Circuit Switched Networks

A Circuit Switched N/w consists of a set of switches connected by physical links.

A connection b/w ‘2’ stations is dedicated path made of one (or) more links. Each connection uses only one dedicated channel on each link.

i.e, each link is divided into n channels either by using TDM (or) FDM.

This circuit consists of 4 switches I, II, III and IV and Multiplexers with n=’3′ channels and one link.

In some circuits Multiplexing can be implicitly included in the switch fabric it self. In this circuit the end systems are connected to a switch for simplicity consider ‘2’ end systems A and M, connected to the switches I and III.

when A needs to communicate with M . A needs to request to a connection to M, which must be accepted by all switches and by M it self- which is called setup phase.

a channel circuit is reserved on each link and the combination of circuits forms a dedicated path. After establishing path data transfer can take place. The next phase is tear down.

i.e, after all data have been transferred. Generally circuit-switching takes place at the physical layer.

Before Communication (starting), the stations must make reservation for the resources like channels, switch buffers switch i/o ports switch processing time and are dedicated during the entire duration of data transfer until the tear down phase.

Data transferred is not packatized that is data is send as a continuous flow b/w source and destination.

there is end-to-end addressing in setup phase.

The 3 phases involved are:-

Circuit switched N/w’s requires ‘3’  setup phases

  1. Connection-setup.
  2. Data transfer.
  3. Tear down.

Setup Phase:-

A dedicated circuit is established before the ‘2’ communicating parties talk to each other.

i.e, creating  a dedicated channels b/w switches. To communicate A with M . initially a requesting process as follows

A to I, I to IV and IV to III, III to M and an acknowledgement in the reverse order after the reception of ‘ack’ a connection is established.

Data Transfer Phase:-

In this phase data transfer occurs b/w the ‘2’ devices.

Tear down phase:-

To disconnect , a signal is sent to each switch to release the resources by any one of station.

Efficiency of Circuit Switched Network:-

These are less efficient in terms of allocated resources. Since all the resources are allocated during the entire duration of the connection  and these resources are un available to other connections.

Delay in this type of N/w’s is due to establishment of connection , data transfer and disconnecting the circuit.

Switching at the physical layer in the traditional telephone N/w uses the circuit switching approach.

Broadcast Routing(dynamic)

In some applications hosts need to send messages to many (or) all other hosts like weather reports, stock market updates (or) live radio programs.

 i.e, sending a packet to all destinations simultaneously is called Broadcasting.

 Different methods of Broadcasting:-

  • first method is to send a packet to all destinations. This is a method wasteful of Band width and source needs to know the complete list of all destinations.

so this is least desirable one.

  • flooding is another way to broadcast a packet, the problem with flooding is that it generates too many packets and also consumes too much of Band width.
  • Third way is to use multi destination routing

In this technique each packet contains a list of destinations (or) a bit map for those destinations.

when a packet arrives at a router,  the router checks all the output lines it requires. The router generates a new copy of the packet for each output line after sufficient number of hops each packet will carry only one destination.

i.e, multi destination routing is like separately addressed packets (to B,C,D,E & D) must follow the same route one of them pays full fare and rest are free.

  • The fourth type of method is to use sink tree (or) spanning tree.

A spanning tree is a subset of subnet that includes all the routers but contains no loops.

if each router knows which of it’s lines belong to spinning tree then it broadcasts packet to all the lines except the one it arrived on.

This is efficient method in terms of Band width usage but problem is to maintain the knowledge of all the nodes of spanning tree at a routes.

  • Last method is to use Reverse path forwarding to approximate behavior of spanning tree.

Consider a subnet and it’s sink tree for router I as root node and how reverse path algorithm works in figure (C) 

on the first hop I sends packets to F, H, J & N. on the second hop eight packets are generated among them 5 are given to preferred paths indicated as circles (A,D,G,O,M)

of the 6 packets generated in third hop only 3 are given to preferred paths (C,E & K) the others are duplicates.

in the fourth hop to B and L after this broadcasting terminates.

advantages of reverse path forwarding:-

  • it is easy to implement.
  • it does not require routers to known about spanning trees.
  • it does not require any special mechanism to stop the process (as like flooding).

The principle is: if a packet arrives on a line if it is preferred one to reach the source it gets forwarded.

if it arrives on a line that is not preferred one that packet is discarded as a duplicate.

ex:-

 

when a packet arrives at ‘L’ the preferred paths are N and P so it forwards the packets to both N and P and if a packet arrives at ‘K’, there the preferred path is M, and N is not preferred so it forwards the packet to M and discards to N.

This is reverse path forwarding.

 

aliasing effect in Sampling

Effect of under sampling (aliasing effect):-

When a Continuous Time  band-limited signal is sampled at, then the successive cycles of the spectrum of the sampled signal overlap with each other as shown below

Some aliasing is produced in the signal this is due to under-sampling.

aliasing is the phenomenon in which a high-frequency component in the frequency spectrum of the signal takes as a low-frequency component in the spectrum of the sampled signal.

Because of aliasing, it is not possible to reconstruct x(t) from g(t) by low pass filtering.

The spectral components are in the overlapping regions and hence the signal is distorted.

Since any information signal contains a large no. of frequencies so the decision of sampling frequency always becomes a problem.

A signal is first passed through LPF  before sampling.

i.e, it is band limited by this LPF which is known as a pre-alias filter.

To avoid aliasing

  1. Pre-alias filter must be used to limit the bandwidth of the signal to f_{m}  Hz.
  2. Sampling frequency must be  f_{s}>2f_{m}.

Pre-alias filter means before sampling is passed through an LPF to make a perfect band-limited signal.

 

FSK Generator /BFSK generator

we know that the input to the FSK Generator is a binary sequence 1010…etc.

FSK generator uses two product modulators upper-modulator and lower-modulator with carriers

 and

 .

A level shifter is there in which the output of the level shifter is

when the input is a binary ‘1’ and ‘0’ volts for the input ‘0’ level shifter.

i.e, 

The working of the FSK generator is as follows when the input binary sequence is ‘1’

on the upper modulator 1 has been shifted to a voltage  so that the output of product modulator 1 is

and on the lower modulator input ‘1’ is passed through an inverter and if the output of the inverter is ‘0’ then the output of the level shifter will not change it remains at ‘0’ volt itself.

then the product modulator 2 output is 

then the overall output

similarly, when the input sequence is a binary ‘0’ 

 

Frequency Shift Keying (FSK)/BFSK

In a Binary FSK system, symbols 1 and 0 are distinguished from each other by transmitting one of two sinusoidal waves that differ in frequency by a fixed amount.

(or)

The frequency of the carrier signal shifted to two frequencies  for symbols ‘1’ and ‘0’ transmission.

The equation for FSK signal is

\[ S_{FSK}(t)= \sqrt{\frac{2E_{b}}{T_{b}}} \ \ cos (2\pi f_{c_{i}}t),\ 0\leq t\leq T_{b} , \ i=1,2 \]

\[ S_{FSK}(t)= 0 elsewhere \]

i.e, 

where 

 is generally a high frequency.

 is a low frequency and vice-versa is also true.

 

 

 

 

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Types of digital Modulation techniques (or) systems:-

Digital Modulation techniques may be classified into coherent (or) Non-coherent techniques, depending on whether the receiver is equipped with a phase-recovery circuit (or) not.

Coherent digital modulation techniques (or) systems Non-coherent digital Modulation techniques (or) systems /Envelope detection.
1. In this scheme, the local carrier generated at the receiver is phase locked with the carrier at the transmitter.

i.e, phase lock exists between Transmitter and Receiver.

 1. There exists no such phase lock between Transmitter and Receiver.

 
2. This is also called  Synchronous detection. 2. This is known as Non-synchronous detection.
3. complexity increases in terms of designing of the receiver. 3. less complexity in terms of designing the receiver.

