ALL INDIA RADIO,UDAIPUR(RAJ.) TRAINING REPORT DEPARTMENT OF ELECTRONICS & COMMUNICATION Refrence: Dr. sunil joshi sir, Dr. naveen agrwal sir Batch: 2013-17 C.T.A.E UDAIPUR MAHARANA PRATAP UNIVERSITY OF AGRICULTURE AND TECHNOLOGY,UDAIPUR

1. Summer Internship at
ALL INDIA
RADIO
(Indian Government Enterprise)
Akashwani, Udaipur
Training Report
From: 4th
June, 2015 To: 18th June,
2015
COLLEGE OF TECHNOLOGY AND
ENGINEERING
(Department of Electronics and Communication
Engineering)

2. Submitted To:
Submitted By: Dr. Navneet Agrwal sir
Abhishek Kumar
(Assistant Professor) B.Tech 2nd
yr.
(E.C.E)
Placement and Training Incharge (E.C.E) 2013/CTAE/171
ACKNOWLEDGMENT
The feeling of euphoria, I have on the successful completion of
the summer training at ALL INDIA RADIO (AIR) is expressible. I
take this opportunity to express my profound gratitude and
indebtedness to permit me to undertake the training in this
esteemed organization.
I would like to pay heartfelt thanks to the respected Head Dr.
Sunil joshi sir for giving the permission to the permission to take
the training.
My sincere gratitude and thanks to Shri Satish Depal

3. (Director Engineering), Shri pankaj sir (Assistant Director and
Training Superintendent) who has given me the opportunity to
perform training at Akashwani Udaipur station.
I express my sincere gratefulness to Shri J.K Purbiya(A.E), Shri
Arun kumar, Shri D.K. Bhagela, Shri Deepak kuril, Shri B.M.
Bhawasar, Shri V.R. Solanki who have spared time to guide me
during entire duration of training.

4. PREFACE
Practical training is a way to implement theoretical knowledge to
practical use. To become a successful engineer it is necessary to
have a sound practical knowledge because it is the only way by
which one can acquire proficiency/skill to work successfully
industries.
It is proven fact that bookish knowledge is not sufficient because
things are not as ideal in practical field as they should be. All India
Radio is one of the best examples to understand the
communication and connectivity in particular of broadcasting
systems.
It is matter of great pleasure that our college authorities have
recommended a practical training of 15 days to supplement our
theoretical knowledge acquired in the college .This report is an
attempt made to study the overall communication system
/related action of AIR, Chetak Circle and Madri station.

5. CONTENTS
1. INTRODUCTION
2. PRESENT SETUP
3. STUDIO CUM OFFICE COMPLEX
4. STUDIO TRANSMITTER LINK
5. AIR CONDITIONING SYSTEM AT STUDIO
6. ANTENNAS
7. TRANSMITTER COMPLEXSPECIFICATIONS
8. 100 KW BEL HMB 140 MW TRANSMITTER
9. CONTROL AND INTER LOCK SYSTEM
10. COOLING TECHNIQUES IN TRANSMITTER
11. ANTENNA TUNING UNIT
12. AKASAVANI IN NEAR FUTURE
13. CONCLUSION

6. INTRODUCTION
Radio Broadcasting was pioneered in India by the Madras
Presidency Club Radio in 1924. The Club worked a broadcasting
service for three years, but owing to financial difficulties gave it up
in 1927.
In the same year (1927) some enterprising businessmen in
Bombay started the Indian Broadcasting Company with stations at
Bombay and Calcutta. This company failed in 1930, in 1932 the
Government of India took over broadcasting. A separate
department known as Indian Broadcasting Service was opened.
The Service was later designated 'All India Radio' (AIR) and
was placed under a separate Ministry-the Ministry of Information
and Broadcasting. The AIR is controlled by a Director General,
who is assisted by several Deputy Directors and a Chief Engineer.
Broadcasting, in its significance, reach and impact,
constitutes the most powerful medium of mass communication in
India. Its importance, as a medium of information and education is
particularly great in a vast and developing country like India where
the reach of the printed word is not very wide or deep. While the
total circulation of all the newspapers in India, including both
English and Indian language papers, is around 8 million, there are,
according to a recent estimate, nearly 400 million (out of a total
population of 625 million) potential listeners to All India Radio.
Broadcasting in India is a national service, developed and
operated by the Government of India. All India Radio (also known

7. as Akashwani) operates this service, over a network of
broadcasting stations located ail over the country.
As a national service, catering to the complex needs of a vast
country. All India Radio seeks to represent in its national and
regional programmers, the attitudes, aspirations and attainments of
all Indian people and attempts to reflect, as fully and faithfully as
possible, the richness of the Indian scene and the reach of the
Indian mind.
AIR Network:
Starting with 6 broadcasting stations in 1947, the AIR today
has a network of 82 broadcasting stations. The 82 radio stations,
grouped into five zones, are the following: North Zone: Ajmer,
Allahabad, Aligarh, Bikaner, Delhi, Gorakhpur, Jaipur, Jodhpur,
Jullundur, Lucknow, Mathura, Rampur, Shimla, Udaipur and
Varanasi: East Zone: Agartala, Aizawl, Bhagalpur, Calcutta,
Cuttack, Dibrugarh. Gauhati, Imphal, Jeypore, Kohima, Kurseong,
Ranchi, Pasighat, Patna, Sambalpur, Shillong, Silchar, Siliguri,
Tawang and Tezu ; West Zone : Ahmedabad, Bhopal, Bhuj,
Bombay, Gwalior, Indore. Jabalpur, Nagpur, Panaji, Parbani, Pune,
Raipur, Rajkot and Sangli; South Zone: Alleppey, Bangalore,
Bhadravati, Calicut, Coimbatore, Cuddapah, Dharwar; Gulbarga,
Hyderabad, Madras, Mysore, Pondicherry, Port Blair,
Tiruchirappalli, Tirunelveli, Trichur, Trivandrum. Vijayawada and
Vishakhapatnam; and Kashmir Zone: Jammu, Leh and Srinagar.
In addition, there are three auxiliary studio centers at Vado-
dara, Darbhanga and Shantiniketan and two Vividh
Bharati/commercial centers, one at Chandigarh and the other at
Kanpur. These cover all the important cultural and linguistic
regions of the country.
The expansion of the broadcasting facility remained limited

