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IN PLANT TRAINNING AT DD
Terrestrial Television

Terrestrial Television is a mode of  television broadcast

Uses Radio waves through transmitting and receiving antenna

Terrestrial Television operates on TV channels in VHF and UHF Band.

VHF :   30 - 300 MHz�

Band I  (40-68 MHz)            TV Channel  ≠  4 Channel Spacing - 7 MHz

Band II  (88-108 MHz)          FM Sound Broadcasting Channel Spacing - 100 KHz

Band III  (174-230 MHz) 	     CH ≠ 5 – CH ≠ 12 Channel Spacing – 7 MHz

UHF  :    300 – 3000 MHz�

Band IV  (470 – 606 MHz)       CH ≠ 21 – CH ≠ 37 Channel Spacing - 8 MHz

Band V  (606 – 798 MHz)       CH ≠ 38 – CH ≠ 61 Channel Spacing - 8 MHz

TV Transmitters in DDK Chennai Modulation of Video and Audio Signal In TV broadcast both the sound signal and �video signal are to be conveyed to the viewer �using radio frequency.

The two signals modulate the carrier waves whose frequencies and type of modulations�are as per established standards. Image frequency (IF) In most of the present day TV transmitters the picture signal is amplitude modulated while the audio signal is frequency modulated on different carriers separated by 5.5 MHz.��PICTURE I F = 38.9 MHz�SOUND I F = 33.4 MHz� TV Channel (VHF) Video modulation Carrier is transmitted with full power One complete sideband is also transmitted Only part of the second sideband is transmitted Why Vestigial side band(VSB) DSB takes too much BW (BT = 2W) for the TV channel SSB is too expensive to implement VSB is compromise between DSB and SSB W  BW  2W Easy to implement receiver Types of Modulation Positive modulation The increase in picture brightness causes increase in the amplitude of the modulation envelope

Negative modulation The increase in picture brightness causes reduction in carrier amplitude i.e. the carrier amplitude will be maximum corresponding to sync tip and minimum corresponding to peak white CCVS Modulated carriers Why negative modulation Pictures contain more information towards white than black and hence the average power is lower resulting in energy saving. (Bright picture points correspond to a low carrier amplitude and sync pulse to maximum carrier amplitude). Impulse noise peaks appear only in black region in negative modulation. This black noise is less objectionable compared to noise in white picture region. Best linearity can be maintained for picture region and any non-linearity affects only sync which can be corrected easily. In CCIR (Consultant Committee for International Radio) system sound carrier is 5.5 MHz above the vision carrier and is frequency modulated. The maximum frequency deviation is 50 KHz. Also the ratio of vision and sound power is 10:1 (20:1 is also employed in some countries) If we assume maximum audio signal is 15 KHz the band width is 130 KHz. According to Carson’s Rule the bandwidth is 2 x (Maximum frequency deviation + highest modulating frequency). However, calculated value(using Bessel’s function) of Bandwidth is 150 KHz i.e. 75 KHz on either side of sound carrier. Power output

The peak power radiated during the sync. tip or sometimes the carrier power corresponding to black level is designated as the vision transmitter power. As transmitter output is connected to an antenna, having a finite gain, the effective radiated power (ERP) is obtained by multiplying the peak power by the antenna gain (w.r.t a half wave dipole). TV Transmitters High Power TV Transmitters both the signals (video and audio) modulate the carrier waves whose frequencies and types of modulations are as per established standards. These modulated carriers are further amplified and then diplexed for transmission on the same line and antenna. Low Power TV Transmitters both the signals (video and audio) are modulated separately but amplified jointly using common vision and aural amplifier. Schematic Block Diagram of a TV Transmitter Functional description Video Input :1V pp; Audio Input :+10dBm Video input is band limited to 5Mhz, amplified and inverted compensated for group delay in DVC nonlinearity precorrection in IF corrector Amplitude modulated at 38.9 MHz IF in Modulator Ring modulator/double diode balanced modulator SAW filter shapes the modulated IF to VSB format VCXO generates IF carrier Audio signal is pre-emphasised, amplified and frequency modulated VCO modulator with centre frequency 33.4 MHz

Group Delay Is a measure of the transit time of a signal through a device, versus frequency. It is a useful measure of phase distortion. Equalizers Correct the waveform distortion of the signal by suitably modifying the amplitude and /or group delay characteristics. Pre-emphasis Boosting of higher frequency components