 
4. probability of error decreases.

Examples:- coherent ASK, PSK, and FSK systems.

 4. error probability increases.

examples:-Non-coherent ASK, PSK, and FSK systems.

 

Base band Vs Pass band Transmission

Baseband data transmission Passband data Transmission
1. The digital data is transmitted over the channel directly, there is no carrier (or) any modulation. 1. The digital data modulates  high-frequency sinusoidal carrier. Hence it is also called as digital CW modulation .

∴carrier is required.

2. This is suitable for transmission over short distances.
Examples:- Ethernet signals operating over a LAN (Local Area Network)
The most common baseband modulation is (PAM) and PCM in local digital computer links. 		2. suitable for long distances transmission.
Examples:- Microwave links, Satellite Communication links are called  Passband communication systems.
3. Baseband transmission sends the information signal as it is without modulation.
i.e, without frequency shifting. 		3. passband transmission shifts the signal(information) to be transmitted in low frequency to a higher frequency.
i.e, Modulation is required.
4. baseband signals are in general low-frequency signals
i. human voice(20Hz-5KHz).
ii. video signal from a TV camera (0Hz-5.5MHz).
Examples:-
The telephone systems used for offices and homes (one room to other) transmits baseband signal as it is the system falls into baseband communication systems. 		4. whereas long-distance call that is transmitted via microwave (or) satellite links uses modulation which is known as passband communication systems.
examples :- Passband Modulation techniques ASK,DPSK,FSK,QPSK,PSK,M-ary PSK etc.
 
   
   

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Drawbacks in Delta Modulation (or) errors in Delta Modulation

Delta Modulation is subject to two types of quantization error

  1. slope Overload Distortion (SOD)/ Slope Overload error
  2. Granular Noise / Granular error.

During the process of digital equivalent integration of x(t) that is approximating x(t) with   there exists an error called Quantization error as shown by

if time instance is (n-1)th instance.

the Quantization error q[n] is of two types in Delta Modulation.

  1. Slope-Overload Distortion:- if the rate of rise of  input signal is so high

i.e, the slope of the signal is so high so that the stair case signal  can not approximate to x(t) .

i.e, as            is large enough

in this case the step size     becomes to small for the stair case approximation   to follow a steep segment of the input wave form x(t) with the result that   falls behind   which can be clearly visible in the figure.

the Qunatization error that exist between x(t) and   in this condition is called as slope overload distortion.

Generaaly DM is often referred as a linear Delta Modulator because the step size  is fixed during approximation process, and also its maximum (or) minimum slopes occur along straight lines.

To avoid slope Overload Distortion, step size must be increased.

Granular Noise (or) Idle Noise:-

In contrast to slope overload distortion Granular noise occurs when the step size  is too large relative to the local slope characteristic of the input wave form  x(t)

∴ This large value of   causes that the stair case approximation  to hunt around a flat segment of the input wave form as shown in the above figure

i.e,     oscillates between   when. x(t) is almost straight.

∴ The error between    and    in this condition is called as Granular noise (or) Idle noise.

To eliminate this error is to make the step size   small.

Granular noise occurs that for a very small variations in the input signal causes a very large variations in the approximated signal  .

Thus we see that there is a need to have a large step size  to accomodate a wide dynamic range of input signal.

and a small step size is required to accurate representation of relatively low-level signals.

i.e, large step size is required to reduce slope overload distortion and small step size is required to reduce Granular noise.

∴ It is clear that the choice of the optimum step size that minimizes the Mean Square value of the Quantization error in a Linear Delat Modulator will be the result of a compromise between Slope overload Distortion and Granular Noise.

To satisfy such a requirement , we need to make the Delta modulator “Adaptive” in the sense that the step size is made to vary in accordance with the input signal x(t).

This can be further discussed in the topic called as “Adaptive Delta Modulation ” scheme (ADM).

Block Diagram of Digital Communication system

Block Diagram of Digital Communication System/Elements of DCS:-
 
A General Communication System can be viewed as a Transmitting unit and a Receiving Unit connected by a medium(Channel). Obviously, Transmitter and Receiver consist of various sub-systems (or) blocks.
Our basic aim is to understand the various modules and sub-systems in the system. If we are trying to understand the design and various features of DCS, it is plus imperative that we have to understand how we should design a transmitter and we must understand how to design a very good quality Receiver. Therefore one must know the features of the channel to design a good Transmitter as well as a receiver that is the channel and its contribution will come repeatedly in digital Communications.
Source:- the primary block (or) the starting point of a DCS is an information source, it may be an analog/digital source, for example, if the signal considered is analog in nature, then
 

the signal generated by the source is some kind of electrical signal which is random in nature. if the signal is a speech signal (not an electrical signal) that has to be converted into an electrical signal by means of a Transducer, which can be considered as a part of the source itself.
Sampling & Quantization:- the secondary block involves the conversion of analog to discrete signal this involves the following steps
Sampling:- it is the process that involves in the conversion of Continuous Amplitude Continuous Time (CACT) signal into Continuous Amplitude Discrete Time (CADT) signal.
Quantization:- it is the process that involves in the conversion of Continuous Amplitude Discrete Time (CADT) signal into Discrete Amplitude Discrete Time (DADT) signal.
Source Encoder:- An important problem in Digital Communications is the efficient representation of data generated by a Discrete Source, this is accomplished by source encoder.
” The process of representation of incoming data from a Discrete source into a more suitable form required for Transmission is known as source encoding”
Note:-The blocks Sampler, Quantizer followed by an Encoder constructs ADC (Analog to Digital Converter).
∴ the output of Source encoder is a Digital Signal, the advantages of Source coding are

  • It reduces the Redundancy.
  • Minimizes the avaerage bit rate.

Channel encoder:- Channel coding is also known as error control coding. Channel coding is a technique that reduces the probability of error by reducing Signal to Noise Ratio at the expense of Transmission Band Width. The device that performs the channel coding is known as the Channel encoder.

Channel encoding increases the redundancy of incoming data, this also involves error detection and error correction along with the channel decoder at the receiver.

Spreading Techniques:- Spread Spectrum techniques are the methods by which a signal generated with a particular Band Width is deliberately spread in the frequency domain, resulting in a signal with a wider Bandwidth.

There are two types of spreading techniques available

1. Direct Sequence Spread Spectrum Techniques.

2. Frequency Hopping Spread Spectrum Techniques.

The output of a spreaded signal is very much larger than incoming sequence. Spreading increases the BW required for transmission, which is a disadvantage even though spreading is done for high security of data.

SS techniques are used in Military applications.

Modulator:- spreaded sequence is modulated by using digital modulation schemes like ASK, PSK, FSK etc depending up on the requirement, now the transmitting antenna transmits the modulated data into the channel.

Receiver:- Once you understood the process involved in transmitter Block. One should perform reverse operations in the receiver block.

i.e the input of the demodulator is demodulated after that de- spreaded and then the channel decoder removes the redundancy added by the channel encoder ,the output of channel decoder is then source decoded and is given to Destination.

Digital Communication systems Vs Analog Communication Systems

 
Introduction:-
Communication is the process of establishing a Connection (or) link between two points (which are separated by some distance) and transporting information between those two points. The electronic equipment used for communication purposes is called Communication equipment. The equipment when assembled together forms a communication system.
Examples of different types of communications

  • Line Telephony & Telegraphy.
  • Radio Broadcasting.
  • Point-to-Point Communication.
  • Mobile Communication.
  • TV Broadcasting.
  • Radar and Satellite Communications.

