Industrial training report

REPORT OF INDUSTRIAL TRAINING
Undergone at
DOORDARSHAN KENDRA AND ALL INDIA RADIO
THIRUVANANTHAPURAM
Submitted by
RESHMI R
Reg. No: 80421
Under the guidance of
Ms. MITHRA S T
M.TECH IN COMMUNICATION ENGINEERING
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
SREE BUDDHA COLLEGE OF ENGINEERING FOR WOMEN
(Afﬁliated to Mahatma Gandhi University)
PATHANAMTHITTA-689625

SREE BUDDHA COLLEGE OF ENGINEERING FOR WOMEN
(Afﬁliated to Mahatma Gandhi University)
ELAVUMTHITTA, PATHANAMTHITTA
BONAFIDE CERTIFICATE
Certiﬁed that this Industrial Training Report submitted by RESHMI R (Reg. No.
80421) has undergone the training at DOORDARSHAN KENDRA and ALL INDIA RA-
DIO with the prior permission and approval from the department.
Guide: Head of the Dept. :
Ms. Mithra S T Ms. Sangeeta T R
Assistant Professor Assistant Professor
Department of ECE Department of ECE
Coordinator: External Examiner:
Ms. Jisha Anu Jose
Assistant Professor
Department of ECE

ACKNOWLEDGMENT
It is a matter of great pleasure and privilege for me to present this report of one month
industrial training. Through this report, I would like to thank numerous people whose con-
sistent support and guidance has been the standing pillar in architecture of this report.
To begin with, my sincere thanks to Dr. E GOPALAKRISHNA SARMA, Principal
of my college. I express thanks to Ms. SANGEETA T R, HOD, Department of Electron-
ics and Communication, who gave encouragement and valuable suggestions throughout the
training. Next, I would like to express my sincere gratitude to my guide, Ms. MITRA S T.
I was privileged to experience a sustained enthusiastic and involved interest from her side.
I would like to mention a great word of gratitude to Ms. JISHA ANU JOSE, Co-ordinator
of M. Tech program, who gave full support throughout the training.
I would like to express my sincere thanks to Mr. S RAMESH (DDE), Mr. BABU
JOHN, Ms. MOLLY VARGHESE (AE) and Mr. OOMMEN CHERIAN who provided
us with the opportunity to undergo training in Doordarshan Kendra, Thiruvananthapuram.
I wish to express my deep gratitude towards Mr. N S SANIL KUMAR, Direc-
tor (Engg.) and all other staff at All India Radio, Thiruvananthapuram for making me a
deep knowledge about various attributes of studios and transmitters.
RESHMI R
i

ABSTRACT
Industrial training is an important phase of a student life. A well planned, properly
executed and evaluated industrial training helps a lot in developing a professional attitude.
It develop an awareness of industrial approach to problem solving, based on a broad under-
standing of process and mode of operation of organization. During a period of one month
training at Doordarshan Kendra (DDK) and All India Radio (AIR), most of the theoretical
knowledge that has been gained during the course of studies is put to test. The great effort
behind the production of each programmes on television and radio have been understood
during this training. DDK and AIR are division of Prasar Bharati, the India’s largest public
broadcaster. DDK Thiruvananthapuram is equipped with two studios, two terrestrial trans-
mitters and one digital uplink station. DDK deals with production, storage and transmission
of television programmes. For these purposes, DDK has various departments. Generation
of a program takes place at studio and the post production activities are controlled by the
PCR. These programs are stored in a video tape recorder. The MSR stores all the circuitry
of the DDK and it directs which recorded programs to go on-air. Earth station transmits or
receives the program to or from the satellite. The last stage is the transmitter which has the
antenna and facilities for terrestrial transmission. It is this transmitted programs that the
public receives either via DTH or terrestrial antenna.
As India’s National broadcaster and also the premier public service broadcaster, AIR
has been serving to inform, educate and entertain the masses since it’s inception, truly liv-
ing up to its motto ”Bahujan Hitaya : Bahujan Sukhaya”. AIR, which is ofﬁcially known
as Akashvani since 1956, has three main transmitters for transmitting their programmes to
almost all parts of the world. The 20 kW medium wave transmitter of AIR is located at
Kulathur which transmits the programs to local regions. 50 kW short wave transmitter of
AIR located at Beemapally transmits programs around the globe using ionosphere reﬂec-
tion property. FM transmitter located at Kudappanakunnu transmits high quality programs.
Studio, control room and the transmitter are the main sections of the AIR Thiruvanantha-
puram for genereation of a program.
ii

LIST OF FIGURES
2.1 General block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Different types of microphones . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 Uplink chain of DES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 Downlink chain of DES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.5 Outside broadcasting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.6 Terrestrial transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.1 Radio communication system . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.2 Block diagram of radio studio . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.3 Block diagram of Earth Station . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.1 Block diagram of MW transmitter . . . . . . . . . . . . . . . . . . . . . . . . 42
3.2 Self radiating MW Mast Antenna . . . . . . . . . . . . . . . . . . . . . . . . 45
4.1 Block diagram of SW transmitter . . . . . . . . . . . . . . . . . . . . . . . . 47
4.2 Curtain antenna at SW transmitter . . . . . . . . . . . . . . . . . . . . . . . . 48
5.1 FM transmitter block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.2 Dipole antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
iii

ACRONYMS
AES Audio Engineering Society
AIR All India Radio
ASI Asynchronous Serial Interface
CAR Central Apparatus Room
CCD Charge Coupled Device
CCU Camera Control Unit
CES Captive Earth Station
DDK Doordarshan Kendra
DES Digital Earth Station
DSNG Digital Satellite News Gathering
DTH Direct-to-Home
DVCPRO Digital Video Casette Professional
IGNOU Indira Gandhi National Open University
IRD Integrated Receiver Decoder
ISDN Integrated Service Digital Network
LNBC Low Noise Block Converter
MPEG Moving Picture Experts Group
MSR Master Switching Room
PCR Production Control Room
PDA Parabolic Dish Antenna
SAW Surface Acoustic Wave
SDI Serial Digital Interface
STL Studio Transmitter Link
TSL Transmitter Studio Link
VLPT Very Low Power Transmitter
VSB Vestigial Sideband
VTR Video storage and Transmission Room
iv

CONTENTS
ACKNOWLEDGMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
ACRONYMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
I DOORDARSHAN KENDRA THIRUVANANTHAPURAM 1
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. TECHNICAL OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Studio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1 Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Camera Control Unit (CCU) . . . . . . . . . . . . . . . . . . . . . 6
2.1.3 Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.4 Microphone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Production Control Room (PCR) . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.1 Vision Mixer(VM) . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2 Audio Mixer or Sound-craft Audio Processor . . . . . . . . . . . . 10
2.3 Video storage and Transmission Room (VTR) . . . . . . . . . . . . . . . . 12
2.3.1 Video Tape Recorder . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.2 Video Recording Methods . . . . . . . . . . . . . . . . . . . . . . 13
2.3.3 Video Editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4 Master Switching Room (MSR) . . . . . . . . . . . . . . . . . . . . . . . 14
2.5 Digital Earth Station (DES) Simulcast . . . . . . . . . . . . . . . . . . . . 14
2.6 Outside Broadcasting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.6.1 Microwave Link . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.6.2 DSNG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.7 Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.7.1 Vision and Sound Signal Ampliﬁcation . . . . . . . . . . . . . . . 20
2.7.2 Exciter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
v

2.7.2.1 Video Chain . . . . . . . . . . . . . . . . . . . . . . . . 21
2.7.2.2 Audio Chain . . . . . . . . . . . . . . . . . . . . . . . . 21
2.7.2.3 IF Combiner & IF Corrector . . . . . . . . . . . . . . . . 21
2.7.2.4 VSB Filter . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.7.2.5 Modulator Module . . . . . . . . . . . . . . . . . . . . . 22
2.7.2.6 Local Oscillator . . . . . . . . . . . . . . . . . . . . . . 22
2.7.2.7 Up-converter Module . . . . . . . . . . . . . . . . . . . 22
2.7.3 Power Supply Circuit . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.7.4 RF Power Ampliﬁer . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.7.5 Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.8 DTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
II ALL INDIA RADIO THIRUVANANTHAPURAM 25
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.1 Other Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2. RADIO COMMUNICATION SYSTEM . . . . . . . . . . . . . . . . . . . . . . 28
2.1 Radio Studio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.1.1 Recording . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.1.1.1 Microphone . . . . . . . . . . . . . . . . . . . . . . . . 33
2.1.2 Editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.1.2.1 Mixing Console . . . . . . . . . . . . . . . . . . . . . . 34
2.1.3 Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.1.4 Playback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.1.4.1 Virtual Studio . . . . . . . . . . . . . . . . . . . . . . . 36
2.2 Control Room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.3 Studio Transmitter Link (STL) . . . . . . . . . . . . . . . . . . . . . . . . 37
2.3.1 Microwave Link . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.3.2 Integrated Services Digital Network (ISDN) . . . . . . . . . . . . . 38
2.3.3 Leased Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.3.4 Captive Earth Station . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.4 Earth Station (ES) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.4.1 Operation of ES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3. MEDIUM WAVE TRANSMITTER . . . . . . . . . . . . . . . . . . . . . . . . 41
3.1 RF Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.1.1 Buffer Ampliﬁer . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.1.2 Pre-driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.1.3 Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.1.4 Combiner and Splitter . . . . . . . . . . . . . . . . . . . . . . . . 42
3.1.5 Power Ampliﬁer (PA) . . . . . . . . . . . . . . . . . . . . . . . . 43
3.1.6 PA Combiner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.1.7 Output Network . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.2 Audio and Modulation Section . . . . . . . . . . . . . . . . . . . . . . . . 44
3.2.1 Audio Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.2.2 Analog to Digital Converter (ADC) . . . . . . . . . . . . . . . . . 44
3.2.3 Modulation Encoder . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.2.4 DC Regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.3 Medium Wave Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4. SHORT WAVE TRANSMITTER . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.1 Component Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.1.1 RF Synthesizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.1.2 Tetrode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.1.3 Dummy Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.1.4 Curtain Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2 Operation of SW Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . 49
5. FM BROADCASTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.1 FM Transmitter Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 50
CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

