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Submitted for the partial fulfillment for the award of the degree of
BACHELOR OF TECHNOLOGY
RAJASTHAN TECHNICAL UNIVERSITY, KOTA
VII SEM (ECE)
Department of Electronics & Communication
ENGINEERING COLLEGE AJMER
(An Autonomous Institute of Govt. of Rajasthan)
Badliya Chouraha,N.H. 8,By-Pass,Ajmer-305002
Website : www.ecajmer.ac.in ,Ph no. 0145-2671773,776,800,801
I wish to express my sincere thanks to DDK, Ajmer(Dordarshan Kendra), Toshniwal
Industries Pvt. Ltd.,Ajmer and All India Radio for the successful completion of my
Industrial Visit to their prestigious organizations. It was a wonderful experience to work
under the supervision of learned teachers and engineers there.
I shall always be grateful and loyal to my teachers who guided us at all times and told us
the advantages of Industrial exposure and encouraged us to do so.
I would also like to express my gratitude towards my parents and friends for their support.
Roll No. – 08EC013
ECE (Final Year)
Govt. Engg. College , Ajmer
Industrial Exposure is an important constituent of any curriculum and the B.Tech. course is
no exception to this general rule. It helps a student in getting acquainted with the manner in
which his knowledge is being practically used outside his institute and this is normally
the different form what we has learnt from books theoriticaly. Hence, when one switches
from the process of learning to that of implementing his knowledge, he finds an abrupt
change. This is exactly why industrial visit session during the B.Tech. Curriculum becomes
all the more important. The provision of training offers a very good opportunity to the
students to supplement their knowledge and skills by working in actual industrial or
corporate environment. This opportunity should be utilized for developing and enhancing
our skills as practicing engineers.
This report describes my industrial visits after the Vth Sem B.Tech.
session, which I completed at DDK, Ajmer(Dordarshan Kendra), Toshniwal Industries Pvt.
Ltd.,Ajmer and All India Radio .
1. Indstrial Visit –Toshniwal Industries Pvt. Ltd.
2. Indstrial Visit – All India Radio
3. Indstrial Visit – Dordarshan Kendra
TOSHNIWAL INDUSTRIES Pvt. Ltd.
1. Industrial Visit –Toshniwal Industries Pvt. Ltd
1.2.2 Optical Pyrometer
1.2.3 Thermal Imagers
1.2.5 Decade Resistance Box
1.2.6 Resistance Temperature Detectors
1.2.7 IR Thermometer
1.2.8 Kelvin Bridge
1.2.9 Light Spot Galvanometer
RESISTANCE TEMPERATURE DETECTORS
For temperature measurement in the range, -200°C to + 850°C Resistance Temperature
Detector (RTD) is preferred to Thermocouple and other sensors because of its higher
accuracy, reliability, compact size and faster response. RTDs find use in almost all
industries like plastic and rubber processing, food industries, pharmaceuticals, chemical &
petrochemical plants, and power plants. It is also used in diesel engines & ships, process
control and laboratories for temperature measurement and control.
RTDs are available with single or double resistance elements and in 2, 3 or 4 wire circuits.
Various types of protection sheaths for protection of the element and screw-in threaded
bushes either fixed (welded) or adjustable by screws (for non-pressure application) or by
compression fitting (for pressure application) for mounting are available.
RTD normally consists of spring-loaded insert, outer protecting sheath with mounting
connections and cast aluminum terminal head. The insert assembly consists of Pt 100
element with silver/copper connection leads, insulated by ceramic multibore insulating
tube/beads in a brass or stainless steel sheath with ceramic terminal block and brass
terminals attached to a spring loaded arrangement.
High accuracy and stability
Wide temperature range; -200°C to +850°C
Fast response & High insulation resistance
Needs only copper cables for long runs.
