Camera (Repaired)

7/31/2019 Camera (Repaired)

1/110

Doordarshan, Indian Television Broadcaster - Informative &

researched article on Doordarshan, Indian Television Broadcaster

Doordarshan, Indian Television Broadcaster

Doordarshan is the public television broadcaster of India and a division ofPrasar Bharati, a public service broadcaster nominated by the Government

of India.

Doordarshan, operated by thePrasar Bharati, is a television broadcasterin India and is an undertaking of the Government of India. Due to thetransmitters and infrastructural facilities of Doordarshan, it is consideredamongst the leading broadcasting organisations throughout the world.Doordarshan successfully completed its 50th year on September 2009.

History of DoordarshanDoordarshan started with a tentative telecast on September 1959

fromDelhi. The infrastructure at that time was small supported by atemporary studio. Regular transmission commenced on 1965, and formed apart of All India Radio. By 1972, the telecast was expandedto Amritsar and Mumbai. Doordarshan was the only channel available attime and by 1975, it was available in seven cities around the nation. In1976, it was detached from All India Radio and was fully managed fromNew Delhi, by two different Director Generals. In 1982, colour televisionsets became available in country and the speech given by the PrimeMinister of that time,Indira Gandhi, was telecast live through out thenation. After this, the 1982 Asian games, Delhi, was also broadcasted by

the channel.

Early Programmes of DoordarshanDoordarshan gained exceeding popularity during the 1980s with its newand groundbreaking shows that could easily connect with the urban andrural audiences alike. Shows likeHum Log, Yeh Jo Hai Zindagi,Buniyaad,Nukkad, along with the epics likeRamayanaandMahabharatawerewatched by viewers throughout the country. Later programmes like BharatEk Khoj, Chitrahaar, Sword of Tipu Sultan, Rangoli, The Great Maratha, EkSe Badkar Ek, Shaktimaan and Superhit Muqabla also were watchedwidely.

Other popular programmes included thrillers like Byomkesh Bakshi,Karamchand, Barrister Roy, Tehkikaat, Reporter and Suraag. Familyoriented shows like Wagle ki Duniya, Fauji, Mr. Yogi, Talaash, Kashish,Srimaan Srimati, Dekh Bhai Dekh, Zabaan Sambhal Ke, Swabhimaan,Shanti, Saagar, Lifeline, Udaan, Circus, Sansaar, Jaspal Bhatti`s Flop Show,Meri Awaaz Suno, Sangharsh, Gul Gulshan Gulfam, Sea Hawks, Tu tu mein
http://www.indianetzone.com/52/prasar_bharati.htmhttp://www.indianetzone.com/52/prasar_bharati.htmhttp://www.indianetzone.com/2/delhi.htmhttp://www.indianetzone.com/2/delhi.htmhttp://www.indianetzone.com/2/delhi.htmhttp://www.indianetzone.com/4/amritsar.htmhttp://www.indianetzone.com/2/mumbai.htmhttp://www.indianetzone.com/4/all_india_radio.htmhttp://www.indianetzone.com/3/indira_priyadarshini.htmhttp://www.indianetzone.com/42/hum_log.htmhttp://www.indianetzone.com/42/hum_log.htmhttp://www.indianetzone.com/42/hum_log.htmhttp://www.indianetzone.com/9/buniyaad.htmhttp://www.indianetzone.com/9/buniyaad.htmhttp://www.indianetzone.com/9/buniyaad.htmhttp://www.indianetzone.com/2/ramayana.htmhttp://www.indianetzone.com/2/ramayana.htmhttp://www.indianetzone.com/2/ramayana.htmhttp://www.indianetzone.com/2/mahabharata.htmhttp://www.indianetzone.com/2/mahabharata.htmhttp://www.indianetzone.com/13/t_v_serial_fauji.htmhttp://www.indianetzone.com/13/t_v_serial_fauji.htmhttp://www.indianetzone.com/2/mahabharata.htmhttp://www.indianetzone.com/2/ramayana.htmhttp://www.indianetzone.com/9/buniyaad.htmhttp://www.indianetzone.com/42/hum_log.htmhttp://www.indianetzone.com/3/indira_priyadarshini.htmhttp://www.indianetzone.com/4/all_india_radio.htmhttp://www.indianetzone.com/2/mumbai.htmhttp://www.indianetzone.com/4/amritsar.htmhttp://www.indianetzone.com/2/delhi.htmhttp://www.indianetzone.com/52/prasar_bharati.htm


2/110

mein and Junoon were also widely accepted. Mythological programmes likeDastan-E-Hatim Tai, Chandrakanta, Alif Laila were also very popular amongthe viewers.

Shows targeted at kids were also much appreciated. Programmes like

Captain Vyom, a Desi version of Star Wars, Potli Baba Ki, Malgudi Days,Stone Boy, Tenali Raman, Sigma, Vikram Betaal, Kile ka Rahasya and DadaDadi ki Kahaniyan are worth mentioning. Many popular internationalprogrammes were also aired, after being dubbed in Hindi, such as JohnnySoko and his flying robot, Street Hawk, Knight Rider, Superhuman SamuraiCyber Squad, and animated shows like the jungle book, He-Man and themasters of universe, Spiderman, Disney adventures were also admired bythe young audience.

Channels of DoordarshanDoordarshan currently has 21 channels, 11 regional channels and 2national channels (DD National and DD News), 1 sports channel (DDSports), 1 international channel and a few more. DD National broadcastsboth regional and national programmes. DD-Sports exclusively telecastvarious sporting tournaments and events, which are of national andinternational significance. It also broadcasts local sports like Kabaddi, Kho-Kho etc. DD News, which was launched by replacing DD Metro, is a 24 hournew channel.

The array of channels offered by Doordarshan include- DD National, DDSports, DD News, Rajya Sabha TV, DD-Lok Sabha, DD Bharti and manyregional channels such as, DD Gujarati, DD Bangla, DD Punjabi, DD Kashir,DD Malayalam, DD Odia, DD Podhigai, DD Saptagiri, DD Sahyadri, DD Urduand DD NorthEast.

National Programmes on DoordarshanThe objective of a common programme broadcast, which will cater topeople in different states, was achieved by Mr. Sathe, Minister forInformation and Broadcast, in the 90 minute National programme, onAugust 15, 1982. This was to consist of news in Hindi and English, andprogrammes reflecting music, dance and other aspects of life, literature andculture of all regions. Although few programmes have been appreciated bythe viewers, but in general it is believed that the output has lacked qualityand standard.

There are seven full fledged centresat Delhi, Mumbai, Kolkata, Chennai, Jalandar, Srinagar, and Lucknow;
http://www.indianetzone.com/3/indian_dd_national.htmhttp://www.indianetzone.com/3/indian_dd_news.htmhttp://www.indianetzone.com/1/kabaddi.htmhttp://www.indianetzone.com/3/indian_mines_-_i.htmhttp://www.indianetzone.com/2/delhi.htmhttp://www.indianetzone.com/2/mumbai.htmhttp://www.indianetzone.com/2/kolkata.htmhttp://www.indianetzone.com/2/chennai.htmhttp://www.indianetzone.com/4/jalandara.htmhttp://www.indianetzone.com/3/srinagar.htmhttp://www.indianetzone.com/39/lucknow.htmhttp://www.indianetzone.com/39/lucknow.htmhttp://www.indianetzone.com/3/srinagar.htmhttp://www.indianetzone.com/4/jalandara.htmhttp://www.indianetzone.com/2/chennai.htmhttp://www.indianetzone.com/2/kolkata.htmhttp://www.indianetzone.com/2/mumbai.htmhttp://www.indianetzone.com/2/delhi.htmhttp://www.indianetzone.com/3/indian_mines_-_i.htmhttp://www.indianetzone.com/1/kabaddi.htmhttp://www.indianetzone.com/3/indian_dd_news.htmhttp://www.indianetzone.com/3/indian_dd_national.htm


3/110

eight transmitting centres at Raipur, Jaipur, Muzaffarpur,Gulbarga,Sambalpur, Hyderabad, Ahmedabad and Nagpur, and relay centres atGwalior, Kanpur, Pune,Allahabad, Amritsar, Bengaluru, Mussoorie, Panaji andAsansol. There are also three Upgraha Doordarshan Kendras (Satelliteprogramme production centres) at Cuttack, Delhi and Hyderabad and also

20 low-power transmitters in many states to provide coverage to nationaland other programmes through relays. Doordarshan has 45 transmitters atwork, and the programmes reach about 28% of the population.

Active Doordarshan

Recently, along with Tata Sky, Doordarshan has launched an InteractiveService, which is offered as a special channel on Tata sky. It is anInteractive Service of Tata Sky to show 4 TV Channels of Doordarshanwhich are not available on Tata sky as normal channels. DD Podhigai, DDGujarati and DD Punjabi are offered in this service. Doordarshan also haslaunched its own Direct-To-Home service, named DD Direct Plus.

International Broadcasting of DoordarshanDoordarshan had also started broadcasting internationally via Satellite andhas a presence in almost 146 countries, globally. But there were sometechnical problems on the availability of the channel in some countries. Theprogrammes and timie slot are not as similar as the broadcast in India. InJuly 2008, transmissions in U.K. and U.S. were stopped.