PART I
DOORDARSHAN KENDRA
THIRUVANANTHAPURAM
1

INDUSTRIAL TRAINING REPORT
CHAPTER 1
INTRODUCTION
Doordarshan (DD) is an Indian public service broadcaster, a division of Prasar Bharati.
It is one of India’s largest broadcasting organizations in terms of studio and transmitter
infrastructure. Recently, it has also started broadcasting on digital terrestrial transmitters.
The DD provides television, radio, online and mobile services throughout metropolitan and
regional India, as well as overseas through the Indian Network and Radio India.
1.1 History
Doordarshan had a modest beginning with an experimental telecast starting in Delhi
on 15th
September 1959, with a small transmitter and a make shift studio. The regular daily
transmission started in 1965 as a part of All India Radio. Television services were separated
from radio on 1st
April 1976. Finally, in 1982, Doordarshan as a national broadcaster came
into existence. Krishi Darshan was the ﬁrst program telecast on Doordarshan.
Doordarshan Kendra (DDK), Thiruvananthapuram is part of the DD India. DDK with
over 35 terrestrial transmitters and 3 production centers serve Kerala, Lakshadweep and
Mahi regions. Inaugurated on 1st
January 1985 by the then Chief Minister of Kerala Shri.
K Karunakaran, DDK Thiruvananthapuram currently produces and telecasts 168 hours of
malayalam programmes per week. 27 transmitters in Kerala, 7 in Lakshadweep and one in
Mahi relay these programmes. Now more than 90 per cent of the 35 million populations
of Kerala, Lakshadweep and Mahi can receive DDK Thiruvananthapuram programmes
through a network of terrestrial transmitters. With the introduction of DTH, almost cent
percent of the population can now receive DDK Thiruvananthapuram programmes with-
out cable connection. Doordarshan studios have been established at Thiruvananthapuram,
Thrichur and Calicut to foster regional diversity. People all over India are watching Do-
ordarshan’s malayalam programmes. It is also received in 64 countries spread over the
continents of Asia, Africa, Europe, Australia and America. Doordarshan operates 21 chan-
nels:
• Two all India channels (DD National and DD News).
Dept. of ECE 2 SBCEW, Elavumthitta

• 11 Regional Language Satellite Channels (RLSC), four State Networks (SN), an Interna-
tional channel, a sports channel (DD Sports) and two channels (Rajya Sabha TV and Lok
Sabha TV) for live broadcast of parliamentary proceedings.
On 17th
November 2014, Doordarshan will be relaunched with new theme of pink
and purple and accompanied by a new punch line ”Desh ka Apna Channel” (country’s own
channel). It was announced by Vijayalaxmi Chabra, director general, Doordarshan.
DD has its own DTH service called DD Direct Plus; it is free of charge. DD India is
broadcast internationally via satellite. It is available in 146 countries worldwide, however,
information on receiving this channel in other countries is not easily available. In the UK,
DD India was available through the Eurobird satellite on the sky system on channel 833
(the logo is shown as Rayat TV). The timing and programming of DD India international is
different from that of India. Transmissions via Sky Digital ceased in June 2008 and those
via Direct TV in the United States in July 2008.
DDK Thiruvananthapuram is equipped with two studios, two terrestrial transmitters
and one digital up-link station. The two terrestrial transmitters are of 10 kW power each.
One is for DD National and the other is for DD News telecasting.

CHAPTER 2
TECHNICAL OVERVIEW
DDK Thiruvananthapuram has the following main departments which manage the
production, storage, transmission and maintenance of the two DD National channels and
the DD Malayalam channel.
1. Studio
2. Production Control Room (PCR)
3. Video storage and Transmission Room (VTR)
4. Main switching Room or Master Switching Room (MSR)
5. Digital Earth Link Station (DES)
6. Transmitter
Figure 2.1: General block diagram
2.1 Studio
The studio has the following inevitable equipments that plays a vital role in the pro-
duction of a television program. They are listed below:
• Camera, lights, microphones and other equipment required for production of a feed.
• Camera Control Unit (CCU).
It is in the studio that all aspects related to the production of a video takes place. The
DDK Thiruvananthapuram has one large studio and a small studio.

2.1.1 Camera
The studio television camera is the beginning of the video signal. It is here that
visible light is transformed or transduced into electrical energy. The video signal remains
in the form of electrical energy, either analog or digital, for most of the remaining process
until a picture monitor (TV set) converts the electrical signal back into visible light.
Camera has a head unit as well as a base unit. The head unit is located in the studio
and the base unit is located in the MSR. The camera is attached to a head which is in turn
attached to the camera support; in our case a tripod and dolly combination. Also there is
a Camera Control Unit (CCU) which is a separate unit in itself which is used to control
the camera. The base unit of the camera houses all the electronics related to the camera.
Whereas the head unit of the camera is the part which the camera man handles in the studio.
This unit reduces the clutter in the studio, which is connected to other parts of the system
through a triax cable. This cable carries power for the camera, signals of the pictures to
and from the camera and also carries the communications in RF to and from the camera.
The head unit of the camera houses the Charge Coupled Devices (CCD) which take in the
light from the viewing area and convert them to electrical signals. Before the light hits the
CCDs in a colour camera, a dichroic prism is used to split the three primary colours RGB
into three and cause them to be absorbed by different CCDs which are kept at the focus of
the lens system. They absorb light from each part of the screen pixel after pixel and for a
moving picture frame after frame. The CCDs improve the apparent limit resolution with
the help of spatial pixel shifting. There are three types of CCDs available which are listed
below:
• Interline Transfer (IT)
• Frame Transfer (FT) and
• Frame Interline Transfer (FIT)
The DDK Thiruvananthapuram studio uses 4 IKEGAMI (HK 399W) cameras in
studio-1 and an Ikegami camera and a SONY camera in studio-2. The Ikegami camera
and Sony both uses FIT type CCDs. The Sony camera gives a digital output where as the
Ikegami gives out an analog output.

2.1.2 Camera Control Unit (CCU)
The output of the cameras is pre-amplified in the camera head unit and then converted
to the camera control unit (CCU) through long multi-core cable (35 to 40 cores), or triax
cable. All the camera control voltages are fed from the CCU to the camera head over
the multi-core camera cable. The view-finder signal is also sent over the camera cable
to the camera head. It is this view-finder signals which helps the camera-man in proper
focusing, adjusting and composing the shots. The video signal so obtained is amplified, H.F
corrected, equalized for cable delays, DC clamped, horizontal and vertical blanking pulses
are added to it. The peak white level is also clipped to avoid overloading of the following
stages and avoiding over-modulation in the transmitter. The composite sync signals are fed
to a distribution amplifier, which normally gives multiple outputs for monitoring. All the
correction regarding the video camera is applied here in the CCU. Parameters like average
brightness, contrast ratio, gamma correction, voltage level, etc observed here and if varies
it can be controlled manually or automatically by the machine.
2.1.3 Lighting
When we shoot outdoor program, the source of light is Sun. The natural effect we see
in outdoor is greatly depends on the proper lighting. Lighting for television is very exciting
and needs creative talent. There are two main reasons to use lighting techniques in studios:
1. When we create an artificial set, to make it look like natural we have to give the proper
lighting effects. Lighting also depends on the mood of the scene.
2. The output of the camera is 2D, while natural scenes we see are 3D. On TV screen to
differentiate the main object from the background and to give 3D effect lighting is must.
In studios, mainly ”Three point lighting” technique is used. The three points are:
1. Key light: It is the main light used to highlight any object or to give attention towards the
person. This is full intensity light used to highlight the depth of the object or human face.
Key light is usually a hard source at an angle of 15◦
to 30◦
to camera axis at an elevation of
about 40◦
.
2. Fill Light: It is 80% intensity of the key light and at the opposite side of the camera axis.
Fill light is used to suppress the shadow made by key light. It is soft light and also used to
fill the light in whole room.

3. Back light: It is used to separate artist from the background ans so to produce 3D
visualization by rim lighting the head and shoulders. It is hard source located at 180◦
of
the camera axis.
The last is the Background Light used to highlight the background of the scene or to
create colour background on white cyclorama.
The three point lighting ratio is 3:2:1 (back: key: ﬁll) in monochrome and 3:2:2 in
colour, which provide good portrait lighting. Intensity and power on/off of lights are con-
trolled from the LCU (Light Control Unit). In DDK, LCU is merged with CCU. Different
light sources used in a studio are listed below:
• Incandescent Light
• Basic Tungsten Filament Lamp
• Tungsten Halogen Lamps (Tungsten Iodine or Quartz Iodine Lamps)
• Compact Source Iodide (CSI) Lamp
• HMI Metal Halide Discharge Lamp
• High Frequency Fluorescent Light Sources
2.1.4 Microphone
Microphone plays a very important role in the art of sound broadcasting. It is a device
which converts acoustical energy into electrical energy. Different types of Microphones are
the following:
a) Dynamic or Moving Coil Microphone: It works based on the principle of mutual induc-
tion.
b) Electret Microphone: It is a modiﬁed form of condenser microphone in which the polar-
ising voltage is avoided. Used in cellphones, computers, PDA and headset microphones.
c) Ribbon Microphone: It is having symmetrical front and rear pickup. It is used in normal
stereo recording.
d) Gun Mike: It has two forms, short gun and long gun, and is highly directional. An
example is the picking of the sound of bat hitting a cricket ball.
e) Lapel Microphone: This kind of microphone can be worn on the body.
f) RF or Cordless Microphone: They have a small FM transmitter which transmits the
collected signals to a nearly placed receiver connected to the sound system.

