadcast is completely digital, which means it has high picture and stereo sound

quality. Early satellite television was broadcast in C-band - radio in the 3.4-gigahertz (GHz)

to 7-GHz frequency range.

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TABLE OF CONTENTS

Acknowledgement

Certificat

Abstract

1. Introduction …………………………………………………………………….7-8

2. History …………………………………………………………………………. 9

3. The Process …………………………………………………………………….10-13

3.1 Up-Link Chain

3.2 Down-Link Chain

4. Satellite Transmission …………………………………………………………14-15

4.1 What is Satellite

4.2 Geo-stationary satellite

5. Frequency Bands ……………………………………………………………….17-18

5.1 Ku band frequencies

6. Compression …………………………………………………………………….19

7. Encryption and Transmission …………………………………………………20-22

7.1 What is encryption

7.2 Bit rate

7.3 MPEG-2 compression technique

7.4 Broadcast centre

8. Communication channel and BW ………………………………………………23

9. Satellite receiving antennas …………………………………………………24-26

9.1 Antenna size

9.2 Antenna f/D ratio

10. Dish materials and construction ………………………………………………...27

11. Offset feed antennas ……………………………………………………………28-30

11.1 Antenna specifications

12. DTH Applications ……………………………………………………………...31-32

13. DTH vs Cable ……………………………………………………………………33

14. Conclusion ………………………………………………………………………....34

15. Future Work ……………………………………………………………………….35

16. References ………………………………………………………………………….36

17. Appendix ……………………………………………………………………….......37

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LIST OF FIGURES

1. Schematic of DTH Broadcasting ........................................................1

2. Block Diagram of Up link chain .........................................................6

3. Block Diagram of Down link chain ....................................................7

4. Schematics of uplinking and Downlinking ........................................8

5. Motion of geostationary satellite ........................................................9

6. C-band vs Ku-band graphical representation .................................12

7. Parabolic reflector ...............................................................................19

8. Offset feed antennas ..........................................................................22

9. Block diagram of set top box ..............................................................25

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1.INTRODUCTION

WHAT IS DTH?

DTH or Direct-To-Home broadcasting is the distribution of television signals from high

powered geo-stationary satellites to a small dish antenna/satellite receiver in homes across the

country.

In DTHTV, you receive the signal from a satellite (which the broadcaster has hired) to a

small dish antenna installed at the rooftop of your house, or an outer wall of your flat. This

signal is decoded by a set-top box, which is provided by the broadcaster and connects to the

dish antenna directly with a cable. The set-top box, in turn, connects to your TV. So you

become the master of your entertainment. Watch the channels you wish. And pay for only

those channels which you wish to watch; you need not pay for Sports channels if you don’t

like sport.

.

Fig1. schematic of Direct-To-Home Broadcasting

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It is a fast emerging alternative due to the following reasons:

1. Economical- It enables customers to receive a minimum of 200 to 300 channels on a

fairly economical basis.

2. Extensive range- satellite broadcast can reach rural and semi-rural areas; where cable

is difficult to install.

3. Interlink- it provides an interlink between different TV centres.

DTH Satellite is used for distinguishing the transmissions which are directly intended for

home viewers from the distribution services of cable television that are carried on the same

satellite. The term DTH in widely used for services offered by lower power satellites that

require larger dishes (up to 1.7m diameter or more) for reception.

DTH has become favourable entertainment mode today as it provides unique features and

quality services. The DTH satellite technology follows digital signals that offer strong sound

system and amazing video quality. In fact, DTH satellite carried by low powered satellites

requires larger dishes that offer digital satellite channels directly to subscribers from DTH

service providers.

Direct-to-Home (DTH) satellite television is the essence of entire satellite broadcast industry

as it offers huge opportunities for both broadcasters and viewers. The rapid development of

digital technology led to the introduction of wide variety of interactive applications in the

television industry by DTH broadcast operators. In addition to this, it provides many

entertainment programmes over a single delivery platform.

DTH Satellite Transmission makes use of Ku band as it is most suitable for such

transmissions.It involves digitally encoded transmission signals that provide higher resolution

picture quality and better audio as compared to traditional Analog signals. DTH satellite TV

has widely grown in popularity at rapid pace as it acquires 9 million subscribers with in two

years across the nation.