8. till independence. In 1947 there were only six radio stations in the
country. Today there are as many as 82 AIR stations. With two
more stations that will start working soon, India's broadcasting
network would cover 89 per cent of the population.
Till the end of 1976 radio licenses had reached a colossal
figure of nearly 1.74 crores, which fetched revenue of Rs. 23.51
crores. Today the radio network has spread to the remote corners of
India. It is now possible to bring sense of unity not only political
but also cultural among the diverse traditions that enrich our land.
AIR's programmes pattern combines three main elements: a
national channel providing programmes of countrywide interest
and significance, a zonal service from each of the four
metropolitan centers (Delhi, Bombay, Calcutta and Madras); and
regional services from individual stations each catering to the
needs and interests of its respective area.
The principal ingredients of 1AIR's programmes output are
Music, Spoken Word, Dramas, and Features. News and Current
Affairs, Commentaries and Discussion, Vivid Bharati and its
Commercial Service, Farm and Home Broadcasts, Programmes for
Special Audiences (like Youth, Women, Children, Industrial
Workers and Tribal Population), and Programmes for Overseas
Listeners broadcast in the External Services.
To enable AIR to reach all sections of the Indian people, its
programmes in the Home Service are broadcast in 20 principal
languages. In addition, the External Services of AIR beam their
programmes to listeners all over the world in 24 languages.
New Services:
The News Services Division of AIR through its central and
regional news bulletins and its current affairs, commentaries and

9. discussions, provides accurate, objective, speedy and
comprehensive coverage of news to listeners at home and abroad.
AIR now broadcasts a total of 239 news bulletins a day, with
duration of 32 hours 17 minutes. Of these, 67 are Central bulletins
broadcast from Delhi in 19 languages, with a daily duration of 10
hours 3 minutes; 57 external bulletins (from Delhi) broadcast in 24
languages for a duration of 7 hours 14 minutes and 15 regional
bulletins from 34 regional centers (including the Prade- shik desk
in Delhi) broadcast in 22 languages and 34 tribal dialects with a
total duration of 15 hours every day.
The major sources of news for AIR are its correspondents at
home and abroad, the news agencies and the monitoring services,
AIR has a total of 206 correspondents. Of these, 111 are part-time.
External Services:
AIR made its first broadcast to listeners outside India on
October I, 1939. Today the External Services of AIR broadcast in
25 languages for about 50 hours daily round-the-clock, reaching
listeners in widely scattered areas of the world.
PRESENT SETUP
Currently there are two complexes in All India Radio,
Udaipur. They are:
1. STUDIO CUM OFFICE COMPLEX
2. TRANSMITTER COMPLEX

10. STUDIO CUM OFFICE COMPLEX,
UDAIPUR
A broadcasting studio is a room in studio complex which has
been specially designed and constructed to serve the purpose of
originating broadcasting programs. Whenever any musician sings
and we sit in front of a performing musician to listen to him, we
enjoy the program by virtue of the superb qualities of our sensory
organs namely ears. However, when we listen to the same program
over the broadcast chain at our home through domestic receivers,
the conditions are entirely different. These changes that we
experience are because of the audio processing that are performed
in a broadcasting studio.
There are three studios at AKASHVANI, UDAIPUR studio
complex. They are:
• MUSIC STUDIO
• TALK STUDIO
• PLAYBACK STUDIO
Music and talk studio are together known as RECORDING
STUDIO. A Recording studio is a facility for sound recording and
mixing. Ideally both the recording and the monitoring spaces are
specially designed by an acoustician to achieve optimum acoustic
properties (acoustic isolation or diffusion or absorption of reflected

11. sound that could otherwise interface with the sound heard by the
listener).
Recording studios may be used by recording musicians, voice
over dialogue replacement in film, television or animation, Foley
or to record their accompanying musical sound tracks. The typical
recording studio consists of a room called “Studio” or “Live
room”, where instrumentalists and vocalists perform; and the
“Control room”, where sound engineers operate professional
audio for analog or digital recording to route and manipulate the
sound.
Following equipment are generally provided in a
recording/dubbing room:
i) Console tape recorders
ii) Console tape decks
iii) Recording/dubbing panel having switches jacks and keys etc.
The above equipment can be used for the following purpose
• For recording of programmes originating from any studio.
• For recording of programmes available in the switching.
• Consoles in control room.
• For dubbing of programmes available on cassette tape.
• For editing of programmes.
• For mixing and recording of programmes.
We can brief the studio arrangements at AIR-UDAIPUR as
follows:
• MUSIC STUDIO
The MUSIC STUDIO is an acoustically treated room attached
to a control room. The studio consists of five microphones and
sufficient musical instruments. The control room consists of
workstations/computers and a control console for adjusting and
checking the quality of the program. These arrangements together
are used for producing musical programmes. Live musical

12. programmes can be also conducted here. SONYSOUND FORGE
is the software which is commonly used for processing the raw
version of the recorded program. The processed version of the
recording is saved to the server and then it is made available for
broadcasting by scheduling it to the program list using the software
VIRTUAL STUDIO.
• TALK STUDIO
The TALK STUDIO is similar to a music studio with an
acoustically treated LIVE ROOM and a CONTROL ROOM. The
live room consists of only two microphones. It is equipped with a
telephone connection which is a user friendly attribute for
recording Phone-in programs. The control room consists of an
additional Phone-in console for conducting Phone-in programs.
The acoustics of the talk studio is entirely different from a music
studio. It is constructed in such a way that the reverberation time is
minimised and no echo is experienced. The recording produced
and processed at the talk studio is then forwarded to the playback
studio for transmission. Talk studio can be also used to produce
live chat programs.
• PLAYBACK STUDIO
A PLAYBACK STUDIO is entirely different from all other
studios. It consists of transmission console, microphones, two
workstations/computers (Master & Standby). Its main function is
co-ordinating the programs, announcements and advertisements.
All the recorded programs will be available in the workstations
used and the programs are sent to the control room for
broadcasting as per the schedule. Before transmission of the first
program a tone of 1 kHz and signature tone will be aired. A GPS
clock is used both in the studio complex and transmitting section,
to avoid time delays.