Figure 2.2: Different types of microphones
2.2 Production Control Room (PCR)
The PCR is also known as studio control room. The PCR is where the post production
activities like minor editing and management of feed during a live program takes place.
The production manager sits in the PCR and directs the camera-men and selects the angles,
sound parameters, etc during the production stage in the PCR. It is in the PCR that we can
control all the studio lights and all the microphones and other aspects. The PCR is where
the phone-in console and other systems are also kept.
A major objective of TV program control facilities is to maintain a smooth continuous
ﬂow of program material. The overall control of program is done in production control
room by the producer with the help of a production assistant, a CCU engineer and an
engineer at vision mixer. They have in front of them, the switching panel of the vision
mixer console and a stack of monitors for the individual cameras, preview monitors of
VTRs and transmission monitor for displaying the switched output, with the aid of which
the program is edited. The PCR consists of the following equipments:
1. Vision Mixer (VM)
2. Audio Mixer (AM)

2.2.1 Vision Mixer(VM)
The Vision Mixer (VM) is the destination point for all the picture sources in the
studio. The output of the studio cameras, video tape recorder, caption scanners, character
generators, etc are fed to the vision mixing unit. A VM or video switcher enables the
program producer to select the desired sources or a combination of the sources in order to
compose the program. The VM is typically 10×6 or 20×10 crossbar switcher selecting any
one of the 10 or 20 input sources to 6 to10 different output lines. The input sources include:
Camera-1, Camera-2, Camera-3, Telecine-1, Telecine-2, VTR-1, VTR-2, Test Signal etc.
The output of the mixer desk is fed to the transmission monitor, transmission chain, etc in
production control area.
Vision mixing is a process of creating video from various sources. Vision mixing
involves basically three types of switching or transitions between various sources. These
are mixing, wiping and keying and digital video effects. VM provides the following oper-
ational facilities for the editing of the TV programs:
• Cut: An instantaneous switch from one video signal to another (or Take selection of any
input source).
• Transition: A controlled change from one video input to another video input or black.
The change can occur through a wipe, cut, dissolve or ”DVE Send” effect.
• Dissolve or mix: ”Fading in or out”. A transition from one video signal to another in
which one signal is faded down while the other is simultaneously faded up.
• Lap Dissolve: Dissolving from one source to another with an overlap mixing.
• Wipe: A transition from one video signal to another, in which the change proceeds ac-
cording to the shape of a speciﬁc pattern. A moving transition line separates the two picture
signals.
• Down-Stream Keyer (DSK): A keyer that places a key ”downstream” of the MLE effects
system output. This ”top level” effect usually consists of a character generator title.
• External Key: A video input (non-primary video) used to produce a key effect. Exam-
ples: character generators and cameras. Character Generator creates the majority of names
and graphics that is to be inserted into programs.
• Chroma Key: An effect in which video from one source replaces video of a speciﬁc hue
in a second video source. The blue and green hues are most commonly used for chroma

keying.
• Luminance Key: An effect in which video from one source is replaced by video that
exceeds a set level in a second video source.
• Self Key: A key effect in which the same video signal serves as both the key signal and
key fill.
• Video: The electrical signal produced by a television camera, character generator or other
image source. The signal amplitude varies in relation to the tonal scale from black to white
presented at the source. White produces the highest amplitude, black produces the lowest
signal amplitude.
• Fade-to-Black: A controlled change of the on-air picture signal level down to black level.
2.2.2 Audio Mixer or Sound-craft Audio Processor
Audio (Sound) mixer is a unit used in the PCR to control all the audio of the incoming
sound from the studio or other source. It is the single most important component used to
control audio in an audio chain. The sound mixer used in DDK Thiruvananthapuram is a
Sound-craft sound mixer. It is located in both the PCRs with a standby arrangement for
each.
All mixers carry out the same basic function; to blend and control the volume of a
number of input signals, add effects and processing where required and route the resulting
mix to the appropriate destination, which could be power amplifiers, the tracks of a record-
ing device or both. A mixer is the nerve centre of these sources, and therefore the most vital
part of any audio system. A mixer performs a variety of functions and add some effects
which are detailed below:
• Equalization: Useful for making both corrective and creative changes to a sound, but
it need to be used with care. Corrective applications include making tonal changes to
compensate for imperfect room acoustics, budget microphones or inaccurate loudspeaker
systems.
• Fixed Equalization: The fixed control influences a relatively large section of the audio
spectrum. Apply too much bass boost and you could find the bass sounds take on a flabby,
uncontrolled characteristic which makes the mix sound muddy and badly defined. This is
because sounds occupying the lower mid part of the spectrum are affected. Similarly, use

too much top boost and the sound becomes edgy with any noise or tape hiss being empha-
sized quite considerably. In a PA situation, excessive EQ boost in any part of the audio
spectrum will increase the risk of acoustic feedback via the vocal microphones.
• Using Effects Units:
1. Reverbation: It is the persistence of sound in a particular space after the original
sound is produced. The ’hanging-on’ of the sound in a room after the exciting signal has
been removed, is called reverberation and the time taken for the sound to decay to one
millionth of its initial value, i.e., 60 dB, after the source has stopped, is termed ’Rever-
beration Time’. Reverberation time is affected by the size of the space and the amount of
reflective or absorptive surfaces within the space. A space with highly absorptive surfaces
will absorb the sound and stop it from reflecting back into the space. Larger spaces have
longer reverberation times than smaller spaces. Therefore, a large space will require more
absorption to achieve the same reverberation time as a smaller space.
Recording studios are carefully designed around the principles of room acoustics to
create a set of spaces with the acoustical properties required for recording sound with preci-
sion and accuracy. This will consist of both room treatment (through the use of absorption
and diffusion materials on the surfaces of the room, and also consideration of the physical
dimensions of the room itself in order to make the room respond to sound in a desired way)
and soundproofing (to provide sonic isolation between the rooms).
2. Delay: It is often used to make a sound ’thicker’ by taking the original sound,
delaying it, then mixing it back with the original sound. This short delay added to the
original sound has the effect of doubling the signal.
3. Echo: It is a popular effect that was used extensively on guitars and vocals in the
60s and 70s. It is not used on vocals so much nowadays, but quite effective on guitars and
keyboards. A neat trick is to set the echo delay time so that the repeats coincide with the
tempo of the song.
4. Chorus & Flanging: Both chorus and flangers are based on a short delay, combined
with pitch modulation to create the effect of two or more instruments playing the same part.
Flanging also employs feedback and is a much stronger effect. Both these treatments work
well on synth pad sounds such as strings and are best used in stereo where they create a
sense of movement as well as width.

5. Pitch Shifters: These change the pitch of the original signal, usually by upto one
octave in either direction and sometimes by two. Small pitch shifts are useful for creating
de-tuning or doubling effects. Which can make a single voice or instrument sound like two
or three, while larger shifts can be used to create octaves or parallel harmonies.
All these effects will be added in the audio processor and the final output will be sent
to VTR along with video in case of a recording or will be telecast live through MSR as is
required.
2.3 Video storage and Transmission Room (VTR)
The VTR is the next section where copies of all programs are stored. All the pro-
grams shot in the camera are simultaneously recorded in the VTR. Also the VTR plays
back all the videos as and when required. Videos of pre-recorded events are queued up
in the VTR and are played back without a break. Videos of famous people and important
events are stored in the central film pool.
2.3.1 Video Tape Recorder
Video Tape Recorder is the most complex piece of studio equipment with analog and
digital processing servo system, microprocessors, memories, logic circuits and mechani-
cal devices, etc. The standardized two inch tape quadrupled head recording machines are
called the video tape recorder and are used for the high quality video tape recording. One
or half inch helical scan tape recorders have been used for outdoor field recording. This
multi-purpose studio digital video cassette tapes, and is designed to record, play back and
edit interlace signals (625/525) as well as record, playback and edit existing DVCPRO sig-
nals (25Mbps). Its 625/525 switching functions makes this studio video cassette recorder
which can be used anywhere in the world. In addition, it corporate digital compression
technology so that the deterioration in picture quality and sound quality resulting from
dubbing is significantly minimized. The compact, light weight 4U size makes carry easier,
even when mounted in a 19 inch rack. The settings for the units set up can be performed
interactively while viewing the screen menus on the monitor, and editing functions include
both assemble and insert editing.

2.3.2 Video Recording Methods
Different types of video recording are possible. The common video recording meth-
ods are given below:
1. Video Tape Recording (Magnetic tape recording)
2. Professional Disks (Blue ray disk recording)
3. Servers (Hard disk based recording)
A recording format is developed by a consortium of ten companies as a consumer
digital video recording format called DV. DV (also called ”mini DV” in its smallest tape
form) is known as DVC (Digital Video cassette). DVCAM is a professional variant of the
DV, developed by Sony and DVCPRO on the other hand is a professional variant of the DV,
developed by Panasonic. These two formats differ from the DV format in terms of track
width, tape speed and tape type.
2.3.3 Video Editing
Basic steps involved in video editing are:
• Assembles the required shots to make a sequence.
• Modify the shots by insertion or deletion.
• Adds special effects.
• Add titles.
Two types of video editing are possible. They are:
1. Linear: Tape to tape/machine to machine editing (linear access to shots).
2. Non-linear: File based editing using softwares (non linear access to shots). Software
used in Doordarshan for Non Linear Editing : Final Cut PRO, DPS Velocity, Adobe Premier
PRO CS.
Non linear editing work ﬂow is given below:
• Open a new project.
• Capture/import video and audio.
• Assemble and reﬁne a sequence in timeline.
• Modify the sequence using various tools.
• Add transitions and effects.
• Add titles.