Now more than 90 percent of population of the country can receiveDoordarshan programmes through a network of nearly 1400 terrestrial

transmitters. Around 46 Doordarshan Studios are producing TV software.The Doordarshan televises through the Official and Associate Officiallanguages, and its regional channels televise through the state dominantlanguages and dominant minority languages.
http://www.indianetzone.com/41/raipur.htmhttp://www.indianetzone.com/37/jaipur.htmhttp://www.indianetzone.com/3/muzaffarpur.htmhttp://www.indianetzone.com/3/gulbarga.htmhttp://www.indianetzone.com/3/hyderabad.htmhttp://www.indianetzone.com/4/ahmedabad.htmhttp://www.indianetzone.com/39/nagpur.htmhttp://www.indianetzone.com/40/kanpur.htmhttp://www.indianetzone.com/23/pune_maharashtra.htmhttp://www.indianetzone.com/4/allahabad.htmhttp://www.indianetzone.com/4/amritsar.htmhttp://www.indianetzone.com/3/bangalore.htmhttp://www.indianetzone.com/5/mussoorie.htmhttp://www.indianetzone.com/43/panaji.htmhttp://www.indianetzone.com/4/asansol.htmhttp://www.indianetzone.com/7/cuttack_orissa.htmhttp://www.indianetzone.com/3/hyderabad.htmhttp://www.indianetzone.com/3/hyderabad.htmhttp://www.indianetzone.com/7/cuttack_orissa.htmhttp://www.indianetzone.com/4/asansol.htmhttp://www.indianetzone.com/43/panaji.htmhttp://www.indianetzone.com/5/mussoorie.htmhttp://www.indianetzone.com/3/bangalore.htmhttp://www.indianetzone.com/4/amritsar.htmhttp://www.indianetzone.com/4/allahabad.htmhttp://www.indianetzone.com/23/pune_maharashtra.htmhttp://www.indianetzone.com/40/kanpur.htmhttp://www.indianetzone.com/39/nagpur.htmhttp://www.indianetzone.com/4/ahmedabad.htmhttp://www.indianetzone.com/3/hyderabad.htmhttp://www.indianetzone.com/3/gulbarga.htmhttp://www.indianetzone.com/3/muzaffarpur.htmhttp://www.indianetzone.com/37/jaipur.htmhttp://www.indianetzone.com/41/raipur.htm


4/110

Analog camcorder: front view

Portable video camera with an integrated VCR that records sounds and

images on the magnetic tape of a compact videocassette.

Video-tape operation controls

Buttons that control viewing of recorded images; they include playback,

stop, pause, fast-forward and rewind.

Eye-cup

Part attached to the eyepiece; the eye is placed on it for viewing.

Near/far dial

Lens focusing ring used to manually adjust the sharpness of an image.

Focus selector

Button used to focus the image automatically or manually.

Power/functions switch

Button used to turn the camcorder on or off and to select the operating

mode including camera, playback and battery recharge.


5/110

Display panel

Movable plate housing and protecting the liquid crystal display.

electronic viewfinder

Small video monitor for viewing the scene to be filmed in order to frame it

and bring it into focus.

Collapsible fins

It controls the amount of light entering the camera lens.

zoom lens

Lens for changing the visual field so that a close-up or distant shot of the

subject can be obtained without moving the camcorder.

How Does The Human Eye Work?

The individual components of the eye work in a manner similar to a camera. Each partplaysa vital role in providing clear vision. So think of the eye as a camera with the cornea,behavingmuch like a lens cover. As the eye's main focusing element, the cornea takes widelydivergingrays of light and bends them through the pupil, the dark, round opening in the center ofthe

colored iris. The iris and pupil act like the aperture of a camera.

Next in line is the lens which acts like the lens in a camera, helping to focus light to thebackof the eye. Note that the lens is the part which becomes cloudy and is removed duringcataractsurgery to be replaced by an artificial implant nowadays.

The Camera The Human Eye


6/110

The very back of the eye is lined with a layer called the retina which acts very much likethe film of the camera. The retina is a membrane containing photoreceptor nerve cellsthat lines the inside back wall of the eye. The photoreceptor nerve cells of the retinachange the light rays into electrical impulses and send them through the optic nerve tothe brain where an image is perceived .The center 10% of the retina is called the

macula. This is responsible for your sharp vision, your reading vision. The peripheralretina is responsible for the peripheral vision. As with the camera, if the "film" is bad inthe eye (i.e. the retina), no matter how good the rest of the eye is, you will not get agood picture.

The human eye is remarkable. It accommodates to changing lighting conditions andfocuseslight rays originating from various distances from the eye. When all of the componentsof theeye function properly, light is converted to impulses and conveyed to the brain where animage is perceived.


7/110

Glossary of Eye Terms:

Anterior ChamberThe cavity in the front part of the eye between the lens and cornea is called the AnteriorChamber. It is filled with Aqueous, a water-like fluid. This fluid is produced by the ciliarybody and drains back into the blood circulation through channels in the chamber angle.It isturned over every100 minutes.

Chamber AngleLocated at the junction of the cornea, iris, and sclera, the anterior chamber angleextends 360

degrees at the perimeter of the iris. Channels here allow aqueous fluid to drain back intotheblood circulation from the eye. May be obstructed in glaucoma.

Ciliary BodyA structure located behind the iris (rarely visible) which produces aqueous fluid that fillsthefront part of the eye and thus maintains the eye pressure. It also allows focusing of the


8/110

lens.

ConjunctivaA thin lining over the sclera, or white part of the eye. This also lines the inside of theeyelids. Cell in the conjunctiva produce mucous, which helps to lubricate the eye.

CorneaThe transparent, outer "window" and primary focusing element of the eye. The outerlayer of the cornea is known as epithelium. Its main job is to protect the eye. Theepithelium is made up of transparent cells that have the ability to regenerate quickly.The inner layer of the cornea is also made up of transparent tissue, which allows light topass.

Hyaloid CanalA narrow channel that runs from the optic disc to the back surface of the lens. It servesan embryologic function prior to birth but none afterwards.

IrisInside the anterior chamber is the iris. This is the part of the eye which is responsible forone's eye color. It acts like the diaphragm of a camera, dilating and constricting the pupilto allow more or less light into the eye.

PupilThe dark opening in the center of the colored iris that controls how much light enters theeye. The colored iris functions like the iris of a camera, opening and closing, to controlthe amount of light entering through the pupil.

LensThe part of the eye immediately behind the iris that performs delicate focusing of lightraysupon the retina. In persons under 40, the lens is soft and pliable, allowing for finefocusingfrom a wide variety of distances. For individuals over 40, the lens begins to become lesspliable, making focusing upon objects near to the eye more difficult. This is known aspresbyopia.

MaculaThe part of the retina which is most sensitive, and is responsible for the central (orreading)vision. It is located near the optic nerve directly at the back of the eye (on the inside).Thisarea is also responsible for color vision.

Optic DiscThe position in the back of the eye where the nerve (along with an artery and vein)enters the


9/110

eye corresponds to the "blind spot" since there are no rods or cones in these location.Normally, a person does not notice this blind spot since rapid movements of the eyeandprocessing in the brain compensate for this absent information. This is the area that theophthalmologist studies when evaluating a patient for glaucoma, a condition where the

opticnerve becomes damaged often due to high pressure within the eye. As it looks like acupwhen viewed with an ophthalmoscope, it is sometimes referred to as the Optic Cup.

Optic NerveThe optic nerve is the structure which takes the information from the retina as electricalsignalsand delivers it to the brain where this information is interpreted as a visual image. Theopticnerve consists of a bundle of about one million nerve fibers.

RetinaThe membrane lining the back of the eye that contains photoreceptor cells. Thesephotoreceptor nerve cells react to the presence and intensity of light by sending animpulse tothe brain via the optic nerve. In the brain, the multitude of nerve impulses received fromthephotoreceptor cells in the retina are assimilated into an image.

ScleraThe white, tough wall of the eye. Few diseases affect this layer. It is covered by theepisclera (a fibrous layer between the conjunctiva and sclera ) and conjunctiva, and eyemuscles are connected to this.

VitreousNext in our voyage through the eye is the vitreous. This is a jelly-like substance that fillsthe body of the eye. It is normally clear. In early life, it is firmly attached to the retinabehind it. With age, the vitreous becomes more water-like and may detach from theretina. Often, littleclumps or strands of the jelly form and cast shadows which are perceived as "floaters".While frequently benign, sometimes floaters can be a sign of a more serious conditionsuch as a retinal tear or detachment and should be investigated with a thoroughophthalmologic examination.

Modulator

Modulator is a device used for modulation so let me explain something about

modulation.


10/110

What is modulation

Modulation

Modulation is a process of superimposing information on a carrier by varying one of its

parameters (amplitude, frequency or phase).

Need for Modulation

Modulating the signal over higher frequency can reduce antenna size. To differentiate among transmissions (stations) Maximum to minimum frequency ratio can be reduced to minimum by modulating the

signal on a high frequency.

Types of Modulation

In general, there are three types of modulation:

a) Amplitude Modulation b) Angle Modulation

c) Pulse Modulation

Amplitude Modulation

If the amplitude of the carrier is varied in accordance with the amplitude of themodulating signal (information), it is called amplitude modulation. This modulation has

been shown in figure 1. We can see this on the screen of oscilloscope.

