DHANALAKSHMI COLLEGE OF ENGINEERING, CHENNAI

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

EC6651 COMMUNICATION ENGINEERING

UNIT- I: MODULATION SYSTEMS

PART- A (2 Marks)

1. Define – Amplitude Modulation Amplitude Modulation defined as the process of changing the amplitude of a high frequency carrier signal in proportion with the instantaneous value of the modulating signal.

2. Define – Modulation Index and percent modulation for an AM wave(N-12) Modulation index is defined as an amount of amplitude change present in an AM waveform .It is also called as coefficient of modulation. Mathematically modulation index is

where m = Modulation index

Em = Peak change in the amplitude of the output waveform voltage

Ec = Peak amplitude of the un modulated carrier voltage Percent modulation gives the percentage change in the amplitude of the output wave when the carrier is

acted on by a modulating signal.

3. Define – Low level Modulation Low level modulation is defined as the modulation that takes place prior to the output element of the final stage of the transmitter. For low level AM modulator class Aamplifier is used.

4. Define – High level Modulation High level modulation is defined as the modulation that takes place in the final element of the final stage

where the carrier signal is at its maximum amplitude. For high level modulator class C amplifier is used.

5. What is the advantage of low level modulation? The advantage of low level modulation is

i. Less modulating signal power is required to achieve a high percentage of modulation.

6. Distinguish between low level and high level modulation.

Sl.No. Low level modulation High level modulation

1. In low level modulation, modulation takes place prior to the output element of the final stage of the transmitter.

In high level modulation, the modulation takes place in the final element of the final stage where the carrier signal is at its maximum amplitude.

2. It requires less power and high percentage of modulation.

It requires high power and less percentage of modulation.

7. Define – Image Frequency

Image frequency is defined as any frequency other than the selected radio frequency carrier that, if allowed to enter a receiver and mix with the local oscillator, will produce a cross product frequency that is equal to the intermediate frequency.

8. Define – Local Oscillator Tracking Local oscillator tracking is defined as the ability of the local oscillator in a receiver to oscillate either above or below the selected radio frequency carrier by an amount equal to the intermediate frequency throughout the entire radio frequency band. .

9. Define – High Side Injection Tracking High side injection tracking is defined as the local oscillator should track above the incoming RF carrier

by a fixed frequency equal to

10. Define – Low Side Injection Tracking Low side injection tracking is defined as the local oscillator should track below the RF carrier by a

fixed frequency equal to .

11. Define – Tracking Error Tracking error is defined as the difference between the actual local oscillator frequency and the

desired frequency. It is reduced by a technique called three point tracking.

12. Define – Image Frequency Rejection Ratio Image frequency rejection ratio is defined as the measure of the ability of pre selector to reject the image frequency. Mathematically, IFRR is

Where,

13. Define – Heterodyning Heterodyning is defined as the process of mixing two frequencies together in a non-linear device or to translate one frequency to another using nonlinear mixing.

14. What are the disadvantages of conventional (or) Double Side Band Full Carrier system?

The disadvantages of DSBFC system are

i. Carrier power constitutes two thirds or more of the total transmitted power. This is a major drawback because the carrier contains no information. The sidebands contain the information.

ii. Conventional AM systems utilize twice as much bandwidth as needed with single sideband systems.

15. Define – Single Sideband Suppressed Carrier AM. Single sideband suppressed carrier is defined as a form of amplitude modulation in which the carrier is totally suppressed and one of the sidebands removed.

16. Define – AM Vestigial Side Band AM vestigial sideband is defined as a form of amplitude modulation in which the carrier and one complete sideband are transmitted and a portion of the second sideband is transmitted.

17. What are the advantages of single side band transmission? The advantages of SSBSC are

i. Power conservation: In SSB only one sideband is transmitted and the carrier is suppressed. So less power is required to produce essentially the same quality signal.

ii. Bandwidth conservation: Single Side Band transmission requires half as much bandwidth as conventional AM double side band transmission.

iii. Noise reduction: The thermal noise power is reduced to half that of a double side band system.