Why Digital?
A General Communication system has two devices and a medium (channel) connecting those two devices. This can be understood that a Transmitter and Receiver are separated by a medium called a Communication channel. To transport an information-bearing signal from one point to another point over a communication channel either Analog or digital modulation techniques are used.
Now Coming to the point, Why Digital communication is preferred over analog Communication?
Why are communication systems, military and commercial alike, going digital?

1. There are many reasons; the primary advantage is the ease with which digital signals compared with analog signals are generated. That is the generation of digital signals is much easier compared to analog signals.
2. Propagation of Digital pulse through a Transmission line:-
When an ideal binary digital pulse propagates along a Transmission line. The shape of the waveform is affected by two mechanisms
Distortion caused on the ideal pulse because all Transmission lines and Circuits have some Non-ideal frequency Transfer function.
Unwanted electrical noise (or) other interference further distorts the pulse waveform.
Both of these mechanisms cause the pulse shape to degrade as a function of line length. During the time that the transmitted pulse can still be reliably identified (i.e. before it is degraded to an ambiguous state). The pulse is amplified by a digital amplifier that recovers its original ideal shape. The pulse is thus “re-born” (or) regenerated.
Circuits that perform this function at regular intervals along the Transmission system are called “regenerative repeaters’. This

is one of the reasons why digital is preferred over
3. Digital Circuits Vs Analog Circuits:-
Digital Circuits are less subject to distortion and Interference than are analog circuits because binary digital circuits operate in one of two states FULLY ON (or) FULLY OFF to be meaningful, a disturbance must be large enough to change the circuit operating point from one state to another. Such two-state operation facilitates signal representation and thus prevents noise and other disturbances from accumulating in transmission.
However, analog signals are not two-state signals, they can take an infinite variety of shapes with analog circuits and even a small disturbance can render the reproduced waveform unacceptably distorted. Once the analog signal is distorted, the distortion cannot be removed by amplification because accumulated noise is irrecoverably bound to analog signals, they cannot be perfectly generated.
4. With digital techniques, extremely low error rates, and high signal fidelity is possible through error detection and correction but similar procedures are not available with analog techniques.
5. Digital circuits are more reliable and can be produced at a lower cost than analog circuits also; digital hardware lends itself to more flexible implementation than analog hardware.
Ex: – Microprocessors, Digital switching, and large-scale Integrated circuits.
6. The combining of Digital signals using Time Division Multiplexing (TDM) is simpler than the combining of analog signals using Frequency Division Multiplexing (FDM).
7. Digital techniques lend themselves naturally to signal processing functions that protect against interference and

jamming (or) that provide encryption and privacy and also much data communication is from computer to computer (or) from digital instruments (or) terminal to computer, such digital terminations are normally best served by Digital Communication links.

8. Digital systems tend to be very signal-processing intensive compared with analog systems.

Apart from pros there exists a con in Digital Communications that is non-graceful degradation when the SNR drops below a certain threshold, the quality of service can change suddenly from very good to very poor. In contrast, most analog Communication Systems degrade more gracefully.

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Analog Communications Quiz or Tutorials

UNIT 1-QUIZ1

  1. Find the modulation index if the amplitude of message signal is Two thirds of the amplitude of carrier signal ———————.
  2. The diagonal clipping in Amplitude Demodulation (using envelope detector) can be avoided if RC time-constant of the envelope detector satisfies the following condition, (here W is message bandwidth and ω is carrier frequency both in rad/sec) ( )
    a. RC<1/W             b. RC>1/W                  c. None of the above         d. RC>1/ω.
  3. Given AM signal is  XAM(t)= 10 (1+0.25 sin 2πfmt) cos 2πfct , then The average side band power given for the above AM signal is ( )
    a. 25W                    b. 12.5W               c.1.5625W                    d.3.125W.
  4. Given AM signal is XAM(t) = 100 (1+0.85 cos 2πfmt) ,then The total power required for the above AM signal is ( )
    a. 25W                   b. 12.5W               c.6.806KW                       d. None of the above.
  5. Consider the AM signal Ac cos Wct + 2 cos Wct cos Wmt   for the demodulation of the signal using envelope detector the minimum value of Ac should be ( ).
    a. 2                          b. 1                         c. 0.5                                    d. 0.
  6. Given AM signal is SAM(t) = 100 (1+0.3 cos 2πfmt +0.4 sin 2πfmt) cos 2πfct i. i.The total power required for the above AM signal is ( )
    a. 5.625W              b. 5.625KW             c.6.806KW                  d. None of the above.
    ii.Modulation index is ( )
    a. 0.53                     b. 0.5                         c. 0.2                               d. None of the above.
    iii.The carrier power is ( )
    a. 5KW                    b.6KW                       c. 7KW                           d.100KW.
    iv. Total current flowing through the transmitter if carrier current is 5A ( ).
    a. 5mA                      b.5.303A                 c. none of these          d. 25A.
  7. If the band width of message signal is 5KHz and the carrier frequency is 200KHz then upper sideband frequencies are( )
    a. 205KHz,190KHz                                                b.205KHz,-205KHz
    c. 205 KHz,-195 KHz                                           d. None of the above.
  8. If the highest frequency of message signal is 5KHz and the carrier frequency is 200KHz then lower sideband frequencies are( )
    a. 205KHz,190KHz                                                b.205KHz,-205KHz
    c. 195 KHz,-195 KHz                                            d. None of the above.
  9. If the bandwidth of message signal is 500Hz then the bandwidth of Amplitude Modulated signal is ( )
    a. 500Hz                    b. 1000Hz                    c.2KHz                     d. None of the above.
  10. If the message m(t)= 10cos⁡2000πt and carrier signal is                                      C(t) = 25 cos 200000 πt then draw the amplitude spectrum of AM signal————— .

UNIT 2- QUIZ 2

  1. Angle modulation is a technique in which the ————— of the is varied with respect to instantaneous values of ————————— by keeping as constant. 2M.
  2. Write the expression for Angle Modulated signal –. 1M.
  3. An Angle Modulated signal is given as 𝑥(𝑡) = 100 cos(2𝜋𝑓𝑐 𝑡 + 4 sin(1000𝜋𝑡)) where 𝑓𝑐 = 10 𝑀𝐻𝑧. 6M.
    i. The Peak frequency deviation is ( )
    a. 2K                           b. 4000                   c. 4π                      d. 8π.
    ii. The Peak- phase deviation is ( ).
    a. 4                              b. 6                           c. 0                        d. None of the above.
    iii. The power of the Modulated signal is ( ).
    a. 10KW.                   b. 5 W                       c. 5 KW                d. 50W.
  4. The amount of change in carrier frequency produced by modulating signal is known as ( ). 1M.
    a. phase deviation                                                            b. amplitude deviation
    c. Frequency deviation                                                  d. none of the above.
  5. The total Transmitted power in FM is equal to the power of ( ) 1M.
    a. An AM signal.                                                            b. an unmodulated carrier
    c. Message signal                                                         d. all of the above.
  6. A 20 MHz carrier is frequency modulated by a sinusoidal signal with frequency 1KHz such that peak frequency deviation is 100KHz what will be the modulation index ( ) 2M.
    a. 100                           b.101                                c. 99                         d.200.
  7. The bandwidth for above FM system will be ( ) 2M.
    a. 101 KHz                 b. 202 KHz                     c. 99 KHz              d. 100 KHz.
  8. Which one of the following is an indirect method of generating FM ( ) 1M.
    a. Armstrong method                                                   b. Varactor diode modulator
    c. Reactance BJT modulator.                                     d. Reactance FET Modulator.
  9. In which of the Modulation system when the modulating frequency is doubled the modulation index reduces to half while modulating voltage remains constant ( ) 2M.                                                                                                        a. Phase                   b. Amplitude                   c. Frequency       d. None of the above.
  10. In FM, the frequency deviation is ( ) 2M.                                                                         a. Proportional to modulating frequency.                                                                         b. Proportional to amplitude of modulating signal.                                                     c. Constant.                                                                                                                                   d. Zero.
  11. In indirect method of FM generation FM is obtained from ( ) 1M.                         a. AM                    b. PM                 c. DSB                              d. FM
  12. Write Carson’s rule –. 1M.
  13. The Bandwidth of NBFM is given as –. 1M.
  14. A 25 MHz carrier is modulated by a 400Hz audio sine wave. The carrier voltage is 4V and the maximum deviation is 10 KHz. The modulation index will be( ) 2M.                                                                                                                                  a. 2.5                  b. 5                     c. 15                        d. 25
  15. For the above problem write the expression of FM wave will be———————————————————————————————–.1M.
  16. For the problem in 14 write the expression of PM wave———————————————————————————————————.1M.
  17. Standard FM broadcast stations uses a maximum bandwidth of ( ) 1M.              a. 150 KHz                   b.75KHz.            c. 200KHz         d. 15KHz.
  18. Which type of oscillators are preferred for carrier generation because of their good frequency stability ( ) 1M.                                                                                 a. LR               b.LC                       c. Crystal                         d. RC.
  19. The oscillator whose frequency is varied by an input voltage is called as ————————————————. 1M.
  20. Maximum deviation results at what point on modulating signal if the system is FM( ) 1M.                                                                                                                      a. Zero crossing of m(t)                                                                                                              b. Peak negative amplitude and peak positive amplitude of m (t).                        c. None of the above.                                                                                                                d. Both a and b.