Resistance element Pt 100, 100 Ohms at 0°C
Fundamental interval 38.5 Ohms change in resistance from 0-100°C
-50°C to + 500°C
(-200°C to + 850°C also available)
No. of elements Single or Double
Insulation resistance 10M Ohms at 500V DC (100 M ohms on request)
They are used in industries, power plants, and metal melting furnaces, salt baths, industrial
process control, laboratories and numerous other applications as
Salt Bath : Neutral/Cyanide/Borax/HSS/Chloride/other
Molten Metal : Zinc/Magnesium/Aluminium/Copper/Brass/Ferrous Alloys/other
Process Furnaces : Glass
High Pressure Stoves.
Ovens & Furnace with : Reducing/Oxidising/Sulphurous/Carbonising
Plating : Galvanising/ Tinning.
A thermocouple consists of two dissimilar metallic Wires joined at one end known as hot
junction. When the hot junction is heated, an emf is produced which depends on the
difference between the temperature of the hot junction and the temperature of free ends
known as cold junction. This thermo emf is measured by galvanometric/potentiometer
metric/digital instruments, to display temperature.
Most common, convenient and versatile devices used to measure temperature.
Sensing devices for measurement, control and recording of temperature from 200°C to
These are available in two basic designs-
Straight type & Angle Type:
Angle type Thermocouples are used when it is not convenient to use Straight Type
Thermocouples or Thermocouple connecting head is desired to be kept away from the
place of insertion of Thermocouple so as to avoid attack of harmful fumes and vapors or
Thermocouple wires welded at one end are called elements. Both the positive and
negative legs of the thermocouple elements are insulated by ceramic insulators (beads) to
avoid short-circuiting and corrosion. A full-length long multibore insulating tube insulates
rare metal thermocouple elements. Depending on the use, a thermocouple assembly has one
(simplex), two (duplex) or more number of elements.
The connecting head is cast aluminum or cast iron with detachable cover and is fixed on
open end of protecting sheath. Thermocouple wires are terminated on a ceramic terminal
block with bass Terminals inside the head. From these terminals, compensating/ extension
leads are taken for connections to the measuring or controlling instruments.
Metallic and /or ceramic sheaths (tubes closed at one end) are put over the thermocouple
elements for protection against corrosive atmosphere and harmful chemical action, which
may be present at the place of use. When the corrosive atmosphere is too severe, an
additional, inner gas tight ceramic sheath is provided for protecting the elements from
corrosion, especially for the expensive rare metal thermocouples. In the case of angle type
thermocouple, this ceramic tube is provided in the hot arm only. General guidelines for
protecting sheath for different applications are given in the table below:
Note: 1) Protective sheaths of other materials, such as Graphite, Cast Iron (for molten
Aluminium), Hastelloy etc.
2) Operating temp. Varies, depending on the atmospheres.
Metallic protective sheaths are also offered with coatings of Tungsten Carbide, Stellite,
Teflon Ceramic, glass etc. and sleeve of tantalum, titanium, hastelloy, nickle, zirconium
etc. are also available for resistance to abrasion/chemical corrosion in special process
Flange or screwed bush is used for mounting the Thermocouple at the place of its use.
Flange in normally adjustable over the protecting sheath or holding tube of ceramic sheath.
They are used in industries, power plants, and metal melting furnaces, salt baths, industrial
process control, laboratories and numerous other applications as
Salt Bath : Neutral/Cyanide/Borax/HSS/Chloride/other
Molten Metal : Zinc/Magnesium/Aluminium/Copper/Brass/Ferrous Alloys/other
Process Furnaces : Glass
melting/Cracking/Roasting/Blast/Calcining/Hydrogenising/ High Pressure Stoves.
(specify process material).
Ovens & Furnace with : Reducing/Oxidising/Sulphurous/Carbonising gaseous
atmosphere (Specify gas details)
Plating : Galvanising/ Tinning.
High performance thermal imagers have never been this affordable. This rugged. Or,
this easy to use … until now.
We, at Fluke, are never satisfied leaving the best tools in the hands of the elite, which
is why we recently added a new member to our thermal imaging family.
Superior image quality
Delivers the clear, crisp images needed to find problems fast with its 320x240
Identify even the smallest temperature differences that could indicate problems with
industry-leading thermal sensitivity (NETD).