Some of major DTH providers in India comprises of Reliance BIG TVDTH, Tata Sky DTH,

DDDirect DTH, Sun DTH services, Airtel DTH and Zee Dish TV

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2.HISTORY

The history of DTH services in India dates back to 1996. But, the proposal couldn’t get

through policy hurdles because of concern over national security. It was finally allowed in

July 2006. DTH service in India started with the state owned DD Direct. Although DD Direct

provided all free channels free of cost but it had very little penetration because of the lack of

incentive for putting the initial investment to buy the set top box. Since this service was

inferior to that provided by normal cable operators and was only partially better than what

one would get from using just the Antenna this could not make any significant strides.

The history of DTH services in India dates back to 1996. But, the proposal couldn’t get

through policy hurdles because of concern over national security. It was finally allowed in

July 2006.

As of now, number of total customers stand at 14 million whereas total cable TV households

number is 75 million. That reflects the huge potential of this industry in the long run.

DD direct, Tata Sky, Sun Direct, Big Digital TV etc are major players. New entrants are

Airtel Digital TV and Videocon. Old and established players like Dish TV and Tata Sky

employ MPEG1-2 technology while majority of other players use MPEG-4 technology.

MPEG-4 technology is more efficient in broadcasting superb quality video and more

channels as well.

DTH service was launched back in 2004 by launching of Dish TV by Essel Group's Zee

Entertainment Enterprises. Dish TV is on the same satellite where DD Direct+ was, DD

Direct+ shifted to Insat 4B which is adjacent to NSS-6.

Dish TV was only DTH operator in India to carry the two Turner channels Turner Classic

Movies and Boomerang. Both the channels were removed from the platform due to unknown

reasons in March 2009. In October 2010 Dish tv added the long awaited Neo Sports and Neo

Cricket on its platform.

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3.THE PROCESS

Technologically speaking, the process starts with the service provider leasing Ku-band

transponders from the satellite. Thereafter, encoder gets into the process of converting video,

audio, and data signals into the digital format.

Once encoding is done, multiplexer mixes these signals. Users have to install a small dish

antenna and set-top boxes which decode those mixed signals and lastly users get to view

numerous TV channels.

For DTH system communication channel is air & Bandwidth is:

Ku2 Band uplink:

13.75 to 14.5 GHz

Ku Band downlink :

10.95 – 11.20 GHz

11.45 – 11.70 GHz

12.50 – 12.75 GHz

The DTH system does not pauperism a telecommunication mesh work that at represent

distributes TV signals to customers. From frugal saucer of view, the aggregation should be

compressed till prodigious digital drawbacks seem. As such, programmers containing frames

with many abstinence haunting objects, such as in a line of basket actress, can be compressed

3 or 4 to a transponder of 36MHz depression dimension. Similarly programmers containing

mostly assistance, KU-BAND frequencies are preferred because these are not unerect to

disturbance from make muzzle to inform communicating and also need much small diam dish

sensitivity. Low supercharged KU-BAND follower transmits in the 11.7 to 12.5 GHz

constitute time the new towering powered versions are allotted 12.2 to 12.7 GHz band for a

video economic action of DTH transmissions.

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3.1 Uplink Chain

DTH broadcasting is basically satellite broadcasting in Ku-Band (14/12 GHz). The main

advantage of Ku-Band satellite broadcasting is that it requires physically manageable smaller

size of dish antenna compared to that of C-Band satellite broadcasting dishes. C-Band

broadcasting requires about 3.6 m PDA (41dB gain at 4 GHz), while Ku-Band requires just

0.6 m PDA (35 dB gain at 12 GHz). The shortfall of this 6 dB is compensated by using

Forward Error Correction (FEC), which can offer 8 to 9 dB coding gain in the digital

broadcasting. Requirement of transmitter power (about 25 to 50 W) is less than that of analog

C-band broadcasting. rain margin has to be kept for reliable connectivity.

Rain margin is provided by operating the transmitter at higher powers and by using larger

size of the dish antenna (6.2 m).

The major drawback of Ku-Band transmission is that the RF signals typically suffer 8 to 9 dB

rain attenuation under heavy rainfall while rain attenuation is very low at C-Band. Fading due

to rain can hamper the connectivity of satellite and therefor

Fig.1 shows the schematic of uplink chain proposed to broadcast a bouquet of 30 video

programs by Doordarshan. The video , programs in digital format, are fed to a Router whose

outputs are divided into three groups A, B and C. Each group contains 10 video sources

multiplexed in a multiplexer. These three multiplexed streams are digitally (QPSK)

modulated individually at 70 MHz Intermediate Frequency (IF). Each group is further doubly

up-converted, first conversion at L-Band (950-1450 MHz) and second conversion at Ku-

Band (12-14 GHz). Groups A, B and C are up-converted to Ku-Band frequencies, ARF

(=13891 MHz), BRF (=13973 MHz) and CRF (=13839 MHz) respectively and are

individually amplified through Klystron High Power Amplifiers (KHPA). The three RF

signals are combined in RF combiner and then finally fed to 6.2 m dish antenna for up-

linking.

