Generation of Amplitude Modulation (AM).

The device which is used to generate an amplitude modulation (AM) wave is known as amplitude modulator. The methods as amplitude modulator Generation may be broadly classified as following:-

1) Low level AM Modulation.

2)High level AM Modulation.

1)Low Level Amplitude Modulation:-

Figure shows  the block diagram of a low level AM modulation system. In a low level amplitude modulation system, the modulation is done at low power level. At low power levels, a very small power is associated with the carrier signal and the modulation signal. Because of this the output power of modulation is low. Therefore the power amplifiers are required to boost the amplitude modulated signals up to the desired output level.

 From block diagram in figure it is clear that modulation is done at low power level. After this the amplitude modulated signal is applied to a wide band power amplifier . A wide band power amplifier is used just to preserve the sidebands of the modulated signal. Amplitude modulated systems , employing modulation at low power levels are also called low level amplitude modulation transmitters.

Square-law diode modulation and switching modulation are examples of low-level modulation.

2)High level Amplitude Modulation:-

Figure  shows the block diagram of a high level AM modulation system. In a high-level amplitude -modulation system, the modulation is done at high power level. Therefore, to produce amplitude modulation at these high power levels, the base band signal and the carrier signal must be at high power levels. In block diagram of figure the modulating signal and carrier signal are first power amplified and then applied to AM  high level modulator. For modulating signal the wide band power amplifier is required just to preserve all the frequency components present in modulating signal.

On the other hand for carrier signal , the narrow band power amplifier is required because it is a fixed frequency signal. The collector modulation method is the example of high level modulation. Before we discuss low level and high level modulation methods in detail, we shall establish the fact that a non- linear resistance of non linear device can be made to produce amplitude modulation when two different frequencies are passed together through it.

Pulse Amplitude Modulation (PAM).

Pulse amplitude modulation may be defined as that type of modulation in which the amplitudes of regularly spaced rectangular pulses vary according to instantaneous value of the modulating or message signal . In fact the pulses in a PAM signal may be of flat top type or natural type or ideal type. Actually all the sampling methods which have been discussed in last sections are basically pulse amplitude modulation methods. Out of these three pulse amplitude modulation methods the flat top PAM is most popular and is widely used. 

The reason for using flat top PAM is that during the transmission the noise interferes with the top of the transmitted pulses and this noise can be easily removed if the PAM pulse has flat top. However , in case of natural samples PAM signal the pulse has varying top in accordance with the signal variation. Now when such type of pulse is received at the receiver it is always contaminated by noise. Then it becomes quite difficult to determine the shape of the top of the pulse ans thus amplitude detection of the pulse is not exact. Due to this errors are introduced in the received signal. Therefore, flat top sampled PAM is widely used signal. 

Working Principle:- 

A sample and hold circuit shown in fig. is used to produce flat top sampled PAM . The working principle of this circuit is quite easy. The sample and Hold circuit consists of two field 

effect transistors (FET) switches and a capacitor. The sampling switch is closed for a short duration by a short pulse applied to the gate G1 of the transistor . During this period the capacitor C is quickly charged up to a voltage equal to the instantaneous sample value of the incoming signal x(t) . Now the sampling switch is opened and the capacitor C holds the charge. The discharge switch is then closed by a pulse applied to gate G2 of the other transistor . Due to this the capacitor C is discharged to zero volts. The discharges switch is then opened and thus capacitor has no voltage.

Hence the output of the sample and hold circuit consists of a sequence of flat top samples .

Research Process

Research process consists of series of actions or steps necessary to carry out research and the desired sequencing of these steps:-

A brief description of these steps is as follows-

1.Formulation

2.Review of Literature

3.Formulation of hypothesis

4.Research Design

5.Determining Sample design

6.Collection of Data

7.Execution of project

8.Analysis of Hypothesis

9.Testing of Hypothesis

10.Generations and Interpretations

11.Preparation of Research Report

1.Formulation  of research problem-

the first step in any research is to formulate a research problem

There are basically 2 steps of research problem:

1.problem which relates to state of nature.

2.problem which relates to relationship between variables

At the very beginning researcher must identity the problem be wants to study.

Essentially two steps are involve in formulation a research problem

1.Understanding the problem thoroughly and the best way of it is to discuss it with ones own colleagues or the experts in that matter.

2.Rephrasing the problem in to meaningful terms from an analytical point of view.
2.Review of Literature-

 After the problem is formulated, a brief summary of it should be written down and this summary is known as synopsis an for getting phd degree it is necessary to submit it to the committee or research board for approval. At this time the researcher should undertake extensive literature survey connected

with the problem. For this purpose journals and published / unpublished bibliographies are first place to go to. The other things that can be referred are academic journals, conference proceedings, Government reports, books, internet sites etc.

3.Formulation of Hypothesis-

 After extensive literature survey, the next step is to formulate working hypothesis. Hypothesis is a tentative assumption made in order to draw out and test its logical consequences. Hypothesis should be very specific and limited to the piece of research in hand because it has to be tested. The role of hypothesis is to guide the researcher by delimiting the area of research and to keep him on the right track. It sharpens the thinking of researcher & focuses attention on more important facts of the problem.

4.Preparation of Research Design-

The next step is to prepare a conceptual structure within which research would be conducted. The function of research design is to provide for the collection of relevant information and evidence with minimum expenditure of effort , time and money.

research objective / purpose may be grouped into 4 categories..