Automatic alignment (parallax correction) of visual and infrared images with Fluke
Optional telephoto and wide angle lenses available for added versatility and special
applications. (easily installable in the field)
Easy to use
Field replaceable batteries give you maximum flexibility no matter where your
work takes you.
Intuitive, three-button menu is easy to use—simply navigate with the push of a
No need to carry pen and paper—record findings by speaking into the imager.
Voice annotations can be recorded with every image you take. Voice comments are saved
along with individual images for future reference.
One-handed focus capability, emissivity correction, reflected background
temperature compensation, and transmission correction increase the accuracy of
measurements in most situations.
Adjustable hand strap for left-or right-handed use.
Everything needed to get started is included.
Optimized for field use in challenging work environments.
Engineered and tested to withstand a 2 m (6.5 ft) drop for the ultimate peace of
mind - When was the last time you dropped a tool or piece of equipment?
Withstands dust and water—tested to an IP54 rating.
Manufactured in the U.S.A.
Inside Electrical distribution & Service (Switchgear & Panels)
Motors, Pumps, etc
Process- Tanks, Pipes
Outside Electrical Utilities
Rheostats are mainly used for regulating electric current in industry and laboratory where
these are used as adjustable resistors in electrical circuits. With three terminal provisions,
these can be used to vary a D C potential smoothly from zero to maximum.
Toshniwal Rheostats consist of resistance wire wound on a former which is made from
solid drawn hexagonal steel tube vitreous enameled, ensuring good mechanical strength
and sturdiness. The tube is fitted in two end castings insulated with micanite cups.
The Brush gear slides on a highly polished square slide rod. The brush is of copper graphite
with pigtail connections. Two heat resisting compression spring hold brush family in
contact with the resistance wires. Copper graphite brush provides necessary lubrication to
prevent wear and tear of wire even at elevated temperatures.
The brush is housed in a slider knob of moulded bakelite designed for easy handling.
Different designs in a single tube and double tube models are available to meet with
demands of different applications.
Industrial quality components.
Trouble-free long service.
Wide range of resistance values and current – carrying capacities.
Tolerance on resistance value + 20% to -5%
H.T. Test 2kV for 1 minute
Temperature rise 375ºC*
Maximum working voltage 500 V
Ambient Temperature 0-45ºC
The application of rheostats is in the field circuits of motors or generators for the control of
speed or voltage, or in control circuits. The rheostat can adjust generator characteristics,
dim lights, and start or control the speed of motors.
The Partial Radiation Pyrometer, ‗PYROPTO‘ is a disappearing filament Optical
for measuring high temperature of incandescent objects, in annealing and hardening
furnaces, in firing kilns, for measuring the temperature of molten and flowing metal or
glass as well as incandescent blocks during forging, pressing or rolling. The temperature
measurement makes use of comparison between the brightness of an electrically heated and
calibrated incandescent filament(reference light bulb) in Pyropto and that of the object to
The special advantage offered by the PYROPTO is the light weight of the instrument
which houses all components of the complete measuring equipment.
Wide temperature range 700 – 2000 º C or 700 – 3500 º C
Fast response and sensitive measuring system
Light weight & portable
Operates on two 1.5V dry cells
RAYTECH MT4 -
The MiniTemp™ IR thermometer—a new way to solve common problems.
Infrared (IR) thermometers have become the preferred tool for diagnostics and inspection
where temperature is an indicator. Raytek IR thermometers are valued by professionals in
a variety of industries—from industrial maintenance to food service, because they quickly,
accurately and safely measure surface temperature! Anywhere that temperature is a factor
in process, product quality or diagnostics, a Raytek IR thermometer should be close at
IR thermometers are easy to use, and since they do not contact the object being measured,
they are the safest way to measure hot, hard-to-reach, or moving parts, while eliminating
potential damage and contamination.
The Raytek MiniTemp MT4 thermometer incorporate many of the same features found in
professional IR thermometers.
What are the benefits of using IR thermometers?
Effectively find your problems quickly and safely, saving time and cost.
IR thermometers are accurate, usually within one degree.
IR thermometers safely read hard-to-reach or inaccessible objects.
