Advantage of modulation

 Need of modulation

1)The baseband transmission has many limitations which can be overcome using modulation.

2)In the modulation ,the baseband signal is translated i.e.,shifted from low frequency to high frequency.

3)reduction in the height of antenna:

4)Avoids mixing of signals:
If the baseband sound signals are transmitted without using the modulation by more than one transmitter,then all the signals will be in the same frequency range i.e. 0 to 20 kHz. therefore,all the  signal get mixed together and a receiver cannot separated them from each other.

hence,if each baseband sound signal is used to modulate a different carrier then they will occupy different slots in the frequency domain(different channels). 

5)Improves quality of reception:
with frequency modulation (FM),and the digital communication techniques like PCM,the effect of noise is reduced to a great extent. this improve quality of reception

6)Multiplexing is possible:  

Multiplexing is a process in which two or more signal can be transmitted over the same communication channel simultaneously.this is possible only with modulation.the multiplexing allows the same channel to be used by many signals.Hence,many TV channels can use the same frequency range,without getting mixed with each other or different frequency signals can be transmitted at the same time.

7)Increases the range of communication:
The frequency of baseband signal is low,and the low frequency signals can not travel a long distance when they are transmitted.they get heavily attenuated(suppressed).the attenuation reduces with increase in frequency of the transmitted signals,and they travel longer distance.the modulation process increases the frequency of the signal to be transmitted.therefore,it increases the range of communication.

why modulation is used to reduction in the height of antenna?

Reduction in the height of antenna.
For the transmission of radio signals,the antenna height must be multiple of(

 λ/4).Here  λ  is the wavelength. λ=c/f  where c is velocity of light and f is the frequency of the signal to be transmitted.The minimum antenna height required to transmitted is baseband signal of f=10 kHz is calculated as follows:

we know that,
         λ=c/f 

where 

     λ= it is wavelength     c=velocity of a light,     f=it is a frequency of the signal to be transmitted.now take a example

f=10Hzantenna height= λ/4=(c/4f)=(3x100000000)/(4x10x1000)                                         =7500meters now we see that antenna size is too large it is  impossible 

Now, let us consider a mdulated signal f=1MHz.   

 antenna height=λ/4                             =c/4f                             =3x100000000/4x1x1000000                             =75 meternow we see that this antenna can be easily installed practically.

Thus, modulation reduces the height of the antenna

example of a micro antenna 

Amplitude modulation

Amplitude modulation

Amplitude modulation is a family of a continuous-wave(CW)modulation systems.In amplitude modulation,the amplitude of a sinusoidal carrier wave is varied in accordance with the baseband (modulating) signal.Amplitude modulation may be defined as a system in which the maximum amplitude of the carrier wave is made proportional to the instantaneous value(amplitude)of the modulating or baseband signal.

In amplitude modulation the maximum amplitude of the carrier wave is made proportional to the instantaneous value of the modulating signal.

In mathematically,

Let us consider a sinusoidal carrier wave c(t) given as 

 c(t)= A cos ωct

where,

ωc is the carrier frequency .

A is a the maximum amplitude of carrier wave.

The standard equation for amplitude modulated(AM)wave may be expressed as

    

                s(t)=x(t) cosωct + A cosωct      .................................(1)

                s(t)=[A +x(t)] cosωct   ..........................................(2)

equation number (2) is a required equation for a Amplitude modulation.


Few points about Amplitude Modulation (AM):
(i) It may be observed that equation (1) or(2) describes the time-domain behaviour of amplitude-modulated signal.
(ii)It may be noted that carrier signal [i.e.c(t)=A cosωct] is a fixed frequency signal having frequency ωc.The modulating or baseband signal x(t) contains the information or intelligence to be transmitted.In the process of amplitude modulation,this information is superimposed upon the carrier signal in the form of amplitude variation of the carrier signal. This means that the information to be transmitted,is now,contained in the amplitude variation of the carrier signal.In other words,in amplitude modulation,the information is transmitted in the form of amplitude variations of the carrier signal.
(iii)The resulting signal from the process of amplitude-modulation is called amplitude modulated signal or simply AM wave. 
(iv)In the process of amplitude modulation,the frequency and phase of the carrier remain constant whereas the maximum amplitude varies according to the instantaneous value of the information signal.
(v)equation 2 represents an amplitude modulated wave.this wave has a constant frequency
ωc and amplitude A + x(t).this implies that the amplitude of the wave is changing around A in accordance with the value of the modulating signal x(t).the frequency of the AM signal remains unchanged and is equal to ωc.
(vi)The AM wave has a time-varying amplitude called as the envelope of the AM wave.This means that the unique property of AM is that the envelope of the modulated carrier has the same shape as the message signal or baseband signal.