UNIT3-QUIZ3
(Radio receivers and Transmitters)

  1. Radio receivers are classified into how many types ( ). 2M.
    a. Three                   b. two                      c. four                             d. none of the above.
  2. The ability of a radio receiver to amplify weak signals is called as ( ). 2M.
    a. Fidelity             b. Selectivity            c. sensitivity                  d. all of the above.
  3. The phenomenon of Picking up of same short wave station at two nearby points on the receiver dial is known as ( ). 2M.
    a. Fidelity            b. sensitivity               c. Double spotting               d. selectivity.
  4. The ability of a receiver to reject unwanted signals is called ( ). 2M.
    a. Selectivity           b. Fidelity                  c. sensitivity                  d. Double spotting
  5. Standard broadcast AM receivers tuned in the frequency range of 540 KHz to 1640 KHz has an intermediate frequency of ( ). 2M.
    a. 455 KHz                 b.1MHz                      c. 20Hz                      d. 200Hz.
  6. Standard broadcast FM receivers tuned in the frequency range of 88MHz -108 MHz has an intermediate frequency of ( ). 2M.
    a. 455 KHz                    b.1MHz                   c. 20Hz                      d. 10.7MHz.
  7. Television receivers in the VHF band(54MHz-223MHz) and in the UHF band(470MHz-940MHz) use an IF between 26MHz and 46MHz with the two most popular values ( ). 3M.
    a. 36 MHz and 46 MHz                                                b. 455 KHz and 46 kHz.
    c. 36 KHz and 46 KHz.                                                 d. none of the above.
  8. In a broadcast FM receiver if the local oscillator is tuned to 98.7 MHz then the image frequency is ( ). 3M.
    a. 88MHz              b. 109.4MHz                   c. 96 MHz                d. none of the above.
  9. In a broadcast AM receiver if the signal is tuned to 530 KHz then Intermediate frequency, local oscillator frequency and image frequency are( ). 3M.
    a. 200 kHz, 730 KHz and 1000 kHz.
    b. 10.7MHz, 15.37MHz and 1000 KHz.
    c. 455 KHz, 985 KHz and 1440 KHz.
    d. None of the above.
  10. In communications, Audio frequency range is —————-. 2M.
  11. In communications, Radio frequency range is—————–. 2M.
  12. Draw the radio frequency spectrum with detailed values starting from Very Low Frequencies (VLF) to Extreme High Frequencies (EHF). 5M.
  13. Draw the block diagram of TRF receiver (only diagram). 5M.

UNIT5-Quiz5
Pulse Modulation Techniques

  1. In Pulse Position Modulation, the drawbacks are ( ) 2M.                 a.Synchronization is required between transmitter and receiver                       b. Large bandwidth is required as compared to PAM                                                 c. None of the above                                                                                                                 d. Both a and b.
  2. In PWM signal reception, the Schmitt trigger circuit is used ( ) 2M.                    a. To remove noise                                                                                                                    b. To produce ramp signal                                                                                                      c. For synchronization                                                                                                            d. None of the above.
  3. In pulse width modulation, ( ) 2M.                                                                                    a. Synchronization is not required between transmitter and receiver              b. Amplitude of the carrier pulse is varied                                                                      c. Instantaneous power at the transmitter is constant                                              d. None of the above.
  4. In different types of Pulse Width Modulation, ( ) 2M.                                                a. Leading edge of the pulse is kept constant                                                                b. Trailing edge of the pulse is kept constant                                                                c. Centre of the pulse is kept constant                                                                              d. All of the above.
  5. In Pulse time modulation (PTM), ( ) 2M.                                                                         a. Amplitude of the carrier is constant                                                                             b. Position or width of the carrier varies with modulating signal                           c. Pulse width modulation and pulse position modulation are the types of PTM                                                                                                                                                 d. All of the above.
  6. Drawback of using PAM method is ( ) 2M.                                                                      a. Bandwidth is very large as compared to modulating signal                                  b. Varying amplitude of carrier varies the peak power required for transmission                                                                                                                                  c. Due to varying amplitude of carrier, it is difficult to remove noise at receiver                                                                                                                                          d. All of the above.
  7. Pulse time modulation (PTM) includes ( ) 2M                                                              a. Pulse width modulation                                                                                                        b. Pulse position modulation                                                                                                  c. Pulse amplitude modulation                                                                                              d. Both a and b.
  8. Calculate the Nyquist rate for sampling when a continuous time signal is given by  x(t) = 5 cos 100πt +10 cos 200πt – 15 cos 300πt ( ) 3M.                            a. 300Hz                                                                                                                                            b. 600Hz                                                                                                                                            c. 150Hz                                                                                                                                          d. 200Hz.
  9. Calculate the minimum sampling rate to avoid aliasing when a continuous time signal is given by x(t) = 5 cos 400πt ( ) 3M.                                                              a. 100 Hz                                                                                                                                            b. 200 Hz                                                                                                                                          c. 400 Hz                                                                                                                                          d. 250 Hz.
  10. A distorted signal of frequency fm is recovered from a sampled signal if the sampling frequency fs is ( ) 2M.                                                                                          a. fs > 2fm                                                                                                                                        b. fs < 2fm                                                                                                                                      c. fs = 2fm                                                                                                                                        d. fs ≥ 2fm.
  11. The desired signal of maximum frequency wm centered at frequency w=0 may be recovered if ( ) 2M.                                                                                                    a. The sampled signal is passed through low pass filter                                              b. Filter has the cut off frequency wm                                                                              c. Both a and b                                                                                                                              d. None of the above.
  12. The frequency spectrum of x(t) is X(f) is given as follows 6M.

Draw the frequency spectrum of sampled signal by assuming suitable values for sampling frequency under the following conditions
i. Over sampling                      ii. Under sampling                         iii. fs = 2fm.