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Signal from Insat 2EIRD 1

ASI

IRD 2

ROUTER

64 x 64Signal from Insat 3C

MUX 1

Multiplexed stream of 10 videos

IRD 30

(1–10)

MUX 2

Multiplexed stream of 10 videos

(11–20)

MUX 3

Multiplexed stream of 10 videos

(21–30)

QPSKMod. 1

Upcon-verter 1

KHPA1 RF

COMBINER

QPSKMod. 2

Upcon-verter 2

KHPA2

QPSKMod. 3

Upcon-verter 3

KHPA3

DirectionalCoupler

7.2 m PDARFA

RFB

RFC

RFA=13891MHz

RFB=13973MHz

RFC=13839MHz

A

B

C

Fig.2.1: DTH Up-linking Setup

Each satellite has its own uplink and downlink frequency. It is also worth mentioning that

uplink frequency is greater than downlink frequency.

Because the uplink frequency can be sent from a way bigger antenna. If Up and Down were

running on the same frequency, they would end up interfering with each other. The uplink

frequency (Earth to satellite) is of a higher value than the downlink to mitigate the free space

spreading losses, and the tropospheric losses (gases, clouds, rain), all of which are related to

wavelength and therefore to frequency.

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3.2 Down-Link Chain

Down-Link or receiving chain of DTH signal is depicted in Fig. 2. There are mainly three

sizes of receiving antenna, 0.6 m, 0.9 m, and 1.2 m. Any of the sizes can be easily mounted

on rooftop of a building or house. RF waves (12/14 GHz) from satellite are

IF signal (950-1450MHz)

through coaxial cable

Set-Top

Box (IRD)

Audio

LNBF

0.6 cm PDA (mounted at roof top)

Video

RF Wave from satellite (12.2-12.7GHz)

T.V

Indoor Unit

Fig.2.2 : DTH Down-linking Setup

picked up by a feed converting it into electrical signal. The electrical signal is amplified and

down converted to L-Band (950-1450) MHz signal. Feed and LNBC are combined in single

unit called LNBF. The L-Band signal goes to indoor unit, consisting of a set-top box and TV

receiver through coaxial cable. The set-top box or Integrated Receiver Decoder (IRD) down

converts the L-Band first IF signal to 70 MHz second IF signal, perform digital

demodulation, de-multiplexing, decoding and finally gives audio/video output to TV for

viewing.

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4. SATELLITE TRANSMISSION

4.1 what is satellite?

A satellite is an object which has been placed into orbit by human endeavor.

Such objects are sometimes called artificial satellites to distinguish them from natural

satellites such as the Moon.

Satellite – basically a spacecraft placed in orbit around earth carrying microwave

receive & transmit equipment on Board

Essentially a Microwave Link Repeater

Frequencies capable of passing through Ionosphere (Microwave frequencies) use

Microwave frequencies permit transmission of data at high rate.

Fig3: schematic of uplinking and downlinking

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Geostationary satellites play an important role for DTH systems.

4.2 WHAT IS GEO STATIONARY SATELLITE?

Geostationary satellites are positioned at an exact height above the earth (about 36000

Km).

At this height they rotate around the earth at the same speed as the earth

rotates around its axis, so in effect remaining stationary above a point on

the earth (normally directly overhead the equator).

As they remain stationary they are ideal for use as communications satellites and

also for remote imaging as they can repeatedly scan the same points on the earth

beneath them.

Polar Orbiting satellites by comparison have a much lower orbit, moving around the

earth fairly rapidly, and scanning different areas of the earth at relatively infrequent

periods.

4.3 Motion of Geostationary Satellite around EARTH

Fig-4 : Motion of geostationary satellite

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4.4 Receiver which point to a geostationary satellite

fig5: receiving antenna of DTH is shown located at the top of a house.

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5.Frequency Bands

Each satellite has its own uplink and downlink frequency. It is also worth mentioning that

uplink frequency is greater than downlink frequency.