From Analog to Digital More than one program/service in one channel through efficient compression (source coding) Powerful error correction mechanisms ensure proper decodeability Quality of reception can be determined more easily. Distribution costs cheaper per service

Quality vs Distance Schematic Block Diagram of Digital Transmitter Source and channel coding Source coder removes non-essential and redundant parts of the picture signal and performs the bit-rate reduction process. Digital compression techniques enable the original data to be compressed so that it can readily be transmitted over the existing transmission path. Digital compression techniques allow many different programmes to be simultaneously transmitted over a single channel. Channel encoder optimises the data for the particular modulation system and transmission channel.

DVB-T Modulator (FEC)�

Special carriers in DVB-T Continual pilots - fixed position in spectrum - fixed position in constellation diagram - used for automatic frequency control Scattered pilots - var. position in spectrum - fixed position in constellation diagram - used for channel estimation and correction TPS carrier - fixed position in spectrum - BPSK modulation - fast information channel from Tx to Rx Digital Terrestrial Transmitter

UHF Antenna – Super turnstile array To obtain an omnidirectional radiation in the horizontal plane Two crossed dipoles are used in a turnstile arrangement They are fed in quadrature from the same source by means of an extra quarter wavelength line

IPT DD
Digital Earth Station,�DSNG and DTH Focus of Presentation Modes of TV signal Distribution Satellite Communication Analog & Digital Communication Digital Communication setup Digital Earth station- DES Digital Satellite News Gathering- DSNG Direct To Home-DTH

Modes of Distribution of TV Programmes Terrestrial Satellite Cable

All the above three modes can be either in Analog or in digital domain. Satellite Communication Started in 1960. Uses Geo Stationary Satellite. Operates in C-Band & Ku-Band. Started in India in 1975 (SITE). First Indian Satellite INSAT launched in 1982. Gulf War brought satellite television to prominence.

To cover Wide Area in one go. To provide signal for distribution over Doordarshan Network & cable. To have interlink between different TV centres for contribution of programmes like News & Current Affairs. To cover uncovered areas.

Satellite Transmission Frequency bands 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

Why uplink frequency is always higher than downlink frequency ? Satellite Transmission: C-Band Frequency band 4000 to 8000 MHz Large sized dish required for reception Useful to System Providers / Cable Operators Mainly used for contribution & distribution

Satellite Transmission: Ku Band Frequency Band  12.5 to 18 GHz Smaller dish ( 60 – 90 Cms) needed for reception Most useful for DTH application Suitable for fly away terminals Coverage limited as compared to C band due to narrow beam Reception susceptible to failure during heavy rains

Satellite Broadcasting �C-band Vs Ku-band Analog �& �Digital �Communication TYPICAL ANALOG E/S SET UP Problems of Analog One programme per channel / transponder Comparatively noisy Ghosts in Terrestrial Transmission Lower quality with respect to VCD, DVD digital media Fixed reception Why Digital ? More programmes per channel / Transponder i.e. spectrum efficient Noise-Free Reception Ghost elimination CD quality sound & better than DVD quality picture Reduced transmission power Flexibility in service planning -quality / Bandwidth trade off Why Digital ? New services like Pay TV, VOD, Teletext, Data, Surround sound, Multimedia etc. Interactive services like E-commerce, E-banking, Tele-quiz, Tele-games etc. Automated operation in broadcast plan Non availability of analog systems in near future Future of TV transmission – DTH, DTT & Digital Cable Digital Communication Setup Digital Base Band signals

Analog signal is sampled at 13.5,6.75,6.75 MHz, encoded into 10 bits PCM - Total bit rate : 270 Mbps.

The Y (luminance), Cr (R-Y) and Cb (B-Y) signals are used for Digitalization.