18. What are the disadvantages of single side band transmission? (N-10) The disadvantages of single side band transmission are:

i. Complex receivers: Single side band systems require more complex and expensive receivers than conventional AM transmission.

ii. Tuning Difficulties: Single side band receivers require more complex and precise tuning than conventional AM receivers.

19. Define – Direct Frequency Modulation Direct frequency modulation is defined as the frequency of constant amplitude carrier signal which is directly proportional to the amplitude of the modulating signal at a rate equal to the frequency of the modulating signal.

20. Define – Indirect Frequency Modulation Indirect frequency modulation is defined as the phase of a constant amplitude carrier directly proportional to the amplitude of the modulating signal at a rate equal to the frequency of the modulating signal.

PART- B (16 Marks)

1. Derive an expression for AM wave and its power relationship. (A-12)

2. Explain a method of generating amplitude modulated signal. Sketch the waveforms of message,

carrier and modulated signals in time domain. (A-11)

3. Derive the power relationship of amplitude modulated signal. (A -11)

4. A carrier wave of 10 MHz is amplitude modulated to a level of 50%, with a tone of 5000 Hz. Sketch

the waveform in time and frequency domain for amplitude distribution. Assume carrier amplitude as

10 V. (N-10)

5. Explain the working of square law detector with a suitable sketch. (N-10)

6. Explain any two methods of generation of DSB-SC AM.

7. What is SSB-SC AM? Explain the generation of SSB-SC wave using phase shift method. Sketch

the transmission bandwidth, frequency, spectrum, phasor diagram. Derive an expression for the

power relationship.

8. What are the advantages of SSB modulation technique? Explain any two methods for generating

SSB-SC. (A-12)

9. Draw the block diagram for generation and demodulation of a VSB signal and explain its operation.

(N-10)

10. Explain the detection of AM signal using envelope detector. (N-09)

11. Explain the operation of a super heterodyne receiver. (N-09)

12. Explain in detail, AM transmitters and TRF receivers.

13. Explain the relationship between FM and PM. (A -11)

14. Compare AM with FM with respect to spectrum, power requirements, sidebands and bandwidth.

(A-08)

15. Derive an expression for narrow band FM wave and draw the necessary waveforms. (A-12)

16. Derive an expression to prove that when a modulating signal with only one frequency component

modulates a carrier frequency, the resulting FM signal has got infinite sideband frequencies.

17. Explain in detail, Armstrong method of FM generation. (A-12)

18. Explain the generation of frequency modulated signal using reactance modulation scheme with

neat diagram. (A-11)

19. Explain the principle of indirect method of frequency modulation with neat diagram. (N-10)

UNIT- 2: DIGITAL COMMUNICATION

PART-A: (2 Marks)

1. What are the advantages of digital transmission? The advantages of digital transmission are:

i. Digital signals are better suited to processing and multiplexing than analog signals. ii. Digital transmission systems are more noise resistant than the analog transmission

systems. iii. Digital systems are better suited to evaluate error performance.

2. What are the disadvantages of digital transmission? The disadvantages of digital transmission are:

i. The transmission of digitally encoded analog signals requires more bandwidth.

ii. It requires additional encoding and decoding circuitry.

3. Define – Pulse code modulation Pulse code modulation is defined as the process in which the analog signal is sampled and converted to fixed length serial binary number. The binary number varies according to the amplitude of the analog signal.

4. What is the purpose of sample and hold circuit? The purpose of sample and hold circuit is to periodically sample the analog input signal and converts those samples to a multilevel PAM (Pulse Amplitude Modulation) signal.

5. State Nyquist sampling rate. Nyquist sampling rate states that, the minimum sampling rate is equal to twice the highest audio input frequency.

6. State the causes of fold over distortion. Fold over distortion states that the minimum sampling rate (fs) is equal to twice the highest audio input frequency (fa).If fsis less than two times fa, distortion will result. The side frequencies from one harmonic fold over the sideband of another harmonic. The frequency that folds over is an alias of the input signal hence, the name “aliasing” or “fold over distortion”.