• Mix audio tracks (Premire Pro saves your adjustments in real time).
• Export the final product to required media (disc, tape or to any other format).
2.4 Master Switching Room (MSR)
The MSR was initially known as Central Apparatus Room (CAR) which stores all
the circuitry of the DDK. All the camera base units, all the vision mixer base units and all
the audio processor base units are kept in MSR. The monitoring and control of all activities
takes place in MSR. It is the MSR which decides what is to go in air. The MSR also
performs some additional functions like logo addition, etc.
MSR is the engineering coordination center for TV station. This room is the cen-
ter of activity for selecting and routing the signals from various sources to transmitters
and Earth station. This room comprises of routine switcher, stab amplifier, video/audio
distribution amplifier, frame synchronizer, digital/satellite clock monitoring system, logo
generator vector scope, video monitor. The control console panel consists of controls for
routing switcher, stab amplifier, frame synchronizer etc and waveform monitors, vector
scope, video monitors, logo generator, patch panel are placed at convenient places for final
monitoring. The switcher unit and other video equipments are put in a standard rack. 16×8
switcher has maximum of 16 inputs and upto 8 independent outputs. Anyone of the input
signal can be switched to anyone or to all the channels at the same time. Change-over
unit is used to provide facilities for selecting video signals from one of the two sources.
The change over of all the inputs can be done from panel or from a remote point. Every
colour has a specific amplitude and phase relations. This can be checked in vectrometer.
Amplitude and phase should be maintained to get correct output on the screen. Waveform
monitor is used to check and monitor the video level at exactly 1 Vpp and to monitor the
audio level at 0 dB.
2.5 Digital Earth Station (DES) Simulcast
Earth Station (ES) is the unit from which program signals are sent (uplink) or receive
(downlink) to/from the Geo-stationary satellite. In DDK Thiruvananthapuram, the INSAT
4B satellite is used. For a given channel an ES is provided a fixed uplink frequency and
a different but fixed downlink frequency. The ES here operates at an uplink frequency

of 6036.5 MHz and downlink frequency of 3811.5 MHz. There are three types of Earth
station. They are :
• Stationary
• Moving (OB Van)
• Flyaway (Mobile ES. e.g., DSNG van)
The various inputs to the ES are MSR, microwave link output, DSNG, OB van. ES
is in fully digital domain. In the MSR, whatever the signal be, it is converted into digital
form. Digital version of audio and video are standard forms, which is known as Audio En-
gineering Society for audio(AES) and Serial Digital Interface for video (SDI) respectively.
The whole system operates with DVB/MPEG2 standards. The uplink chain of the ES is
shown below.
Figure 2.3: Uplink chain of DES
In the ES all the signals are in digital form, which requires high data rate. So for
the uplinking compression of the signal is required. The compression segment has an
MPEG encoder, digital multiplexer and digital modulator. The encoder converts the SDI
signals to Asynchronous Serial Interface(ASI) signals. Modulator is used to carry these
compressed signal using high frequency carrier. In DDK Thiruvananthapuram, QPSK

(Quadrature Phase Shift Keying) modulator is used. The output of modulator (70 MHz)
is sent to an up-converter. 70 MHz signal is in IF range and so it is up-converted to the
RF range using an up-converter. Up converted signal is in milliwatts, which means it is not
enough for transmission. So the up converted signals are sent to an High Power Ampliﬁer
(HPA). We can use HPAs like Klystron or Travelling Wave Tube (TWT). In DDK Thiru-
vananthapuram, TWT is used, which converts the low power signal to 20 MW. Then this
RF signal with the required power and high frequency is given to a Parabolic Dish Antenna
(PDA) through a rectangular wave-guide for up linking to satellite. The uplinked signal
is received again by the same PDA for monitoring purposes. The signal between ES and
satellite are given along line of sight which means there must be a clear path from Earth to
satellite.
Figure 2.4: Downlink chain of DES
The satellite is equipped with its own dish antenna which receives the uplink sig-
nals and feeds them to a receiver. The signal is then ampliﬁed and changed to a different
frequency, which is the downlink frequency. This is done to prevent interference between
uplink and downlink signals. The downlinked signal is then again sent to the transmitter
which again retransmits it. Each satellite has a transponder and a single antenna, which
receives all signals and another one transmits all signals back. A satellite transmits signals
towards earth in pattern called the satellite footprint of the satellite.
Reception or downlinking is also done at the ES. The receiver at the ES is known

as Integrated Receiver Decoder (IRD). For receiving the signal from satellite a high gain
antenna is used. A LNBC is attached to the antenna. It is the Low Noise Block Converter
(LNBC) which converts the signal to low band (L-band). Because, L-band is less affected
by noise. The signals are down-converted to an IF signal and passed on to the demultiplexer
block, where the signals are reformatted as required by the terrestrial network.
2.6 Outside Broadcasting
Figure 2.5: Outside broadcasting
For live broadcasting like any match or event, Outdoor Broadcasting (OB) van is
used. OB van consist of all the equipments that are present in the studio for telecasting. So
it is referred to as a mini studio. It is constructed on four wheels and so it is also called a
studio on wheels. OB van is usually divided into four parts:
1. First and the largest part is the production area or the sitting area for all directors and
producers.
2. The second part of the van is for the audio engineer.

3. The third part is the VTR area or ”tape room”. The tape room has LSM (Live Slow
Motion) operators. They play, replay and roll-outs that leads to commercial breaks or show
the highlights of the event at the end of the play. These operators can also playback in slow
motion or pause to show a key part of the action.
4. The fourth part is the transmission where the signal is monitored by and engineered for
quality control purposes and is transmitted or sent to other trucks.
If there is live program to be telecast, OB van has two option for transmission:
1. Microwave link
2. DSNG
2.6.1 Microwave Link
Audio and video signals are feed to microwave transmitter via microwave link. Mi-
crowave link is used in between Kudapanakunnu and Kanakakunnu transmitter. From Ku-
dappanakunnu to Kanakakunnnu, the input video is processed and up-converted. Approxi-
mate transmit power is 600 mW.
Another small carriage van for microwave transmitter is attached with the main van
and also diesel generator is taken wherever van goes.
2.6.2 DSNG
In DSNG (Digital Satellite News Gathering) audio/video input is respectively pro-
cessed by audio/video encoder as per the MPEG-2 standards. The audio and video along
with other data are multiplexed. Multiplexed data are forward error corrected using con-
ventional coding techniques. Error corrected codes are QPSK modulated at 70 MHz. The
modulated signal is up-converted to the power ampliﬁers. Ampliﬁed signal is coupled to
uplink dish.
2.7 Transmitter
The last stage is the transmitter which has the antenna and facilities for terrestrial
transmission. A radio transmitter is an electronic circuit which transforms electric power
into a radio frequency alternating current. The energy in such a rapidly-reversing current
can radiate off a conductor (antenna) as electromagnetic waves (radio waves). The trans-

mitter also carries information, such as an audio or video signal, onto the radio frequency
current to be carried by the radio waves. When they strike the antenna of a radio receiver,
the waves excite similar (but less powerful) radio frequency currents in it. The radio re-
ceiver extracts the information from the received waves.
Figure 2.6: Terrestrial transmitter
DDK Thiruvananthapuram has two transmitters. DD-1 (DD National) transmitter
transmits on channel 9 at a frequency 203.25 MHz (V) and 208.75 MHz (A) (.). DD-
2(DD News) transmitter transmits on channel 11 at a frequency of 217.25 MHz (V) and
222.75 MHz (A) (-). There are mainly three types of transmitters for transmitting DD-1
and DD-2 programmes; High Power Transmitters (HPTs), Low Power Transmitters (LPTs)
and Very Low Power Transmitters (VLPTs). 4 HPTs, 21 LPTs and 13 VLPTs relays DD-
1 programmes. 3 HPTs, 2 LPTs and 7 VLPTs relays DD-2 programmes. HPTs are 10
kW or 20 kW transmitters with a range of 70 kms. LPTs are 100 W or 300 W or 500 W
transmitters with a range of 15 kms. VLPTs are 10 W transmitters with a range of 5 kms.
All the TV transmitters have the same basic design. They consist of an exciter fol-
lowed by power ampliﬁers which boost the exciter power to the required level.
The transmitter design is based on solid state techniques and employs modular con-
struction. The video and audio signals are processed in the exciter electronics and modu-
lated at low level, at IF frequency of 38.9 MHz and 33.4 MHz respectively. The modulated

IF signals are combined and passed through IF corrector and VSB filter. SAW filter is
used for vestigial side-band shaping. The combined signal is up-converted to desired chan-
nel frequency and amplified in linear power amplifier to obtain 100 W (sync peak) visual
power and 10 W aural power. RF is finally routed to antenna through channel filter and
directional coupler.
2.7.1 Vision and Sound Signal Amplification
In HPTs the vision and sound carriers can be generated, modulated and amplified
separately and then combined in the diplexers at the transmitter output. Because of errors
caused by TV diplexers, a special group delay equalization circuit is needed here.
In LPTs, on the other hand, sound and vision are modulated separately but amplified
jointly. This is common vision and aural amplification. The intermodulation products are
more prominent here and so special filters are required for suppressing them.
2.7.2 Exciter
The exciter stage determines the quality of a transmitter. It contains pre-corrector
units both at base band as well as at IF stage, so that after passing through all subsequent
transmitter stages, an acceptable signal is available.
The 1 Vpp input video signal is limited to 5 MHz in low pass filter and is compensated
for group delay in delay equalizer and receiver pre-corrector unit. The resulting signal is
subjected to DC restoration by clamping at back porch, amplified and inverted in video
processor. The output of the video processor is fed to visual modulator where the same is
amplitude modulated with negative polarity at 38.9 MHz IF and amplified.
The audio signal is frequency modulated at IF of 33.4 MHz in a varactor VCO mod-
ulator. The VCO oscillates at centre frequency of 33.4 MHz. The incoming audio is passed
through a balanced to unbalanced transformer and pre-emphasised in a 50 µs pre-emphasis
network. Signal is then amplified and applied to varactor diodes. The information con-
tained in the amplitude variation of audio is converted into frequency variation in the VCO.
The VCO frequency deviates about centre frequency in proportion to audio amplitude. The
centre frequency of VCO is maintained at 33.4 MHz which is below vision IF by 5.5 MHz.
This is achieved by a Phase Locked Loop (PLL).