13. BLOCK DIAGRAM OF STUDIO
CONTROL ROOM STUDIO CONSOLE

14. The Studio console is the major equipment used in the
STUDIO CONTROL ROOM. It is with the help of this device the
different programmes that are produced and those that are received
from other stations routed to air. The various inputs to the console
are the programmes from various studios, the programmes that are
received using a C BAND receiver which is broadcasted from
Delhi and the programmes that are received via an ISDN link from
Calicut and Thiruvananthapuram. The Outputs from the console is
taken through two master amplifiers among which one is active at
a time. This output is directed to the STUDIO TRANSMITTER
LINK (STL).
CONTROL ROOM AUDIO CONSOLE INPUTS
AND OUTPUTS

15. STUDIO TRANSMITTER LINK:
The programs produced at the Studios are not transmitted
from the same complex with intention of preventing the problems
due to interference and radiation. Instead, the programs are
transmitted from the transmission complex which is situated at
Avanoor. The high quality sound programmes from AIR studio
centre are normally transported to the AIR transmitting centre with
the help of a transmission link named as the STUDIO
TRANSMITTER LINK (STL).
AIR is having three types of STL called STL-01, STL-02 and
STL-05. The numbers 01, 02 and 05 describe the number of base
band (50Hz – 15 kHz) channels that could be transported. At
Thrissur, we are using STL-01 since we are transmitting only one
base band channel
For quality transmission of the programmes, STL is realised
using four methods. They are:
• A microwave link
• 10W FM transmitter link
• ISDN link
• BSNL dial up link
1. MICROWAVE

16. Radio and television broadcast companies originate their
signals in studios, but must get them to the transmitter site. In
many cities, a nearby hill or mountain holds most of the
transmitters. A microwave studio transmitter link (STL) delivers
the signal without wires. Positioned at a fixed location and using
radio waves, a microwave transmitter sends those waves across
space to be received by a microwave receiver at another fixed
location. Microwave is broadband, so it can transmit a substantial
amount of information from point to point, for use in cell phone
and wireless Internet service, with no need for any other equipment
between the two fixed locations.
The microwave STL system consists of a transmitting system
(STL-TX) housed in the studio premises and a receiving system
(STL-RX) housed in the AIR transmitting centre. A low loss cable
connects the STL TX/RX to the microwave dish antenna of
diameter 2m mounted on an approximately 50m tall self-
supporting tower at either end. In addition, a VHF service channel
in duplex mode is provided at both the ends for voice
communication between the AIR studio and transmitting end
through a multi-element yagi antenna mounted on the top of the
tower. The need for the service channel arises from the fact that
there is no RF monitoring facility of the transmitter sound program
at STL-TX.
The STL system is meant to operate unattended round the
clock. The microwave STL TX/RX is powered by an external
power supply unit kept adjacent to the STL rack with floating
batteries. This unit takes 230V, 50Hz AC and supplies 24V DC to
STL TX/RX. The service channel is energised by another external
power supply unit placed over that of STL TX/RX.
SERVICE CHANNEL (RT 33) (VHF Link)
The service channel is mounted at the top of the transmitter
and receiver racks. It IS a VHF 1613-88 MHz) trans-receiver. The
transmitter output power is 15 watts YAGI( antenna mounted at the

17. top of the towers on either end is used for the service channel This
antenna may be used both in horizontal and vertical polarizations
Normally vertical polarization is used The hand set with a press to
talk (PM switch is employed at either end for service
communication. These units can be revised from the racks and kept
at any other convenient location at either end M/s Melton has
developed an interface unit with which telephone facilities can
be extended to the transmitter sole with this service channel
without the use of land lanes.
2. Integrated Services Digital Network (ISDN)
Integrated Services Digital Network (ISDN) is a set of
communication standards for simultaneous digital transmission of
voice, video, data, and other network services over the traditional
circuits of the public switched telephone network. It was first
defined in 1988 in the CCITT red book. Prior to ISDN, the
telephone system was viewed as a way to transport voice, with
some special services available for data. 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.
There are several kinds of access interfaces to ISDN defined
as Basic Rate Interface (BRI), Primary Rate
Interface (PRI), Narrowband ISDN (N-ISDN), and Broadband
ISDN (B-ISDN).ISDN 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.
For AIR, The ISDN link is facilitated by the BSNL. Air is
making use of BROADBAND ISDN. In addition to an STL system
ISDN acts as a channel for live broadcasting of AIR programmers.
BROADBAND ISDN (B-ISDN): The original or basic version of
ISDN employs baseband transmission on copper wires. But B-

18. ISDN uses broadband transmission at 1.5Mbps for transmission of
voice, video and data at the same time. B-ISDN requires fiber optic
cables and is less widely available as it has relied mainly on
evolution of fiber optics. According to CCITT, B-ISDN is “a
service requiring transmission channel capable of supporting
transmission rates greater than the primary rate”.
SALIENT FEATURES OF ISDN:
• ISDN is a fast network
• ISDN is a telephone network
• Integrated services
• Digital network
3. FM TRANSMITTER
Here in AIR, UDAIPUR, we use 60W FM transmitter link.
The principle of working of a modern FM transmitter is given in
the block diagram, The L and R audio signals are converted into
the stereo signal by a stereo coder. The stereo signal also called the
MULTIPLEXED signals then frequency modulates the VFH
oscillator which is a voltage controlled oscillator (VCO) OF THE
PHASE LOCKED LOOP (PLL). The PLL is an automatic
frequency control system in the FM transmitter is maintained
within the specified tolerance limits of +2 KHz. In this
arrangement the phase of the VHF oscillator is compared with that
of a reference crystal oscillator operating at10MHz. As the VHF
oscillator can operate at any assigned in the FM broadcasting band
of 87.5MHz-108MHz, the factor N will vary from 8750-
10800Hz.The phases of the output from the two frequency dividers
are then compared in a phase comparator and the resultant error
amplified rectified and filtered to get a dc error voltage of positive
negative polarity which corrects shift in the VHF oscillator
frequency. The FM signal obtained at the output of VHF oscillator
is then amplified in a VHF power amplifier with an output power

19. of1.5KW. This amplifier is the basic building block in the series of
FM transmitters. It is a wide band amplifier so that no tuning is
requires when the operating frequency is changed.
4. BSNL Dial Up Link
This link between the studio complex and the transmitter is
the least preferred and least used one. If all the other system fails
then the program signals are transmitted via the regular BSNL
telephone cables. Techniques are used at the transmission station to
receive these signals and then it is fed to the modulator.