7. Define – Overload distortion Overload distortion is defined as the magnitude of sample which exceeds the highest quantization interval.

8. Define – Quantization Quantization is defined as the process of changing the actual values to the standard values.

9. Define –Dynamic range Dynamic range is defined as the ratio of the largest possible magnitude to the smallest possible magnitude. Mathematically, dynamic range is

10. Define – Coding efficiency Coding efficiency is defined as the ratio of the minimum number of bits required to achieve a certain dynamic range to the actual number of PCM bits used. Mathematically,

11. Define – Companding Companding is defined as the process in which the higher amplitude analog signals are compressed prior to transmission, and then expanded at the receiver.

12. Define – Slope Overload Slope overload is defined as the value of analog signal which is greater than the delta modulated value.Slope overload is reduced by increasing the clock frequency and by increasing the magnitude of the minimum step size.

13. Define – Granular Noise Granular noise is defined as the original input signal has relatively constant amplitude, the reconstructed signal has variations that were not present in the original signal. Granular noise can be reduced by decreasing the step size.

14. What is adaptive delta modulation? (A-12) Adaptive delta modulation is similar to delta Modulation (DM) with the ability to adjust the slope of the tracking signal. In feedback adaptation, the adaptation is made based on the history of the quantizer’s output.

15. Define – Peak Frequency Deviation for FSK Peak frequency deviation (f) is defined as the difference between the carrier rest frequency and either the mark or space frequency.

16. Define - Modulation Index for FSK The modulation index in FSK is defined as

where, h = FM modulation index called the h factor in FSK. = fundamental frequency of the binary modulating signal. f = Peak frequency deviation.

17. Define – Bit Rate

Bit rate is defined as the number of bits that are conveyed or processed per unit of time.

18. Define – Baud Rate Baud rate is defined as the number of bits transmitted per second.

19. Define – QAM Quadrature Amplitude Modulation is defined as a form of digital modulation where digital information is contained in both the amplitude and phase of the transmitted carrier.

20. Write the relationship between the minimum bandwidth required for an FSK system and the bit rate. The relationship between the minimum bandwidth required for an FSK system and the bit rate is given below

where, B = minimum bandwidth (Hertz)

f = minimum peak frequency deviation (Hertz) and = bit rate

PART- B (16 Marks)

1. Explain the generation of PPM and PWM signals. (A-12)

2. Explain in detail, the PAM modulation and demodulation process.

3. How are analog signals converted into digital signals in PCM? (N-09)

4. Compare PCM with DM. (A-12)

5. Explain in detail, the generation of Adaptive Delta Modulation. (A-12)

6. With neat sketch, explain the generation of delta modulated signal and derive the expression for

SNR. (A-11)

7. What are the drawbacks of DM? Explain any one method to it. (A-11)

8. Explain the functioning of each section in a PCM transmitter and receiver with a neat block diagram.

9. Explain the noise performance of delta modulation.

10. Explain quantization noise in PCM system. How is it reduced?

11. Explain the principle of DPCM, with a neat diagram. How does it differ from DM?

12. Explain in detail, the block diagram and waveforms for DM and ADM.

13. Explain the concept of DPSK and QPSK in data communication. (A-11)

14. Explain QPSK modulation scheme with its constellation diagrams? (A-11)

15. Explain in detail, the concept of QAM and draw the constellation diagram of 16 QAM. (A-11)

16. Explain the working principle of ASK modulator and detector with neat diagrams. (N-10)

17. Draw ASK, FSK, PSK signals to transmit the data stream 1111000111. (N-10)

18. Explain in detail, FSK and PSK modulation techniques. (N-09)

19. For the binary data transmission, derive the expressions and waveforms for ASK, FSK and PSK

schemes.