Simple to use
Laser Point (MT4)
Large, easy to read display
Temperature Range (MT4) -18º to 400ºC (0º to 750ºF)
ºC or ºF selectable
Check for heat created by loose connectors or buildup. Instantly
troubleshoot problems in battery banks and power panel terminations, ballasts, switch
gears, and fuse connections, and identify hot spots in the output filters on DC battery
Check moving parts in motors and gear work for
hot spots. Temperature change can indicate developing problems in many types of
equipment, from ovens and boilers to freezers. Routine temperature audits of generators
and their bearings can prevent expensive repairs.
Monitor HVAC/R components for quick energy audits and room
balancing in a short time.
Troubleshoot engine problems:
Temperature is a vital indicator of how well cooling
systems are performing, or whether friction, vibration and other conditions are creating
wear in braking systems and bearings.
Monitor process line equipment. Check the temperature of
different products on production lines from rubber tires to plastic and cellophane wrapping
to chocolate bars.
ALL INDIA RADIO, AJMER
Owned by PRASAR BHARTI
Broadcasting Corporation of INDIA
2 Industrial Visit –All India Radio
2.2 Power Supply
2.2.1 Transmission Lines
2.2.2 Grid Input
2.3.1 Amplitude Modulation
2.3.2 Angle Modulation
2.4.1 10 KW HMB 104 Medium Wave Transmitter
2.4.2 100 KW HMB 140 Medium Wave Transmitter
2.5 Antenna System
2.5.1 Marconi Anetnna
High power transmitter in Ajmer was established on 11th
initially it was started with 20KW power and connected to AIR Jaipur station.
In 1987, its power is raised up to 200KW. Its range covers almost all over
HPT in Ajmer is located at longitude 74°43´00´´ and latitude
26°31´07´´. ALL INDIA RADIO is situated 10 Kms far from the Ajmer Bus
Stand at N.H.No.8 in NORTH direction,near GAGWANA village. It
is120Kms far from Jaipur in SOUTH direction in the state of RAJASTHAN.
A.I.R. is working under the Ministry of INFORMATION AND
BROADCASTING. It is broadcasting under PRASAR BHARTI
CORPORATION of INDIA. Its range covers almost all over Rajasthan.
High Power Transmitter Akashwani Ajmer
Relay Transmitter From Jaipur
Transmitter Salient Features →
MAKE/TYPE → BEL HMB 140.
RADIATED POWER → 2×100 KW.
FREQENCY → 603 KHz.
WAVELENGTH → 497.51 Mtrs.
MAST HEIGHT → 200 Mtrs.
ELECTRICAL HEIGHT → 248 Mtrs.
MAST BASE IMPEDENCE → 778.4+j50.3 Ohms.
SITE AREA → 238656 SQ.MT,
→ 140 BIGHA.
TRANSMISSION HOURS → 05:55 − 09:30.
→ 11:45 − 15:00.
→ 17:00 − 23:20.
• AJMER TO DELHI 215 Kms.
• AJMER TO UJJAIN 256 Kms.
• AJMER TO UDAIPUR 223 Kms.
• AJMER TO BIKANER 197 Kms.
• AJMER TO JODHPUR 221 Kms.
POWER SUPPLY → Two 11KV overhead feeder
From MADAR and
GAGWANA. Two Stand by
Modulation means to ―CHANGE―. In
modulation , some characteristics of carrier wave
is changed in accordance with the intensity of the
signal. The resultant wave is called modulated wave
or radio wave and contains the audio signal. In India,
Amplitude modulation is used in radio broadcasting.
When the amplitude of high frequency carrier wave is
changed in accordance with the intensity of the signal
it is called Amplitude Modulation. In amplitude modulation, only the amplitude of the
carrier wave is changed in accordance with the intensity of the carrier signal. However the
frequency of the modulated wave remains the same i.e. carrier frequency. In amplitude
modulation, the amplitude of the carrier wave changes according to the intensity of the
signal and the frequency of the amplitude modulated wave remains the same i.e. carrier
To oscillate at a consistent frequency, the crystal is kept in a oven. The
temperature of the oven is maintained between 68 to 72o
C and the corresponding
indication is available in the meter panel. Crystal oven is heated by +12 V. One crystal
oscillator with a stand by has been provided. It gives an output of 5 V square wave which is
required to drive the Transistor Power Amplifier. The crystal oscillator works between 3
MHz and 6 MHz for different carrier frequencies.Different capacitors are used to select
different frequency ranges.