20. BLOCK DIAGRAM OF STL
TRANSMITTER
I/P
RECEIVER
AIR CONDITIONING SYSTEM AT
STUDIO

21. The air conditioning at the studio complex is done using AC
plants. There are 3 AC plants at the studio complex each with a
capacity of XX tonnes among which 2 are sufficient for the
purpose. These two plants supply conditioned air to two different
parts of the studio via AC ducts that runs all over the ceiling. The
AC plant consists of Blowers and a water circulation system that
carries the hot air out of the building. The hot water is cooled at a
cooling tower where water is cooled by dissipation of heat to the
surroundings. A fan is also attached to the cooling tower for easy
cooling.
ANTENNAS
Antenna is usually a metallic device (a rod or a wire) used for
radiating or receiving electromagnetic waves. The radio frequency
power developed in the final stage of a transmitter is delivered
through cables/feeders, without themselves consuming any power
to the transmitting antenna. The RF energy gets converted into
electromagnetic waves and travels in the free space at the speed of
light. The receiving antenna picks up the radio waves and delivers
useful signal at the input of a receiver for reception of signals. The
transmitting and receiving antennae are reciprocal in the sense, any
characteristics of the antenna in general applies equally to both.
Antennas play a vital role in AIR also since these are the
communication links between the various stations and the
transmitter complex as well. As the purpose differ the shape, size
and specifications varies in case of Antennas. In an AIR station we
can see a wide variety of Antenna systems. These include:
• A C-band receiver antenna with a dish whose diameter is
about 5m. This antenna receives signals from other stations
like Delhi.
• A DTH receiver antenna with a dish whose diameter is about

22. 1m. This antenna receives signals from stations like Calicut
and Thiruvananthapuram
• Yagi antennas are mounted on the top of a mast of height
around 45 m. This is the transmitter antenna for the
microwave studio transmitter link. And a similar receiver
antenna is mounted on a mast of height about 50m. This
enables the line of sight communication between the studio
and the transmitter.
• Similar to microwave transmitter antennas, FM transmitter
and receiver antennas are also mounted on the same masts at
the studio and transmitter complexes.
• Private FM channels have also installed their antennas on the
mast at the transmitter complex.
• A self-radiating mast of height 122m which itself acts as the
antenna is present at the transmitter complex.
• Another self-radiating mast is present at the studio complex
which was used in earlier times. This mast, having a power
dissipation capacity of 20kW has decommissioned and is left
as it is.
TRANSMITTER COMPLEX,
AVANOOR
POWER SUPPLY TO THE TRANSMITTER
COMPLEX

23. X
TRANSFORMER
500 KVA
11KV/440V
X
100KW BEL HMB 140-MW
TRANSMITTER
A radio transmitter is an electronic device which, with the aid
of an antenna, produces radio waves. The transmitter itself
generates a radio frequency alternating current which is applied to

24. the antenna. When excited by this alternating current, the antenna
radiates radio waves. The transmitter combines the information
signal to be carried with the radio frequency signal which
generates the radio waves, which is often called the carrier.
Here in All India Radio, UDAIPUR; the 100KW BEL
HMB transmitter performs amplitude modulation in which the
information is added to the radio signal by varying its amplitude.
This transmitter mainly consists of these parts:
• A power supply circuit to transform the input electrical
power to the higher voltages needed to produce the required
power output.
• A quartz crystal oscillator that generates sinusoidal wave at
a frequency of 4MHz and associated frequency dividers to
divide the high frequency wave to the transmission frequency
630kHz.
• A modulator circuit to add the information to be transmitted
to the carrier wave produced by the oscillator. This is done by
varying some aspect of the carrier wave. The information is
provided to the transmitter in the form of an audio signal
whose content is the program produced at the studio.
Transmitter complex includes the following rooms:
• Power supply
• HT room
• Transmitter
• Cooling
POWER SUPPLY IN 100kW HMB 140MW
TRANSMITTER
1. Main supply to Transmitter: 415 V 3PHASE 50Hz AC
2. Supply voltage to PA and Modulator: HT 11kV (Thyristor
Controlled for smooth variation)

25. 3. Screen Voltage to PA Valve: 800V
4. Screen voltage to Modulator valve: 1070V
5. Plate Voltage to RF Driver: 1900V
6. Grid bias to PA Modulator & RF Driver: -650V
7. Supply voltage to cathode of RF Driver: -600V (Supplied by
way
Way of a tap on -650V supply)
8. Screen voltage of RF Driver: -100V
9. Thycon unit: +12V DC & -12V DC
10. Audio unit: +24V & +10V
11. Reflectometer: +15V & -15V
12. Control units:
• VDDB : +15V Logic Circuits
• VDDC : +12V Relays
• VDDD : +15V For indication lamps
• VDDE : -15V Comparator

26. Transmitter section includes RF, Audio as well as modulator
stages. RF section generates the required operating frequency, here
630 kHz. Audio stage makes the audio to reach up to the power
requirement. Modulator stage further modulates the audio with the
RF.

27. RADIO FREQUENCY STAGE (RF STAGE)
The RF chain consists of a crystal oscillator followed by a
wide band transistorized power Amplifier developing an output of
12-15 watts. This is followed by a driver stage using 4-1000A
valve working in class AB condition. This stage delivers a driving
voltage of 900V peak to the grid of PA. The PA stage consists of
CQK-50 ceramic tetrode valve working as a Class-D Amplifier.
The PA stage works into output impedance of 120 ohms delivering
a carrier of 100 KW. The stage is also high level anode modulated
by the modulator. The stage has been provided with a composite
anode circuit to provide for generation of class-D waveforms,
harmonic suppression and matching of anode impedance to the
output impedance.
• CRYSTAL OSCILLATOR:
The basic frequency determining unit is the crystal oscillator.
Two oscillator circuits are provided one in circuit and one is in
standby. The crystal oscillator is a self-contained unit including its
power supply and a proportionately controlled oven and gives an
output of 5V square wave which is required to transfer the
Transistor power Amplifier.
The 12 volts DC required for operating the unit as well as the
crystal oven is derived from a rectifier and a voltage regulator. The
crystal oscillator works between 3MHz and 6MHz for different
carrier frequencies. The basic oscillator is a pierce circuit with
crystal as the frequency determining element.
• TRANSISTOR POWER AMPLIFIER:
The power amplifier is a self-contained unit including its