20. Explain the working of a FSK modulator and demodulator with the signal constellation diagram.

21. Draw the block diagram of BPSK transmitter and receiver and explain the modulation scheme with

appropriate constellation diagram.

UNIT-3: SOURCE CODES, LINE CODES AND ERROR CONTROL

PART-A (2 Marks)

1. Define – Shannon Entropy Shannon entropy, which quantifies the expected value of the information contained in a message. Entropy is typically measured in bits, or bans. Shannon entropy is the average unpredictability in a random variable, which is equivalent to its information content.

2. Define –Shannon Source Coding Theorem Shannon's source coding theorem (or noiseless coding theorem) establishes the limits to possible data compression, and the operational meaning of the Shannon entropy.

3. Define – Shannon Limit The Shannon limit or Shannon capacity of a communication channel is the theoretical maximum information transfer rate of the channel, for a particular noise level.

4. Define – Huffman Coding Huffman coding is an entropy encoding algorithm used for lossless data compression. The term refers to the use of a variable-length code table for encoding a source symbol (such as a character in a file) where the variable-length code table has been derived in a particular way based on the estimated probability of occurrence for each possible value of the source symbol.

5. What are the uses of Modified Huffman coding? Modified Huffman coding is used in fax machines to encode black on white images (bitmaps). It combines the variable length codes of Huffman coding with the coding of repetitive data in run-length encoding.

6. Define – Signal to Noise Ratio Signal to Noise Ratio is defined as the ratio of the strength of electrical or other signal carrying information to that of unwanted interference. It is expressed in decibels.

7. Define – NRZ

Non-return-to-zero (NRZ) line code is a binary code in which 1s are represented by one significant condition (usually a positive voltage) and 0s are represented by some other significant condition (usually a negative voltage), with no other neutral or rest condition.

8. Define – RZ

Return-to-zero (RZ) describes a line code used in telecommunication signals in which the signal drops (returns) to zero between each pulse. This takes place even if a number of consecutive 0's or 1's occur in the signal. The signal is self-clocking.

9. Define - Error Control Coding Error control coding is a developing method for coding to check the correctness of the bit stream transmitted. The bit stream representation of a symbol is called the codeword of that symbol.

10. Mention the types of error control.

The types of error control codes are 1) Linear Block Codes 2) Repetition Codes 3) Convolution Codes

11. Define – Linear Block Codes

A code is linear if two codes are added using modulo-2 arithmetic produces a third codeword in the code. Consider a (n, k) linear block code. Here 1) n represents the codeword length 2) k is the number of message bit 3) (n – k) bits are error control bits or parity check bits generated from message using an appropriate

rule.

12. Define –Repetition Codes

This is the simplest of linear block codes. Here, a single message bit is encoded into a block of n identical bits, producing an (n, 1) block code. This code allows variable amount of redundancy. It has only two codewords

i. all-zero codeword ii. all-one codeword.

13. Define – convolution Codes

A convolution code is a type of error-correcting code in which Each m-bit information symbol (each m-bit string) to be encoded is transformed into an n-bit symbol, where m/n is the code rate and the

transformation is a function of the last k information symbols, where k is the constraint length of the code.

14. Define – Block Codes Block codes comprise the large and important family of error-correcting codes that encode data in blocks. The Block Codes are conceptually useful because they allow coding theorists, mathematicians, and computer scientists to study the limitations of all block codes in a unified way. Such limitations often take the form of bounds that relate different parameters of the block code to each other, such as its rate and its ability to detect and correct errors.

15. Define – Modified AMI Codes Modified AMI codes are Alternate Mark Inversion (AMI) line codes in which bipolar violations may be deliberately inserted to maintain system synchronization. There are several types of modified AMI codes, used in various T-carrier and E-carrier systems.

16. Define – Shannon Fanon Coding In Shannon Fanon coding, the symbols are arranged in order from most probable to least probable, and then divided into two sets whose total probabilities are as close as possible to being equal. All symbols then have the first digits of their codes assigned symbols in the first set receive "0" and symbols in the second set receive "1".