Analog Communication Lab viva questions

EXPERIMENT WISE VIVA QUESTIONS ANALOG COMMUNICATION LAB

Amplitude Modulation:

  1. What is meant by Modulation? What is the need for modulation?
  2. What are different types of analog modulation techniques?
  3. What are the other names of message signal? What are the other names of carrier signal?
  4. Write the equation of AM signal and explain each parameter in that equation?
  5. Define Amplitude Modulation? Define modulation depth or modulation index?
  6. What is the range of Audio frequency signals? What is the range of Radio frequency signal?
  7. What are the applications of Amplitude modulation?
  8. How many generation methods are there to generate an AM wave? What are the methods of demodulation of an AM wave?
  9. Explain the operation of diode detector circuit?
  10. Write the formula for modulation index? Differentiate under, over and perfect modulation in AM?
  11. As the amplitude of message signal increases, modulation index increases or decreases?
  12. Define single tone modulation? In laboratory type of AM is single tone modulation or not?
  13. Draw the frequency spectrum of AM wave?
  14. If modulation index is 100%, calculate the ratio of total power to carrier power of an AM wave?
  15. If µ=1 in an AM wave what is the amount of power saving in an AM wave? What is the band width of an AM wave?
  16. Explain the operation of AM modulator? Explain the operation of 8038 circuit in AM modulator?
  17. Explain the procedure of Amplitude modulation? What is the significance of Emax and Emin points in AM wave?
  18. Plot message, carrier and AM signals?
  19. What is meant by envelope detector?
  20. The frequency of AM wave follows — (message signal frequency or carrier frequency)?
  21. The amplitude of AM wave at fc +fm is— and The amplitude of AM wave at fc -fm is—–
  22. In amplitude modulation the amplitude of ——— is changing with respect to ——
  23. Envelope of AM signal follows————– (message signal/ carrier signal)?
  24. What are the advantages and disadvantages of AM?
  25. How demodulated signal differs from original signal in AM?
  26. The two important distortions that can appear in the demodulated output of an envelope detector are————– and—————————- –.
  27. Differentiate high-level and low-level modulations in AM?
  28. What is trapezoidal rule?

Balanced Modulator:

  1. What are the disadvantages of AM?
  2. Most of the power in AM spectrum is carried by ————
  3. Define DSBSC modulation?
  4. How DSBSC is more efficient than AM in terms power saving, explain?
  5. What is meant by frequency response?
  6. Draw the magnitude response or amplitude spectrum of DSBSC signal?
  7. The signal generated by balanced modulator is———–
  8. Draw the wave form of DSBSC wave and AM wave, and differentiate those two waveforms?
  9. Give the equation of DSBSC signal?
  10. What are the generation methods of DSBSC?
  11. What are the demodulation methods of DSBSC?
  12. What is the bandwidth of DSBSC signal?
  13. Define Costas loop and it’s operation?
  14. Amount of power saving in DSBSC signal is————
  15. Coherent detection means?
  16. Give the practical applications of balanced modulator?
  17. Explain the operation of product modulator?
  18. Why the circuit is called balanced modulator?
  19. If the circuit is operating in balanced state, the modulation index value is——- –.
  20. Explain the working procedure of 1496 IC for the generation of DSBSC wave?
  21. As message signal amplitude increases, carrier suppression in dB’s ———
  22. Plot message, carrier and DSBSC waves and explain each wave clearly.
  23. How do you differentiate modulation by demodulation?
  24. Explain the significance of local oscillator frequency in modulators and in
  25. Differentiate synchronous and non synchronous detection techniques in analog modulators?
  26. The phase shift at zero crossings in DSBSC wave is——- –.
  27. What is Quadrature carrier multiplexing?
  28. How DSBSC is different from SSB?

Frequency Modulation:

  1. Define Frequency modulation? How it is different from phase modulation?
  2. Write equation of FM wave, explain each parameter in it?
  3. Draw the amplitude spectrum of FM wave?
  4. Give the Carson’s rule in FM?
  5. Define modulation index β, frequency deviation?
  6. Differentiate Narrow band FM with Wide band FM?
  7. Explain the FM operation using 8308IC?
  8. Draw message, carrier and FM waves and explain each wave clearly?
  9. Explain the methods for generation of FM and its demodulation?
  10. How FM wave is different from PM wave?
  11. Give the practical applications of FM?
  12. State advantages and disadvantages of FM?
  13. The range of speech signals is——— –.
  14. Type of Modulation used in radios is——- –.
  15. Type of modulation used for voice signals in T.V — and for video signals in V is—- –.
  16. Noise immunity is more in which analog modulation technique———– –.
  17. FM is more robust to noise compared to AM, why?
  18. Carson’s rule is for———- –.
  19. In commercial FM broadcasting, the audio frequency range handled is only up to—- –.
  20. The transmission band width required for commercial FM broadcasting is——– –.
  21. Define Hilbert transform?
  22. Explain capture effect in FM broadcasting?

Pre-emphasis and De-emphasis:

  1. Define pre-emphasis and De-emphasis processes in
  2. Why Pre-emphasis is used at Transmitter of FM and de-emphasis at FM receiver?
  3. Draw the pre-emphasis circuit and explain its working in detail?
  4. Draw de-emphasis circuit and explain its working in detail?
  5. Draw the frequency response characteristics of pre-emphasis and de-emphasis explain each one in detail?
  6. Calculate the cut-off frequencies of pre-emphasis and de-emphasis circuits practically
  7. Pre-emphasis circuit operation is similar to——— –.
  8. De-emphasis circuit operation is similar to——— –.
  9. What is the necessity of boosting up high frequencies in frequency modulation communication system?
  10. Define 3dB frequencies?

Sampling and reconstruction:

  1. Define sampling theorem? What is the need for sampling?
  2. What are the necessary and sufficient condition for sampling and reconstruction of a signal?
  3. Define Nyquist rate and Nyquist interval in sampling theorem?
  4. If message frequency is 2 KHz and sampling frequency is 2 KHz,4 KHz, 8 KHz and 16 KHz in each case the number of samples are—————————– –.
  5. What are different types of sampling techniques?
  6. What was the effect on sampled signal if fs < 2 fm ?
  7. Draw the amplitude spectrum of sampled signal if fs < 2 fm, fs =2 fm, fs > 2 fm.
  8. What is aliasing effect in sampling? How to avoid it?
  9. Why do we use pre-filtering in sampling?
  10. What do you mean by reconstruction of sampling theorem?
  11. What are the types of filters used in reconstruction?
  12. Define sample and hold process?
  13. Differentiate second order, fourth order and sixth order low pass filters in reconstruction process.
  14. Explain the sampling and reconstruction process in detail by using the trainer
  15. Define band pass sampling?
  16. How sampling is different from PAM?
  17. Define a continuous time signal or an analog signal. Give some examples of analog signals.
  18. Define a discrete time signal. Give some examples of discrete
  19. What is the difference between discrete and a digital signal?
  20. Define a digital signal? Give some
  21. What is the need for converting a continuous signal into a discrete
  22. Explain about zero-order hold circuit.
  23. How to convert an analog signal into digital signals?

Digital signal processors operates———— as inputs.As the number of samples increases, the reconstruction of original signal becomes?

Pulse Amplitude Modulation:

  1. What is the basic principle of PAM?
  2. Name some Pulse Modulation techniques?
  3. Define PAM?
  4. How PAM is different from AM?
  5. Can we produce a PAM signal using a sampling circuit?
  6. Differentiate PAM output with sampling output?
  7. Does PAM come under Analog modulation technique or Digital Modulation technique?
  8. What is the Bandwidth of PAM?
  9. Compare BW of PAM and AM?
  10. Draw waveforms of PAM. explain each one briefly.
  11. What are the advantages of PAM over AM?
  12. What are the advantages and Disadvantages of PAM?
  13. Explain the working procedure PAM kit?
  14. Can we use PAM technique in TDM?
  15. Differentiate uni-polar and bi-polar PAM.
  16. What do you mean by zero order holding? And draw the circuit diagram of zero-order hold circuits?
  17. What are the drawbacks of PAM?
  18. Explain the working of PAM demodulation circuit?
  19. Define Flat-Top sampling?
  20. Draw the circuit diagram of Flat-Top Sampled circuit?
  21. What was the roll off characteristics of sinc pulse?