This is because the uplink frequency can be sent from a way bigger antenna. If Uplink and

Downlink were running on the same frequency, they would end up interfering with each

other. The uplink frequency (Earth to satellite) is of a higher value than the downlink to

mitigate the free space spreading losses, and the tropospheric losses (gases, clouds, rain), all

of which are related to wavelength and therefore to frequency.

Higher the frequency, lesser the wavelength. So high frequency can be received using smaller

antenna in satellite, which is more practical. Whereas on the earth, we can have bigger

antennas.

Frequency band Up Link Down Link

C-band 6 GHz 4 GHz

X-band 8 GHz 7GHz

Ku-band 14 GHz 11 GHz

Ka-band 30 GHz 20 GHz

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5.1 KU BAND FREQUENCIES

Digital broadcast satellite transmits programming in the Ku frequency range (10 GHz to 14

GHz).

Rain Fade Effects on Ku-band Transmissions

There is one major drawback to satellites down linking signals at frequencies greater than 10

GHz: the signal wavelength is so short that rain, snow, or even rain-filled clouds passing

overhead can reduce the intensity of the incoming signals (Figure 6-14). At these higher

frequencies, the lengths of the falling rain droplets are close to a resonant submultiples of the

signal's wavelength; the droplets therefore are able to absorb and depolarize the microwaves

as they pass through the Earth's atmosphere.

Fig6: C-band vs Ku-band graphical representation

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6.COMPRESSION

The two major providers in the United States use the MPEG-2 compressed video format --

the same format used to store movies on DVDs. With MPEG-2 compression, the provider can

reduce the 270- Mbps stream to about 5 or 10 Mbps (depending on the type of programming).

This is the crucial step that has made DBS service a success. With digital compression, a

typical satellite can transmit about 200 channels. Without digital compression, it can transmit

about 30 channels.

At the broadcast center, the high-quality digital stream of video goes through an MPEG-2

encoder, which converts the programming to MPEG-2 video of the correct size and format

for the satellite receiver in your house.

The MPEG encoder analyzes each frame and decides how to encode it. The encoder

eliminates redundant or irrelevant data, and extrapolates information from other frames to

reduce the overall size of the file. Each frame can be encoded in one of three ways:

As an intraframe - An intraframe contains the complete image data for that frame.

This method of encoding provides the least compression.

As a predicted frame - A predicted frame contains just enough information to tell the

satellite.

Receiver how to display the frame based on the most recently displayed intra frame

or predicted frame. This means that the frame contains only the data that relates to

how the picture has changed from the previous frame.

As a bidirectional frame - To display a bidirectional frame, the receiver must have

the information from the surrounding intraframe or predicted frames. Using data from

the closest surrounding frames, the receiver interpolates the position and color of

each pixel.

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7.ENCRYPTION AND TRANSMISSION

After the video is compressed, the provider needs to encrypt it in order to keep people from

accessing it for free. Encryption scrambles the digital data in such a way that it can only be

decrypted (converted back into usable data) if the receiver has the correct decryption

algorithm and security keys.

7.1 What is Encryption?

Encryption is an electronic method of securing the video and audio of any TV program so

that satellite, cable, and broadcast TV services can maintain control over the distribution of

their signals. To receive encrypted or "scrambled" TV services, cable and SMATV system

operators, hotel chains, private satellite networks, and home dish owners must possess a

compatible decoder that can sense the presence of the encrypted TV signal and then

automatically decode the pictures and sound Premium program services purchase the rights to

movies from film production companies with the understanding that every individual will pay

for the right to view them. Programmers also are very concerned about hotels, bars, and other

commercial establishments that derive monetary benefit from signal piracy.

Within a particular region, program producers may license more than one broadcast outlet for

use of their programs. The program producer may require that broadcasters encrypt their

signals whenever the broadcaster airs the producer's copyrighted material. This strictly limits

reception of the programming to the market for which each broadcaster is licensed. In some

areas of the world, satellite broadcasters periodically must switch from a free-to-air to an

encrypted transmission mode whenever required under their respective agreements with the

program copyright owners.

Each IRD contains a unique numerical address number that is installed at the factory. The

satellite TV programmer's authorization center sends a coded conditional access message

over the satellite that includes this unique address. This authorization message can turn on an

individual IRD so that it can receive a particular service or group of services, or turn off an

IRD in the event that the subscriber fails to pay the required monthly subscription fee.

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Moreover, the authorization center can use this addressable feature to selectively turn off and

on large groups of decoders. Group IRD control is used to selectively "black out" TV events,

such as a live championship boxing match, in certain countries for which the programmer

does not own the distribution rights.