The digital standard is known as Serial Digital Interface (SDI)

Audio signal (AES/EBU) either separate or it may be in embedded with Video signal. Rec 601 / 4:2:2 Sampling Audio Standard AES-3 1992 (r1997) Format 	Serial transmission of two channels of 	sampled and linearly encoded data Physical	Shielded twisted-pair (100 meters max.) XLR I/O 	Output – male pins with female shell�	Input – female pins with male shell XLR wiring	Pin 1 – shield, earth, ground�	Pin 2 – signal�	Pin 3 – signal Electrical	110 ohm source�	2 V to 7 V p-p across 110 ohm (balanced)�	Rise/Fall time 5-30 ns�	Intrinsic Jitter – 0.025UI AES Digital Audio Signal

Embedded Audio Standards

SMPTE 272M Formatting AES/EBU Audio and Auxiliary Data into Digital Video Ancillary Data Space for standard definition to be used within SMPTE 259M

SMPTE 299M 24-Bit Digital Audio Format for HDTV Bit Serial Interface to be used within SMPTE 292M Embedded Audio

SD Embedded Audio Embedded Audio Data placed within HANC data Up to 16 channels of embedded audio are specified for HANC Assembled into four groups (1,2,3,4) Each group contains 4 audio data channels each. In SD the audio sample is divided up into the 20bit audio sample and the 4 bit AUX No embedded audio data at switching point or during EDH The data is carried in the Cb Y Cr Y* samples

Video Sources are Collected as SDI or PAL/NTSC signals�� All the video and audio sources are MPEG-2 encoded ��MPEG-2 Re-multiplexing to build up a MPTS transport stream. A MPTS stream contains between 8 and 18 channels��QPSK Modulation of the streams delivered by MPEG-2 Re-multiplexers ��In between each processing step (MPEG-2 encoding,MPEG-2 Re-multiplexing and QPSK modulation) PAL, SDI, ASI and IF routers are interleaved. These routers performs redundancy management (in n+1 or n+p basis) and signals re-routing�

Nextream Statistical Multiplexing « Flextream » Statistical Multiplexing « Flextream » Modulation (Channel Adaptation) �IF Stage Quadrature phase shift keying (QPSK)

Provides high degree of ruggedness against channel noise and interference Encoded digital symbols, each composed of 2 bits, are processed by a conventional Gray – coded QPSK modulator QPSK Modulation & Service Planning Modulation & Service Planning Modulation & Service Planning Link Budget Uplink antenna Gain : 58.21 dB ( 7.2 mtr dia) EIRP Uplink : 76.35 dB Wave guide loss: 3 dB HPA Power: 130 Watts G/T satellite : 4 dB/K ( Delhi) Uplink rain margin: 6 dB C/No Uplink: 96.27 dB EIRP downlink: 51.50 dB ( Delhi) G/T receive antenna : 13.5 dB/K ( 0.6 mtr dia) Downlink rain margin: 5dB C/No Downlink: 83.45 dB C/No overall : 83.22 dB Eb /No : 7.43 dB ( FEC=3/4) Eb /No margin : 1.53 dB The most widely used narrow beam antennas are reflector antennas. The shape is generally a paraboloid of revolution. Link Budget

Up-converters High Power Amplifier High Power Amplifier PDAs Antenna systems The most widely used narrow beam antennas are reflector antennas. The shape is generally a paraboloid of revolution. For full earth coverage from a geostationary satellite, a horn antenna is used. Horns are also used as feeds for reflector antennas. A small earth terminal, the feed horn is located at the focus or may be offset to one side of the focus. Large earth station antennas have a subreflector at the focus. In the Cassegrain design, the sub reflector is convex with an hyperboloid surface, while in the Gregorian design it is concave with an ellipsoidal surface. PDAs Antenna systems Prime Focus

Cassegrain

Off set True Offset Focal Antenna True Offset Focal Antenna Why Offset? Avoid blockage/ LNBF shadow: Low gain

For a reflector antenna, the area is simply the projected area. Thus for a circular reflector of diameter D, the area is A = p D2/4 and the gain is G = h (p D / l )2 which can also be written �			G = h (p D f / c)2 since c = l f, where c is the speed of light (3 ´ 108 m/s), l is the wavelength, and f is the frequency.

The gain increases as the wavelength decreases or the frequency increases.

For example, an antenna with a diameter of 2 m and an efficiency of 0.55 would have a gain of 8685 at the C-band uplink frequency of 6 GHz and wavelength of 0.050 m. The gain expressed in decibels (dB) is �10 log(8685) = 39.4 dB. Thus the power radiated by the antenna is 8685 times more concentrated along the boresight direction than for an isotropic antenna, which by definition has a gain of 1 (0 dB). At Ku-band, with an uplink frequency of 14 GHz and wavelength 0.021 m, the gain is 49,236 or 46.9 dB.