28. power supply and delivers an output of about 12W and on output
impedance of 75 ohms. The stage works as a switching amplifier
and is wide band. However, the output filters are to be selected for
the frequency ranges 525-1150 kHz & 1150-1650 kHz. The unit
works on a 20V DC which is derived by the rectifier. It is followed
by the transistorized regulator and series pass transistor.
• RF DRIVER:
The RF Driver stage provides the driving power required to
develop an output of 100 KW to the final amplifier. Moreover, the
wave shape required for Class D operation of the final stage is also
generated in the driver.
4-1000A tetrode valve is used as a driver valve. The ac plate
load impedance of the tube is around 2.4K ohms which needs to
the matched to an effective PA grid load of 710 ohms. In order to
generate the required Class D driving waveform which is an
approximate square wave comprising of fundamental frequency
and 20% of the third harmonic grid of the final tube has got a
parallel tuned circuit at third harmonic frequency.
• RF POWER AMPLIFIER:
The final stage RF amplifier consists of a single tube, CQK-
50 beam power tetrode delivering carrier power output of 100 KW.
High level anode modulation is used using a class B modulator
stage. The screen of the PA tube is also modulated by a tap on
modulation transformer.
The plate load impedance of the PA stage is about 750 ohms
and the output impedance is 120 ohms. The complex PA circuit
matches the plate to the output impedance. In addition, the Class D
operation of the stage needs third harmonic impedance at the plate.
In addition, the output circuit should prevent radiation of harmonic
frequencies. The plate circuit provides all these functions.

29. AUDIO FREQUENCY STAGE (AF STAGE)
The AF Stage supply the Audio power required to amplitude
modulates the final RF stage. The output of the AF stage is super
imposed upon the DC voltage to the RF PA tube via modulation
transformer. An auxiliary winding in the modulation transformer,
provides AF voltage necessary to modulate the screen of the final
stage. The modulator stage consists of two CQK 25 ceramic
tetrode valves working in push pull class B configuration. The
drive stages up to the grid of the modulator are fully transistorized.
• High Pass Filter
The audio inputs from the speech rack are fed to active High
Pass Filter. It cuts off all frequencies below 60Hz. Its main
function is to supress the switching transistor from the audio input.
This also has the audio attenuator and audio muting relay which
will not allow AF to further stage till RF is about 70kW of power
• AF Pre-Amplifier
The output of the high pass filter is fed to AF Pre-Amplifier,
one for each balanced audio line. Signal from the negative
feedback network from the secondary of the modulation
transformer and the signals from compensator also are fed to this
unit.
• AF Pre-Corrector
Pre-Amplifier output is fed to the AF Pre-Correctors. As the
final modulator valve in the AF is operating as class B, its gain will
not be uniform for various levels of AF signals. That is the gain of
the modulator will be low for low level, input, and high for high

30. level AF input because of the operating characteristics of the
vacuum tubes. The Pre corrector amplifies the low level signal
highly and high level signal with low gain. Hum compensator is
used to have a better signal to noise ratio.
• AF Driver
2 AF drivers are used to drive the two modulator valves. The
driver provides the necessary DC bias voltage and also AF signal
sufficient to modulate 100%. The output of AF driver stage is
formed by four transistors in series as it works with a high voltage
of about -400V. The transistors are protected with diodes and zener
diodes against high voltages that may result due to internal tube
flashover. There is a potentiometer by which any clipping can be
avoided such that the maximum modulation factor will not exceed.
• AF Final Stage
AF final stage is equipped with ceramic tetrode CQK 25.
Filament current of this tube is about 210 amps at 10V. The
filament transformers are of special leakage reactance typeand
their short circuit current is limited to about 2-3 times the normal
load current. Hence the filament surge current at the time of
switching ON will not exceed the maximum limit.
A varistor at the screen or spark gaps across the grid are to
prevent over voltages. As the modulator valve is condensed vapour
cooled tetrodes, deionised water is used for cooling. The valve
required about 11.5 L /minute of water. Two water flow switches
WF1 and WF2 in the water lines of each of the valves protect
against low or no water flow. Thermostats WT1 and WT2 in each
water line provides protection against excessive water temperature
by tripping the transmitter up to standby if the temperature of the
water exceeds 70 degree Celsius.
Modulation condenser and modulation choke have been
dispensed due to the special design of the modulation transformer.

31. Special high power varistor is provided across the secondary
winding of the modulation transformer to prevent transformer over
voltages.
CONTROLAND INTERLOCK
SYSTEMS IN TRANSMITTER
Control and interlocking circuits of the transmitter are to perform
four major functions:-
• Ensure correct switching sequence.
• Safety of the equipment
• Safety of the operating personnel.
• Indication of the status of the transmitter.
In the following paragraph the details regarding the above aspects
are dealt briefly:
1. Switching Sequence of Transmitter
a) Ventilation
b) Filament
c) Grid bias or medium tension
d) High tension.
a. Ventilation: All the transmitters handle large amount of power.
Basically the transmitters convert power from AC mains to Radio
frequency and Audio frequency energy. The conversion process
always results in some loss. The loss in energy is dissipated in the
form of heat. The dissipated energy has to be carried away by a
suitable medium to keep the raise in temperature of the
transmitting equipment within limits. Hence, in order to ensure that
the heat generated by the equipment is carried away as soon as it is
generated the ventilation equipment need to be switched on first.