Once the signal is compressed and encrypted, the broadcast center beams it directly to one of

its satellites. The satellite picks up the signal with an onboard dish, amplifies the signal and

uses another dish to beam the signal back to Earth, where viewers can pick it up.

7.2 Bit Rate

The amount of data information being transmitted in one second of time is called the bit rate,

expressed in bits per second (b/s). A bit rate of one thousand bits per second is called a kilobit

per second (kb/s); one million bits per second a megabit per second (Mb/s); and one billion

bits per second a gigabit per second (Gb/s).

A bit rate of more than 200 Mb/s would be required to digitize a broadcast quality video

service without any signal impairment. This would require the use of several satellite

transponders to relay just one uncompressed digital video signal. It therefore is essential that

some form of signal compression be used to dramatically reduce the number of bits required

for digital TV transmissions.

7.3 MPEG-2 COMPRESSION TECHNIQUES

MPEG compression is accomplished through the use of four basic techniques: preprocessing,

temporal prediction, motion compensation, and quantization coding. Preprocessing filters out

nonessential visual information from the video signal-information that is difficult to encode,

but not an important component of human visual perception. Preprocessing typically uses a

combination of spatial and temporal nonlinear filtering.

Motion compensation takes advantage of the fact that video sequences are most often highly

correlated in time-each frame in any given sequence is very similar to the preceding and

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following frames. Compression focuses on coding the difference between frames rather than

the encoding of each frame in isolation. Moreover, many of the changes that occur from

frame to frame can be approximated as translations involving small regions of the video

image. To accomplish this, an encoder scans subsections within each frame-called macro

blocks-and identifies which ones will not change position from one frame to the next.

7.4 THE 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. The

providers use the MPEG-2 compressed video format — the same format used to store movies

on DVDs. With MPEG-2 compression, the provider can reduce the 270-Mbps stream to

about 3 or 10 Mbps (depending on the type of programming). This is the crucial step that has

made DTH service a success. With digital compression, a typical satellite can transmit about

200 channels. Without digital compression, it can transmit about 30 channels. At the

broadcast center, the high-quality digital stream of video goes through an MPEG-2 encoder,

which converts the programming to MPEG-2 video of the correct size and format for the

satellite receiver in your house.

DTH-BENEFITS

• Cost effective communication, information and entertainment to all .

• Small size terminals can provide up to 4000 TV channels and 2000 radio channels through a

click of a button and thus brings world’s at least information, news, entertainment to your

home .

• DTH services are transparent providing digital quality video, audio, radio, and IP to all at

equal prices and other benefits with reliability.

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8. COMMUNICATION CHANNEL AND BAND-WIDTH

In a communications system, the part that connects a data source to a data sink is known as

channel.

Bandwidth refers to the data transmission capacity of a communications channel. The greater

a channel's bandwidth, the more information it can carry per unit of time.

The term technically refers to the range of frequencies that a channel can carry. The higher

the frequency, the higher the bandwidth and thus the greater the capacity of a channel. This

capacity might more appropriately be referred to as throughput.

For digital devices, the bandwidth is usually expressed in bits per second (bps), kilobits per

second (kbps) or megabits per second (mbps). For analog devices, the bandwidth is expressed

in cycles per second, or Hertz (Hz).

The required bandwidth can vary greatly according to the type of application. For example,

the transmission of simple ASCII text messages requires relatively little bandwidth, whereas

the transmission of high resolution video images requires a large amount of bandwidth.

Nevertheless, bandwidth is often insufficient. This is due to such factors as the continued

increase in the numbers of users (especially of the Internet), the growth in the demand for

applications which require more bandwidth and the high cost of upgrading some portions of

networks (particularly replacing copper wire connections to individual homes and offices

with optical fiber). Thus, an important principle in the design of network protocols continues

to be the conservation of bandwidth.

For DTH system communication channel is air and Band-Width is :

Ku Band Uplink : 13.75 to 14.5 GHz

Ku Band Down links : 10.95 to 11.2 GHz

11.45 to 11.70 GHz

12.50 to 12.75 GHz

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RECEIVE TERMINALS

The receive terminals are basically for the reception of the signals being beamed from the

transmission station. The terminal consists of the following:

• receive type solid offset antenna

• LNB feed system

• Interface cables &

• Set top box

The terminal can be placed outside the window of a high rise building, on the ground or a

roof mount. The terminals can be used as per the contents being beam by the transmission

stations.