SINGLE TONE MODULATION:

amplitude modulation in which we assumed that baseband or modulating signal is a random signal which contains a large number of frequency components. This means that a carrier signal(fixed frequency signal) is modulated by a larger number of frequency components.
amplitude modulation in which the modulating or baseband signal consists of only one(single)frequency i.e.modulation is done by a single frequency or tone. this type of modulation is known as single tone amplitude modulation.

what is modulation??

MODULATION

Modulation is a fundamental requirement of a communication system.Modulation may be defined as a process by which some characteristic of a signal known as a carrier is varied according to the instantaneous value of another signal known as modulating signal.the signals containing intelligence of information to be transmitted are called modulating signal.these modulating signals containing intelligence or information to be transmitted are called modulating signals.These modulating signals containing information are also called baseband signals.Also the carrier frequency is greater than the modulating frequencies and the signal which results from the process of modulation is known as modulated signal.Modulation may be classified as continuous wave modulation and pulse modulation.If the carrier wavefrom is continuous in nature then the modulation process is called as continuous-wave(CW)modulation.the example of this type of modulation are amplitude modulation and angle modulation

A modulation is method or process send the information signal with the help of carrier signal that means is two signals are used namely the modulating signal(information signal) and the carrier.
carrier is a high frequency sinusoidal signal.
In the modulation process,some parameter of the carrier wave is varied in accordance with the information signal.
 

suppose that you want to send a information signal to another person..you are a transmitter  and person is a receiver. a distance between to transmitter and receiver there have many noise and traffics in this time your information signal losses the power that way receiver is not found your information signal. because the voice signal(in the electrical form )cannot travel long distance in air.
How to overcome this situation ?we are used to modulation technique.
 In the process of modulation ,the carrier wave actually acts as a carrier which carriers the information signal from the transmitter to receiver.
let's take a example :

 you want to go  to a market and  how to you will  go?? you choose a vehical like car,bus,taxi etc.. and you are a passenger... home to market your distance..
  suppose that a carrier signal is a car..and you are a information signal. source to destination you will go  with the help of carrier this all prosecc is called modulation

carrier

you as a (information)

go to market with the help of carrier

electronic components.

ELECTRONIC COMPONENTS:

capacitors: capacitors is passive elements. it is a physical device which is capable of storing energy by virtue of a voltage exiting across it. the voltage applied across the capacitor sets up an electric field within it and the  energy is stored in the electric field. 

A capacitor is basically meant to store electrons( or electrical  energy), and release them whenever required. Capacitance is a measure of a capacitor's ability to store charge and is measured in farads(F).Farad,the unit of capacitance is very large,so microfarad (uF) or micro-microfarad(uuF) is usually used 1 uF and 1uuF,also called the picofarad(pF).

A capacitor offers low impedance to ac but very high impedance to dc.so capacitors are used to couple alternating voltage from one circuit to another circuit and at the same time to block dc voltage from reaching the next circuit.It is also  employed as a bypass capacitor where it passes the ac through it without letting the dc to go through the circuit across which it is connected.A  capacitor forms a tuned circuit in series or in parallel with an inductor.

capacitors are used for waveform generation , filtering , blocking and differentiator, In combination with inductors,they make possible sharp filter for separating desired signals from background.

different type of capacitors

capacitor is basically meant to store electrical energy.

inductors:

 an insulator is physical device which is capable of storing energy by virtue of a current flowing through it.An inductor  has  been defined as a physical device which is capable of storing energy by virtue  of a current flowing through it. An inductor is a circuit components which opposes the change of current flowing through it varies in magnitude and/or direction.

In case of an inductor current does not change instantaneously.It offers high impedance to ac but very low impedance to dc i.e., it blocks ac signal but passes dc signal.