32. Normally the cooling provided in a transmitter could be classified
on the following lines:
• Cooling for the tube filaments.
• Cooling for the tube Anodes.
• General cooling of the cubic.
• Cooling for coils, condensers, Resistors etc.
The cooling equipments comprise of blowers, pumps and heat
exchangers. Another important consideration is that during the
switching off sequence the cooling equipments should run a little
longer to carry away the heat generated in the equipments. This is
ensured by providing a time delay for the switch off of the cooling
equipment. Normal time delay is of the order of 3 to 6 minutes.
The water flow and the air flow provided by the cooling
equipments to the various equipments are monitored by means of
air flow and water flow switches. In case of failure of water or air
flow, these switches provide necessary commands for tripping the
transmitter.
b. Filaments: All the transmitters invariably employ tubes in their
drive and final stages of RF amplifiers and sub modulator and
modular stages of AF amplifiers. After ventilation equipments are
switched on and requisite air and water flow established, the
filament of the tube, the control and interlocking circuits have to
take care of the following points.
The cold resistance of the filament is very low and hence
application of full filament voltage in one strike would result in
enormous filament current and may damage the tube filament.
Hence it becomes necessary to apply the filament voltage in steps.
Various methods adopted are:
i. Use of step starter resistance. Here the filament voltage of the
tubes is given through a series resistance (called step starter

33. resistance). The series resistance which limits the initial filament
current is shorted and after a time interval by the of a timer switch.
ii. Use of special filament transformer which allows slow build-up
of the filament voltage.
iii. Application of filament voltage in 3 or 4 steps.
The emission from the tubes depends upon the temperature of the
filament. Generally it takes some time for the filament to reach a
steady temperature after it is switched on. Hence, it is not desirable
to draw any power from the tube till it attains a stable temperature.
This means that the further switching on process has to be
suspended till the filament temperature and hence the emission
becomes stable. This aspect is taken care of by providing a time
delay of 3 to 5 minutes between the filament switching on and the
next sequence namely bias switching on.
c. Bias and Medium Tension: For obvious reasons the control
grid of the tube has to be given the necessary negative bias voltage
before its anode voltage can be applied. Hence, after the
application of full filament voltage and after the laps of necessary
delay for the filament temperature to become stable bias voltage
can be switched on. Along with bias generally anode and screen
voltages of intermediate stages and driver stages are also switched
on. Application of bias and medium tension makes available very
high voltages for the various transmitter equipment. Hence, in
order to ensure the safety of the personnel access to these
equipment should be forbidden before the application of bias and
medium tension. This is ensured by providing the interlocking so
that the bias and medium tension can be put on only after all the
transmitter and other HV equipment doors are closed to prevent
access.
Connection of load (Antenna/Dummy load)

34. After the application of ventilation, filament and bias the anode
voltage can be switched on. But before the anode voltage can be
increased the interlocking circuit is to ensure that the load of the
transmitter namely antenna or dummy load is connected to the
transmitter. The tuning process of the various RF stages is
complete and none of the tuning motors are moving.
Application of screen voltage
In the case of tetrode tubes, the screen voltage to the tube should
not be applied before the application of anode voltage to keep the
screen current and screen dissipation within limits. This is taken
care of by an interlocking provision that the screen voltage is
applied only after the anode voltage reaches a certain
predetermined value well above the normal screen voltage.
Release of Audio frequency
The application of AF signal to the AF stage in the absence of
carrier power would result in the operation of modulation
transformer with no load connected. This is not desirable.
Therefore, the AF signal should be applied to the audio frequency
stages only when the RF power amplifier is delivering the nominal
power. Normally AF frequency signal to the AF stage is released
only when the carrier power is approximately 80% of the normal
power.
2. Safety of the equipment
The various transmitting equipment and auxiliaries are to be safe
guarded against over loads etc. The various safety provisions
provided in the transmitter are as follows:
• All the existing machineries are provided with switches with

35. magnetic and thermal overload release.
• The air flow and water flow switches and temperature
sensors monitors the air flow and water flow of the cooling
medium. If the air and water flow fall below a certain
predetermined value, it ensures the necessary tripping
sequence.
• Water levels in the reservoir and water conductivity are
monitored constantly.
• Momentary release of air flow and water flow switches due
to some turbulence for a short duration will not result in the
tripping of the transmitter. However, if the fault persists for a
few seconds then the tripping will result.
• Sometimes thermal sensors are embedded in the filament
transformers to monitor its temperature.
• The filament voltage of various high power tubes is
monitored.in case of low or high filament voltage tripping of
the transmitter filament is initiated.
• Circuit breakers associated with various rectifiers such as
grid bias, screen voltages etc. Protect the rectifiers and
associated equipment against over currents.
• All the vital currents of the tubes and stages are monitored
and indicated by means of panel meters. This is to monitor
abnormality if any on the various operating conditions.
• Also current operated over load relays are provided in the
cathode, screen grid and anode circuits to protect the tubes
and the associated rectifiers in case any of these respective
currents exceed a predetermined value. The operation of
over load relays are indicated by means of flags or latched
lamps
• The standing wave ratio on the load side is monitored
suitably and signal is used to trip the transmitter anode

36. voltage in case of VSWR is higher than the predetermined
value.
• Spark detectors are provided in various cubicles to ensure
the tripping sequence in case of sparking to prevent damage
to the equipments.
• Normally the over currents are counted over a period of time
and if number of over currents occur in a short interval the
transmitter is tripped up to the filament.
• In addition to the above safety provisions spark gaps and
varistor provided at various high voltage points offer
protection to the equipment against high RF voltage.
• In some of the transmitter a crow bar device is provided to
short circuit the stored energies in the power supply circuit
in case of over load. This provision is to protect the high
power tubes.
3. Safety for the personnel
Since very high voltages are encountered in transmitters the
operating personnel are to be protected by coming into contact
with these high voltages accidently. The safety interlocking
generally comprises of:
• An earthing switch which earths all the high voltage supplies
before the access to the cubicles keys are allowed.
• A key exchange panel where the key to the transmitter
cubicles can be utilized only after the earthing switch is put
ON. The earthing switch is interlocked in the bias circuit and
hence the operation of the earth switch automatically
switches OFF up to bias. This provision ensures that the
cubicle doors can be opened only when the bias and medium
voltages are switched OFF and earthed through the earthing
switch.