Transistor Power Amplifier:→
Oscillator output is fed to the Transistor Power Amplifier (TRPA). It gives an
output of 12Watt across 75 ohms. It works on + 20 V DC,derived from a separate rectifier
and regulator. For different operating frequencies, different output filters are selected.
(Low Pass Filter).
A 4-1000 A tetrode is used as a driver which operates under class AB condition,
without drawing any grid current. About 7 to 10 Watts, of power is fed to the grid of the
driver through a 75 : 800 ohms RF Transformer, which provides proper impedance
matching to the TRPA output and also provides the necessary grid voltage swing to the
RF Power Amplifier:→
CQK - 50, condensed vapour cooled tetrode valve is used as a PA stage. High
level anode modulation is used, using a class B Modulator stage. The screen of the PA tube
is also modulated by a separate tap on modulation transformer. Plate load impedance of
the PA stage is about 750 ohms and the output impedance is 120 ohms, and it is matched
by L-C components.
PA output circuit:→
PA Output Circuit (HMB-140)
The L-C combination of the output circuit provides the following:→
→ The required load impedance for Class D operation that is
there should be a third harmonic impedance in addition to the fundamental impedance.
→ Matches the plate impedance of 750 ohms to the feeder impedance of 120 ohms at the
→ Filters all the 2nd and 3rd harmonic before the feeder.
CLASS D OPERATION:→
The 100KW BEL Transmitter type HMB 140 uses class D operation in output stage.
This is particularly done for increasing the efficiency of the transmitter as the energy saving is
one of the main aspects in the design of a transmitter.In class C, the two waveforms are
sinusoidal and thus considerable voltage and current exist simultaneous across the tube and it
results in power loss as well.
In class D, 17%third harmonic is added to the grid drive to get the plate current
waveform. This plate current requires third harmonic impedence in addition to fundamental in
the plate circuit of the PA stage. The large voltages and currents do also not exist simultaneously
across the tube resulting in lower power loss. The conduction angle in class D is larger and
hence for a given DC current the peak current is lower.
AF Stage (HMB-140)
The AF stage supply the audio power required to amplitude modulate the final RF stage.
The output of the AF stage is superimposed upon the DC voltage to the RF PA tube via
modulation transformer. An Auxiliary winding in the modulation transformer, provides the
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 input from the speech rack is fed to active High Pass Filter. It cuts off all
below 60 Hz. Its main function is to suppress the switching transistors from the audio
This also has the audio attenuator and audio muting relay which will not allow AF to
further stage till RF is about 70 kW of power.
The output of the High Pass Filter is fed to the AF Pre-amplifier, one for each
balanced audio line. Signal from the negative feed back network from the secondary of the
modulation transformer and the signals from the compensator also are fed to this unit.
Pre-amplifier output are 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
signal. That is the gain of the modulator will be low for low level, input, and high for high
level AF input because of the operating characteristics of the vacuum tubes. Hence to
compensate for the non linear gain of the modulator. 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.