Carrier freq. fcAmplitude Ac

Fig. 1 Amplitude Modulation

Modulating Signal freq. fmamplitude Am

Amplitude ModulatedDSB Signal

Carrier amplitude corresponding to negative peak of signal iszero for 100% modulation (Am=Ac)

Vc(t)

Vm(t

(t)

Spectrum of AM signal


11/110

The spectrum of AM signal is shown in figure 2. If fm = modulating frequency fc = Carrier

frequency. The Spectrum of AM signal will be as below :

LSB

Carrier

USB

fc-fm fc fc+fm0

Frequency

Leve

l

Fig. 2 Spectrum of AM Signal

Power in the carrier,

2c

2

cc )A(2

1A

2

1P

Power in the sideband,

2

A)m(

4

1

2

Am

2

1PP

2c2

a

2

causblsb

Power in the upper side band(Pusb) = Power in the lower side band (Plsb)

Hence total power, Pt = Pc + Pusb + Plsb

where Ac = Amplitude of the carrier

ma = Modulation Index = Am/Ac

Am = Amplitude of the modulating signal


12/110

Bandwidth,

mmcmc f2)ff()ff(BW

Variation of AM Signals

DSB - FC : Double sidebands with full carrier. This is used in MW and SW

Transmitters.

DSB - SC : Double sidebands with suppressed carrier. This method is used for

transmission of chroma signals in TV and stereo signal in FM

transmitter.

VSB : Vestigial sideband. This method utilises one side band (usually USB)

with carrier and a portion of other sideband. This is used for picture

(video) transmission in television.

SSB : Single Side band : In this method only one side band (without carrier)

is utilised for transmission. There is considerable saving in power and

bandwidth. But as the carrier is not transmitted it becomes difficult to

recover the signal at the receiver end. Hence the receiver circuit is

complex. The use of this method is restricted to special purpose only,

such as military communications.

ISB : Independent side band : In this method each side band carries a

different message and hence they are independent of each other. A

reduced carrier is also inserted so as to facilitate an easy detection.

This method is used in Telephone system.


13/110

Generation of AM Signal

There are two methods of generation of AM signals :

i) Low Level Modulation Systemii) High Level Modulation System

i) Low Level Modulation

One which generates many additional frequencies and hence it requires filtering and so to avoid

loss of power in filtering, it should be generated at low power level. This is shown in figure 3.

In low level modulation, all the amplifiers following the modulator stage, have to be linear. This

system of modulation is used in TV transmissions.

A B C D E F G

AM Output

Mod. Signal

Fig. 3 Low Level Modulation

A = Stable Oscillator E = Amplifier Chain

B = Buffer Amplifier F = Intermediate Power Amplifier

C = Frequency Multiplier G = Final Power Amplifier

D = Modulator

ii) High Level Modulation

This method does not give rise to many additional frequency and so filtering is not required.

This is best suited for higher power amplification. Medium wave and short wave transmissions

use this method of modulation. This is shown in figure 4.


14/110

High level modulator can be operated in class 'C' configuration. As the earlier stages operate at

the carrier frequency only (or, in some cases at its sub-harmonics), all these stages can also be

operated in class 'C' mode.

A B C E F D

AM Output

Mod. Signal

Fig. 4 High Level Modulation

GE

High level modulation leads to higher efficiency, better linearity and higher output power for a

given device. However, high level modulation requires a significantly high modulating signal

power whereas low level modulation does not.

Non-linear Amplitude Modulator

This modulator utilizes the non-linearity of the active device characteristics near the origin. Thishas been shown in figure 5.

Fig. 5 Non-linear AM Modulator

+Vc(t)

AM Modulatedoutput

Modulationsignal

CarrierGenerator

-

Angle Modulation

Variation of the angle of carrier signal with time results in angle modulation. It is of two types


15/110

a) Frequency Modulationb) Phase Modulation

Frequency Modulation

If the frequency of the carrier is varied in accordance with the amplitude of the modulating signal

(information), it is called frequency modulation. This has been shown in figure 9.

Maximum frequency corresponding to positve peak amplitude of modulation signal

Fig. 9 Frequency Modulation

Minimum frequency corresponding to negative peak amplitude of mod. signal

Carrier freq. fcAmpli tude Ac

Modulating Signal freq. fmamplitude Am

Freq. Modulatedsignal

Vc(t)

Vm(t

V(t)

A frequency modulated signal has a large number of frequency components even when the

modulating signal is a single frequency signal. The adjacent frequency components are spaced

just fm apart. These components lie on both sides of the carrier and are symmetrically placed

about it. The amplitudes of the corresponding component are equal. The components, with

frequencies (fc + fm) and (fc - fm) are called the first order side bands. The amplitude of each of

the first order side bands is AJ1 (mf). The components with frequencies (fc - nfm) and (fc - nfm),

where n is an integer, are called the nth order side bands. The amplitude of carrier is AJ0 (mf).

The relative amplitudes of various side bands, therefore, depend upon the index of modulation

alone, the amplitude of a particular side bands being equal to the Bessel function of the

corresponding order. The spectrum is shown in figure 10.


16/110

fc = 1000 kHzfm = 1 kHzmf = 0.5

f = 0.5 kHz

0.9385

f Frequency

Fig. 10 Spectrum of FM Signal

mf = 1.0

f = 1 kHz

0.7652

f Frequency

mf = 2.0

f = 2 kHz

0.2239

f Frequency

mf = 5.0f = 5 kHz

0.1776

Frequencyf

From the above we find that the process of frequency modulation results in a reduction of carrier

amplitude and generation of an infinite number of side bands. Generally, a limited number of

side bands closer to the carrier frequency will have significant amplitudes.

Power

This holds true for any type of a modulating signal and for any value of modulation index.

Where, Ac = Amplitude of the carrier

Am = Amplitude of the modulating signal

signalulatingmodtheofFrequencyf

deviationFrequencyf

IndexModulationf

f

f

f

m

m

mmf

Band width of FM signal

carrierulatedmoduntheofPowerA2

1p 2cc


17/110

Band width can be defined as that frequency range which accommodates the carrier and the

closest side bands contributing at least 98% of the total signal power. (Carson rule).

BW = 2 (mf+ 1) fm = 2 (mf fm + fm) = 2 (f + fm)

Generation of FM signal

There are two methods of generation of FM signal :

a) Direct Method of FM generation. B) Indirect Method of FM generation.

Direct Method of FM Generation

i) Varactor Diode Modulator

This modulator has been shown in fig. 11. It makes use of a varactor diode (also known as

varicap or capacitance diode). The capacitance of this diode varies with the applied biasvoltage (DC voltage + modulating voltage). The diode forms, at least partially the tuning

capacitor of the tank circuit, that determines the frequency of the oscillator. The capacitance

varies with the applied modulating voltage and so does the frequency.

Fig. 11 Varactor Diode Modulator

FM output

Cb

Cd Vd

RFC

Vo

X(t) Mod. Sig., X(t)

T

Q

Cd

-Vcc

C L

Operation of the Circuit

Vo - provides a suitable bias to the varactor diode.

Cb - blocking capacitor. It blocks the DC bias voltage of varactor diode so that operating

point of transistor and bias voltage of varactor diode can be chosen independently.

)t(x Modulating signal.

Cd - Diode capacitance at its operating voltage.

Ct - total capacitance of the tank circuit


18/110

Ct - C + Cd

RFC : Radio frequency choke. It blocks the oscillation going to bias voltage Vo.

The modulating signal added to DC voltage Vo through transformer T. Hence the capacitance

of varactor diode is varied in accordance with the modulating signal. This capacitance becomes

the part of the main tank circuit. Accordingly, frequency of oscillation is controlled by themodulating signal. The FM output is taken from the collector of the transister through a buffer

amplifier so that the load impedance on the oscillator is essentially constant.

ii) Voltage controlled oscillator (VCO) modulator

This circuit has been given in figure 12. It is an astable multi-vibrator. Its frequency of

oscillation depends upon the applied DC voltage. Hence, if the applied voltage is made to vary

in accordance with the modulating signal, by putting the DC supply and the modulating signal

voltage in series, the frequency of oscillation will vary with the modulating signal. This type ofcircuit will produce a rectangular wave form of varying frequency from which it is not difficult to

derive the corresponding sinusoidal signal.

Fig. 12 VCO Modulator

Rc

-V Mod. Sig.-Vcc

RcR1 R2

C1 C2

T2

T1

Operation of the circuit

The circuit generates a periodic rectangular waveform. Its time period T is given by


19/110

T = 0.69 (R1 C1 + R2 C2)

With R1 = R2 and C1 = C2 we get T = 0.69 (RC + RC) = 1.38 RC

From this we find that the period T does not depend on supply voltage. It depend on the valuesof R and C only. This type of multi-vibrator operates at a fixed frequency.

Now, if we disconnect the resistance R1 and R2 from the Vcc and connect these two resistances

to an auxiliary voltage -V (modulating signal) shown as dotted line in t figure, the frequency of

oscillation becomes function of both Vcc and -V. The time period T is given by,

V

Vcc1nlRC2T

Hence, now by putting V in series with Vcc and varying it we can get a variable frequency which

will be in accordance with the V (modulating signal). From this rectangular wave we can getsinusoidal waveform by passing it through band pass filter.