Digital Earth Station Digital Earth Station Earth Station is a uplink center from which the signals are fed to Satellite for distribution in a specified area covered by the Satellite.

The signal is up-linked from the earth station and received by many down link centers in TV broad casting.

It is a very important part of satellite communication system for broadcasting of signals. Earth Station classification Analog Earth Station

Analog / Digital Simulcast

Digital Earth Station

ASNG

DSNG

C-band or Ku-band

Salient Features of Digital Earth Station Latest State-of-the art facility used. Full redundancy of chain components available Turn around( without bit rate control)/Re-encoding facility available Statistical Multiplexing employed for optimum transponder utilization. Provision to add EPG/CAS exists in uplink equipment.

Satellite Broadcasting -Digital Tremendous savings in satellite capacity. 10 to 14 TV channels per 36 MHz Transponder        ( DVB-S, MPEG 2 )

25 to 50 TV channels in 36 MHz Transponder         ( DVB-S2, MPEG 4 / WM 9)

Excellent quality of signal reception.

New services like VOD,PPV etc. Major Components of Digital Earth Station

(Digital Satellite News Gathering) DSNG Uplink & Downlink Early DSNG Present DSNG Present DSNG PDA System Present DSNG Main Components of DSNG Typical DSNG Setup 1+1 configuration Types of PDA Flyaway DSNG PDA Cassegrain PDA Prime Focus PDA Offset PDA Drive-away DSNG PDA Drive-away DSNG PDA Assembling an Offset PDA Ku band PDA (Auto Tracking) Types of Uplink Feeds Feed Horn Corrugated Horn for Feed Combiner & Feed Why TRF is needed? Transmit Reject Filter

Why LNB is needed? Low Loss Cable Co-axial Cable Single Braiding

Double Braiding

Foil Shielding RF Connectors N connector

F connector Frequency Bands for Satellite Communication Telemetry of Satellites

100% potential TV population should be covered preferably with multi-channel television services by the end of 10th Plan. Why Ku-band Transmission ? Alternate technology for cost-effective & quick 	expansion of television coverage for individual reception              	   	Due to scattered pattern of population in the uncovered area 				comprising of mostly hilly, inaccessible & remote terrains, 					expansion by terrestrial mode is not economically viable as 				shown below: Expansion		Coverage		Cost			Duration			No. of           			mode          	  (% of population)    (Rs. Crores)	of imple-    		channels 																	mentation Terrestrial		90%				4500			45 Years		1 10%				3500			8-10 years		1

Satellite			100%				35				9 months		33

Multi-channel individual reception possible with a  small   	sized dish antenna system No dependency on Cable Operator

Television Coverage in the Country - A few facts Total Households 		-	202 million

Total TV Households 		-        90 million Total Terrestrial only 	-	 45 million                                          (DD Exclusive) Households

Total Cable       		-	 45 million                                       Households Total Non-TV Households 	-        112 million Covered by Terrestrial TV 	-	92 million                        Signal of Doordarshan Not covered by Terrestrial/	-	20 million                Cable TV Signal (Primary Target for DD Direct Plus DTH Service)

Unique features of DD Direct+ One time expenditure for procuring receive system by viewer No monthly/activation charges from the subscriber No smart card/CAM module required for reception Cost effective alternate to cable TV Truly ‘AAM AADMI’ ka DTH

Details of Project Implementation April 2003	- In principle approval by 		 Planning Commission June 2003	- Approval of pilot project 		 by EFC Nov. 2003	- Approval by CCEA 29 June 2004	- Launch of trial service 16 Dec. 2004	- Inauguration by Hon’ble PM

Space segment 5 Ku-band transponders (36MHz each) met by Department of Space (DOS) by providing 54 dBW EIRP transponders in NSS-6 located at 95 degrees east. Service to be shifted to co-located INSAT- 4B    (93.5 degrees east) on its becoming operational sometime in 2005/2006 (will not necessitate re-orientation of existing receive antenna due to co-location of the two satellites) Annual lease charges per transponder per year 						 = US$ 1 million

Receive Eqpt.for DD Direct+ Receive Eqpt. consists of a 60 /90 cm Dish Antenna, a Block converter and a Set Top Box (STB) STB readily available in the open market Dealers of the equipment available all over the country. Indicative cost of the receive system –                     Rs 3000 to Rs 3500. Cost likely to come down further with volumes.