    Pulse Width Modulation (PWM):

    1. Define PWM?
    2. Differentiate PWM, PAM and PPM?
    3. Name the applications of Mono-stable multivibrator?
    4. What is a Multivibrator?
    5. Differentiate Monostable, Bi stable and Astable Multivibrators?
    6. How a Monostable Multivibrator produces a PWM signal?
    7. What are the other names of PWM?
    8. Define Pulse Duration Modulation?
    9. What is Pulse Time Modulation?
    10. Draw PAM and PWM signals and each one in detail.
    11. Draw PWM signal with respect to message signal?
    12. In PWM —————- of Pulse carrier signal is changing with respect to message signal.
    13. Explain the operation of PWM circuit.
    14. 555 timer in Monostable mode produces————.
    15. 555 timer in Astable mode produces——————.
    16. What are the advantages of PWM over PAM?
    17. What is the difference between PWM and FM?
    18. Which type of noise is affecting the amplitude of PWM signal?
    19. Which system is more immune to noise (PWM or PAM)?
    20. What are the disadvantages of PWM?
    21. What are the applications of PWM?
    22. Band Width of PWM is—————-.
    23. Band width of PAM is—————-.

      Pulse Position Modulation (PPM):

      1. Define PPM?
      2. The information is conveyed by ————- of Pulses in PPM.
      3. In PWM information is conveyed by————— of pulses.
      4. In PAM information is conveyed by————— of pulses.
      5. What are the advantages and disadvantages of PPM?
      6. Compare PPM with Phase Modulation.
      7. PAM is similar to————————–.
      8. PWM is similar to————————–.
      9. PPM is similar to————————–.
      10. Differentiate Analog Modulation Techniques with Pulse Modulation Techniques.
      11. What are the applications of PPM?
      12. Draw PPM signal with respect to message signal.
      13. Draw PPM signal with respect to PWM signal.
      14. Explain the operation of PPM Modulator?

        Phase Locked Loop (PLL):

        1. What are the applications of PLL?
        2. Why this circuit is called Phase Locked Loop?
        3. What are the three components of PLL circuitry?
        4. Explain the operation of PLL by using a Block Diagram?
        5. Define free-running frequency?
        6. Define Lock range and Capture range of a PLL?
        7. What is meant by Frequency synthesizer?
        8. Why PLL is used in FM Receivers/
        9. How PLL is used in FSK demodulation circuits?
        10. What do you mean by Lock state in a PLL?
        11. What is meant by Pull in time in PLL?
        12. Phase Detector or Phase Comparator is used for ——————.
        13. Why VCO is used in feedback loop of PLL?
        14. What are the input and Output signals of a VCO in a PLL?
        15. What are the advantages and Disadvantages of PLL?
        16. Why Lock range is greater than Capture range in a PLL?

          Time Division Multiplexing (TDM):

          1. Define the concept of Time Division Multiplexing?
          2. Differentiate Multiplexing and Sampling?
          3. What are the different types of Multiplexing Techniques?
          4. Does TDM come under analog Multiplexing or Digital Multiplexing?
          5. Define a frame in a TDM?
          6. Why synchronization is required in TDM?
          7. Why multiplexing is required?
          8. What do you mean by inter-leaving gaps in TDM frame?
          9. If two signals of frequencies 2KHz and 4 KHz are multiplexed in time –domain then draw TDM signal
            1. Without inter-leaving gap.
            2. with inter-leaving gap of 10 ms.
          10. What are the advantages and Disadvantages of TDM?
          11. Differentiate TDM with FDM?
          12. What are the advantages of TDM over FDM?
          13. Explain the operation of TDM using trainer kit used.
          14. Synchronous TDM means?

            Additional Questions:

            1. What is a filter?
            2. Differentiate Active and Passive Filters?
            3. Why LPF is used in Demodulation Circuits?
            4. Why pre-filtering is required in sampling?
            5. Anti-aliasing is achieved by using———– in Sampling Circuits?
            6. Define Single-tone modulation in AM and FM?
            7. Why FM receivers are more immune to AM receivers?
            8. BW of Narrow band FM is ——————.
            9. BW of AM is ———————————-.
            10. How to calculate Image frequency of a Radio Receiver?
            11. Define Power Spectral Density.
            12. Define AWGN noise.
            13. Define SNR.
            14. Where do we use Hilbert Transform?
            15. Over modulation in AM means….
            16. What is µ value when AM wave is similar to DSBSC wave?

Digital Communications Slip Test Questions

Slip test-1

  1. In a PCM system, if the Quantization levels are increased from 2 to 8,                 i. Find the change in Signal to Quantization Noise ratio.                                ii.Find the change in Transmission Bandwidth.
  2.  i. Convert the following signal x(t) = 10 cos (200πt) to a discrete signal x[n] if sampling rate is 1000Hz.                                                                                       ii. Write the advantages of Digital Communication system over Analog Communication system.

PART-B

  1. Draw the Basic Block Diagram of Digital Communication System and explain each block in detail.                                                                                                                             
  2. Deduce the expression for Signal to Quantization noise ratio in PCM system.                                                                  Slip test-2
  1. A PCM source transmits four samples (messages) with a rate 2B samples /second. The probabilities of occurrence of these 4 samples (messages) are equally likely Find out the information rate of the source.                                                           
  2. A source produces 26 symbols with equal probability what is the average information produced by this source?     

PART-B

  1. State Mutual information. Prove any three properties of Mutual information.                 
  2. A source alphabet has 10 symbols with the given probabilities 0.02, 0.04, 0.17, 0.02, 0.16, 0.06, 0.03, 0.27, 0.20, 0.03 construct Shannon-Fano coding and calculate the efficiency.                                                                                                                             

Digital Communications Quiz with solutions

UNIT-1

QUIZ

  1. The band width  needed to transmit Television video plus audio signals of bandwidth 4.2 MHz using Binary PCM  quantization level of 512 is (  c     )         a. 2 MHz            b. 25.6MHz                        c.37.8MHz                    d.75.6MHz
  2. A signal m(t)has a bandwidth of 1.0 KHz and exhibits a maximum rate of change of 2.0 volts/sec. The signal is sampled at a sampling frequency of 20 KHz and quantized using delta modulator. The minimum step size to avoid slope overload is (  b    )                                                                                                                      a. 1.0mV        b. 0.1mV                c.10.0mV                      d.0.01mV
  3. For a 10 bit PCM system, the signal to Quantization noise ratio is 62 dB. If the number of bits are increased by 2, then the signal to Quantization noise ratio will be (  c      )                                                                                                                    a. Increased by 6 dB                                   b.  Decrease by 6 dB                                       c. Increased by 12 dB                                  d. Decrease by 12 dB
  4. Write the condition to eliminate slope overload error in a Delta modulation system—————————
  5. Write the condition to eliminate slope overload error in a Delta modulation system if the input is a single-tone signal—————————
  6. For which value of A , A-law has linear transfer characteristics——————–.
  7. For which value of µ , µ-law has linear transfer characteristics——————–.
  8. In a PCM system if the step size is 5V , then the Quantization noise in dB is   (  d    )                                                                                                                                             a. -5 dB.          b. -3.18dB       c. -10dB                      d. 3.18dB.
  9. Draw the characteristics of Mid-rise and Mid-tread type Quantizers ————–
  10. The maximum slope of the signal ———————-
  11. The sampling rate of the signal ————————–
  12. The step size in a 8- bit pcm system if the input signal to PCM is oscillating between [+4V,-4V] is—————————–