Indirect method of FM Generator

Armstrong method

In this method frequency modulation is obtained through a phase modulator. The modulating

signal is integrated prior to modulating the carrier, so that the output of the phase modulator

becomes a frequency modulated signal. Fig. 13. The required phase modulated signal isgenerated with the help of a double side band - SC modulator. In this method index of

modulation is limited to 0.5.

Fig. 13 Armstrong method of FM generation

Integrater PhaseModulator

FM OutputModulatorsignal

Input

Detection of AM Signal


20/110

There are many types of detectors for detecting various form of AM signals. One such detector

is Envelope Detector, which is used for detection of DSB - FC signal. The operation of this

detector is discussed below :

Envelope Detector

The circuit diagram of envelope detector along with wave form is shown in Fig. 14 (a) and (b).

During positive half cycle of the input, capacitor C charges to almost the peak value of the half

cycle. When the level of input voltage starts falling, the diode D is reversed biased by the

voltage on the capacitor. The capacitor discharges through the resistance R with a time

constant RC. The discharging of the capacitor continues, till, in the next positive part of the

carrier cycle, the input voltage exceeds the capacitor voltage. Then, the diode conducts again

and the whole process repeats. Thus, in each carrier cycle, the capacitor charges to nearly the

peak value of the cycle.

The time constant RC should be sufficiently large so as to reduce the carrier frequency ripples,

but at the same time sufficiently small in order to allow the voltage on the capacitor to follow the

modulation envelope. When these requirements meet, the output follow the peaks of the carrier

cycles i.e. it follows the envelope of the input, hence the device is called as peak or envelope

detector. The practical circuit will be somewhat different from the circuit of fig. 14.

Fig. 14 Envelope Detector

DiodeCurrent

RC

D

OutputAM Input

OutputVoltage

t

t

(a)

(b)

Detection of FM Signal

The process of detection of FM signal is the process of deriving a voltage that varies in

proportion to the instantaneous frequency of the received FM signal. There are many methods


21/110

to detect FM signal. If the received signal is modified in such a way that its amplitude varies in

accordance with its instantaneous frequency, then the envelope detector of figure 14 can be

successfully utilised for FM detection. One such circuit is discussed here.

Resonant circuit Discriminator (Slope Detector)

This detector has been shown in fig. 15. The tuned circuit is driven by a current source. The

current is frequency modulated. The circuit is detuned in such a way that the carrier

frequency lies on the positive slope of the characteristics. Hence, resulting voltages across the

tuned circuit varies with the frequency of the input current

Fig. 15 Resonant Circuit discriminator

RC

D

Output

FM Input

-Vcc

C

Q

In a FM detector, the output should be independent of the input amplitude variations, if any.

Hence, it is common practice to proceed an FM detector by a limiter, so that the input amplitude

variation gets removed.

Phase Modulation

If the Phase of the carrier is varied in accordance with the amplitude of the modulating signal

(information), it is called phase modulation. Since this modulation has got minimum use, it is not

discussed here.

UPCONVERTER


22/110

It is also known as Block Up-converter . It is used to for converting the lower

frequency into higher frequency . For exampleModern BUCs convert from the L

band to Ku band, C band and Ka band. Older BUCs convert from a 70 MHz intermediate

frequency (IF) to Ku band or C band. BUCs used in remote locations are often 2 or

4 W in the Ku band and 5 W in the C band. The 10 MHz reference frequency is usually

sent on the same feedline as the main carrier. Many smaller BUCs also get theirdirect

current (DC) over the feedline, using an internal DC block.

BUCs are generally used in conjunction with low-noise block converters (LNB). The

BUC, being an up-converting device, makes up the "transmit" side of the system, while

the LNB is the down-converting device and makes up the "receive" side.
http://en.wikipedia.org/wiki/L_bandhttp://en.wikipedia.org/wiki/L_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/C_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/Megahertzhttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/C_bandhttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Low-noise_block_converterhttp://en.wikipedia.org/wiki/Low-noise_block_converterhttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Carrier_wavehttp://en.wikipedia.org/wiki/C_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Megahertzhttp://en.wikipedia.org/wiki/Ka_bandhttp://en.wikipedia.org/wiki/C_bandhttp://en.wikipedia.org/wiki/Ku_bandhttp://en.wikipedia.org/wiki/L_bandhttp://en.wikipedia.org/wiki/L_band


23/110

Fig shows up-convertor


24/110

Fig. illustrates PDA attached with up-convertor


25/110

Amplifier

When we cannot hear a stereo system we increase the volume, when the picture

on our T.V is too dark we increase the brightness control. In both of these caseswe are taking a relative weak signal and making it stronger( i.e. increasing power

of the signal). The process of increasing the power of a.c. signal is called

amplification . The circuits used to perform these functions are called amplifiers.

An amplifier may be defined as a device which produces larger electrical output

of similar characteristics to that input parameters. It increases magnitude of the

current or voltage input by means of energy drawn from external source. The

input signal may be obtained from a phonograph cartridge, tape head, or

transducer such as thermo-couple, pressure gauge, etc. The output signal may be

supplied to loud speaker in an audio amplifier, motor in servo amplifier, a relay in

a control application, etc.

An amplifier can be defined as the device which produces larger electrical output

of similar characteristics than that of input parameters . It increases the

magnitude of current or input voltage by means of energy drawn from external

source . The input signal may obtained from a transducer such as thermocouple,

pressure gauge etc .

As explained above, an amplifier needs a source for amplification, this may be

provided by battery or a d.c source resulting from a rectifier and a filter

combination. The amplifier also contains at least one active device. This may be

electron tube ,bipolar transistor or field effect transistor which can provide a

control function. Basically, the active device converts the energy from d.c source

into energy at output of amplifier which is proportional to a input signal . The a.c

input signal merely supplies a means of converting d.c to a.c convertion whichtakes in the tube of the transistor. The control is merely established with

comparatively little input signal power.

The amplifier in which instantaneous output signal is proportional to the

corresponding input signal is called a linear amplifier.


26/110

On the other hand an amplifier in which output is not directly proportional to the

input , is called non linear amplifier

Fig. showing working of amplifier

Classification of Amplifier

The linear amplifier may be classified according to their mode of operation i.e

the way they operate on predetermined set value . The descriptions are based on

following factors :

1. As based on the input

(a)Small- signal amplifier (b) Large signal amplifier

2. As Based on the output

(a)Voltage amplifier (b) Power amplifier

3. As based on transistor configuration

Circuit carrying large electrical

current

Circuit carrying small

electric current Amplifier modifies larger

current based on smaller


27/110

(a)Commonemitter (CE) amplifier (b) Common base(CB)

configuration

Common-collector (CC) configuration

4. As based on biasing conditions

(a) Class-A (b) Class -B (c) Class-AB (d) Class-C

5. As based on nature of load resistance

(a)Untuned amplifiers (Wide -band amplifier)

(b)Tuned amplifier (Narrrowband amplifier)

6. As Based on frequency response

(a)Direct coupled (DC) amplifier (b)Audio frequency (AF) amplifier

Radio frequency (RF ) amplifier

(c)Ultra high frequency(UHF)and microwave frequency amlifier

7. As based on number of stages

(a)Singlestage amplifier (b) Multistage amplifier

8. As based on method of coupling between the stages

(b)DC(direct coupled) amplifier (b) RC coupled amplifier

(c) (c) Transformer coupled amplifier

Transistor as an amplifier

In the circuit NPN transistor is used .Therefore the basic circuit I known as basic

common emitter amplifier. Here Vb-b is supply forward bias emitter base

junction and Vcc supply reverse biases the collector base junction . This biases the

transistor to operate in active region Vs is a sinusoidal a.c input signal source . It

has a source resistance Rs. The magnitude of signal source voltage is such that it is


28/110

always forward biased emitter based junction regardless of the polarity of the

signal

First of all , let us assume that there is no a.c signal source. Under this condition

d.c collector current (Ic) flows through the collector load (Rc) . This is called zerosignal current or quiescent operating current. Now let an a.c signal be applied

between emitter base junction. During the positive half of a.c input signal . The

forward bias across the emitter base junction is increased . As a result more

electrons are injected into the base and reach the collector, which increase the

collector current . The increased collector current produces greater voltage drop

across the resistance Rc. However during the negative halfcycle forward bias

across emitter-base junction is decreased . Due to this collector current

decreases. The decreased collector current produces smaller drop acrossresistance Rc.

It is evident from above discussion that small a.c signal at the input produces

large a.c signal at the output. Thus transistor acts as an amplifier

Basic common emitter amplifier

Class A Power Amplifier


29/110

A class A power amplifier may be defined as a power amplifier In which the

output current flows for the fullcycle (i.e.,360 degree) of applied input signal as

shown in fig.

Thus we can say that transistor remains in forward biased state for the full periodof input cycle. Fig. shows schematic circuit diagram for series fed class-A amplifier

or large signal using resistive load Rc.

A series fed class A amplifier


30/110

Note that the term series fed means that the load Rc has been connected in series

with the transistor output. However this circuit is not used for the purpose of

power amplification because the collector efficiency is very poor. However this

circuit can provide clear understanding of class A amplifier to the readers. Fig.

shows the output characteristics with operating point Q . Here ICQ and VCEQ

represents no signal collector current and collector-emitter voltage respectively.