Two 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 transistor in series as it works with a high
voltage of about -400 V. the transistors are protected with diodes and zener diodes against
high voltages that may result due to internal tube flashovers. There is a potentiometer by
which any clipping can be avoided such that the maximum modulation factor will not
AF Final Stage:→
AF final stage is equipped with ceramic tetrodes CQK-25. Filament current of this
tube is about 210 Amps. at 10V. The filament transformers are of special leakage
reactance type and their short circuit current is limited to about 2 to 3 times the normal load
current. Hence the filament surge current at the time of switching on will not exceed the
Modulation condenser and modulation choke have been dispensed with due to the
special design of the modulation transformer. Special high power varistor is provided
across the secondary winding of the modulation transformer to prevent transformer over
In modern A.M. transmitters power valves are used in the PA and modulator
stages, which are condensed vapour cooled ceramic tetrodes. In the old generation
transmittes, triodes are used in the PA, modulator and exciter stages. Both the tetrodes and
triodes tubes are capable of being operated at high voltages (11 kV DC) and large anode
current of the order of 50 Amps. They also draw large filament current of about 620 Amps
at 24 volt CQK-350. Hence the tubes dissipate large amount of power which require
The tube is installed vertically with the heating connections at the bottom. Handle
and transport the tube with utmost care : vibrations and external impacts can cause invisible
damage. Avoid sudden movement. Slowly insert the tube in the connection head so that
sudden impact is avoided. If the dead weight of the tube is not sufficiently to overcome
contact resistance in the connection head, apply gentle pressure. The ceramic parts must be
always kept clean. If necessary, they should be cleaned with alcohol or acetone but no
circumstances should they be rubbed with emery paper.
The contact surfaces are coated with a heat resistant lubricant film, which does not
attack silver. Electrical connections and connection head are provided with contact rings
for all electrodes including the anode. The connection head is stationary. It supports and
locate the tube, which can be inserted into the connection head only in a certain position.
This position is determined by the guide groove on the anode.
All the ceramic tetrodes used in AIR transmitters are directly heated thoriated
tungsten cathode. The filament voltage should not vary beyond +5% of the rated filament
voltage. The filament voltage must always be measured at the concentric contact rings
using sub-standard volt meter. The cathode cum filament has only a very small resistance
when cold. Hence the filament voltage is applied and increased smoothly as per the design
of the transmitter. In some transmitters, the filament voltage is applied in steps. In some
transmitter, the design of the filament transformer is such, it will restrict the surge current
to 3 to 4 times the normal steady current.
The screen grid current can become dangerously high, even at normal screen grid
voltage, when the anode voltage is lower than that of the screen grid. Hence the screen grid
supply will be switched ON only when the anode voltage has become about 40% or so of
the anode voltage.
A separate air cooling has been arranged to control the temperature of the ceramic
cylinder and all metal ceramic seals in addition to the condensed vapour cooling. There
must not be any high frequency on the supply leads. To ensure this filament RF by pass
condensers are provided.
Cooling System Used 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 (Ajmer)
transmitter at present→
a) Air cooling.
b) 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) Condensed Vapour Cooling in HMB-140BEL 100 kW MW
In BEL 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. A high velocity water flows through the valve jaket 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 cylinderical 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
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
PARALLEL OPERATION OF TRANSMITTER
Need For Parallel Operation:→
At times it may not be possible to get the required power from the single
transmitter for the required coverage of the broadcast service. In such conditions, it is
essential to combine two or more transmitters to get the required power. Besides combined
operations also facilitate operation of single transmitter in case of failure of one transmitter
thereby achieving reliability of the service.
Like parallel operation of alternators/generators there are three conditions to be
satisfied for parallel operation of two transmitters. They are
→ Frequency of the transmitter should be the same.
→ The phase of the signal of the transmitters at
combiner should be the same.
→ The power levels of both the transmitters should
be such that the amplitude at the combiner is
In order to meet the first condition, it is possible to use one frequency source for
transmitters. Hence if there is any drift in the frequency, it will be common to both the
The phase of the signal of the transmitters depends upon the tuning stages which employ
active amplifiers. Different circuits give different phase shift. In order to offset this
difficulty a phase shifting network is employed in the oscillator circuit. The signal going to
one of the transmitters is passed through this network and hence the phase angle can be
The third requirement for parallel operation is more stringent and requires constant
monitoring for proper operation of combiner to get equal amplitude or power level at the
same impedance of the output. Therefore matching the network for offering equal load
impedance to both the transmitters is absolutely essential. Different methods are used for
getting the proper matching.
Such a network used for combining shall be such that it should →
→ Should offer equal load impedance to both the
→ Shall be able to continue the operation even if
one of the transmitter goes off the air.