10.SATELLITE RECEIVING ANTENNAS

10.1 Antenna size considerations:

The selection of the appropriate antenna size helps in keep in the network up and healthy.

It is decided based on the following:

• Satellite EIRP at the particular location.

• Rain attenuation at the location.

• Adequate Eb/No for reception of excellent picture quality.

The satellite dish is a parabola of revolution, that is, a surface having the shape of a parabola

rotated about its axis of symmetry. The resulting paraboloid shares one key property of

25

optical lenses: it is able to form an image of whatever object is placed in front of it. The

largest optical and radio telescopes employ the parabolic reflector to gather and concentrate

electromagnetic radiation. Any antenna surface irregularities or any departure from the

precise parabolic shape will degrade the image resolution. As is more often the case,

however, low-resolution performance is the result of the installer's failure to grasp the

importance of using good antenna assembly techniques.

Fig:7-parabolic reflector

The parabolic curve has the property of reflecting all incident rays arriving along the antenna

reflector's axis of symmetry to a common focus located to the front and centre.

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10.2 Antenna f/D Ratio

The f/D ratio of the antenna is the ratio of focal length to dish diameter, measured in the same

units (Figure 5-10). A paraboloid reflector that is 3 m in diameter and with a focal length of

1.26 m therefore will exhibit an f/D of 0.42. The f/D ratio selected by the antenna designer

also determines the depth of the dish itself, that is, the amount of contour or "wraparound" of

the paraboloid within its fixed diameter. A long-focus (high f/D) paraboloid reflector will

have a shallow contour, while a short-focus paraboloid reflector resembles a deep bowl. The

deepest reflectors have a f/D ratio of 0.25. This places the focal point directly in the plane of

the antenna aperture.

An antenna design with a large value of f/D requires a feed horn that has a narrower beam

width, so that the edge illumination of the antenna can be maintained. This typically is

between 10 and 15 dB below the value produced at the center of the reflector. Conversely, a

small value of f/D will require a feed horn with a wider beam width.

27

Paraboloid antennas that are 3 m or less in diameter (at 4 GHz) commonly use a 12-dB feed

illumination taper, while larger antennas will use a 15-dB taper. The antenna designer must

make a trade-off between antenna gain and noise temperature, balancing the entry of random

noise due to feed horn over illumination or low antenna elevation angle with the noise

contribution of the antenna side lobes in the antenna radiation pattern.

Although the long focal length employed by the shallow dish design increases the

illumination of the reflector surface, there are distinct disadvantages to this design approach.

Moreover, antenna noise increases as antenna elevation increases. Shallow dishes are more

susceptible to intercepting Earth noise when pointing at low elevation angles. Finally, the

shallow dish is more susceptible to picking up terrestrial interference from terrestrial

microwave stations.

The deep-dish design trades off gain in order to lower antenna noise performance. The deep-

dish design is an attractive alternative for locations that potentially may experience terrestrial

interference (TI) problems or at installations that require low antenna elevation angles. The

deep-dish design positions the feed horn relatively close to the rim of the reflector. Therefore,

the deep dish has a greater ability to shield the feed horn from potential TI sources. However,

the feed horn is so close to the reflector that it cannot effectively illuminate the entire surface.

11,DISH MATERIALS AND CONSTRUCTION

The reflector's surface material must be constructed out of metal in order to reflect the

incoming microwave signals. Some antenna reflectors appear to be manufactured out of

plastic or fiberglass; however, these dishes actually have an embedded metal mesh material

that reflects the incoming satellite signals to the front and center of the dish.

The solid one-piece metal antenna is most always the dish with the best performance

characteristics because there can be no assembly errors and the reflector normally will

maintain its precise shape over the lifetime of the system. Solid petal antennas constructed

out of four or more metal panels are generally the next best performance value, as potential

assembly errors are limited to variations along the seams between panels.

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12.Offset-feed Antennas

One oval dish design that is the antenna of choice for most digital DTH satellite TV service

providers is called the offset-fed antenna (Figure 5-5). Here the manufacturer uses a smaller

subsection of the same paraboloid used to produce prime focus antennas (see Figure 5-6), but

with a major axis in the north/south direction, and a smaller minor axis in the east/west

direction.

The offset paraboloid eliminates aperture blockage, reduces antenna noise temperature, and

resists the accumulation of ice and snow by placing the feed below the reflector and angling it

upwards. In this case, the reflector acts as if it were a portion of a much larger paraboloid.