UNIT-2

QUIZ 2

  1. Entropy is a measure of ——————————– 3M.  
  2. The capacity of a band – limited AWGN channel in terms of kbps if the average received signal power to noise power spectral density is 1000 and the bandwidth is approximately infinite is (  a    )   [Hint: Shannon’s bound Cinfinity =  S/No]                                                                                                                        a.  1.44        b. 1.08                                c. 0.72                           d. 0.36
  3. If Y= g(X) where g denotes a deterministic function, then the conditional entropy H(Y/X) is (  b ) 3M.                                                                                                           a. ≠ 1         b.  = 0                           c. = 1                           d. ≠ 0
  4. A Source generates three symbols with probability of 0.25, 0.25, and 0.50 at a rate of 3000 symbols per second. Assuming the symbols are generated independently from the source, the most efficient source encoder would have average bit rate of ( b ) 4M.                                                                                             a. 6000 bits/sec                                                         b. 4500 bits/sec                                 c. 3000 bits/sec                                                         d. 1500 bit/sec.
  5. A source generates four equi-probable symbols. If the source coding is adopted, the average length of the code for 100% efficiency is ( c )                       a. 6 bits / symbol                                                          b.   3 bits / symbol                           c.  2 bits / symbol                                                        d.  4 bits / symbol
  6. Draw the channel diagram of Binary Erasure channel and write its channel matrix ………………………..
  7. For a Binary Symmetric Channel the entropies of X & Y are if the conditional probability p=0.5, where X & Y are input & output random variables of BSC  (   d     )3M                                                                                                                          a. 1,0           b. 0,0               c. 0,1                           d. 1,1
  8. Match the following   (  d    )                                                                                                       a. Lossless channel                                           1.  only one non-zero element in each row                                                                                                                                        b. Deterministic channel                                2. Only one non-zero element in each row and each column.                                                                                                   c. Noiseless channel                                           3. Only one Non-zero element in each column.                                                                                                                                d. for a noiseless channel                                  4. H(Y/X)=0 and H(X/Y)= 0. a. none of these                                                  b.   b-3,c-4,a-1,d-2                                    c. c-4,d-3,a-1,b-2                                             d.  b-1,c-2,a-3,d-4.
  9. Given a Binary Symmetric Channel, the expression for Entropy is (pis conditional probability of error   ——————- 3M.  

Digital Communications Unit-3 Quiz with Solutions

UNIT3

QUIZ3[CO3]

  1. The number of Parity check bits in an (n, k) Linear Block codes are (    b      )      a.n                b. (n-k)                       c.  (n+k)                       d. k
  2. The Hamming Weight of the following code words 10011101 & 00111100 is      (   c   ) 2M.                                                                                                                                       a. None of these      b. 4, 5              c.5, 4                           d.3,4
  3. A cyclic code can be generated using———————— and A block can be generated using——————-.(   c   )                                  a.Generator matrix & Generator polynomial.                                                          b.Generator matrix & Generator matrix.                                                            c.Generator polynomial & Generator matrix.                                                            d.None of the above.
  4. The rate of a Block code is the ratio of(    c     )                                                                a.Message length to Block length.                 b.Block length to message length.  c.Message weight to Block length.                 d.None of the mentioned.
  5. The syndrome in LBC is calculated using , where Y represents received code word   (     a       ) 2M                                                                                                                      a. S= Y HT          b. S = YH                    c. S= YT H                  d. S= YT HT
  6.  A non-Zero value of Syndrome in a Block code represents ( b    ) 2M.                  a.No error during transmission.     b.An error occurred during transmission.   c.Both a and  b                                         d.None of the above.
  7. The transmitted code word(X) in an LBC can be obtained from received code word( Y) by using the equation (  a   ), where E represents error vector.              a. X= E + Y           b.  X = X.Y                  c. X= E.Y                    d. X= X/Y
  8. The parity check matrix of a (6,3) block code if Generator matrix is G  3M.             ——————-.
  9. In the above question find the Code words corresponding to message vectors [110] and [111]——————-. Ans: [110110], [111000].
  10. For the Q.8. Find the syndrome value when the received code word is 001111—-4M. Ans: syndrome value [0 0 1]
  11. For a (7,4) cyclic code , the generator polynomial is given as find the codeword  for the data 1100       Non systematic codeword is—————- .Ans:  1011100              Systematic codeword is——————–.Ans: 1011100.

    UNIT-4

    QUIZ-4

    1. The modulation technique that provides minimum probability of error is (  b   ). a. ASK                  b. PSK                   c. DPSK                        d.FSK
    2. At a given probability of error, binary coherent FSK is inferior to binary coherent PSK by (  c  )                                                                                                         a. 6 dB                b. 2 dB           c.  3 dB           d.  0 dB             e. None of these.
    3. If Eb, the energy per bit of a binary digital signal, is 10-5watt-sec and the one-sided power spectral density of the white noise, No= 10-6 W/Hz, then the output SNR of the matched filter is  (   d    )                                               a. 26 dB         b.  20 dB          c. 10 dB          d. 13 dB          e. None of these
    4. In which system, bit stream is portioned into even and odd stream (   c   )  a. BPSK                  b.  MSK            c. QPSK                     d.  FSK
    5. Optimum filter can be called as———when the input noise is white noise (  a   ) 2M.                                                                                                                        a. Matched filter   b.  High pass filter        c. Low pass filter      d. None of these
    6. The probability of error of ASK is ————————————.
    7. The probability of error of FSK is ————————————.
    8. Write the expression for QPSK modulation —————————————-2M.
    9. Draw the block diagram of DPSK system————————————.
    10. A pulse g(t) = A cos(πt/2T) for 0 ≤ t ≤ T is transmitted over an AWGN channel with two sided noise power spectral density No/2 Watts/Hz. The impulse response of the matched filter is (  a     )                                                           a. A sin (πt/2T)                                                            b.   A rec (πt/2T)                           c. A rec (π(T-t)/2T)                                                    d. A sin (π(T-t)/2T)           
    11. If the probability of error function of a modulation scheme is Pe = (½) erfc(x) thenthe same Pe interms of Q-function is ( b   )                                             a. Q ( 31/2 * x)                    b. Q (21/2 * x)                c. Q(x)             d. none of these.

 

 

Analog Communications Important Questions unit 2 (FAQ)

UNIT 2:

Short answer questions:

  1. What is meant by Carson’s rule? Problem on calculation of Bandwidth of FM signal using Carson’s rule.(imp)
  2. Distinguish between NBFM and WBFM.(imp)
  3. Problems on instantaneous phase and frequency.
  4. What is the basic principle involved in Phase discriminator?
  5. Define capture range and lock range of a PLL.
  6. Problem on Armstrong method of generation of a WBFM signal?(imp)
  7. Capture effect and threshold effects in FM (very very imp).
  8. Problems on carrier swing, frequency deviation, BW, modulation index etc.
  9. Phasor diagrams of NBFM and AM.
  10. What is the need for limiter in FM receivers? (Very very imp).
  11. Find the maximum Frequency deviation of Frequency Modulated signal given by  S(t) = 10 cos(1000000 *pi*t + 5 sin(2000*pi*t)).
  12. A carrier signal 10 cos(8x 106πt) is modulated by a modulating signal               5 cos(30x 103πt)  then i. Find the Band width of Frequency Modulated signal assuming  kf  =15KHz.   ii.     Calculate Highest Frequency and lowest Frequency of FM signal.  iii. Find  Modulation index of FM signal.
  13. Compare Frequency Modulation with Phase Modulation.

