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UNIT -5: Communication Systems

Introduction to Communication Systems

Every day, in our work and in our leisure time, we come in contact with and use a variety of modern

communication systems and communication media, the most common being the telephone, radio, television, and

the Internet. Through these media we are able to communicate (nearly) instantaneously with people on different

continents, transact our daily business, and receive information about various developments and events of note

that occur all around the world. Electronic mail and facsimile transmission have made it possible to rapidly

communicate written messages across great distances.

Can you imagine a world without telephones, radio, and TV? Yet, when you think about it, most of these modern-

day communication systems were invented and developed during the past century. Here, we present a brief

historical review of major developments within the last two hundred years that have had a major role in the

development of modern communication systems.

2. Types of Communication

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Verbal Communication:

1. Oral Communication: Oral communication is information spoken by mouth; the use of speech. Some of the

examples of Oral Communication are: Face to face communication,Telephonic Communication, Public Address

System (Speech), Informal rumor mill (Grape Wine), Audio & Visual Media(Radio, TV), Lectures, Conference-

Interchange of views, Meetings, Cultural Affairs.

2. Written Communication: Communication by means of written symbols (either printed or handwritten). Some

of the examples are: Orders, Instructions, Letters, Memos, Reports, Policy manuals, Information Bulletin,

Complaint System, Suggestion System, etc

Nonverbal Communication:

1. Body Language includes facial expression, eye contact, postures, gestures, touch.

2. Para Language is the way we say something rather than what we say, is another nonverbal code.

3. Space and Time Space Language includes surroundings (Design & Language). It communicates social status also.

4. Sign Language: A sign language is a language which, instead of conveyed sound patterns, uses visually

transmitted sign patterns.

3. IEEE Spectrum for Communication Systems:

4.MODULATION: Radio signals can be used to carry information. The information,

which may be audio, data or other forms, is used to modify (modulate) a single frequency known

as the carrier. The information superimposed onto the carrier forms a radio signal which istransmitted to the receiver. Then “THE PROCESS OF SUPERIMPOSITION A LOW

FREQUNCY SIGNAL ON ONE OF THE VARIBLES OF A HIGH FREQUNCY WAVE

(CARRIER)”.

There are many different varieties of modulation but they all fall into three basic categories, namely amplitude

modulation, frequency modulation and phase modulation.

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(1)Amplitude modulation: Amplitude modulation (AM) is a technique used in electronic communication,

most commonly for transmitting information via a radio carrier wave. Amplitude Modulation occurs when a

voice signal's varying voltage is applied to a carrier frequency. The carrier frequency's amplitude changes in

accordance with the modulated voice signal, while the carrier's frequency does not change.

When combined the resultant AM signal consists of the carrier frequency, plus UPPER and LOWER sidebands. This

is known as Double Sideband - Amplitude Modulation (DSB-AM), or more commonly referred to as plain AM.

Another type of analog modulation is known as Vestigial Sideband. Vestigial Sideband modulation is a lot like

Single Sideband, except that the carrier frequency is preserved and one of the sidebands is eliminated through

filtering. Analog bandwidth requirements are a little more than Single Sideband however.

Vestigial Sideband transmission is usually found in television broadcasting. Such broadcast channels require 6 MHz

of ANALOG bandwidth, in which an Amplitude Modulated PICTURE carrier is transmitted along with a Frequency

Modulated SOUND carrier.

(2)Frequency Modulation (FM)

Frequency Modulation occurs when a carrier's CENTER frequency is changed based upon the input

signal's amplitude. Unlike Amplitude Modulation, the carrier signal's amplitude is UNCHANGED. This

makes FM modulation more immune to noise than AM and improves the overall signal-to-noise ratio of the communications system. Power output is also constant, differing from the varying AM power

output.

The amount of analog bandwidth necessary to transmit a FM signal is greater than the amount

necessary for AM, a limiting constraint for some systems.

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Q.1What is the difference between Amplitude modulation and frequency modulation?

ANS1.

1. In case of frequency modulation the change in amplitude may be due to noise. If we make use of amplitude

limiters in FM receivers then we can completely vanish this noise effect.

2. FM waves are waves having constant amplitude. These are independent of the modulation. So, due to this the

power transmission of these waves is also constant. The power transmission of FM waves is better than that of the

AM signals.

3. In FM signals, all the transmitted power can be used, but in AM wave the transmission carriers contain most of

the power. So, complete use of power is not possible.

4. In FM wave’s noise can be controlled by increasing the deviation up to some amount. This is impossible in case

of AM waves.

5. VHF and UHF are the bands of FM broadcasting. In these bands noise effect is very less. But on the other hand

bands of AM broadcasting such as MF and HF has higher effects.

6. Co-channel interference can be reduced by using some space wave in FM broadcasting.

The major disadvantages of FM are:

1. Complex apparatus is used to transmit and receive the FM wave.

2. FM waves needs 10 times larger channel width than that of the AM waves.

3. The reception area of FM waves is less than that of AM waves. Due to this wide area communication using the

Fm waves is not possible.;

Instrumentation & Control

(1)Introduction to Transducers: Transducers play an important role in the field of

instrumentation and control engineering. Any energy in a process should be converted from one form into

another form to make the communication from one rectification sector to another. Transducer is a device which converts one form of energy into another form i.e,. the given non-electrical

energy is converted into an electrical energy.

Types of transducers :There are two types of transducers, they are:

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(1)Active transducers:

Active transducer is a device which converts the given non-electrical energy into electrical energy by itself.

Thermocouple, Photovoltaic cell and more are the best examples of the transducers

(2)Passive transducers:

Passive transducer is a device which converts the given non-electrical energy into electrical energy by external

force. Resistance strain gauge, Differential Transformer are the examples for the Passive transducers.