PART- B(16 Marks)

1. Write the properties of entropy. (A- 11)

2. A source transmits two independent messages with probabilities of (p) and (1-p) respectively.

Prove that the entropy is maximum when both the messages are alike. Plot the variation of entropy

(H) as a function of probability (p) of the messages.

3. An analog signal is band limited to B Hz and sampled at Nyquist rate. The samples are quantized

into 4 levels. Each level represents one message. Thus there are 4 messages. The probabilities of

occurrence of these 4 levels (messages) are p1 = p4and p2 = p3. Calculate the information rate of

the source.

4. i) Prove that, if there are M numbers of equally likely messages, then entropy of the

source is log2M.

ii) Prove that the upper bound on entropy is the number of messages(M) emitted by the source.

5. Explain in detail, the procedure of Shannon-Fanon coding and Huffman coding schemes. (A-12)

6. Apply Shannon-Fanon coding scheme to a source which generates symbols x1, x2, x3, x4 with the

probabilities 1/8, 1/2, 1/4 and 1/8 respectively. Determine the coding efficiency. (A-12)

7. Code the symbols using Huffman coding for five symbols of the alphabet S = (S0, S1, S2, S3, S4) of

discrete memory less source. The probabilities areP(S) = (0.4, 0.2, 0.2, 0.1, 0.1). (A-11)

8. A discrete memory less source has five symbols x1, x2, x3, x4 and x5 with probabilities 0.4, 0.19,

0.16, 0.15 and 0.15 respectively.

i. Calculate the Shannon-Fanon code for the source and calculate code efficiency.

ii. Calculate the Huffman code for the source and compare the two techniques of

source coding.

9. Compare the coding schemes HDBP with MBNB in terms of bandwidth, SNR and transmission

efficiency. (A-12)

10. Explain Bandwidth-SNR trade off. (A -12)

11. Draw the polar, unipolar, bipolar and manchester NRZ line code format for the information

(101100). (A-11)

12. Explain error control codes with an example for each. (A -11)

13. Explain in detail, convolution codes.

14. Explain the coding and the decoding process of block codes.

UNIT – 4: MULTIPLE ACCESS TECHNIQUES

PART-A (2 Marks)

1. What is Multiplexing? Multiplexing is a process of combining several message signals for their simultaneous

transmission over the same channel.

2. Define – Spread Spectrum Modulation

In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal (e.g. an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth.

3. What are the different types of spread spectrum methods techniques?

The different types of spread-spectrum methods are BPSK / DSSS QPSK / DSSS, MSK / DSSS, coherent slow frequency-hop spread spectrum (FHSS), non-coherent slow-frequency-hop spread spectrum, non-coherent fast frequency-hop spread spectrum, and hybrid DSSS/FHSS.

4. List the applications of spread spectrum.

Spread spectrum and CDMA are cutting-edge technologies widely used in operational radar, navigation and telecommunication systems and play a pivotal role in the development of the forthcoming generations of systems and networks.

5. What are the advantages of SDMA? (A-12)

SDMA Space Division Multiple Access is a channel access method used in radio telecommunication systems such as mobile cellular networks. SDMA is based on the creation of parallel data streams travelling from multiple antennas (also known as spatial (multiplexing).

6. Mention the applications of multiple access techniques used in wired communication. Time division multiple access (TDMA) is a channel access method for shared medium

networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own

time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity.

7. Mention the advantages of CDMA system. (N-10)

The advantages of CDMA system are:

i. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code)

ii. CDMA is used as the access method in manymobile phone standardssuch ascdmaOne,CDMA2000(the3Gevolution of CDMAOne), andWCDMA(the 3G standard used byGSMcarriers), which are often referred to as simplyCDMA

8. What is FDMA?

Frequency Division Multiple Access or FDMA is a channel access method used in multiple-access protocols as a channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, or channels. It is particularly common place in satellite communication. FDMA, like other Multiple Access systems,

coordinates access between multiple users.