1.Exploration

2.Description 

3.Diagnosis

4.Experimental/Hypothesis

The research design should be flexible and it should provide apportunity for considering many different aspects of a problem fit is of exploratory nature.
The following points should be considered while preparing a research design:
1.The means of obtaining information.
2.The availability and skill of researcher and his staff.
3.The time available for research.
4.The cost factor relating to research i.e finance available for research . There are number of research design such as: Experiment and non Experiment research design.
5.Determining Sample Design:-
All the items under consideration in any field of enquiry or research constitute a universe or population. If all these items are included in our study then it is known as census method of enquiry.
For example
1.Random Sampling
2.Systematic Sampling
3.Stratified Sampling
Non probability samples are those in which there is some bias on the part of researcher.
6.Collection of Data:-
For carreing out any research successfully data collected should be adequate and should be based on nature of enquiry.
There are several ways of collecting data and these differ on the basis of time cost money cost and other resources at the disposal of research.
The data to be collected is of 2 types.
1.Primary data is data which is collected for the first time by researcher himself.
2.Secondary data is data which has been collected by someone else earlier and is used by research for his research.
7.Execution of Project:-
It is a very important step in research process. The data collected would be adequate and dependable if project is executed in right manner. The research should see that project is executed in a systematic manner and within prescribed time.
If data is to be collected by interviews then steps should be taken for selection of right person and proper training should be given to him. Occasional field check should be made to ensure that interviewers are doing their assigned job efficiently and sincerely.If details to be collected by means of structure questionarie then questions as well as answers should be coded so the data can be readily matching processed.
8. Analysis of data:-
Analysis of data refers to computation of certain measures along with serearching for pattrens of relationship that exist among data groups.It requires editing classification and codification of data tabulation and then drawing statistical interference out of arranged data. After tabulation of data analysis process involves calculation of various percentages coefficient etc. By applying various statical methods and tools so as to find out whether observation support theory on not . In this case our problem will be whether the two means value differ significantly or the difference  just due to fluctuations of sampling.

 9.Testing of Hypothesis:-
After data has been analysed the research is in a position to test the hypothesis formed earlier. He has to test whether the facts support the hypothesis or not? The various test such as t test z test chi sequar test f test have been designed for this purpose . Hypothesis may be tested either by using one test or one or more test depending upon the object and significance of research study.
10.Generalization and interpretations:-
When Hypothesis is tested and up held several times then it is possible for researcher to build a theory . This is known as Generalization.
If there is no hypothesis then researcher might explain his findings on the basis of some theory . This process is known as interpretation.
11.Preparation of research report:-
The last step in research process is to prepare report of what has been done or achieved by him .It is not an easy task and proper care should be kept while preparing it.
It may stood as follows .
1.Preliminary pages-
Title page
Acknowledgment
Preface
Table of contents
List of tables and charts etc.
2.Main text
Introduction
Main report
Summary of findings
Conclusion
Suggestions
3.The End matter.
Appendics
Bibliography etc.

555 Timer.

The 555 IC  is available as an 8-pin metal can, an 8-pin mini DIP(dual-in-package) or a 14-pin DIP, This IC consists of 23 transistors , 2 diodes and 16 resistors. The explanation of terminals coming out of the timer IC is as follows. The pin number is used in the following discussion refer to the 8-pin DIP and 8-pin metal can packages.

Pin1: grounded Terminal-

All the voltages are measured w.r.t this terminal.

Pin2: Trigger Terminal-

This pin is an inverting input to a comparator that is responsible for transition of flip-flop from set or reset. The output of the timer depends on the amplitude of the external trigger pulse applied to this pin.

Pin3: Output Terminal-

Output of the timer is available at this pin. There are two ways in which a load can be connected to the output terminal either between pin3 and ground pin or between pin3 and supply pin .The load connects between pin3 and supply in is called the normally  on load and that connected between pin 3 and ground pin is called the normally off load.

Pin4: Reset Terminal-

To disable or reset the timer a negative pulse is applied to this pin due to which it is referred to as reset terminal. When this pin is not to be used for reset purpose. It should be connected to +vcc to avoid any possibility of false triggering.

Pin5: Control Voltage Terminal-

The function of this terminal is to control the threshold and trigger levels. Thus either the external voltage or a pot connected to this pin determines the pulse width of the output waveform. The external voltage applied to this pin can be used to modulate the output waveform. When this pin is not in used , it should be connected to ground through a 0.01uf to avoid any noise problem.

Pin6: Threshold Terminal-

This is the non-inverting input terminal of comparator 1, which compares the voltage applied to this terminal with s reference voltage of +2/3 vcc . The amplitude of voltage applied to this terminal is responsible for the state of flip-flop.

Pin7: Discharge Terminal-

This pin is connected internally to the collector of transistor and mostly a capacitor is connected between this terminal and ground. It is called discharge terminal because when transistor saturates ,capacitor discharges through the transistor. When transistor is cutoff, the capacitor charges at a rate determined by external resistor and capacitor.

Pin8: Supply Terminal-

 A supply voltage of +5v to   +18v is applied to this terminal with respect to ground .

The timer combines a relaxation oscillator, two comparators, an R-S flip-flop and a discharge capacitor.R-S flip -flop A pair  of cross-coupled transistors each collector drives the opposite base through resistance.On the other hand if transistor Q1 is cut off, its collector voltage , which is approximately equal to _vcc . drives the transistor Q2 into saturation. The low collector voltage of this transistor then keeps the transistor Q1 in cutoff.

Depending on which transistor is saturated, the Q output is either low or high. By adding more components to the circuit , an R-S flip-flop is obtained , R-S flip-flop is a circuit that can set the Q output to high or reset it low. The circuit latches in either two states. A high S input sets Q to high a high R input  resets Q To low. Output Q remain in given state until it is triggered into the opposite state.