It may be observed that when an a.c. input signal is applied, the operating point

shifts up and down causing output current and voltage to vary about. The output

current is increased to Ic max. and falls to Ic min. The same fasion the collector

emitter voltage increases to Vce max. and falls to Vce min.

Output characteristics of class A amplifier

Class B Power Amplifier

In class-B operation transistor is biased in such a way that the zero signal

collector current is zero. This means that class-B operation does not need any

biasing system. The operating point is cut-off as shown in fig.. It remains in

forward bias only for half cycle of a.c. input signal.


31/110

Illustration of class B operation

As shown in fig. during the positive half cycle of the input a.c signal the circuit is forward biased,

and hence the collector current flows. On the other hand in the negative half of input a.c signal,

the circuit is reversed biased and hence no collector current flows.

CLASS AB POWER AMPLIFIER

In class AB power amplifiers, the biasing circuit is so adjusted that operating point

Q lies near the cut- off voltage. During the small portion of negative half cycle

and complete positive half cycle of the signal ,the input circuit remains forward

biased and hence the current flows. But during small portion (less than half cycle)

of negative cycle, the input circuit is reversed biased and therefore no collector

current flows during this period . Class AB operation needs a pushpull to achieve

a full output cycle.

Why Maximum Power is used in the Transmitter design

The Maximum Power Transfer Theorem is not so much a means of analysisas it is an aid to system design. Simply stated, the maximum amount ofpower will be dissipated by a load resistance when that load resistance isequal to the Thevenin/Norton resistance of the network supplying the power.If the load resistance is lower or higher than the Thevenin/Norton resistanceof the source network, its dissipated power will be less than maximum.


32/110

This is essentially what is aimed for in radio transmitter design , where theantenna or transmission line impedance is matched to final power amplifierimpedance for maximum radio frequency power output. Impedance, the

overall opposition to AC and DC current, is very similar to resistance, andmust be equal between source and load for the greatest amount of power to

be transferred to the load. A load impedance that is too high will result inlow power output. A load impedance that is too low will not only result in lowpower output, but possibly overheating of the amplifier due to the powerdissipated in its internal (Thevenin or Norton) impedance.

Taking our Thevenin equivalent example circuit, the Maximum PowerTransfer Theorem tells us that the load resistance resulting in greatestpower dissipation is equal in value to the Thevenin resistance (in this case,0.8 ):

With this value of load resistance, the dissipated power will be 39.2 watts:

Power dissipation increased for both the Thevenin resistance and the total

circuit, but it decreased for the load resistor. Likewise, if we increase the

load resistance (1.1 instead of 0.8 , for example), power dissipation will

also be less than it was at 0.8 exactly:


33/110

If you were designing a circuit for maximum power dissipation at the loadresistance, this theorem would be very useful. Having reduced a networkdown to a Thevenin voltage and resistance (or Norton current andresistance), you simply set the load resistance equal to that Thevenin orNorton equivalent (or vice versa) to ensure maximum power dissipation atthe load. Practical applications of this might include radio transmitter final

amplifier stage design (seeking to maximize power delivered to the antennaor transmission line), a grid tied inverterloading a solar array, or electricvehicle design (seeking to maximize power delivered to drive motor).

The Maximum Power Transfer Theorem is not: Maximum power transferdoes not coincide with maximum efficiency. Application of The MaximumPower Transfer theorem to AC power distribution will not result in maximumor even high efficiency. The goal of high efficiency is more important for ACpower distribution, which dictates a relatively low generator impedancecompared to load impedance.

Similar to AC power distribution, high fidelity audio amplifiers are designedfor a relatively low output impedance and a relatively high speaker loadimpedance. As a ratio, "output impdance" : "load impedance" is known asdamping factor, typically in the range of 100 to 1000.

Maximum power transfer does not coincide with the goal of lowest noise. For

example, the low-level radio frequency amplifier between the antenna and a

radio receiver is often designed for lowest possible noise. This often requires

a mismatch of the amplifier input impedance to the antenna as compared

with that dictated by the maximum power transfer theorem.

REVIEW:

1. The Maximum Power Transfer Theorem states that the maximumamount of power will be dissipated by a load resistance if it is equal


34/110

to the Thevenin or Norton resistance of the network supplyingpower.

2. The Maximum Power Transfer Theorem does not satisfy the goal ofmaximum efficiency.

Star- Delta Transformation

In many circuit applications, we encounter components connected together

in one of two ways to form a three-terminal network: the Delta, or (also

known as the Pi, or ) configuration, and the Y (also known as the T)

configuration.


35/110

It is possible to calculate the proper values of resistors necessary to formone kind of network ( or Y) that behaves identically to the other kind, asanalyzed from the terminal connections alone. That is, if we had twoseparate resistor networks, one and one Y, each with its resistors hiddenfrom view, with nothing but the three terminals (A, B, and C) exposed for

testing, the resistors could be sized for the two networks so that there wouldbe no way to electrically determine one network apart from the other. Inother words, equivalent and Y networks behave identically.

There are several equations used to convert one network to the other:

and Y networks are seen frequently in 3-phase AC power systems (a topiccovered in volume II of this book series), but even then they're usuallybalanced networks (all resistors equal in value) and conversion from one to

the other need not involve such complex calculations. When would theaverage technician ever need to use these equations?

A prime application for -Y conversion is in the solution of unbalanced bridgecircuits, such as the one below:

After the -Y conversion


36/110

If we perform our calculations correctly, the voltages between points A, B,

and C will be the same in the converted circuit as in the original circuit, and

we can transfer those values back to the original bridge configuration.

Resistors R4 and R5, of course, remain the same at 18 and 12 ,

respectively. Analyzing the circuit now as a series/parallel combination, we

arrive at the following figures:


37/110

We must use the voltage drops figures from the table above to determine

the voltages between points A, B, and C, seeing how the add up (or

subtract, as is the case with voltage between points B and C):

Now that we know these voltages, we can transfer them to the same points

A, B, and C in the original bridge circuit:


38/110

Voltage drops across R4 and R5, of course, are exactly the same as theywere in the converted circuit.

At this point, we could take these voltages and determine resistor currentsthrough the repeated use of Ohm's Law (I=E/R):

At this point, we could take these voltages and determine resistor currents

through the repeated use of Ohm's Law (I=E/R):


39/110

The voltage figures, as read from left to right, represent voltage drops

across the five respective resistors, R1 through R5. I could have shown

currents as well, but since that would have required insertion of dummy

voltage sources in the SPICE netlist, and since we're primarily interested in

validating the -Y conversion equations and not Ohm's Law, this will suffice.

REVIEW:

1.Delta () networks are also known as Pi () networks.2.Y networks are also known as T networks.3. and Y networks can be converted to their equivalent counterparts

with the proper resistance equations. By equivalent, I mean thatthe two networks will be electrically identical as measured from thethree terminals (A, B, and C).

4. A bridge circuit can be simplified to a series/parallel circuit byconverting half of it from a to a Y network. After voltage dropsbetween the original three connection points (A, B, and C) have beensolved for, those voltages can be transferred back to the originalbridge circuit, across those same equivalent points.


40/110

Class AB- Power Amplifier used in Ujjain LPT

Class AB operation

Class AB Push-Pull Amplifier


41/110

The basic circuit of class AB push-pull amplifier is shown above in fig., here the

voltage drop across resistor R2 is so adjusted that it is approximately equals to

cut-in voltage(0.5 for Si and 0.1 for Ge). Now the operation becomes AB type i.e.

the collector current flows more than half the cycle of input signal but less than

complete cycle.

Advantages and drawbacks of Push-pull amplifiers

Advantages

(i) Because of absence of even harmonics in the output of push-pull

amplifier, such a circuit gives more output per active for a given amount

of distortion for a given output per transistor.

(ii) The dc component of the collector currents oppose each other

magnetically in the transformer core. This eliminates any tendency

toward core saturation and consequent non-linear distortion that may

arise from the curvature of the transformer magnetization curve.

(iii) Another advantage of this system is that the effects of ripple voltage

that may be continued in the power supply because of inadequate

filtering will be balanced out. This cancellation results because the

currents produced by the ripple voltages are in the opposite direction in

the transformer winding and so will not appear in the load. Off-course


42/110

the power supply hum will also act on the voltage amplifier stages and

so will be the part of the input to the power stage. The hum will not be

eliminated by the push-pull circuit.

Drawbacks

The drawbacks of the push-pull amplifiers are as under:

(i) Requirement of two identical transistors.

(ii) Need of use of driver stage to furnish two equal and opposite voltages

at the input.

(iii) Need of bulky and expensive transformer.

Nonlinear Distortion

Any unwanted change in shape of an a.c. signal is called distortion. One common

problem that occurs in common-emitter amplifier is called nonlinear-distortion.

The ouput waveform from an amplifier experiencing nonlinear is shown in fig(a).

Output waveform illustrating non-linear distortion


43/110

Notice the difference between the shape of the negative alteration of the

signal(normal) and that of its positive alteration(distorted). Non-linear distortionis caused by driving the base emitter junction of the transistor into its non linear

operating region. This point is illustrated by fig (b) which shows basic

characteristics of a transistor.