(2) Thermocouple: A thermocouple is a device consisting of two different conductors

(usually metal alloys) that produce a voltage, proportional to a temperature difference, between

either ends of the two conductors. Thermocouples are a widely used type of temperature sensor

for measurement and control

[1] and can also be used to convert a temperature gradient into electricity. They are inexpensive,

[2] interchangeable, are supplied with standard connectors, and can measure a wide range of

temperatures. In contrast to most other methods of temperature measurement, thermocouples are

self powered and require no external form of excitation. The main limitation with thermocouples

is accuracy, specifically, system errors of less than one degree Celsius (C) can be difficult to

achieve

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A thermocouple measuring circuit with a heat source, cold junction and a measuring instrument.

(2)RTD - RTDs - Resistance Temperature DetectorsWhat is a Resistance Temperature Detector? Resistance Temperature Detectors (RTD), as the name implies, are

sensors used to measure temperature by correlating the resistance of the RTD element with temperature. Most

RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core. The element is

usually quite fragile, so it is often placed inside a sheathed probe to protect it. The RTD element is made from a

pure material whose resistance at various temperatures has been documented. The material has a predictable

change in resistance as the temperature changes; it is this predictable change that is used to determine

temperature.

Common Resistance Materials for RTDs:

Platinum (most popular and accurate)

Nickel

Copper

Balco (rare)

Tungsten (rare)

RTD Styles and Types:

(a)RTD Elements

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The RTD element is the simplest form of RTD sensor. It consists of a piece of wire wrapped around a ceramic or

glass core. Because of their compact size, RTD elements are commonly used when space is very limited

(b) RTD Surface Elements

A surface element is a special type of RTD sensor. It is designed to be as thin as possible thus providing good

contact for temperature measurement of flat surfaces.

(c ) RTD Probes:

The RTD probe is the most rugged form of RTD sensors. A probe consists of an RTD element mounted inside a

metal tube, also known as a sheath. The sheath protects the element from the environment. OMEGA offers a

wide variety of probes in various configurations

(3 ) Strain gauge: A strain gauge (also strain gage) is a device used to measure the strain

of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of

strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The

gauge is attached to the object by a suitable adhesive, such as cyanoacrylate.

The strain gauge has been in use for many years and is the fundamentalsensing element for manytypes of sensors, including pressure sensors,load cells, torque sensors, position sensors, etcThe

majority of strain gauges are foil types, available in a wide choiceof shapes and sizes to suit a variety

of applications. They consist of apattern of resistive foil which is mounted on a backing material.

Theyoperate on the principle that as the foil is subjected to stress, the resistance of the foil changes

in a defined way.

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( Typical foil strain gauge. The gauge is far more sensitive to strain in the vertical direction than in the horizontal

direction. The markings outside the active area help to align the gauge during installation.)

(1)The strain gauge is connected into a Wheatstone Bridge circuit with a combination of four active gauges (full

bridge), two gauges (half bridge), or, less commonly, a single gauge (quarter bridge). In the half and quarter

circuits, the bridge is completed with precision resistors.

(1) Gage facter:

LOAD CELL:The basic definition of a load cell will come in the form of a transducer. This is a

device that is used to convert a specific force into a signal that is electrical.

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FIG(1) :How Do Load Cells Work

If you are not specifically working with load cell devices, this information may not be very important. However, for

those that work with a force on a consistent basis, this information will be quite beneficial. By converting force into

a measurable amount of deformation or strain, this will provide an individual with the ability to measure

consistencies or inconsistencies in a conversion. Not only can that force be measured, it can also be used in

separate phases.

Q.1:How Do Load Cells Work?

Ans.1:It’s important to realize that a load cell can consist of more than one strain gauge. Sometimes they will

consist of one, two, or even four different strain gauges depending on the type of cell that has been created. The

strain gauge is the actual item that is used to measure deformation or resistance of the electrical wire receiving the

current. Now, it’ll be important to understand that there are different types of cells. They use fiber optics,

pneumatic, washer, button, and hydraulics instead of strain gauges. Depending on the type of cell that has been

created will determine the type of output that particular cell will provide.

Bimetal:Bimetallic strip is made by bonding strip of two metal with different of thermal thermal coefisien

together.When the strip is heated, it tends to bend to the side that has a smaller coefisient of thermal

expantion.When it is cooled, it tend to bend to the biger coefisient of thermal expantion.

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5. Integrated circuit:

An integrated circuit or monolithic integrated circuit (also referred to as IC, chip, or microchip) is an electronic

circuit manufactured by lithography, or the patterned diffusion of trace elements into the surface of a thin

substrate of semiconductor material. Additional materials are deposited and patterned to form interconnections

between semiconductor devices.

Fig. 5.8: Integrated circuits

These are have been two types:

1. Analog integrated circuits

2. Digital integrated circuits

Generations: vlsi, SSI, MSI and LSI

(1)vlsi: Main article: Very-large-scale integration

Upper interconnect layers on an Intel 80486DX2 microprocessor die

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The final step in the development process, starting in the 1980s and continuing through the present, was "very

large-scale integration" (VLSI). The development started with hundreds of thousands of transistors in the early

1980s, and continues beyond several billion transistors as of 2009.

FIG:5.9 Upper interconnect layers on an Intel 80486DX2 microprocessor die

In 1986 the first one megabit RAM chips were introduced, which contained more than one million transistors.

Microprocessor chips passed the million transistor mark in 1989 and the billion transistor mark in 2005.[15] The

trend continues largely unabated, with chips introduced in 2007 containing tens of billions of memory transistors.

BY: SHUBHAM KHANDELWAL

(FARRE.IN)

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