9. Define – Time Division Multiplexing Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at

each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern.

10. Distinguish between TDMA and FDMA

TDMA :

Time division multiple access (TDMA) is a channel access method for shared medium (usually radio) networks. It allows several users to share the same frequency channel by dividing the signal into different time slots

FDMA: Frequency Division Multiple Access or FDMA is a channel access method used

in multiple-access protocols as a channelization protocol. FDMA gives users an individual allocation of one or several frequency bands, allowing them to utilize the allocated radio spectrum without interfering.

11. What are the advantages and the disadvantages of FDMA?

The advantages and the disadvantages of FDMA are :

FDMA or Frequency Division Multiple Access, allows users to access a single channel, through a shared frequency; this system is advantageous as it is run through a satellite and offers usersthe chanceto share a channel easily without time delays.

The disadvantage of FDMA is the expense of running the system, which requires costly, custom filters and other technical equipment.

12. What is CDMA?

Code division multiple access(CDMA) is achannel access methodused by variousradiocommunication technologies. CDMA is an example of multiple access, which is where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies.

13. What are the disadvantages of CDMA?

The disadvantages of CDMA are: 1. As the number of users increases, the overall quality of service decreases 2. Self-jamming 3. Near- Far problem arises

14. What is space division multiple access (SDMA)?

Space Division Multiple Access (SDMA) is a channel access method based on creating parallel spatial pipes next to higher capacity pipes through spatial multiplexing and diversity, by which it is able to offer superior performance in radio multiple access communication systems.

15. What are the differences between FDMA, TDMA and CDMA?

CDMA :

1. Same frequency is used by every user and simultaneous transmission occurs.

2. Every narrowband signal is multiplied by wideband spreading signal, usually known as codeword. Every user has a separate pseudo-codeword, i.e., orthogonal to others only the desired codeword is detected by the receivers and others appear as noise. It is mandatory for the receivers to know about the transmitter’s codeword.

FDMA :

1. Bandwidth of Channel is relatively narrow (30 KHz), known as narrowband system Little or no equalization is needed for spreading symbol time.

2. Framing or synchronization bits are not needed for continuous transmission.

TDMA :

1. All slots are assigned cyclically. 2. Overhead trade-offs are size of data payload and latency.

PART- B (16 Marks)

1. Explain the different spread spectrum techniques.

2. Explain in detail, TDMA and FDMA techniques, with a neat diagram. (A-12)

3. Explain in detail, CDMA and compare its performance with TDMA and FDMA.

(A-12)

4. Explain frequency division multiple access technique with a neat block diagram. Explain its application in communication. (A-11)

5. Explain the application of CDMA in wireless communication. (A-11)

6. Explain the various multiple access techniques used in wireless communication with their merits and demerits. (N-10)

UNIT- 5: SATELLITE, OPTICAL FIBER-POWERLINE, SCADA

PART - A (2 Marks)

1. Define - Geo Synchronous Satellite Geo synchronous or geo stationary satellites are those that orbit in a circular pattern with an

angular velocity equal to that of Earth. Geosynchronous satellites have an orbital time of approximately 24 hours, same as the earth thus geosynchronous satellites appear to be stationary as they remain in a fixed position in respect to a given point on earth.

2. State Snell’s law.

The angle of refraction can be larger smaller than the angle of incidence, depending on the refractive indexes of the two materials. Snell’s law stated mathematically is

N1 sinФ1 = N2 sinФ2

Where, N1- refractive index of material1 N2-refractive index of material2

Ф1- Angle of incidence Ф2 - Angle of refraction

3. Write about the uplink and downlink frequencies used in satellite communication system. (N-10)

`Transmissions from base station to mobile units are called forward links, whereas transmissions from mobile units to base station are called reverse links. Forward links are called uplinks.

4. Define Angle of Inclination

The angle of inclination is the angle between the earth equatorial plane and the orbital plane of a satellite measured counterclockwise at the point in the orbit where it crosses the equatorial plane traveling from south to north

5. What is geosynchronous satellite?

Geosynchronous satellite provides a ’Big picture’, view, enabling coverage of weather events. This is especially useful for monitoring severe local storms and tropical cyclones.