Normally a transmitter is operated so that the base emitter junction stays in the

Linear region of the operation. In this region , a change in VBE causes a

linear(constant rate)change in IB. If the transistor is operated in nonlinear

operating region, a change in VBE causes a nonlinear change in IB. It is evident if

we compare the slope of the curve immediately above and below Vk. Since the

slope of the curve changes, the rate of change in IB also changes.

The base -emitter junction of a transistor may be driven into its nonlinear

operating region in one of the two sets of circumstances:

1. A transistor is normally biased so that IB have a value well within the linear

region of operation. If an amplifier is poorly biased so that the Q-point

value of is near the non-linear region of operation , an relative small a.c.input signal will drive the transistor into non-linear region of operation and

as a result nonlinear distortion will result

2. The amplifier input signal (high)may be sufficient to drive the well biased

amplifier into non linear operation causing non-linear distortion because


44/110

high amplification of the input signal increases the amplitude of the input

signal and noise corrupts the amplitude of the signal.

The solution to the first problem is to redesign the amplifier for high values of

IB, while for the second problem solution is to reduce the amplitude ofamplified input signal.

Nonlinear distortion can cause a variety of problems in communication

engineering. In stereos ,it may cause the audio to sound grainy or may even

cause the tones of various musical instruments to change . In televisions,

crossover distortions in video circuitry can cause distortions in the picture on

the CRT. To avoid these types of problems, amplifier design normally emphasis

on avoiding cross-over distortion , since amplifiers are generally designed to

avoid nonlinear distortion problems. The most common cause of non-linear

distortion is overdriving an amplifier.

Cross-Over Distortion

In addition to distortion introduced due to non-linearity of the collector

characteristics and due to non- matching of the two transistors, there is one

source of distortion that is caused by non-linearity of input characteristics.

Recall that the silicon transistors must have at least 0.5V to 0.6V of forward

base emitter bias before they will go into the conduction. Since in class-B push

pull amplifier, the forward bias is produced by input signal, both of transistors

will be non-conducting, when the input signal is approx. (+-)0.5 V. This forms a

dead-band in the input and produces cross-over distortion in the output. In

simple words cross-over conducting as shown in fig. The distortion introduced

is called cross-over distortion because it occurs in the time operation cross-

over from one transistor in pushpull amplifier to the other in the same.. The

same is shown in fig. using transfer characteristics of the two transistors.

To eliminate cross-over distortion, it is necessary to add a small amount of

forward bias to take the transistor to the average of conduction or slightly

beyond. This does slightly lowers the efficiency of the circuit and there is a

wastage of stand-by power, but it eleviates the cross-over distortion problem.


45/110

Technically, the operation of the circuit lies between class A and class-B mode.

Therefore the circuit operation is often reffered to as being class AB operation

Illustration of cross-over distortion

Earth stations

Types, construction and sizes

There are two types of earth-stations. Those that receive only and those that

receive and transmit. Receive- only stations are used principally for the reception

of television signals emitted by satellites, when they are usually known as TVRO

stations. They are also used for receiving data and other forms of information that

can be displayed visually or in printed form. For two way links between users,

such as telephony, video-conferencing and computer tie-ups, stations at each end

are provided with both transmission and reception facilities.

Both types of stations employ similar geometries to capture and focus the signals

arriving from the satellite ( down link signals) and to aim signals at the satellite (to

uplink ) . Fig. shows how the downlink signals are captured by the earth-station

antenna, which usually takes the form of a parabolic circular dish and which

reflects the captured signals to the focus of the parabola ,where a collecting


46/110

horn is mounted. For transmission purposes, the horn emits signals which are

reflected off the parabola to form the uplink beam.

Mounting a horn in this manner, at the focus of a circular dish, means that a

structure has to be provided for the mounting , and this structure interferes withline-of-sight of dish, reducing its efficiency. For this reason many new stations

employ now employ parabolic dishes that are elliptical in front view with horn

offset from centre line of the dish. The dishes are elliptical so that they present an

apparent circular shape as seen from the satellite, to give a circular cone into the

horn.

Fig. 1


47/110

Signals entering the horn-or leaving it must be conducted to and from the

amplifying equipment in the station. This conduction takes place through a

length of a waveguide rectangularsection tubing of a size dependent on

the operating frequencies .In some designs of small stations this waveguide is

used as the horn- mounting structure to minimize interference .To minimize

losses in conduction , the waveguide length must be kept short as possible. This

is easier in offset designs than in than with centrefed circular dishes. The

shortest length of all is achieved by what is known as Casegrain antenna. Here by

using double reflectors, the amplifying equipment can be mounted directly

behind the horn. This type of antenna is however seen in only the largest and

most expensive Earth stations where maximum performance is essential.

Fig. 2 shows casegrain feed amplifier


48/110

Fig.3 shows the principal components of transmission and reception equipments

in a small earth station used for voice, data and video exchange in KU-band

business service. On the transmit side, incoming digital signals are mixed together

in a multiplexer to produce a combined data stream which is then passed into a

modulator. The to produce a combined data stream which is then passed to a

modulator. The modulator is fed with an intermediate frequency (IF) carrier,

which operates at 70 Mhz or 140 Mhz depending on the characteristics of the

system; this carrier is changed in phase (modulated) according to whether a digit

1 or a 0 is being imposed on it. An IF amplifier then filters and amplifies the

phased carrier and passes it to an up-convertor which changes the carrier

frequency to that of space system-in this case ,14 Ghz carrier is passed through

Fig 3


49/110

high power amplifier(HPA) to the antenna for up-linking to the satellite.

Depending on the receive sensitivity of the satellite, the size of the earth station

antenna and quantity of the traffic to be handled, the R$F output power of HPA

can vary from about 50 watts to 1 or 2 kilowatts.

The receive side operates in reverse. The phased 12GHz carrier arriving from

satellite is passed first into low noise amplifier typically, today a field effect

transistor (FET) amplifier. The carrier is down converted to IF and is filtered and

re-amplified at that frequency at that frequency. After amplification the signal

passes into demodulator which detects the phase shift into carrier and converts

them into original digits which first imposed the changes into transmission

station. The final digital stream is then demultiplexed into the original voice data

and video signals intended for receiving station.


50/110

Fig. 4


51/110

Fig. 5


52/110

Fig. 6

EIRP

EIRP is a product of the RF power of the satellite and its antenna gain. EIRP

stands for equivalent isotropic radiated powersometimes effective is used instead

ofequivalent. It is the term used universally in satellite communication because it

the one component that provides measure of the quality of the downlink service

offered by the satellite independently of its coverage and its power. It thusenables suppliers and users to compare the qualities of competing satellite

system without having worry about what area they cover or what power the

satellite produce.


53/110

Fig 7

The gain of the antenna is directly proportional to its diameter, and inversely

proportional to the wavelength of frequency being used. The working formula for

gain is:

G= e (D/ )

Where e is the efficiency of the design ,usually taken as 55%

is the constant 3.14

D is the antenna diameter in meters

is the antenna diameters in meters.

Putting in the values of e and , this reduces to

G= 5.4( D/ )

Take an example of an antenna 1m in diameter, working at 12Ghz:

Then D= 1 = 0.025


54/110

G = 5.4 x 40 = 8640 = 39.4 dBi

As another example, take 1.5 m antenna working at 4Ghz

D = 1.5 = 0.075

G = 5.4 x 40 = 2160 =33.3 dBi

Fig. 4 shows a range of gains against varying diameters and frequencies. To

obtain EIRP , all that is necessary is to add these gains to the output power of

the satellite amplifiers ,also expressed in dBW. If, in both examples, the the

output power per transponder is 20 watts that is 13 dBW ( as 1 W = 0.65 dBW),

the EIRP of the first example is 39.4 +13= 52.4 dBW. The EIRP of the second

example is 33.3 + 13= 46.3 dBW.

Fig. 8

Then to obtain the same EIRP of 52.4 dBW which is 80 watts

This clearly is the case because in halving the diameter of antenna case because in

halving the diameter of the antenna its gain would be reduced by a factor of

4(D2)i.e. 4D square, so to maintain same EIRP, the power must be increased by a

factor of 4.


55/110

It is not possible to increase or decrease the EIRP by simply changing antenna

diameters and output powers at will. It was observed that the conical beam

produced by circular antenna is dependent on antenna diameter, and the size of

the beam determines the coverage area that will be seen on the earth. Thus its

coverage area that determines the size of the antenna and once it is fixed EIRP

can be altered only by changing the output power.

The relationship between the size of the antenna of the conical beam and

antenna diameter is given by the formula:

= 70 ( /D)

Where

= halfpower beamwidth in degrees

= operating wavelength in meters

D= antenna diameter in meters

Thus the beamwidth of 1m diameter antenna operating at 12Ghz ( =0.025m)

is

= (70 x 0.025) /1 = 1.75 degrees


56/110

Fig. 9

Up-link Transmission

Traffic Handling capacity on the uplink, with the earth-station transmitting to

the satellite is dependent on the same three factors that determine the same

downlink capacity- EIRP, gain, and noise are those associated with the satellite.