But because only a portion of this imaginary reflector exists, the feed is designed just to

illuminate that portion. The offset-fed antenna then performs just as it would as a part of the

larger dish, and directs its beam exactly the same way.

The offset-fed antenna design offers several distinct advantages over its prime focus

counterparts. There is no feedhorn blockage, an important consideration when the antenna

aperture is less than one meter in diameter. Moreover, antenna designers can reconfigure the

required antenna aperture as a flatter, more nearly vertical reflector, with the added advantage

of pointing the feed skywards, away from the hot-noise source of the Earth. Because of these

29

advantages, the offset-fed antenna can achieve higher efficiency levels than prime focus

antennas normally attain, usually in the 70 percent range. The point is the dish's feed horn,

which passes the signal onto 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 block down 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.

30

12.1Antenna Specifications:

Reflector Size 65cm

Type Offset Feed

Frequency 10.7 to 12.75GHz

Antenna Gain >36.75dBi @12.75GHz

3dB Beam width <3.2 degree

10dB Beam width <5.2 degree

Aperture efficiency >70%

Surface Accuracy <0.01"

Material Steel! Aluminum

Elevation Angel Range 15 to 50 degree

Cross Polar Discrimination on major axis. >27dB

VSWR max 1.3

Noise Temperature < 35 Kelvin

Offset Angle 25 degree

F/D ratio 0.6

31

SET TOP BOX

Simplified Block Diagram

The typical block diagram of the Set top box is as shown in following figure,

Fig:8- Block diagram of Set Top Box

LNB

SMART

CARD

CONVENTIO

NAL MIX. &

LOCAL

OSCCI.

ADC QPSK

DEMOD

.

SYNCHRONI

ZER VITERBI

DECODER

R/S

DECODER

MPEG

TRANSPORT

DEMULTIPL

EXING

MPEG

DECODE

R

DAC

VIDEO

ENCODER CONTROLE

PROCESSOR

CODITIONAL

ACCESS

SYSTEM

32

As per the diagram, the set top box accepts the entire down converted band and separates out

the individual transponder frequency. Then signals are first converted to fixed IF and then

QPSK demodulated. The bandwidth of QPSK signals is 27.5 MHz as the bit rate is 27.5

Mb/s. It is observed that 11 digital channels are multiplexed in 27.5 MHz bandwidth. The

power supply for LNB, polarization selection signals as well as LO setting signals are send

by the set top box itself by using the same cable between the LNB and set top box.

After the QPSK demodulation, the digital bit stream obtained contains several multiplexed

channels as well as error control bits. The bit stream is processed to correct and detect errors,

de-interleaved, and decrypted. A digital demultiplexer then extracts the bits for wanted

channel, and sends them to MPEG decoder, and finally generates analog Audio and Video

signals with DIA converters to drive TV set.

The paid channels are encrypted, and a smart card having the correct key for decryption is

required to view the paid channels. The key is provided by the paying monthly rent by the

user.

13.DTH APPLICATIONS

a) To view pay & free-to-air TV channels of various DTH platform on your home TV.

b) Doordarshan free-to-air services providing 40 TV channels with no subscription fees is

an attractive preposition to people in urban and rural areas. These channels comprises of DD

channels and popular channels of news , sports , information , entertainment etc.

c) One can scan the entire globe with a motorized dish using a CI set top box with CAM

modules and watch TV channels of several DTH platforms visible to the

dish terminals.

d) A number has started IP broadcast with return channel on PSTN line and this would be for

education and other application.

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13.WhyDTH NOT CABLE?

Digital picture.The picture quality in DTH TV is much better. The quality of picture is

uniform across all channels, whereas in cable the quality of picture is inconsistent—some

channels are clear but the balance is fuzzy and snowy.

Digital audio.You get the stereophonic sound. So if you’ve got a home theatre, connect it

to your set-top box. You’ll get better sound effects.

Electronic programmed guide (EPG).It’s an on-screenguide that showsthe programme

schedule or listing of all the channels. So you can find out what’s playing on any channel.

You can also set reminders for programmes you wish to watch and get synopses of the

programmes. Set up your favorite channel list. The list of EPG features varies from

broadcaster to broadcaster.

Payment modes.You pay only for what you watch. Payment is in advance. Recharge is

easy with various sources like the Internet, mobile phones, vouchers from vendors, etc.