2.7.2.1 Video Chain
The input video signal is fed to a video processor. In VHF transmitters LPF, delay
equalizer and receiver pre-corrector precede the video processor. Low Pass Filter (LPF)
limits incoming video signal to 5 MHz. Group delay introduced by LPF is corrected by
delay equalizer. It also pre-distorts the video forDelay compensating group delay errors
introduced in the subsequent stages and diplexers. Receiver pre-corrector pre-distorts the
signal providing partial compensation of GD which occurs in domestic receivers. DP/DG
Corrector is also used in the exciter preceding LPF for pre-correcting the differential gain
and differential phase errors occurring in the transmitter.
The functions of video processor are amplification of video signal and clamping at
back porch of video signal. The functions of vision modulator are amplification of Vision
IF at 38.9 MHz and linear amplitude modulation of Vision IF by video from the video
processor in a balanced modulator.
2.7.2.2 Audio Chain
Aural Modulator unit consists of audio amplifier, VCO, mixer and APC. Audio Am-
plifier is a balanced audio signal at + 10 dBm from studio is converted to unbalanced signal
by audio transformer. VCO is a varactor tuned oscillator. Its frequency can be varied by a
coil. Transistor TR-17 forms the oscillator. VCO output is frequency modulated by the au-
dio signal. Output level is 0 dBm. VIF signal from IF oscillator and aural IF from VCO are
injected at the mixer. The mixer output is 5.5 MHz. This is processed, divided to produce
a square pulse at 537 Hz. For phase comparison reference pulses are derived from TCXO
oscillating at 1.1 MHz after suitable division. The phase difference develops error voltage
if the frequency variation is present. This voltage is applied to VCO to correct frequency
when PLL is unlocked due to frequency shift.
2.7.2.3 IF Combiner & IF Corrector
The modulated aural IF and vision IF are combined in a wide band amplifier and
passed through IF corrector for pre correcting DP/DG and response error. The corrected
signal is fed to VSBF and mixer (up converter) unit for up conversion by mixing the same
with LO signal. The VSBF and mixer unit contains a SAW filter for VSB shaping, an

ALC amplifier for automatic level control and a mixer for up conversion, a helical filter
and amplifiers. Automatic level control (ALC) is achieved by using a pin-diode as load
to amplifier. PIN diode is biased by an error signal obtained by comparing a d.c. voltage
corresponding to RF taken either from driver stage or final PA with a fixed reference in a
comparator.
2.7.2.4 VSB Filter
Surface Acoustic wave (SAW) filter provide a very steep side band response with
high attenuation outside designated channel. It has a linear phase characteristic with a low
amplitude and group delay ripple.
2.7.2.5 Modulator Module
This unit is an IF modulator which receives the video and audio signals and generates
a modulated IF signal containing an amplitude modulated video carrier of 38.9 MHz and
frequency modulated audio carrier of 33.44 MHz. Inputs are processed and carriers are
generated. AGC and Muting Control is introduced.
2.7.2.6 Local Oscillator
Local oscillator frequency required for up conversion is given by f0 = fc + fV IF . The
LO signal corresponding to a particular channel in old exciters is obtained by generating a
f0/4 signal in TCXO, multiplying the same by 4 in a harmonic multiplier and then mixing
the resulting signal in a mixer with a vision IF sample. The mixer output is passed through
a high pass filter and amplified.
2.7.2.7 Up-converter Module
The up-converter module comprises of local oscillator module (synthesized) and
IF/RF converters (Mixer) to generate RF at channel frequency. In this unit, IF gain and
slope is set. Group delay equalization and amplitude pre-correction of IF is done. IF output
level is set. LO output is mixed with IF to produce RF This unit also provides 500 kHz
reference signal to modulator unit.

2.7.3 Power Supply Circuit
Power supply circuit is used to transform the input electrical power to the higher
voltages needed to produce the required power output.
2.7.4 RF Power Amplifier
Solid state power amplifiers are used for terrestrial transmitters. These power ampli-
fiers are used to increase the power of the signal and also to increase the range of the radio
waves.
2.7.5 Antenna
TV antenna system is that part of the broadcasting network which accepts RF energy
from transmitter and launches electromagnetic waves in space. The polarization of the
radiation as adopted by Doordarshan is linear horizontal. The system is installed on a sup-
porting tower and consists of antenna panels, power dividers, balun, branch feeder cable,
junction boxes and main feeder cables. Dipole antenna elements, in one or the other form
are common at VHF frequencies where as slot antennae are mostly used at UHF frequen-
cies. Omni directional radiation pattern is obtained by arranging the dipoles in the form of
turnstile and exciting the same in quadrature phase. Desired gain is obtained by stacking
the dipoles in vertical plane. As a result of stacking, most of the RF energy is directed in
the horizontal plane. Radiation in vertical plane is minimized.
In the high power TV transmitting antenna system, half wave dipole elements are
mounted on the four faces of a square tower of suitable dimension for getting an approx-
imate omni directional horizontal radiation pattern. Following types of VHF TV LPT an-
tenna are being used in Doordarshan Network :
(a) Band III BEL make, half wave dipole V antenna.
(b) Crossed folded dipole (turnstile) Halios make Band-III antenna.
(c) Folded dipole (turnstile) Scala make Band-I antenna.
Antenna panels are stacked vertically and mounted on a tower having some 30 meter
height. Slot antenna elements are used as electromagnetic waves radiator at UHF frequen-
cies. The UHF LPT para-slot (SL-B) antenna manufactured by SCALA is an array of slot
antenna.

2.8 DTH
Television is the most popular device to provide entertainment to the public with its
ability to receive the video and audio with high quality. Today, the TV channels come by
the following three ways:
• By the transmitter means regular reception by all the TV receiver.
• By the cable operator which provides channel bouquet with some subscription charge
and
• Through Direct-to-Home (DTH).
DTH service is the one in which a large number of channels are digitally compressed,
encrypted and beamed from very high power satellites. The programmes can be directly
received at homes. This mode of reception facilitates the use of small receive dish antennas
of 45 cm to 60 cm diameter installed at convenient location in individual buildings without
needing elaborate foundation/space etc. Also, DTH transmission eliminates local cable
operator completely, since an individual user is directly connected to the service providers.
However, a digital receiver is needed to receive the multiplexed signals and view them on
a TV. DTH, in sharp contrast to cable TV, lends itself to easy monitoring and control.
Transmission in Ku band is most appropriate and widely used for the purpose. Free
DTH service is provided by DDK. Ku band frequency range is 11.7 GHz to 12.8 GHz.
Such a high frequency transmission reduces the dish size.
Digital transmission of TV signal by terrestrial, satellite and cable modes uses DVB
(Digital Video Broadcasting group)-T, DVB-S and DVB-C standards. DTH uses DVB-S
standard.

PART II
ALL INDIA RADIO
THIRUVANANTHAPURAM
25

CHAPTER 1
INTRODUCTION
Radio is a powerful mass medium used in education for disseminating information,
imparting instruction and giving entertainment. It spreads information to a greater group of
population thereby saving time, energy, money and man-power in an effective way. Now
small and handy transistors are available with even poorest of people. A small transistor can
carry the message to any place on the earth. Due to its portability and easy accessibility
radio could found its place everywhere. When one hears radio, simultaneously one can
imagine happenings in his/her mind. So it is called as ”theatre of blind” or a ”stage for the
mind”.
Radio Broadcasting is a one-way wireless transmission over radio waves intended to
reach a wide audience. Stations can be linked in radio networks to broadcast a common
radio format, either in broadcast syndication or simulcast or both. Audio broadcasting also
can be done via cable radio, local wire television networks, satellite radio, and internet
radio via streaming media on the Internet. The signal types can be either analog audio or
digital audio.
The earliest radio stations were simply radio telegraphy systems and did not carry
audio. The very ﬁrst claimed audio transmission which could be termed a broadcast oc-
curred on Christmas Eve in 1906, and had to make by Reginald Fessenden. Broadcasting
began in India with the formation of a private radio service in Madras (presently Chennai)
in 1924.
As India’s National broadcaster and also the premier public service broadcaster, All
India Radio (AIR) has been serving to inform, educate and entertain the masses since it’s
inception, truly living up to its motto ”Bahujan Hitaya : Bahujan Sukhaya”. AIR originates
programming in 23 languages and 146 dialects. AIR has a three-tier system of broadcast-
ing. These three levels of programmes are the national, regional and local each having
distinct audiences.
National programmes are broadcast from Delhi for relay by the capital, regional and
local radio stations. Some of these are the National programme of talks and features in

Hindi and English, the National programmes of drama and music. The National channel of
All India Radio located in Delhi broadcasts programmes which are heard on medium wave
and also on short wave.
The Regional stations in different states form the middle tier of broadcasting. They
originate programmes in the regional languages and dialects. Regional channels are lo-
cated in the major linguistic-cultural region of every state. 116 regional channels are spread
over 29 states and 6 Union Territories including the North-Eastern service at Shillong that
projects the vibrant cultural heritage of the North-Eastern region of this country. The re-
gional channels, broadcast largely on the medium wave frequency, follow a composite
programme pattern comprising of music-classical, light, folk and film, news and current
affairs, radio plays, features, farm and home programmes, programmes on health and fam-
ily welfare and programmes for woman, children etc.
Local Radio is relatively a newer concept of broadcasting in India. Local radio sta-
tions serve small communities, showcase local culture and broadcast area specific pro-
grammes for the benefit of the community. The transmission is in the FM mode. At present
there are 86 Local Stations spread across the country.
AIR’s objective is to provide information, education and entertainment, for promot-
ing the welfare and happiness of the masses (Bahujana Hitaya Bahujana Sukhaya).
1.1 Other Services
• News-on-phone service: All India Radio launched news-on-phone service on 25
February 1998 in New Delhi; it now has service in Chennai, Mumbai, Hyderabad, Indore,
Patna and Bangalore. The service is accessible through STD, ISD and local calls. There are
plans to establish the service in 11 more cities: Ahmedabad, Bhopal, Guwahati, Gwalior,
Jabalpur, Jaipur, Kolkata, Lucknow, Ranchi, Simla and Thiruvanthapuram. English and
Hindi hourly news bulletins may be heard live.
• Direct-to-Home service: This service is offered on 21 channels via Insat.