As with the satellite, the EIRP of the satellite is the product of its antenna gain

and its transmitter power, as with the earth station the receive performance

of the satellite is its G/T, but here its not possible to increase the antennadiameter to improve the performance because the diameter has already been

decided to its coverage area. Further the antenna is not looking at clear sky,

with its low noise temperature of 40K , but the earth which emits radiation at

300K. Thus the receive performance of the satellite is constrained by its

relative lack of gain and higher noise, and is invariably poor than the earth


57/110

station working with it. To compensate for this the earth station simply uses

power in its transmit amplifier. Unlike the satellite which is limited in the the

power it can transmit, higher power in the earth station causes no supp-ly

problems, because power usually in the range of few hundred watts, is simply

drawn from the mains. However because of radiation spill- over that can occur

with small antennas , the output RF power of the earth-station may be

restricted to prevent interference with the adjacent satellites. All stations are

indeed subject to international and national regulations on this matter of

interference. In some cases to provide an adequate uplink EIRP without

exceeding regulatory limitations the gain of the earth station has to increased

by increasing the diameter of but expense of more reduced bandwidth and

thus need for more accurate pointing.


58/110

Fig. 10


59/110

Fig.11

Pointing an Earth-station

All operators of commercial communication satellite provide tables to show users

whwer to point their Earth-stations to find the satellite that they are going to use.

The users locates his exact latitude and longitude in the tables, which then show him

the the required elevation of the antenna (degrees from horizontal) and azimuth

(degrees clockwise from true North).

Fig..is a general chart ,showing elevation and azimuth angles for any earth station

and any satellite location in geosynchronous arc. Here, longitude difference need to

be known, that is the number of degrees between longitude of station and that ofsatellite. Generally minimum elevation of 5 degrees is satisfactory. Below this

,station can pick interference from terrestrial radio sources and suffer from earth

heat radiation , which will incread=se noise in the system.

The chart will clearly offer only an approximation of elevation and azimuth angles,

but is good enough for very small Earth-stations of about 1m diameter or less. These


60/110

can capture satellite initially in their relative broad beamwidth, using the chart, then

the antenna can be fine-pointed to receive the best signal. Larger stations need

more accurate, tabular pointing data.

Operators tables should also show when the Sun-Blinding will occur , that is,

when the station satellite and the sun are in the same line, which occurs twice peryear. The Suns temperature increases overall noise in the station receiver, which

will interfere in communication few minutes when conjunction occurs.

Fig.12


61/110

List of Satellite Name and look angle are calculated by azimuth and elevation

are given below:-

Transponder

Receiver Section transmitting section

6Ghz 4Ghz 4 Ghz

input

Filter Pre-

amplifier

Down-

converter

High-

Power

Amplifier

Filter


62/110

FIG. 1

INSAT 1A(SSL)

Insat-1 was a multi-purpose satellite system to provide two high power TV broadcast

and twelve telecommunications national coverage transponders, in addition to also

providing meteorological services.

The Insat-1A was launched by a Delta in April 1982 but was abandoned in September

1983 when its attitude control propellant was exhausted.

When Insat-1B was launched on 30 August 1983, it almost suffered the same fate as

the Insat-1A. It was not until mid-September that Ford and Indian controllers succeededin deploying its solar array. By then it had been stationed at 74E in place of Insat-1A.

Full operational capability was achieved in October 1983. It continued to operate into

1990 with all its 4375 two-way voice or equivalent circuits in use. Around 36,000 earth

images were returned.

Eleven of its 12 C-band transponder and its two S-band transponders provided direct

nationwide TV & communications to thousands of remote villages, plus a detailed

weather and disaster-warning service. Around 35,000 Indian built 3 to 3.6 meter

diameter, earth receive only terminals were in place to supply rural communities with

social and educational programs. It was relegated to spare status on 17 July 1990 bythe Insat-1D. The Insat-1B was finally removed from GEO in August 1993, after being

replaced at 93.5E by Insat-2B. Total cost of Insat-1B and its backup Insat-1C, including

the PAM-D launch was estimated at $140 million.

The Insat-1C satellite was launched on 21 July 1988 from Kourou for location at 93.5E

to bring the Insat system up to full capacity. Half of the 12 C-band transponders and its


63/110

two S-band transponders were lost when a power system failure knocked out one of the

two buses, but the meteorological earth images and its data collection systems were

both fully operational. Earth lock was lost 22 November 1989 and the satellite was

abandoned. Reported insurance payout was $70 million.

The specification for the Insat-1D is the same as the Insat-1B but with expanded batteryand propellant capacities. Launched on 12 June 1990 to conclude the first generation

Insat series. Launch was planned for 29 June 1989 but 10 days before it was seriously

damaged during launch preparation, when a crane hook fell on it. The fully insured

satellite was repaired by Ford Aerospace at a reported cost of $10 million. It also

suffered $150,000 of damage during the October 1989 Californian Earthquake. It

assumed prime role from Insat-1B on 17 July 1990. Design life was seven years.

Nation: India

Type / Application: Communication / Meteorology

Operator: Insat

Contractors: Ford Aerospace

Equipment: 12 C-band transponder, 2+1 S-band transponders,

Configuration: Insat-1 Bus

Propulsion: R-4D-11

Power: Deployable solar array, batteries

Lifetime: 7 years

Mass: 1152 kg (#1A, 1B); 1190 kg (#1C, 1D)

Orbit: GEO


64/110

Satellite Date LS Launch Vehicle Remarks

Insat 1A 10.04.1982 CC LC-17A Delta-3910 PAM-D

Insat 1B 30.08.1983 CC LC-39A Shuttle[PAM-D] withChallenger F2 (STS 8)

Insat 1C 21.07.1988 Ko ELA-1 Ariane-3 withECS 5

Insat 1D 12.06.1990 CC LC-17B Delta-4925
http://space.skyrocket.de/doc_lau_det/delta-3910_pam-d.htmhttp://space.skyrocket.de/doc_lau_det/delta-3910_pam-d.htmhttp://space.skyrocket.de/doc_lau/sts.htmhttp://space.skyrocket.de/doc_lau/sts.htmhttp://space.skyrocket.de/doc_stage/pam-d.htmhttp://space.skyrocket.de/doc_stage/pam-d.htmhttp://space.skyrocket.de/doc_stage/pam-d.htmhttp://space.skyrocket.de/doc_sdat/sts-ov.htmhttp://space.skyrocket.de/doc_sdat/sts-ov.htmhttp://space.skyrocket.de/doc_sdat/sts-ov.htmhttp://space.skyrocket.de/doc_lau_det/ariane-3.htmhttp://space.skyrocket.de/doc_lau_det/ariane-3.htmhttp://space.skyrocket.de/doc_sdat/ecs-1.htmhttp://space.skyrocket.de/doc_sdat/ecs-1.htmhttp://space.skyrocket.de/doc_sdat/ecs-1.htmhttp://space.skyrocket.de/doc_lau_det/delta-4925.htmhttp://space.skyrocket.de/doc_lau_det/delta-4925.htmhttp://space.skyrocket.de/doc_lau_det/delta-4925.htmhttp://space.skyrocket.de/doc_sdat/ecs-1.htmhttp://space.skyrocket.de/doc_lau_det/ariane-3.htmhttp://space.skyrocket.de/doc_sdat/sts-ov.htmhttp://space.skyrocket.de/doc_stage/pam-d.htmhttp://space.skyrocket.de/doc_lau/sts.htmhttp://space.skyrocket.de/doc_lau_det/delta-3910_pam-d.htm


65/110

Radio Wave Spectrum


66/110

Fig. shows allotment of various frequency bands and bandwidth used by various services for

operation


67/110

Spectrum:

The electromagnetic spectrum is the range of all possible frequencies

ofelectromagnetic radiation. The "electromagnetic spectrum" of an object is thecharacteristic distribution of electromagnetic radiation emitted or absorbed by that

particular object .Now as we have understood the meaning and bandwidth allocation we

can understand something about the famous 2G spectrum

What is 2G Spectrum

The 2G spectrum scam in India involved the issue of 1232 licenses by the ruling

Congress-led UPA allianceof the 2Gspectrum to 85 companies including many new

telecom companies with little or no experience in the telecom sector at a price set in the

year 2001.

The scam involved allegations regarding

the under pricing of the 2G spectrum by the Department of

Telecommunications which resulted in a heavy loss to the exchequer, and

the illegal manipulation of the spectrum allocation process to favour select

companies

The issue came to light after the auction of airwaves for3G services which amounted

to 677,190 crore (US$151.01 billion)to the exchequer. A report submitted bythe Comptroller and Auditor General based on the money collected from 3G licenses

estimated that the loss to the exchequer due to under pricing of the 2G spectrum was

176,379 crore (US$39.33 billion).

The scam came to public notice when the Supreme Court of India took Subramaniam

Swamy's complaints on record.

If the communication engineers were aware of the spectrum allocated to them at the time of

allocation this scam could have been avoided.