Interactive services.This is one important point where you can differentiate between

broadcasters. All the broadcasters offer interactive TV services. Whether it is ordering a

cooking recipe, booking tickets or watching details of a match, everything is controlled

by these applications. With movie-on-demand, you can watch a movie of your choice.

Signal reception in remote areas.Another advantage of DTH is the availability of

satellite broadcast in rural and semi-urban areas where cable is difficult to install.

Radio facility.In DTH service we can have the radio facility also which is not provided

by thecable service provider.

Movable.

Channels lockfacility.

Less wiring.

No dependency on cable operatorfacility.

Less wiring.

No dependency on cable operator.

Recording.

34

CONCLUSION

DTH projects in India are just a beginning and we are taking the advantage of DTH

revolution. Direct to home connects urban, rural and remote areas of the country and provides

desire information communication, education and entertainment at the click of a button.

1. Broadband noise will have negligible effect on GMRT Observations, as the minimum

separation distance is 90 meters with the assumption that there is no DTH system in 100

meter circle from any of the GMRT antennas. Care must be taken for arm antennas.

2. Narrow band noise can cause RFI, in spectral line observations below 400MHz, if located

at about 2 km from a GMRT antenna.

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FUTURE WORK

1. It is useful to be able to control LNB without set top box so as to understand the exact

spectrum at LNB o/p. Effort is to be put to make the circuit on page 18 (or some other

approach) work.

2. Effect of Narrow band noise on GMRT must be studied in detail. Towards this, a DTH

Receiver needs to be installed on an evaluation basis at the GMRT Guest Housel

Recreation Room and test observations in spectral line mode perfonned with different

"poorly made" coaxial cables to link the LNB and STB. Careful check for lines seen in

nearby antennas like C3, C4, and C9 etc in 235 and 325 MHz bands would help in getting

a clearer picture regarding the severity of the problem/s in a controlled manner.

3. Finally, to restrict possible RFI, one can design a Hair Pin Filter with provision of passing

DC and 22 KHz tone which can be added between the LNB and set top box. This will

only allow the required satellite signals and attenuate noise in the GMRT band.

Depending on the result of (2) above, we may have to plan a strategy of adding such units

BEFORE THE STB at installations in nearby villages.

36

REFERENCES

1. http://www.newtec.eu/applications/broadcast/direct-to-home-dth-satellite-broadcast/

2. http://www.mumbaispace.com/dth/dth-india.htm

3. http://www.exchange4media.com/e4m/media_matter/matter_230903.asp

4. http://www.slideshare.net/RavikantSharma/dth-pptpowerpoint-presentation-dth-in-india-

dth-service-provider

5. http://www.slideshare.net/guestcecd24b/dth-power-point-presentation

6. http://www.scribd.com/doc/37060766/DTH-PPT

7. http://www.vijaypadiyar.in/blog/2011/04/is-mpeg4-better-than-mpeg2-for-dth

37

APPENDIX

1. MPEG standards

MPEG stands for Motion Picture Experts Group. It is a working group of experts that was

formed by ISO and IEC to set standards for audio and video compression and transmission.

Currently, DD, DishTV, TataSky services employ MPEG2 standard, while Airtel Digital TV,

Reliance BigTV, Videocon use MPEG4 standard. MPEG-2 standard is considerably broader

in scope and of wider appeal – it supports interlacing and high definition. MPEG-2 is

considered important because it has been chosen as the compression scheme for digital

satellite TV services like Dish Network, digital cable television signals, SVCD and DVD

Video.It is also used on some Blu-ray Discs.

MPEG4 is a better compression technique than MPEG2. In addition to more efficient coding

of video, MPEG-4 moves closer to computer graphics applications.

2. Ku band

Refers to a portion of electromagnetic spectrum in the frequency range of 10.7 - 15GHz.

The Ku band (Kurtz-under band) is primarily used for satellite communications, particularly

for editing and broadcasting satellite television. This band is split into multiple segments

broken down into geographical regions, as determined by the ITU (International

Telecommunication Union).

More specifically, The Ku band is a portion of the electromagnetic spectrum in the

microwave range of frequencies ranging from 11.7 to 12.7GHz (downlink frequencies) and

14 to 14.5GHz (uplink frequencies).

3.CAS scheme

CAS stands for conditional access system, which is a digital mode of transmitting TV

channels trough a set-top box (STB). The transmission signals are encrypted and viewers

need to buy a set-top box to receive and decrypt the signal. The STB is required to watch

only pay channels, not free-to-air channels, like Doordarshan.