→ Shall facilitate to dissipate the unbalanced power
flowing through the combiner network.
The most common network which is used is a bridged ―T‖ network. It has four
reactive networks . Two capacitive and two inductive and all are having impedance‘s equal
to that of feeder line. The bridged arm also has got one resistive load equal to feeder
impedance. This shall take care of the unbalances in the network.
Procedure for tuning and combining:→
Tune each arm of the network for impedance equal to load impedance.
Connect the network and terminate the load impedance.
Measure the load impedance offered at each of the transmitter. It should be equal to
load impedance. If not adjust the reactances.
Open and short-circuit the output point of one of the transmitter (in off condition) and
measure the load impedance at the other transmitter. It should not change.
Now put on the transmitters with a single oscillator source.
If there is unbalance try to adjust with the phase control of oscillator for minimum
Modulate the transmitter slowly to see whether there is unbalance. If so check the audio
phase to each of the transmitter.
ANTENNA TUNING UNIT
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 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.
The signals from ATU are fed to Marconi type antenna. It is 200mtrs high and
supported on insulators and guys. In AM transmitter full antenna is used for transmission.
The signals propogates parallel to the ground. MW propogates along the surface of the
earth. Because of the differaction the wavefront gradually tilts over. As the wave
propogates over the earth it tilts over more and the increasing tilts causes greater short
circuiting of the electric field component of the wave and hence field strength reduces and
it will vanish at some distance.
DOORDARSHAN KENDRA, AJMER
3 Industrial Visit – Doordarshan Kendra
3.2 DDK, Ajmer- An overview
3.3.1 Main Switching Room
3.3.2 Digital Earth Link Station
22.214.171.124 Uplinking And Downlinking
Doordarshan the largest (literally Far Vision) is the public television broadcaster of India
and a division of Prasar Bharati of broadcasting organizations in the world in terms of the
infrastructure of studios and transmitters.
It is a public service broadcaster nominated by the Government of India.
Today, Doordarshan present network of 31 Programme Production Centers and 553
transmitters of varying power reaching about 82 percent of country‘s population.
THE DOORDARSHAN KENDRA AJMER
Doordarshan Kendra Ajmer is
a part of DD India, the largest television network in the world.
Doordarshan started in 2008
inaugurated by Mrs. Vasundhra Raje.
Transmitter used 5KW
Signal Coverage Area 70km
It transmits DD National
Through its home satellite INSAT-2A and DD News through INSAT-2B.
BROADCASTING IN DOORDARSHAN KENDRA
DDK Ajmer have following main components that manages transmission and maintenance
of two channels DD National and DD News.
1. MAIN SWITCHING ROOM (MSR)
2. DIGITAL EARTH LINK STATION
MAIN SWITCHING ROOM (MSR):
The MSR stores all the
circuitry of the DDK.
The monitoring and control of
all activities takes place in MSR.
It is the MSR which decides
what is to go in air.
It is the heart of the studio.
Most of the switching electronics is kept e.g. camera base stations, switcher main
frame, SPG, Satellite receivers, MW link, DDA and most of the patch panels.
Signal is routed through MSR. Signal can be monitored at various stages.
DIGITAL EARTH LINK STATION
Satellite offers the unique possibility to transmit images and sound from almost anywhere
on the planet from a fully equipped uplink truck.
Earth Station is a very important part of satellite communication system for
broadcasting of signals.The earth station is in fully digital domain.
The uplink station has an uplink chain, simulcast transmitters, audio ,video processors, up
converters, modulators etc. It is a uplink center from which the signals are fed to
Satellite for distribution in a specified area covered by the Satellite.The signal is up
linked from the Earth Station and received by many down link centers in TV broad
casting via PDA.
Uplinking And Downlinking
The output of modulator (70MHz) is sent to an up converter. The up converted signals are
sent to an HPA. Then this signal is given to a PDA (parabolic dish antenna) for up linking
to satellite. The uplinked signal is received again by the same PDA for monitoring
The signal between earth station and satellite are given along line of sight which means
there must be a clear path from earth to satellite. The uplink signal is fed from the earth
station by a large PDA. The satellite is equipped with its own dish antenna which receives
the uplink signals and feeds them to a receiver. The signal is then amplified and changed to
a different frequency which is downlink frequency. This is done to prevent interference
between uplink and downlink signals.