37. • In addition to the above, earth hooks are provided at various
parts of the cubicles and high voltage equipment area. The
operating professional are too short through these hooks are
high voltage points before any work is undertaken in these
equipment.
• Some of the transmitters are also provided with additional
shorting switches in the cubicles which short the supplies in
the cubicle as soon as the door is opened.
4. Indication Lamps
The indication lamps are provided in the transmitter to
indicate the status of switching ON of the transmitter as well as to
indicate the occurrence of over load etc. These indication lamps are
provided to help the fault diagnosis.
COOLING TECHNIQUES IN TRANSMITTER
In high power A.M. transmitter, lot of power is dissipated in the
valve as the input power is not fully converted into output R.F.
power due to the efficiency of the amplifier which never reaches
100%. Hence the valves have to be cooled. In addition filaments
are drawing large current of the order of 210 Amps at 10 volt for
CQK valve. Hence they also have to be cooled. The dissipated
heat in the valves also circulates in the concerned cubicle and heat
develops there. Hence some kind of cooling has to be provided to
the transmitting equipment. Different types of cooling are used in
AIR transmitter at present.
• Air cooling

38. • Vapour cooling
• Condensed vapour cooling
a) Air Cooling
At present forced air cooling is used in AIR transmitters. A
blower sucks the air through an Air filter and a guided duct system
and the forced air is passed on to the required transmitting tubes.
There has to be minimum air flow to cool the valves. Hence there
will be an air operated Air Flow Switch (Relay) AFR : the AFR
will close only when sufficient amount of air has been built up
with the blower. Otherwise, AFR will not close and filament
cannot be switched on. Sometimes, if the filter is not cleaned,
sufficient air may not go out of the blower. Hence the blower
needs periodical cleaning.
b) Vapour Cooling System
This system is used in 100 kW BEL Transmitters. For very
high power valves and efficient cooling, air cooling is not
sufficient. Hence some of the valves like BEL 15000, BEL 75000
etc. are cooled by vapour cooling. (Hence called Vaptron). Here
the principle of heat required to convert water into steam at its
boiling point is used (Latent heat of steam). The valves are kept in
an in-tight water container filtered and de-ionized water. This
water has high resistivity and comes in contact with anode. The
water containers called "Boilers" are provided with inlet and outlet
pipes.

39. Fig. 1 Block Diagram of Vapor-Cooling System
The inlet pipes are interconnected at the bottom to keep the
water level same in all the boiler and the outlet pipes are joined at
the top which provides passage of the steam to the condensing
equipment known as Heat Exchanger.
The heat produced at the anode of the vacuum tubes is
absorbed by water and gets converted into steam. The steam thus
produced goes up through the glass-tube to the steam pipe and to
the heat exchanger mounted on top of the transmitter room. The
condenser is made of copper tubes. This is a mono-block fine tube
moulded from copper in extrusion moulding system and has high
terminal conductivity. Steam flows inside the tube and cool air is
forced outside through the fins and the action of heat exchange
takes place. Now the steam is condensed to water and the cooled
water flows down through the water pipe due to gravity back to the
boiler.
c) Condensed Vapour Cooling in HMB-140BEL 100 kW

40. MW XTR:
In BEL/BBC solid state transmitter of 100 KW/300 kW MW
and 50 KW/100KW/500KW SW transmitters, condensed vapour
cooling is used for the PA and modulator valves. Here a
circulation of fast flowing stream of de-mineralized water is used.
High velocity water flows through the valve jacket and transforms
into vapour due to the dissipation of power in anodes. The tubes
are fitted with a specially formed anode which sits in a cylindrical
cooler. Due to the fast flow of water, the vapour is condensed to
water as soon as they are formed. Hence the cooling efficiency is
much higher. The temperature of water coming from the
transmitter can theoretically reach about 900
C, but in practice, it is
desired to about 700
C in normal programme modulation.
Filaments of the tubes are cooled by forced air by means of a
high pressure blower. It also cools the R.F. driver valves, the third
harmonic and second harmonic suppression coils.
The demineralized water is pumped by pumps (one in circuit
and one as standby) from the water tank to the PA and modulator
tubes through the water piping. At the inlet/outlet of each tube, a
double ball valve is provided to facilitate shutting off water supply
when the valve is required to be changed. Except for changing the
valve, this should be kept in open condition always. (Lever in the
horizontal position).

41. Fig.2 Water Flow Circuit 100 kW HMB 140
ANTENNA TUNING UNIT (ATU)
Antenna Tuning Unit (ATU) is to match the feeder line
impedance to the mast impedance of MW Transmitters for
maximum transmission of power. So ATU is located between the
mast base and the feeder line and is very close to the mast base.
Commonly “Feeder Unit” which is located in the aerial field,
houses the ATU.
Generally the mast impedance (aerial impedance) is obtained
in a complex form i.e. the real part (resistive) and the imaginary
part (reactive) component. When the mast impedance is expressed
in polar form then negative angle indicates the mast is capacitive
and positive angle indicates the mast is inductive. Whether the

42. mast impedance is inductive or capacitive depends on the height of
the mast in terms of wave length (). If the height is less than /4, it
will be capacitive and inductive if more than /4. This can be
measured with impedance bridges.
ATU can be designed in a number of ways. The method used
may be different in different conditions. Criteria depend on the
requirements. Especially when directional antenna system is
employed by splitting power to different antenna, the phase angle
of the network is the most important parameter. In other cases
mostly, simplicity and safety against lightning is important. One of
the methods adopted in the past was the reactive component of the
mast impedance is neutralised, by putting opposite reactive
component of same value in series at mast end side, to make the
mast impedance purely resistive (i.e. for inductive mast the series
reactance should be capacitive and vice versa). Then the resistive
part of the mast impedance can be matched to the feeder line
impedance by selecting a suitable matching network. This
matching network can be L, T or network, and can be designed as
phase lag or phase lead type. In these cases if a capacitor is put in
series, there is every possibility of puncturing of capacitors due to
lightning. Hence this method is being discouraged.
The second method, which is most commonly used now, is
first to convert the antenna impedance into a parallel combination.
Most of the bridges used to measure the mast impedance measure
it in the series form.
At AIR, Thrissur we are using the first method and the
matching network used is a pi network. Here the mast impedence
is 56+81.60j ohms and the feeder impedence is 121.60 ohms. The
possibility for puncturing the capacitor bank is minimized by