A piece of wire, or a conductor of any type,has inductance i.e., a property of opposing  the change of current through it.By coiling the wire the inductance is increased as the square of the number of turns. the inductance is represented by a English capital latter L and measured in henrys. 

      specially made components consisting of coiled copper wire called the inductors. Inductors are of two types viz.,air-core(wound on non-ferrous)and iron-core(wound on ferrite cores). Inductors range in value from the tiny (few turn air-core coils of 0.1 uH used in high frequency systems) to iron-core choke coils 50H or more for low frequency applications.
The inductors can be classified into filter chokes, audio-frequency chokes and radio-frequency chokes.
Filter chokes has many turns of fine wire wound on an iron core made of laminated sheets of E- and I-shapes and is used in smoothing the pulsating current produced by rectifying ac into dc. Generally power supplier use filter chokes having inductance ranging from about 1H to 50H,capable of carrying current up to 500 mA.

Resistors: resistors are employed in amplifiers as loads for active devices,in bias networks,and feedback elements.

• 

LED: LED is stand for a light emitting diodes.LED is work on forword wise and there are two terminal anode and cathode(+ve and -ve).all opto electronic devices is the so called LED(light-emitting diode),which  emits a fairly narrow bandwidth of visible (usually red,orange,yellow or green) or invisible(infrared) light when its internal diode junction is stimulated bt a forward electric current/voltage (power).LEDs have typical power-to-light energy conversion efficiencies some 10 to 50  times greater  than of a simple tungsten lamp and have very fast response times,(approximately 0.1us compared with tens or hundred of milliseconds dor a tungster lamp),and are thus widely employed as visual indicators and as moving light displays.

the operation of light-emitting diode(LED) is based on the phenomenon of electroluminance,which is the emission of light from a semiconductor under the influence of an electrical field. the recombination of charge carriers take place in a forward P-N junction as the electrons cross from the N- region and recombine with holes exiting in P-region. free electrons are in the conduction band of energy levels,while holes are in the valence energy band. therefore, the electrons are at high energy levels than the holes. for the electrons to recombination with the holes,they must give some of their energy. typically,these electrons give up  energy in the form of heat and light.

 In silicon and germanium diodes,most of the electrons give up their energy in the form of heat. however, with GaAsP,and GaP semiconductor, the electrons give up their energy by emitting photons. If the semiconductor is transluscent, the light will be emitted and the junction becomes a source of light,i.e., a light-emitting diode (LED). LEDs emit no light when reverse biased. in fact,operating LEDs in reverse bias mode will quickly destroy them.
(+ve)→→→←←(-ve)

picture of led and there use

• 

  
  
  

  • picture of some electronic components

Advantage of LEDs:

• LEDs are miniature in size and can be stacked together  to form numeric and alphanumeric displays in high density matrix.
• Smooth control of light intensity from an LED because  light output from an LED is a function of current flowing through it.
• LEDs are economical and have a high degree of reliability because they are manufactured with the same type of technology as is used for transistors and ICs.
• LEDs can be operated over a wide temperature range (0-70 degree C).
• The switching time (both on and off) is less than 1 ns. so they are very suitable where dynamic operation of large number of arrays is involved.
• LEDs are available in different colours like red,yellow , green, and amber.
• They need moderate power.They are used where low dc power is available.
• they occupy small area.
•  LEDs that emit visible light are widely used in instrument display panel indicator,digital watches ,calculators,multimeters,  intercom,telephone switchboards,etc. LEDs  that emit invisible infrared light find application in remote control schemes,object detectors,burglar alarm systems;and other areas requiring invisible radiation.

why radars use in military?

Applications of radars in military:

1. Detection and ranging of enemy targets even at night.
2. Directing guided missiles.
3. searching for submarines.
4. Early warning  regarding approaching aircraft or ships.
5. Aiming guns at aircraft and ships.

The reradiated energy on being received back at the radar station gives information about the location of the target. the location of the target include range, angle and velocity parameters. the range is the distance of the target from radar station. the angle could be azimuth or elevation angle for static targets and velocity for moving targets.
for satisfactory location of target,the received power(echo power) must be appreciable. accordingly, the amount of power(energy)required to be radiated by the radar transmitter must be tremendous,typically few kW to MW.such high power at high frequencies can be generated using magnetrons. 

What is radars?