CHAPTER 2
RADIO COMMUNICATION SYSTEM
Radio is the transmission of signals through free space by electromagnetic (radio)
waves with frequencies below visible light in the radio frequency range from about 3 KHz
to 300 GHz. Electromagnetic radiation travels by means of oscillating electromagnetic
ﬁelds that pass through the air and vacuum of space. Information such as sound is carried
by systematically modulating some property of the radiated waves such as their amplitude
frequency or pulse width. When radio waves strikes an electrical conductor the oscillating
ﬁelds induce an alternating current in the conductor. The information in the wave can be
extracted and transformed back into its original form.
Figure 2.1: Radio communication system
Figure shows how radio communication happens. Information such as sound is trans-
formed into an electrical signal which is applied to a transmitter. The transmitter sends the
information through space on a radio wave. A receiver intercepts some of the radio wave
and extracts the information bearing electronic signal which is converted back to its orig-
inal form by a transducer such as a speaker. Radio systems used for communication have
the following elements:
1. Transmitter and Modulation: The transmitter consists of a source of electrical energy
producing alternating current of desired frequency of oscillation. It contains a system to

modulate some property of the energy produced impress a signal on it. This modulation
is as simple as turning the energy on and off, or altering more subtle properties such as
amplitude, frequency, phase or combinations of these properties. The transmitter sends the
modulated electrical energy into tuned resonant antenna.
a) Amplitude modulation
b) Frequency modulation
c) Angle modulation
Classical radio communication systems use frequency division multiplexing as a
strategy to split up and share the available radio frequency bandwidth. Modern radio com-
munication systems include those that divide up a radio frequency band by time division
multiplexing and code division multiplexing.
2. Antenna (or aerial): It is an electrical device which converts electric currents into ra-
dio waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In
transmission, a radio transmitter applies an oscillating radio frequency electric current to
the antenna’s terminals, and the antenna radiates the energy from the current as electro-
magnetic waves (radio waves). In reception, an antenna intercepts some of the power of an
electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to
a receiver to be amplified. Within the atmosphere, radio waves can be reflected, refracted,
and diffracted in the same manner as light and heat waves.
3. Resonance: Electrical resonance of tuned circuits in radios allow individual stations to
be selected. A resonant circuit will respond strongly to a particular frequency, and much
less so to differing frequencies. This allows the radio receiver to discriminate between mul-
tiple signals differing in frequency.
4. Receiver and demodulation: In radio communication, a radio receiver is an electronic
device that receives radio waves and converts the information carried by them to usable
form. It is used with an antenna. The electromagnetic wave is intercepted by a tuned re-
ceiving antenna. This antenna captures some of the energy of the wave and returns it to
the form of oscillating electrical currents. Radio receiver uses electronic filters to separate
a wanted radio signal from all other signals picked up by the antenna and amplifies it to a
level suitable for further processing and finally converts through demodulation and decod-
ing the signal into a form usable for the consumer such as sound. Various types of radio

receiver may include:
a. Consumer audio and high ﬁdelity audio receivers and AV receivers used by home stereo
listeners and audio and home theatre system enthusiasts as well as audiophiles.
b. Communication receivers used as a component of a radio communication link.
c. Simple crystal radio receivers.
d. Satellite television receivers used to receive television programming from communica-
tion satellite in geostationary orbit.
e. Measuring receivers are calibrated laboratory grade devices that are used to measure the
signal strength of broadcasting stations, the electromagnetic interference radiation emitted
by electrical products as well as to calibrate RF attenuators and signal generators.
Radio Wave Transmission Paths: There are two principal ways in which electromag-
netic (radio) energy travels from a transmitting antenna to a receiving antenna. One way is
by ground waves and the other is by sky waves. Ground waves are radio waves that travel
near the surface of the earth (surface and space waves). Sky waves are radio waves that are
reﬂected back to Earth from the ionosphere.
2.1 Radio Studio
The studio centre comprises of one or more Transmission studios, recording and
dubbing room, a control room and another ancillary rooms like battery room, AC room,
tape library etc. The studio centres in AIR are categorized as Type I, II, III and IV. The
number of studios and facilities provided in each type are different. For example a type I
studio has a transmission studio, music studio with announcer booth, a talks studio with
announcer booth, one recording/dubbing room and a Read Over Room. Type II has one
additional drama studio. The other types have more studios progressively.
The studio complex of AIR Thiruvananthapuram (Type IV), is located at Vazhutha-
caud. The studio complex in AIR consists of 7 studios for transmission, recording and
editing the programmes. The live programmes are also set up in these studios. The
recorded/live programmes are then transmitted to MW, SW and FM transmitters, Alap-
puzha MW and to Earth station through transmission links. Different type of studios in
AIR are:
a. Recording studios:

1. Talk studio: Recording of programmes like interview is done.
2. Drama studio.
3. Music studio: Two music studios in AIR (for light music and classical music).
b. Playback studios:
1. PB1 for Regional channel (MW).
2. PB2 for IGNOU and news.
3. PB3 for Ananthapuri FM.
4. ROR for Phone in Programmes.
Figure 2.2: Block diagram of radio studio
There is a table and a microphone in each studio. Before one enters this room, there
is a small enclosed place called sound lock, which prevents unnecessary outside sounds
from entering the studio. The studios are so designed without any interference to ensure
that outside noises are not recorded. For this, besides the sound lock and heavy doors,
the ceiling and walls are constructed with perforated woollen panels. Also, proper air-
conditioning is maintained in the studios. The studios are to be specially treated to give an
optimum reverberation time and minimum noise level. The entry to the studios is generally
through the sound isolating lobby , sound lock. Outside of every studio entrance, there is a
warning lamp, which glows ’Red’ when the studio is ’ON-AIR’. The studios have separate

announcers booths attached to them where ﬁrst level fading, mixing and cueing facilities
are provided. The main functions of a studio are:
• Recording
• Editing
• Scheduling
• Transmission play back
• Reports preparation
• RN channel recording
• Off broadcast recording
• Storage of programmes
• Deleting of broadcast programmes
The preferred location of studio will depend, in the ﬁrst instance, on the intended
market for the studio. For example, many studios are located for easy access by local
clients. Some studios are located in the country for a quieter working ambience.
2.1.1 Recording
Sound recording is an electrical or mechanical inscription of sound waves, such as
spoken voice, singing, instrumental music, or sound effects. The two main classes of sound
recording technology are analog recording and digital recording.
Acoustic analog recording is achieved by a small microphone diaphragm that can
detect changes in atmospheric pressure and record them as a graphic representation of the
sound waves on a medium such as a phonograph. Analog sound reproduction is the reverse
process, with a bigger loudspeaker diaphragm causing changes to atmospheric pressure to
form acoustic sound waves.
Electronically generated sound waves may also be recorded directly from devices
such as an electric guitar pickup or a synthesizer, without the use of acoustics in the record-
ing process other than the need for musicians to hear how well they are playing during
recording sessions.
Digital recording and reproduction converts the analog sound signal picked up by
the microphone to a digital form by a process of digitization, allowing it to be stored and
transmitted by a wider variety of media. Digital recording stores audio as a series of binary

numbers representing samples of the amplitude of the audio signal at equal time intervals,
at a sample rate high enough to convey all sounds capable of being heard.
The following are the commonly used audio recording formats in AIR.
• MP3: MPEG-1 or MPEG-2 Audio Layer III more commonly referred to as MP3, is a
patented encoding format for digital audio which uses a form of lossy data compression. It
consumes less space for compression but has poor audio quality.
• WAV: Waveform Audio File Format (WAVE), or more commonly known as WAV due to
its file name extension, also, but rarely, named, Audio for Windows is a Microsoft and IBM
audio file format standard for storing an audio bit-stream on PCs. To reduce transmission
loss, they use high sampling rate.
• Compact Disc or CD: It is an optical disc used to store digital data. The format was
originally developed to store and play back sound recordings only (CD-DA), but was later
adapted for storage of data (CD-ROM).
2.1.1.1 Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into
an electrical signal. The sensitive transducer element of a microphone is called its element
or capsule. A complete microphone also includes a housing, some means of bringing the
signal from the element to other equipment, and often an electronic circuit to adapt the out-
put of the capsule to the equipment being driven. A wireless microphone contains a radio
transmitter. Depending on the relationship between the output voltage from a microphone
and the sound pressure on it, the microphones can be divided into two basic groups.
1. Pressure Operated Type: In such microphones only one side of the diaphragm is exposed
to the sound wave. The output voltage is proportional to the sound pressure on the exposed
face of the diaphragm with respect to the constant pressure on the other face. Moving
coil, carbon, crystal and condenser microphones are mostly of this type. They are omni-
directional.
2. Velocity or Pressure Gradient Type: In these microphones both sides of the diaphragm
are exposed to the sound wave. Thus the output voltage is proportional to the instantaneous
difference in pressure on the two sides of the diaphragm. Ribbon microphone belongs to
this category and its polar diagram is figure of eight.