43. installing a lightening arrest in the self-radiating mast. This will
keep the pi network arrangement intact from the threats of
lightening.
The self-radiating mast is a part of the ATU. Its base is
separated from the ground using porcelain insulator. This prevents
the signal from earthing. The mast is held vertical using stay wires.
For a certain area, Copper bars are laid radiantly on the earth
surface for the sake of proper earthing.
AKASHAVANI - In near future….
• DIGITAL RADIO MONDIALE (DRM)
DRM is the only universal non-proprietary digital radio
system for the short wave, medium wave and long wave AM
broadcast bands. Many existing transmitters can be easily
modified with an inexpensive upgrade to carry DRM signals,
enabling a single tower to broadcast over a large geographic
area so that the listeners can receive the same station with
near FM quality sound. Commercial and public international
broadcasters, as well as national radio networks and local
radio stations, have begun transmitting regular DRM
broadcasts and special programs.
The frequencies required are exposed to highly fluctuating
propagation conditions. In this frequency range the waves are
influenced by the ionosphere and they are reflected
depending on the time of day, season and the relative number
on sunspots. Thanks to the digital standards the AAC+ audio
coding and the COFDM technology, signal transmission now
promises outstanding quality as compared to conventional

44. AM broadcasting.
DRM can use the existing band plan and the frequency grid
present in the medium wave, short wave and long wave. The
technology therefore facilitates the transmission from analog
to digital transmission technology, which can cover large
areas end to end at a favourable price. Due to external
influences on the transmission conditions, the transmission
parameters can be adjusted to match the propagation
conditions.
One advantage from using DRM plus is significantly lower
power consumption of the transmission systems.
• DIGITALIZATION
Digitalization of program production facilities, transmission
facilities and uplink stations has been undertaken to ensure
good quality convergence-ready content, which will also
support interactive radio services like news on phone, music
on demand etc.
• FM RADIO STATION
AKASHAVANI, Thrissur is about to launch a new FM radio
station which is transmitted at a frequency 111 MHz This
project which is undergoing the paper level proceedings is
expected to be trial running very soon. This project if brought
into existence will help in increasing the listenership of
AKASHAVANI by means of broadcasting a set of listener
friendly programs.

45. • Computerization of AIR stations and offices is in progress to
facilitate online exchange of information and improvement of
efficiency. Stations with digital equipments including
computerized hard disk based workstations for recording,
dubbing, editing and playback facilities etc. are being
provided at all the major stations.
• Control archives and regional archives have valuable
collection of historical and cultural important recordings in
their libraries. The audio program material available on
analog audio tapes is being converted into digital and stored
on CD’s. It is proposed to provide control archive at Delhi
and regional archives at four stations of AIR such as
Mumbai, Kolkata, Chennai and Hyderabad connected in the
network so that the archival material can be shared among
the stations. Provision of digitalization of analog material &
refurbishing the old recordings at these stations for release in
market in CD format is also proposed.
• Digitalization and automation of NEWS gathering NEWS
production and NEWS broadcast activity has already been
introduced at NEWS services division of AIR in Delhi and
regional NEWS units. Under IInd plan it is proposed fully
digitalize and have NEWS room automation at all the
regional NEWS units by providing NEWS automation
software, computer server and workstations etc. This facility
is further extended to seven more regional stations of AIR.
• Up-linking facility used for distribution of programs through
satellite is being digitalized by augmenting the existing
capital earth stations with digital uplinks. New digital captive

46. earth stations (Uplinks) have been installed at Varanasi,
Rohtak, Leh, Dehradun, Silchar and Aurangabad. Digital
downlink facilities have also been installed at most of the
stations.
• Analog microwave links, used for transportation of programs
from studio to transmitter, are proposed to be replaced by
digital microwave links. New digital microwave STL
equipments have been installed at Cuddaph, Vijayawada,
Srinagar, Patna, Jodhpur, Chandigarh, Jaipur, Kota and
Aurangabad. Twenty one numbers of Portable MSS terminals
have been procured for NEWS gathering in the network.
• Digitalization of studio which includes digitalization of
switching consoles, audio processor, cables, amplifiers,
equalizers, audio ports, jacks etc.
CONCLUSION
Broadcasting, in its significance, reach and impact,
constitutes the most powerful medium of mass communication. In
India, All India Radio operates this service, over a network of
broadcasting stations located over the country. Starting with 6
broadcasting stations in 1947, the AIR today has a network of 82
broadcasting stations. AIR's programed pattern combines three
main elements: a national channel providing programmes of
countrywide interest and significance, a zonal service from each of
the four metropolitan centers (Delhi, Bombay, Calcutta and
Madras); and regional services from individual stations each
catering to the needs and interests of its respective area.
Currently there are two complexes in AIR UDAIPUR, Studio

47. cum office complex and the Transmitter complex. In studio
complex, there are three studios, MUSIC, TALK and the
PLAYBACK. The first two together called to be the recording
studio facilitates sound recording and mixing whereas the latter
helps in coordinating the programs, announcements and
advertisements. The Studio console is the major equipment used in
the STUDIO CONTROL ROOM. The various inputs to the
console are the programmes from various studios, the programmes
that are received using a C BAND receiver which is broadcasted
from Delhi and the programmes that are received via an ISDN link
from Calicut and Thiruvananthapuram. The Outputs from the
console is taken through two master amplifiers among which one is
active at a time. This output is directed to the STUDIO
TRANSMITTER LINK (STL). This further route the programs to
TRANSMITTER at Avanoor.
The source to the transmitter complex is also realized using
MICROWAVE, FM TRANSMITTER, ISDN or BSNL DIAL UP
links. In AIR UDAIPUR, transmitter performs amplitude
modulation in which the information is added to the radio signal by
varying its amplitude. The transmission frequency is at 630 kHz
generated by a quartz crystal oscillator. RF driver stage provides
the driving power required to develop an output of 100 KW to the
final amplifier. High level anode modulation is used using a class
B modulator stage. The AF Stage supply the Audio power required
to amplitude modulates the final RF stage. The modulator stage
consists of two CQK 25 ceramic tetrode valves working in push
pull class B configuration. The drive stages up to the grid of the
modulator are fully transistorized. The transmitter complex is also
equipped with various control and interlocking systems. Due to the
high power evolved, cooling systems are also provided, utilizing
ionized air, vapor and condensed vapor cooling techniques. The
transmitter complex is also equipped with a HT room for providing
the required power supplies.

48. There is also an ATU to match the feeder line impedance to the
mast impedance of MW transmitter for maximum transmission
of power, located between mast base and the feeder line. The
information in its modulated form is further given to the self-
radiating mast provided with proper earthing.