RADARS

Radar is a basically a means of gathering information about distant objects or targets by sending electromagnetic(EM) waves to them and thereafter analyzing reflected waves or the echo signals. Radar evolved a few years before World war II. it was a radar that gave birth to microwave technology. in fact the early researchers found out that the highest frequencies gave the most accurate results. higher frequencies produce the best echoes,make it possible to detect smaller targets and permit the use of smaller antennas. a radar can detect static or mobile objects or targets and is the most effective method for guiding a pilot with regard to his location in space and also for warning the approach of an enemy plane for similar purposes.
A radar can detect static or mobile objects or targets and is the most effective method for guiding a pilot with regard to his location in space and also for warning the approach of an enemy plane for similar purposes.
We know that if an electromagnetic wave encounters sudden change in conductivity  σ, permittivity  ε or permeability  μ in the medium, a part medium, a part of the electromagnetic energy gets absorbed by the second medium and is reradiated. This sudden change in the electrical property of the medium constitutes the target.

The reradiated energy on being received back at the radar station gives information about the location of the target.The location of the target includes range,angle and velocity parameters.the range is the distance of the target from radar station.The angle could be azimuth or elevation angle for static targets and velocity for moving targets.

For satisfactory location of the target,the received power(echo power) must be appreciable.
Accordingly,the amount of the power(energy) required to be radiated by the radar transmitter must be tremendous,typically few kW to MW.such high frequencies can be generated using magnetrons.

 

we know that if an electromagnetic wave  encounters sudden change in conductivity ,permittivity or permeability in the medium,a part of the electromagnetic energy gets absorbed by the second medium and is re radiated. this sudden change in the electrical property of the medium constitutes the target.


In general,radars consist of a transmitter, a receiver, a display and antennas. The received  echo signal after it is processed by the receiver is displayed on the radar screen.It is very much possible to detect the height,speed and direction of travel of the target by space tringulation and by the time taken for the echo to come back after  reflection from the target . the display screen can be similarly calibrated to indicated the target data.

The general requirement for any radar system are summarised below.

1.The duplexer should be automatic in its operation.
2. The radar transmitter should remain silent during the echo period.
3. The transmitter pulse should be quite powerful to counter the attenuation during forward and return joureneys.
4. The received echo pulse being weak,the receiver should be extermely sensitivity and at the same time immune to noise signals.It should have necessary amplification,signal processing circuitry and capability to display the target information on the radar screen.
5. The radar antenna should be highly directive and have a large gain so that it can radiate a strong signal and receive a weak pulse.
 

Advantages of a Radar:

i) Radar can see rain,fog,snow , darkness and haze .

ii) Radar can determine the range and angle.

What is communication system?

COMMUNICATION SYSTEM

communication system is to transmit message (data)of a source to a user. communication may be define as a connection between two points for information exchange. the electronic equipment used for communication purpose,are referred to as communication equipment.
communication is a simply the basic process of exchanging information.
The electronic equipment which are used for communication purpose,are called communication equipment. Different communication system are line telephony and line telegraphy,radio telegraphy,radio telegraphy and radio telegraphy,radio broadcasting,point-to-point communication and mobile communication,computer communication, radar communication,television broadcasting,radio telemetry,radio aids to navigation,radio aids to aircraft landing etc.
The earliest communication system namely line telegraphy originated in eighteen forties. In addition to this, line telephony came a few decades later whereas radio-communication could become possible in the beginning of twentieth century on invention of triode valve.
Radio communication was further greatly improved during World War II.It became more widely used through the invention of transistor,integrated circuits(ICs) and other semiconductor device in the subsequent years.Also,in recent years,communication has become more widespread with the use of satellites and fiber optics.

THE COMMUNICATION PROCESS:

In the most fundamental sense,communication involves the transmission of information from one point to another through a succession of process as listed ahead:
(i) The generation of a thought pattern or image in the mind of an originator.
(ii)The description of that image,with a certain measure of precision,by a set of oral visual symbols.
(iii)The encoding of these symbols in a form that is suitable for transmission over a physical medium of interest.
(iv)  The transmission of the encoded symbols to the desired destination.
(v)the decoding and reproduction of the original symbols.
(vi)The recreation of the original thought pattern or image,with a definable degradation in quality, in the mind of a recipient.



communication system are line telephony and line telegraphy,radio broadcasting,point-to-point communication and mobile communication ,computer communication,radar communication,television broadcasting,radio telemetry etc.    