2.1.2 Editing
The recorded audio signals are further edited by using editing software. Editor is a
computer application for audio editing. i.e., manipulating digital audio. In AIR, Sound
forge by Sony is used. Editors designed for use with music typically allow the user to do
the following:
• Record audio from one or more inputs and store recordings in the computer’s memory as
digital audio.
• Edit the start time, stop time, and duration of any sound on the audio timeline.
• Fade into or out of a clip (e.g. an S-fade out during applause after a performance), or
between clips (e.g. cross-fading between takes).
• Mix multiple sound sources/tracks, combine them at various volume levels and pan from
channel to channel to one or more output tracks.
• Apply simple or advanced effects or filters, including compression, expansion, flanging,
reverb, audio noise reduction and equalization to change the audio.
• Playback sound (often after being mixed) that can be sent to one or more outputs, such
as speakers, additional processors, or a recording medium.
• Conversion between different audio file formats (MP2, MP3, WAV etc), or between dif-
ferent sound quality levels.
2.1.2.1 Mixing Console
Change image to consoles in AIR. A mixing console is an electronic device for com-
bining , routing, and changing the level, timbre and/or dynamics of audio signals. A mixer
can mix analog or digital signals, depending on the type of mixer. The modified signals
(voltages or digital samples) are summed to produce the combined output signals. A typi-
cal analog mixing board has three sections:
1. Channel inputs or low level modules.
2. Master controls or master modules.
3. Audio level metering.
The channel input strips are usually a bank of identical monoaural or stereo input
channels. The master control section has sub-group faders, master faders, master auxiliary
mixing bus level controls and auxiliary return level controls. In addition it may have solo

monitoring controls, a stage talk-back microphone control, muting controls and an output
matrix mixer. On smaller mixers the inputs are on the left of the mixing board and the
master controls are on the right. In larger mixers, the master controls are in the center with
inputs on both sides. The audio level meters may be above the input and master sections or
they may be integrated into the input and master sections themselves.
Each channel on a mixer has a sliding volume control (fader) that allows adjustment
of the level of that channel. Fader has a switch beneath it. When we click on it, a pulse is
generated and transmitted through the connector RJ235 to the computer. The signals are
summed to create the main mix, or combined on a bus as a submix, a group of channels
that are then added to get the final mix.
• Master output controls: Subgroup and main output fader controls are often found to-
gether on the right hand side of the mixer or, on larger consoles, in a center section flanked
by banks of input channels. Matrix routing is often contained in this master section, as
are headphone and local loudspeaker monitoring controls. Talkback controls allow con-
versation with the artist through their monitors, headphones or in-ear monitor. A test tone
generator might be located in the master output section. Aux returns such as those signals
returning from external processors are often in the master section.
• Audio level metering: Finally, there are usually one or more VU or peak meters to indi-
cate the levels for each channel, for the master outputs and to indicate whether the console
levels are clipping the signal.
Audio mixing is done in following two ways:
1. Required equipments are selected and then outputs are mixed before feeding to an am-
plifier. This is called low level mixing. This is not commonly used now days.
2. Low-level output of each equipment is pre-amplified and then mixed. This is called high
level mixing.
From backside of the console master module output is get. This output goes to two
computers. i.e., it goes to soundcard of computer. Unbalanced soundcards are used in non-
professional area. In AIR, balanced soundcards are used. Soundcard output are given to
announcer booth and speaker for checking the correctness of the recorded program. Main
output goes to control room.

2.1.3 Scheduling
The edited audio clip is saved and scheduled for transmission. At first we have to
browse the saved program, then schedule it for transmission. Using AIR Browser software
we can schedule the transmission time and date of the audio. After scheduling, copy of the
program or the audio clip goes to playback studio, standby and server.
2.1.4 Playback
The edited audio signals ready for transmission are played in transmission studios
before sending it to the control room. AIR Virtual Studio is the software used in AIR for
playback.
2.1.4.1 Virtual Studio
The Virtual Studio Software package is a complete software solution for any radio
broadcasting setup. This package is an integrated solution for programme recording, edit-
ing, secured storage, categorization, scheduling, on-air transmission, logging, commercial
billing etc with very high security features. Components of the software includes:
• Virtual Player: It is operated by the announcers in playback studios. The software helps
the announcers in selecting the program schedules and arranging the different datas easily.
• Transmission Logger: The announcer creates play-list for a particular transmission in
this area and plays back the same from this area. This includes the programs schedule for
a particular period of time for one week,month etc.
• AIR Browser: Using AIR Browser software we can schedule the transmission time and
date of the audio.
• Commercial Manager: Using this module the PEX of the commercial section can create
a commercial bank, create a commercial capsule, send the commercial capsule to the play-
back studio for transmission and can take print out of daily production sheet.
• Audio CD Lister: Useful for extracting audio tracks from CD and they can be enqued in
the play list area for play back of the selected cuts.
• Central File Manager: It is used to delete the files from playback computers, which are
already broadcast.
• RN Channel Recorder: The duty officers use this module for recording RN channel mes-

sages. Automatic recording is also possible. Recordings are done in two formats: MP3 for
monitoring and MP2 for broadcast purposes.
• Library manager: It is a software used after scheduling to bring program to a library.
2.2 Control Room
The control room is the main technical area of the radio station. Whatever is spoken
in the studio or played from a CD player or computer is sent to this control room. All
the programmes are sent from here to the transmitter. Thus, mixing and switching are the
important operations taking place in the control room. It is the place, connected with all the
other segments of broadcast. Studio change-over takes place here. Windows Server 2008
is the server OS used here. Switching console is the main equipment used in the control
room and it provides the following functions:
• Switching of different sources for transmission like news, OBs, other satellite based
relays, live broadcast from recording studio.
• Level equalisation and level control.
• Quality monitoring.
• Signalling to the source location.
• Communication link between control room and different studios.
Outside Broadcast (OB) is the electronic ﬁeld production (EFP) of television or radio
programmes. An ”OB Unit” is a mobile production unit (with equipment and crew) which
is able to travel to a location and provide broadcast coverage. Equipments used in AIR for
OB : Nagra, Sonifex, Marantz, Sony, Mixers, ISDN eqpuipments, Mic etc.
2.3 Studio Transmitter Link (STL)
STL sends a radio station’s audio from the broadcast studio to a radio transmitter in
another location. Depending on the locations that must be connected, a station may choose
either a point-to-point (PTP) link on another special radio frequency, or a newer all-digital
wired link via a dedicated line. Radio links can also be digital, or the older analog type, or
a hybrid of the two. Even on older all-analog systems, multiple audio and data channels
can be sent using sub-carriers. Stations that employ an STL usually also have a transmitter-
studio link (or TSL) to return telemetry information. Both the STL and TSL are considered

Broadcast Auxiliary Services (BAS).
In All India Radio, the transmission link refers to the communication channel that
connects the studio to the transmitters. The 3 main transmitters located at different parts of
Thiruvananthapuram are:
a. 20 kW MW Transmitter at Kulathur.
b. 50 kW SW Transmitter at Poonthura.
c. 10 kW FM Transmitter at Kudappanakkunnu.
In addition, there is a 200 kW MW transmitter at Alappuzha. The programmes from
the studio are transmitted to the above mentioned transmitters using either any one or more
of the following facilities.
2.3.1 Microwave Link
Microwave link is a communication system that uses a beam of radio waves in the
microwave frequency range to transmit video, audio, or data between two locations, which
can be from just a few feet or meters to several miles or kilometres apart. Following are the
properties of microwave links:
i. Involve line of sight (LOS) communication technology.
ii. Affected greatly by environmental constraints, including rain fade.
iii. Have very limited penetration capabilities through obstacles such as hills, buildings and
trees.
Microwave links are used in communications between satellites and base stations,
and in short range indoor communications.
2.3.2 Integrated Services Digital Network (ISDN)
ISDN is a set of communication standards for simultaneous digital transmission of
voice, data and other network services over the traditional circuits of the PSTN. The key
feature of ISDN is that it integrates speech and data on the same lines, adding features
that were not available in the classic telephone system. It is a circuit switched telephone
network system, which also provides access to packet switched networks, designed to allow
digital transmission of voice and data over ordinary telephone copper wires, resulting in
potentially better voice quality than an analog phone can provide.

2.3.3 Leased Line
Leased line is a service contract between a provider and a customer, whereby the
provider agrees to deliver a symmetric telecommunications line connecting two or more
locations in exchange for a monthly rent (hence, the term ’lease’). It does not have a
telephone number. It is always active and is available 24 hours a day for use by a designated
user. In AIR Thiruvananthapuram, the digital leased lines are the dedicated lines provided
by BSNL (permanent fibre optic connection or telephone line connection).
2.3.4 Captive Earth Station
AIR requires Captive Earth Stations (CES) to uplink its radio programmes for dis-
tribution in its network through satellite. The programmes uplinked by this CES will be
received by other AIR stations with their Radio Networking (Receive) Terminals (RNT)
and used either for recording or for retransmission through their terrestrial transmitters.
2.4 Earth Station (ES)
Earth station consists of indoor as well as outdoor subsystems. The indoor subsys-
tems are arranged in three racks to ensure smooth flow of RF and control signals. The three
racks are Baseband and IF Rack (BBIF Rack), C-Band High Power Amplifier Rack (HPA
Rack) and Monitoring Rack. The outdoor subsystem comprises of 6.1 M Prime focus type
antenna system with two port feed.
The BBIF rack houses the subsystems/units used in baseband processing and encod-
ing/modulation of signals in the uplink (Transmitter path) to get the IF frequency signal.
The HPA rack houses the subsystems/units used in up conversion, amplification of the RF
signal for final transmission (uplink) to the antenna system and a dehydrator unit. The mon-
itoring Rack houses all the receiving equipment for reception of both C-Band and S-Band
signals.
2.4.1 Operation of ES
Information to be transmitted is delivered to the earth station via coaxial cable, fibre,
terrestrial microwave, or satellite. The devices in the transmitter chain typically consist of
the multiplexer, the modulator, the up converter, a high power amplifier, and the antenna.