6. What is meant by Apogee and Perigee?

The distance of the satellite from the earth varies according to its position. Typically two points of greatest interest are the highest point above the earth – the Apogee and the lowest point –the Perigee

7. Define – Look Angle

The coordinates to which the earth station antennas must be pointed to communicate with the satellite is called look angles.

8. List any two advantages and disadvantages of geosynchronous satellite. The Advantages of Geosynchronous satellite are

i. Satellites have revolutionized global communications, television broadcasting and weather forecasting and have a number of defence applications.

The Disadvantages of Geosynchronous satellite are

i. High altitude. ii. Incomplete Geographical coverage.

9. Define –Numerical Aperture

The Numerical Aperture of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light

10. Expand EIRP.

In communication systems, Equivalent Isotropically Radiated Power (EIRP) is the amount of power that a theoretical isotropic antenna would emit to produce the peak power density observed in the direction of maximum gain.

11. State the advantages of fiber optic system. (N-10)

The advantages of fiber optic system are:

i. Less expensive ii. Less signal degradation

iii. Higher carrying capacity iv. Low power v. Light weight

12. Define – Critical Angle The Critical angle (minimum angle for total internal reflection) is determined by the

difference in index of reflection between the core and cladding materials.

13. Define- Single Mode Fibre A single mode optical fibber is an optical fibre designed to carry the light only directly down

the fibre.

14. What is SCADA? SCADA (Supervisory Control And Data Acquisition) is a system operating with coded

signals over communication channels to provide control of remote equipment.

15. What are the advantages of optical fiber communication?

The advantages of optical fiber communication are: i. Greater information capacity ii. Immunity to crosstalk iii. Immunity to static iv. Interference Environmental v. Immunity Safety vi. Security

16. Define – Critical angle for a Fibre

Critical angle is defined as the minimum angle of incidence at which a light ray may strike the interface of two media and result in an angle of refraction of 0°or greater.

17. Define – Single Mode and Multimode propagation Single mode propagation is defined as the only one path through which the light propagates down the cable. Multimode propagation is defined as the light propagates down the cable through one or more path.

18. Define – Modal Dispersion

Modal dispersion or pulse spreading is caused by the difference in the propagation times of light rays that take different paths down a fiber. Modal dispersion can occur only in multimode fibers. It can be reduced by using single mode step index fibers and graded index fibers.

19. Define – Angle of Elevation

Angle of elevation is the vertical angle formed between the direction of travel of an electromagnetic wave radiated from an earth station antenna pointing directly toward a satellite and the horizontal plane.

20. Define – Azimuth Angle

Azimuth is the horizontal angular distance from a reference direction, either the southern or northern most point of the horizon.

PART- B (16 Marks)

1. Explain satellite link with a neat sketch. (A-12)

2. Explain satellite link budget system. (A-12)

3. Write short notes on satellite subsystems. (N-10)

4. Derive the satellite system link equation.

5. Derive the expression for numerical aperture of an optical fiber.

6. Explain multiple access techniques in satellite communication.

6. Explain INSAT. (A-12)

7. Explain optical fiber communication link with a neat sketch. (A-11)

8. Compare optical fiber cable with RF cable. (A-11)

9. Compare single mode step index, multimode step index and multimode graded index optical fibers.

(A-11)

10. List out the advantages of using optical fibre as a medium of communication in a telephone

network.

11. Explain the losses associated with fibre optic communication systems.

12. Explain the primary characteristics of light detectors.

13. Explain the principle of operation of avalanche photodiode.

14. Write the merits and demerits of optical communication systems. What are the essential

components required for establishing an optical link? What are the various losses associated with

it?

15. Draw the ray propagation into an optical fiber cable. Derive an expression for the acceptance

angle.

16. Explain the principle of operation of power line carrier communication.