The down linked signal is then again sent to the transmitter which again retransmits it.
Each satellite has a transponder and a single antenna 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. The footprint is strongest at centre and the footprint is used to see if the earth
station will be suitable for the reception of the desired signal.
The base band segment comprises of baseband subsystems at studio site and base band
subsystem at earth station site. This baseband segment processes two video Programmes.
The base band segment is monitored and controlled using a PC placed near the base band
earth station equipments called base band NMS PC.For monitoring of video programmes
professional video monitor, LCD video monitor and audio level monitor are provided in the
base band segment. An operator console has one 14‖ professional video monitor a video
audio monitor unit for quantitative monitor of video programmes and a personal computer
for centralized merit and contention of earth station sub system.
The last stage is the transmitter which has the antenna and facilities for terrestrial
1. Based on POWER :
1. VLPT / Transposer (10W)
2. LPT (100W, 300W, 500W)
3. HPT (1kW, 10kW,20kW)
2. Based on FREQUENCY:
An antenna (or aerial) is a transducer designed to transmit or receive electromagnetic
waves. In other words, antennas convert electromagnetic waves into electrical currents and
A 6.3m diameter
antenna with a
erection, ease of
Most of the parts of
the panel and
are made up of
which has corrosion resistance and yield strength.
Antenna Type Limited steer X-Y type
Reflector Diameter 6.3m
X-axis 45 to 90 degrees in steps
Y-axis _+40 degree at any position in steps
Wind Resistivity 2mm rms for winds upto 60 km/hr
Survival upto 200 km/hr
Bands- S-Band C-Band
Frequency Range 2555MHz to 2635MHz 3700MHz to 4200MHz
Polarization Left hand circular Linear and changeable
Antenna Gain 41.8db at 2GHz 44.8db at 4GHz
VSWR 1.25max 1.30max
Volt Axial Ratio Better than 3db Less than 3db
Reciever System G/T 14/db/K at 2600MHz 29.4/db/K at 4GHz
The 6.3 m diameter antenna is made up of 4 quarter segment.
Each and every quarter is made up of 10 segments fixed on five trusses. Panels which are
fixed to the trusses are made up of fine aluminum expanded mesh strengthened with the
help of channel sections and tee sections whose ends are fixed to the backup structure.
Trusses are composed of aluminum square tubes and the welded back up made up of hub
and 20 trusses.
A simple tubular steel space frame makes up most of the mount structure. It allows rotation
about x-axis as well as y axis.
The x axis drive rod is connected between the top of the mounted structure and the concrete
The y axis drive rod is connected between the base of the x axis bearing mount and the
reflector back up structure on the left hand side as viewed from the rear of the antenna. The
mount is rigidly attached to the concrete base which is facing north such that it can survive
even in wind speeds up to 200 kemp.
Fixing the feed onto the antenna-
The feed is supported by a set of four pipes called as a quadruped.
It is fixed before the whole antenna structure is hoisted, that is, it is fixed on the ground
itself before the whole antenna structure is fixed.
Care should be taken that the feed is at the exact focus of the reflector. Feed entrances and
cable output ports are covered with waterproof Teflon sheet to prevent the entry of
moisture into the arrangement.
The reflector is treated in the following order before installation
(a)Etch primer is applied after caustic soda acid treatment
(b)Painted with white matt paint
The mount is treated with the following-
(a)A hot dip which galvanizes all steel parts
(b)Etch primer treatment
(c)White enamel paint is applied as a last coating
As per the curriculum of Rajasthan Technical University for III year B.Tech
Degree, I have completed my Industrial visit of 3 days at ―ALL INDIA
RADIO,AJMER‖, ―DOORDARSHAN,AJMER‖, ―TOSHNIWAL
INDUSTRIES AJMER‖ and I have learned about their process and