The multiplexer combines the individual channels onto a single data stream. The informa-
tion can be encrypted and encoded with a forward error correction code. The modulator
modulates the baseband signal containing the desired information onto an intermediate
frequency (IF) carrier. The up-converter changes the carrier to the radio frequency (RF)
signals used to transmit the signal, such as C-band (6 GHz) or Ku-band (14 GHz). The
high power amplifier (HPA) amplifies the modulated RF signals from the output of the up-
convertors to the required power at the input terminals of the antenna. Finally, the antenna
transmits the amplified RF signal to the satellite.
Figure 2.3: Block diagram of Earth Station

CHAPTER 3
MEDIUM WAVE TRANSMITTER
The Medium Wave (MW) transmitter is the medium wave broadcasting facility of
AIR. The MW band ranges from 535 kHz to 1605 kHz. This frequency band ideal for both
local and continent-wide service. During the daytime, medium and high powered medium
wave AM radio stations have a normal reception range of about 20 to 250 miles (32 to
400+ km).The MW transmitters of AIR are from 1 kW to 500 kW power. AIR Thiru-
vananthapuram employs a 20 kW transmitter which is located at Kulathur. The programs
are transmitted at a frequency of 1161 KHz .The peculiarities of MW transmitter at Thiru-
vananthapuram is,
• Transmission Frequency - 1165 kHz
• Range - 2192 km2
• Band width - 9 kHz
• Carrier power - 20 kW
• Transmitter output impedance - 4.2 Ω
Apart from the main transmitter at Kulathur, AIR employs a 2×100 kW high
power secondary transmitter at Alappuzha with a transmission frequency of 576 kHz.
The recorded/live programmes from the AIR studio at Vazhuthacaud are transmitted to
MW Transmitter, Kulathur through STL, CES and ISDN and MW transmitter, Alappuzha
through DLL (BSNL).
AIR Thiruvananthapuram employs the DX20 AM transmitter for transmission of
programs in MW. The transmitter can be broadly divided into the following blocks:
1. RF Section
2. Audio and Modulation Section
3.1 RF Section
The RF Section RF synthesizer generates an RF signal and then amplifies the signal
to a level high enough to drive the power amplifier stage. In the power amplifier stage, the
RF amplifier outputs are combined and fed to a band pass filter/output network and then

to a 230 Ω RF output point.The pi matching network allows convenient matching to loads
that are not exactly 230 Ω.
Figure 3.1: Block diagram of MW transmitter
3.1.1 Buffer Amplifier
It amplifies the RF synthesizer output and provides a stable input signal to drive the
pre-driver stage.
3.1.2 Pre-driver
The Pre-driver stage uses one of the 79 identical and interchangeable RF amplifiers.
The pre-driver amplifies the buffer amplifier signal to a high enough level to operate the 14
RF amplifiers used in the driver stage.
3.1.3 Driver
The Driver Stage consists of the combined output of upto 14 RF amplifier modules.
3.1.4 Combiner and Splitter
The outputs of the 14 RF amplifiers in the driver stage are combined by the Driver
Combiner and this combined RF output from the driver stage feeds the RF Drive Splitter.
The RF splitter provides separate RF signals to the individual RF amplifiers in the power
amplifier. 128 separate RF drive cables to the PA Module inputs provide additional isolation

so that a fault at one module input will have little or no effect on other RF drive signals.
The 16 connectors from the splitter provide connections for two sets of eight coaxial cables.
Each group of eight cables from each connector form a cable bundle which goes to an input
connector on a PA Combiner/Motherboard.
3.1.5 Power Amplifier (PA)
Power Amplifier (64 RF Amplifiers) consists of 64 identical RF amplifier modules.
The PA stage may be thought of as a digital to analog converter where the output is a high
power, amplitude modulated, RF signal. The action of the RF combiner and RF amplifier
modules produce RF voltage ’steps’ at the combiner output. The power output of each RF
amplifier depends on the total number of modules switched on at any time.
3.1.6 PA Combiner
The Power Amplifier stage is made up of 64 plug-in RF amplifier modules. Sixteen
ferrite core toroid transformers on each combiner/motherboard combine the RF voltage
outputs of the modules through a solid copper rod which passes through the center of
the transformers. The module outputs are series combined by the toroidal transformer to
develop the total RF voltage. RF samples from various points on the RF combiner are
distributed to various circuits elsewhere in the transmitter (Output network).
3.1.7 Output Network
The Output Network transforms the low impedance of the PA combiner output to a
230Ω output impedance.The impedance transformation is accomplished in two sections:
the Bandpass Filter stage and the pi matching stage. The bandpass filter stage completes
the digital to analog conversion by filtering out the individual ’step’ voltages generated by
the RF amplifiers. The pi network provides for impedance matching into antenna systems
that are not perfect 230 Ω loads. The output network also includes RF sample circuits for
the output monitoring and control circuitry to provide power monitoring, VSWR metering
and protection against high VSWR conditions.

3.2 Audio and Modulation Section
The Modulation Section of the transmitter accepts an analog audio input signal and
converts it to a digital signal. The digital signal is then processed or encoded to control the
RF amplifiers which produce the Digital Amplitude Modulation. Circuit boards in the mod-
ulation section include the Analog Input Board, Analog to Digital Converter, Modulation
Encoder and DC regulator.
3.2.1 Audio Input
Audio is fed into the Analog Input Board where it is processed .This processing
includes attenuating the high audio frequencies for medium wave band channel spacing
and adding a DC component to determine the carrier power. This (Audio + DC) signal is
sent to the ADC. A second (Audio + DC) signal is sent to the DC Regulator.
3.2.2 Analog to Digital Converter (ADC)
The (Audio + DC) signal is sampled at a 400 kHz to 800 kHz rate depending on the
transmitter operating frequency, by the ADC. The ADC converts the (Audio + DC) signal
from the analog input board into a 12 bit digital signal.
3.2.3 Modulation Encoder
It converts the 12 bit digital audio information into control signals which turn the RF
amplifier modules in the PA stage ON and OFF to generate the transmitter carrier and the
instantaneous modulation level.
3.2.4 DC Regulator
It produces the B+ (+5 V DC) and B- voltages used by the modulation encoder. The
(Audio + DC) sample from the analog input board modulates the DC Regulator B- output
voltage. The modulated B- is a bias voltage for the RF amplifier modules in the PA stages,
which varies the turn-on/turn-off times of the modules to optimize distortion and noise
performance.

3.3 Medium Wave Antenna
MW antenna exist close to the surface of the earth and the radio waves from them
travel close to the earth as ground waves. MW antenna have to be placed vertically, so that
they radiate vertically polarised signals. They are broadly of two types :
• Mast isolated from ground and fed at its base.
• Grounded mast fed at a suitable point along its height.
Figure 3.2: Self radiating MW Mast Antenna
As most of the AIR MW towers are of the ﬁrst category. The MW self supporting
mast antenna could be excited in 3 different methods. The ﬁrst method requires an insulator
at the base of the mast. The second method is called shunt feed and the third top feed.

CHAPTER 4
SHORT WAVE TRANSMITTER
Radio communication can be defined as the interchange of intelligence, signals and
symbols between two or more places employing radio waves as the medium of transmis-
sion. Ionospheric (sky wave) propagation is a subclass of radio wave propagation which is
used for long distance communication. The ionized region in the upper atmosphere called
ionosphere is able to reflect back the EM waves of frequencies between 2 MHz and 30
MHz. EM waves of frequency more than 30 MHz are not reflected back from the iono-
sphere, rather they penetrate it.
Since Short Wave (SW) propagation takes place after reflection from the ionosphere,
it is also called ionospheric propagation. Extremely long distance i.e., round the globe com-
munication is also possible with the multiple reflections of sky waves. SW communication
is a subclass of radio communication which uses the upper MF (medium frequency) and
the entire HF (high frequency) portion of the radio spectrum, between 1,800 kHz to 30,000
kHz. SW radio received its name because the wavelengths in this band are shorter than 200
m (1500 kHz) which marked the original upper limit of the medium frequency band first
used for radio communications. SW radio is used for broadcasting of voice and music, and
long-distance communication to ships and aircraft, or to remote areas out of reach of wired
communication or other radio services.
The 50 kW SW transmitter was authorized by AIR Thiruvananthapuram on 6th
November 1994. It comes under the south regional service section of AIR. This trans-
mitter provides reliable program reception throughout India and the Middle East. Due to
the splitting up of F-layer during day time hours, different frequency bands are used for
transmission during day and night. So this transmitter uses 5010 kHz carrier frequency
during night (17:15-07:45 IST) and 7290 kHz carrier frequency during day (08:00-15:30
IST).
The modulation scheme used for the SW transmission is Amplitude Modulation
(AM). In AM, the amplitude of the carrier is varied in accordance with the instantaneous
amplitude of the message signal. In general, the modulation schemes used for AM can be

classified as high level and low level modulation. In low level amplitude modulation, the
carrier signal is first modulated and the overall modulated signal is then amplified. Since in
the low level modulation scheme, the modulation takes place in the initial stages of ampli-
fication, the modulation circuitry has to handle only low power which reduces the circuit
complexity. In high level amplitude modulation, the carrier is first amplified and the am-
plified carrier is then modulated. So, here the modulation takes place in the final stage
of amplification, the modulation circuitry has to handle high power which increases the
circuit complexity. In the 50 kW SW transmitter of AIR Thiruvananthapuram, high level
amplitude modulation is used.
4.1 Component Description
Figure 4.1: Block diagram of SW transmitter
4.1.1 RF Synthesizer
The RF synthesizer allows the transmitter to radiate a large number of discrete fre-
quencies over a relatively wide band. A typical RF synthesizer consists of a bank of oscil-
lators producing different fixed frequencies.
4.1.2 Tetrode
A tetrode is an electronic device having four active electrodes. The term most com-
monly applies to a 2 grid vacuum tube. It has 3 electrodes of a triode and an additional

screen grid which significantly changes its behaviour. The grid nearest to the cathode is
the ”control grid”; the voltage applied to it causes the anode current to vary. The second
grid, called ”screen grid” or sometimes ”shield grid”, provides a screening effect, isolating
the control grid from the anode, reducing the parasitic capacitance between the two. This
helps to suppress unwanted oscillation, and to reduce an undesirable effect in triodes called
the ”Miller effect”. Power tetrodes are commonly used in radio transmitting equipment,
because the need for neutralization is less than that of triodes. In a SW transmitter, tetrode
valves are used to provide amplification as well as amplitude modulation.
4.1.3 Dummy Load
A dummy load is a device used to simulate an electrical load, usually for testing
purposes. In radio this device is also known as a dummy antenna or a radio frequency
termination. It is a device used in place of an antenna to aid in testing a radio transmitter. If
a transmitter is tested without a load, such as an antenna or a dummy load, the transmitter
could be damaged. The radio energy that is absorbed by the dummy load is converted to
heat.
4.1.4 Curtain Antenna
Figure 4.2: Curtain antenna at SW transmitter
The curtain antenna is a high gain directional antenna, designed for medium and long
range communication. They are used when sectional coverage is desired, providing high
antenna efficiency and the highest tolerance for unfavourable environmental conditions. T
Curtain antennas are available in two sizes. A low-band array covers the 6, 7, 9 and 11 MHz

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