Application of PN diode

Application of PN diode:

An ideal P-N junction diode is a two terminal polarity sensitive device that has zero resistance when it is forward biased and infinite resistance(i.e.,diode does not conduct)when reverse biased.Because of this property the diode find use in many application as enumerated below:

zener diode

1. As a rectifiers in dc power supplies.
2. In demodulation or detector circuits.
3. In clamping networks employed as dc restorers in TV receivers and voltage multipliers.
4. In  clipping circuits used as wave shaping circuits in computers,radars,radio and TV receivers. 
5. As a switches in digital logic circuits.The same P-N junction with different doping concentrations finds special applications as follows:(i) As zener diodes in voltage regulators,peak clippers,and in switching operation.(ii) As tunnel diodes as a relaxation oscillator at microwave frequencies.(iii) As light-emitting diodes (LEDs)in digital displays.(iv) As varactor diodes in tuning sections of radio and TV receivers.
6. pn diode use in LED.
7. LASER diode in optical communication.
8. zener diode use in voltage regulator.
9. PIN diode use in optical communication.
10. use in clipping circuits as a wave shaping circuits in computer,radars,radio and TV receivers.

LASER

Difference between FET and BJT

Field effect transistors:

FET is a majority carrier device,and is,therefore,often called a unipolar transistor while BJT operates by the injection and collection of minority carriers;since in the device, both holes and electrons take part in conduction it is called a bipolar transistor.Like its bipolar counterpart,the FET is a three-terminal (namely,drain,source and gate) semicondctor device in which current conduction is by-one type of majority carriers(electrons in case of an N-channel FET or holes in a P-channel FET).unlike the BJT, FET needs virtually no input (bias signal) current.field-effect devices are controlled by an electric field(or voltage) and give an extremely high input impedance-most important advantage over BJT devies.

Field-effect transistors(FETs )are of several types such as junction field-effect transistors(JFETs),metal semiconductor field-effect transistors(MESFETs) and metal-insulator semiconductor field-effect transistors (MISFETs).

• FET is majority carrier device,and is,therefore,often called a unipolor transistor.
• FET is a three terminal device (Gate,source,drain).
• FET is a voltage controller device.
• FET give an extremely high input impedance.
• many types of FETs are present...JFETs,MESFETs and MISFETs.   

picture of a  chip (using FET)

Bipolar junction transistors:

A transistor may consist of a layer of P-type material sandwiched between two layers of N-type material as shown in fig in the former case the transistors is referred to as a P-N-P transistor and in latter case,as N-P-N transistor.Each type of transistor has two P-N junctions-one junction between the emitter and base,called the emitter-base junction or simply the emitter junction and the other junction between the base and collector junction.thus a transistor is like two P-N junction diodes have all the characteristics. The two junctions give rise to three region provided with three terminals called the emitter,base and collector as shown in fig.the emitter, base and collector correspond in a general way to the cathode,grid and plate or anode of a vacuum triode.

picture of BJT (three terminal shown in figure base,collect,emitter)



• BJT operates by the injection and collection of minority carriers.
• in BJT both holes and electrons take part in conduction,so it is called bipolar transistor.
• it is a current controller device.
• BJT is  a three terminal device (emitter,collector & base).
• BJT is referred to as a P-N-P transistor and N-P-N.

  

  N-P-N transistor

what is conductor,insulator and semiconductor??

conductor :

conducting materials are good conductors of electricity and are characterized by a larger electrical conductivity and small electrical resistivity.

• silver.
• copper.
• aluminium etc.

  

  copper wire

 Insulator:

Insulating materials are characterized by poor electrical conductivity  and are used to block current from flowing where it is not to pass. 

• glass.
• rubber.
• wood.
• quartz etc...

  

  picture of glass

semiconductor:

there is another group of materials which are neither good conductors nor good insulators. at room temperature such materials have conductivites considerably lower than those of conductor and much higher than those insulators.such  materials are called semiconductor. below the example of a semiconductor(c,si,pb,sn,Ge) you want to know about active and passive component click here  active and passive components

• carbon(C)
• silicon(Si)
• Lead(Pb)
• Tin(Sn)
• Germanium(Ge)

• 

  diode made in si and Ge