Transmitting Antenna

The satellite also contains an transmitting antenna to transmit a signal back to the

earth.
http://en.wikipedia.org/wiki/Rangehttp://en.wikipedia.org/wiki/Electromagnetic_radiationhttp://en.wikipedia.org/wiki/2Ghttp://en.wikipedia.org/wiki/Department_of_Telecommunicationshttp://en.wikipedia.org/wiki/Department_of_Telecommunicationshttp://en.wikipedia.org/wiki/3Ghttp://en.wikipedia.org/wiki/Crorehttp://en.wikipedia.org/wiki/United_States_dollarhttp://en.wikipedia.org/wiki/Comptroller_and_Auditor_Generalhttp://en.wikipedia.org/wiki/Crorehttp://en.wikipedia.org/wiki/United_States_dollarhttp://en.wikipedia.org/wiki/Supreme_Court_of_Indiahttp://en.wikipedia.org/wiki/Subramaniam_Swamyhttp://en.wikipedia.org/wiki/Subramaniam_Swamyhttp://en.wikipedia.org/wiki/Subramaniam_Swamyhttp://en.wikipedia.org/wiki/Subramaniam_Swamyhttp://en.wikipedia.org/wiki/Supreme_Court_of_Indiahttp://en.wikipedia.org/wiki/United_States_dollarhttp://en.wikipedia.org/wiki/Crorehttp://en.wikipedia.org/wiki/Comptroller_and_Auditor_Generalhttp://en.wikipedia.org/wiki/United_States_dollarhttp://en.wikipedia.org/wiki/Crorehttp://en.wikipedia.org/wiki/3Ghttp://en.wikipedia.org/wiki/Department_of_Telecommunicationshttp://en.wikipedia.org/wiki/Department_of_Telecommunicationshttp://en.wikipedia.org/wiki/2Ghttp://en.wikipedia.org/wiki/Electromagnetic_radiationhttp://en.wikipedia.org/wiki/Range


68/110

Down-linking

Down-Linking is a process in which RF(radio-frequency) signal from the satellite is

sent back to earth. The 6Ghz signal is down-converted to 4Ghz RF-signal in the

satellite and then sent to back earth, therefore the process is known as Down-linking. The earth station unit contains large number of parabolic antennas for

receiving the RF from the satellite. The RF is then sent to the system unit after

that it passes through a number of units described below:-

RF PDA RF System Unit RF Receiver IRD RF Audio/Video Switcher RF Exciter RF BPF

RF

Transmitting Antenna Tower Directional Coupler

Parabolic-Dish Antenna

The parabolic dish antenna is placed at the receiving earth-station to receive the

RF-signal from the satellite. Its shape is parabolic so that it could receive the

maximum signals from the satellite. The only difference in the casegrain feedantenna and parabolic dish antenna (PDA) is that casegrain feed contains two

convex reflectors. The one is larger and the other which is smaller is placed above

the larger at a fixed distance. The shape of the dish is parabolic or convex shaped

because all the RF-signals coming from different directions will concentrate at a

point and highly concentrated good quality signal could be obtained.


69/110

Skin Effect

It follows the faradays Principle

Feed LNBC

18 V dc

The RF-signal from the satellite is received by the PDA(parabolic dish antenna) at

the receiver end, the 18 volts DC from the system unit and the RF-signal from the

PDA both travels in the opposite direction from the same co-axial cable as shown

in the fig. therefore this effect is known as skin effect.

Michel Faradays Experiment

Faraday's ice pail experiment demonstrated that the charge resided only on the exterior

of a charged conductor, and exterior charge had no influence on anything enclosed

within a conductor. This is because the exterior charges redistribute such that the

interior fields due to them cancel. This shielding effect is used in what is now known as

a Faraday cage.

An external electrical field causes the charges to rearrange, which cancels the field inside.

Satellite System Unit

+(ve)-(ve)

RF

Electrons e-
http://en.wikipedia.org/wiki/Faraday%27s_ice_pail_experimenthttp://en.wikipedia.org/wiki/Faraday_cagehttp://en.wikipedia.org/wiki/Faraday_cagehttp://en.wikipedia.org/wiki/Faraday%27s_ice_pail_experiment


70/110

Faradays law:

Emf = N

Basically there are 6 units at the LPT(low power transmitter) they are as follows

:-

1. Monitoring Unit and

(i) Pattern Generator

* Colour Step Amplifier

2. Receiver Unit

3. Satellite System Unit

4. Processing Unit

5. Transmitting Unit

6. Power Unit

1.Monitoring Unit

It contains two set of coloured T.V receivers in which input signal enters. The T.V has

large variety of functions in it, for example, has it functions to reset the contrast,

brightness, colour, sharpness , etc.. It has a function channel scan in which it scans the

different channels. It also has a significant function in the menu section of the T.V.

functions in which a T.V can adjust itself according to the different systems adopted by

the world. This system contains different systems as follows:-


71/110

The PAL System (Phase Alternation by Line)

Television encoding systems by nation; countries using the PAL system

are shown in blue.

PAL, short for Phase Alternating Line, is an analogue television colour encoding

system used in broadcast television systems in many countries. Other commonanalog television systems are NTSC and SECAM. This page primarily discusses

the PAL colour encoding system. The articles on broadcast television

systems and analogue television further describe frame rates, image resolution

and audio modulation. For discussion of the 625-line / 50 field (25 frame) per

second television standard

This system is adopted by India in the year . This system was developed by

keeping the in account the interest of common and poor people of India.

This system emphasized on the compatibility and reverse compatibility.

This means that a black and white television should be capable of showing

colored transmission, similarly a coloured television should be capable of

showing black and white transmission. The detailed of PAL system is shown

in the chain shown in the fig. The list of countries adopting PAL along-with

India is shown below:-
http://en.wikipedia.org/wiki/Analogue_televisionhttp://en.wikipedia.org/wiki/NTSChttp://en.wikipedia.org/wiki/SECAMhttp://en.wikipedia.org/wiki/Broadcast_television_systemshttp://en.wikipedia.org/wiki/Broadcast_television_systemshttp://en.wikipedia.org/wiki/Broadcast_television_systemshttp://en.wikipedia.org/wiki/Broadcast_television_systemshttp://en.wikipedia.org/wiki/SECAMhttp://en.wikipedia.org/wiki/NTSChttp://en.wikipedia.org/wiki/Analogue_television


72/110

History:-

In the 1950s, the Western European countries commenced planning to introduce

colour television, and were faced with the problem that the NTSC standard

demonstrated several weaknesses, including colour tone shifting under poortransmission conditions. To overcome NTSC's shortcomings, alternative standards were

devised, resulting in the development of the PAL and SECAM standards. The goal was

to provide a colour TV standard for the European picture frequency of 50 fields per

second (50 hertz), and finding a way to eliminate the problems with NTSC.

PAL was developed by Walter Bruch at Telefunken in Germany. The format was first

unveiled in 1963, with the first broadcasts beginning in the United Kingdom in 1964 and

Germany in 1967,[1]though the one BBC channel initially using the broadcast standard

only began to broadcast in colour from 1967.

Telefunken was later bought by the French electronics manufacturerThomson.

Thomson also bought the Compagnie Gnrale de Tlvisionwhere Henri de

France developed SECAM, the first European Standard for colour television. Thomson,

now called Technicolor SA, also owns the RCA brand and licenses it to other

companies; Radio Corporation of America, the originator of that brand, created the

NTSC colour TV standard before Thomson became involved.

The term PAL is often used informally to refer to a 625-line/50 Hz (576i) television

system, and to differentiate from a 525-line/60 Hz (480i) NTSC system.Accordingly, DVDs are labeled as either PAL or NTSC (referring informally to the line

count and frame rate) even though technically the discs do not have either PAL or

NTSC composite colour. The line count and frame rate are defined as EIA 525/60 or

CCIR 625/50. PAL and NTSC are only the method of colour transmission.

Colour Encoding:-

Both the PAL and the NTSC system use a quadrature amplitude

modulated subcarriercarrying the chrominance information added to the luminance

video signal to form a composite video baseband signal. The frequency of thissubcarrier is 4.43361875 MHz for PAL, compared to 3.579545 MHz for NTSC. The

SECAM system, on the other hand, uses a frequency modulation scheme on its two line

alternate colour subcarriers 4.25000 and 4.40625 MHz.

The name "Phase Alternating Line" describes the way that the phase of part of the

colour information on the video signal is reversed with each line, which automatically
http://en.wikipedia.org/wiki/Field_(video)http://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Walter_Bruchhttp://en.wikipedia.org/wiki/Telefunkenhttp://en.wikipedia.org/wiki/PAL#cite_note-ITU-0http://en.wikipedia.org/wiki/PAL#cite_note-ITU-0http://en.wikipedia.org/wiki/PAL#cite_note-ITU-0http://en.wikipedia.org/wiki/Technicolor_SAhttp://en.wikipedia.org/wiki/Henri_de_Francehttp://en.wikipedia.org/wiki/Henri_de_Francehttp://en.wikipedia.org/wiki/European_Standardhttp://en.wikipedia.org/wiki/RCA_(trademark)http://en.wikipedia.org/wiki/RCAhttp://en.wikipedia.org/wiki/576ihttp://en.wikipedia.org/wiki/480ihttp://en.wikipedia.org/wiki/DVDhttp://en.wikipedia.org/wiki/Quadrature_amplitude_modulationhttp://en.wikipedia.org/wiki/Quadrature_amplitude_modulationhttp://en.wikipedia.org/wiki/Subcarrierhttp://en.wikipedia.org/wiki/Co

Date post:	04-Apr-2018
Category:	Documents
Upload:	harshul-phadke
View:	214 times
Download:	0 times

Camera (Repaired)

Documents