Long answer questions:

  1. Explain the operation of balanced slope detector in detail.
  2. Explain in detail about frequency spectrum of WBFM signal using Bessel functions.
  3. write in detail about generation methods of FM signal
  4. Direct method of generation
  5. Indirect method of generation (Armstrong method).(very very imp)
  6. What is ratio detector? Explain its working in detail with neat circuit diagram. Explain how ratio detector provides amplitude limiting?
  7. What is amplitude limiter? Draw its circuit diagram explain its working. Why amplitude limiter is needed in FM receivers justify.(very very imp)
  8. Compare and contrast foster seeley discriminator with ratio detector.
  9. What is PLL? What are the applications of PLL? Explain the working of PLL with neat block diagram.(imp)
  10. How audio frequency signal is demodulated by using PLL? Explain in detail.
  11. Write about pre-emphasis and de-emphasis circuits in detail. Give the significance of pre-emphasis and de-emphasis.(imp)
  12. In an FM system if the AF is 500 Hz and its amplitude is 2.4V with a frequency deviation of 4.8 KHz. If the AF voltage is increased to 7.2V then find the modified frequency deviation calculate BW in above two cases.
  13. Design Armstrong FM generator for the generation of WBFM signal with frequency deviation=75 KHz and using the NB carrier as 100 KHz and second carrier as 10 MHz Find the suitable multiplying factors. Assume the message signal is defined in the range 100Hz-15 KHz.
  14. Draw the block diagram of single-tone NBFM signal if message signal is.
  15. Derive an expression for an FM signal with carrier frequency fc and a modulating signal Obtain an expression for its spectrum.
  16. Why an FM system is preferred over an AM system?

Unit 2

Assignment 2

  1. Explain the generation techniques of FM signal using Direct and Indirect methods in detail.
  2. Explain the working of the following demodulator circuits of FM                        i. Balanced slope Detector for FM modulation.                                                            ii. Foster-Seeley discriminator.                                                                                         iii. Ratio-detector.
  3. Explain the detection of FM signal using PLL.
  4. Explain in detail about pre-emphasis and De-emphasis circuits in FM.

Unit 2

Assignment 2 

  1. Illustrate the working of PLL using a Block Diagram. Define capture range and Lock range in PLL.                                                                                                                 5M.
  2. Sketch the circuit diagram of Ratio-detector and explain working of it in detail. 5M.
  3. Sketch the frequency response curves & compare the working of pre-emphasis and De-emphasis circuits in FM communication System.

TUTORIAL TEST 2

Answer any three of the following

  1. In an FM system if the AF is 500 Hz and its amplitude is 2.4V with a frequency deviation of 4.8 KHz. If the AF voltage is increased to 7.2V then find the modified frequency deviation calculate BW in above two cases.
  2. Explain in detail about frequency spectrum of WBFM signal.
  3. Draw the block diagram of single-tone NBFM signal if message signal is
  4. Write any four differences between NBFM and WBFM.

Basic Electronics Important Questions Unit 5 (FAQ)

UNIT-5

Data Acquisition systems: Study of transducer (LVDT, Strain gauge, Temperature, Force).

Photo Electric Devices and Industrial Devices: Photo diode, Photo Transistor, LED, LCD, SCR, UJT Construction and Characteristics only.

Display Systems:  Constructional details of C.R.O and Applications.

ASSIGNMENT- UNIT5

  1. Explain with neat sketch, the working principle of LVDT.
  2. Give the applications of CRO. Explain the Block diagram of Cathode ray tube in detail. 10M.
  3. Write a short note on LED and LCD.

Short Answer questions:     

  1. Distinguish between photodiode and LED.
  2. Why is SCR known as negative resistance device?
  3. What are the different types of transducers used for the measurement of temperature. Explain the principle of any of these.
  4. Draw the symbol of a SCR and VI characteristics .explain its principle of operation.
  5. What is meant by sensitivity in a CRO and explain the necessity of a saw tooth generation of a CRO.
  6. What are the important characteristics of an LCD?
  7. What is an LVDT? By means of a neat sketch explain how a LVDT is used in measurements.
  8. Give the block diagram of a CRO, Explaining the importance of each block.
  9. Explain about an instrumentation amplifier.
  10. Write a note on UJT.
  11. How are DIAC and TRIAC different from operational point of view.
  12. What is a transducer?
  13. List out the applications of a SCR.
  14. Explain the principle involved in a strain gauge.
  15. Draw the symbols of SCR, TRIAC, DIAC and UJT.

Long Answer questions:      

  1. Explain the working of Cathode Ray Tube of CRO with neat block diagram in detail.
  2. What are the applications of CRO?
  3. Differentiate Photo Diode and Photo Transistor in detail in terms of operation and applications.
  4. Differentiate LED and LCD in detail in terms of operation and applications.
  5. Explain the working of SCR and draw the characteristics of it.
  6. Explain the working of UJT and draw the characteristics of it.

 

ALL THE BEST

Prepared by         P.Lakshmi Prasanna

 

 

Basic Electronics Important questions units 4 (FAQ)

Unit-4:  Operational Amplifiers – Introduction to OP Amp, characteristics and applications – Inverting and Non-inverting Amplifiers, Summer, Integrator, Differentiator, Instrumentation Amplifier.

Digital System: Basic Logic Gates, Half, Full Adder and Subtractors.

ASSIGNMENT- UNIT4

  1. What are the four basic building blocks of Op-Amp explain each block in detail. 10M.
  2. Write in detail about Instrumentation amplifier.
  3. Design and realize Full Subtractor (Give the necessary expression and Truth table and Circuit diagram)

Short Answer questions:     

  1. What are the ideal characteristics of OP-AMP?
  2. What is an operational amplifier? Mention some of its applications.
  3. A 5mV, 1 kHz sinusoidal signal is applied to the input of an OP-amp integrator for which R=100KΩ and C=1µF.Find the output voltage.
  4. What are the different parameters of an OP-amp? Sketch the circuit of a summer using OP-amp 741to get Vo= -(-V1+2V2-3V3).
  5. Write a note on basic logic gates.
  6. Draw the truth table of an EX-OR gate.
  7. State and prove De-Morgan’s theorems. Discuss the working of half adder and full adder and give their truth tables.
  8. Write a note on universal gates.
  9. Realize OR gate using NAND gates.
  10. What is half Subtractor? Realize full Subtractor using using NAND gate only.
  11. What is an op-amp? List the four building blocks of an op-amp.
  12. Draw the schematic symbol of an op-amp in detail. Write the expression for output voltage of an op-amp?
  13. What are the applications of op-amp?
  14. What are the advantages of op-amp?
  15. Why op-amp is named as op-amp?
  16. What are universal gates and why those are called as universal gates?
  17. Draw EX-OR and EX-NOR gates and give the truth tables of each gate.
  18. Name some basic logic gates draw their symbols and give the corresponding truth tables.
  19. Draw half adder and half Subtractor.

Long Answer questions:

  1. Draw and explain block diagram of op-amp in detail. Or what are the basic building blocks of an op-amp explain in detail.
  2. Write in detail about
  3. Half adder/ Full adder.
  4. Full Subtractor/ Half Subtractor.
  5. Explain the operation of inverting and non-inverting amplifier circuits using op-amp and calculate gain of each circuit in closed loop configuration.
  6. Define common mode rejection ratio (CMRR).a differential amplifier has a differential mode gain of 100 and common mode gain of 0.01 then find CMRR in dB?
  7. Write in detail about instrumentation amplifier.
  8. Explain the operation of the following circuits of op-amp in open loop configuration.    a. Non –inverting amplifier.        b.   Inverting amplifier  c.  Differential amplifier.
  9. What are the characteristics of practical op-amp?
  10. Define slew rate of op amp? Problem on calculation of Slew rate.
  11. Explain how op-amp is used as  Summer and difference amplifier or Subtractor.

 

Prepared by                                                                                       P.Lakshmi Prasanna

 

 

Basic Electronics Important Questions Unit 3 (FAQ)

UNIT – 3

Unit-3:  Feedback concepts: Properties of negative feedback amplifiers, Classification, Parameters. Oscillators: Barkhausen’s Criterion, LC Type and RC type oscillators and crystal oscillator. (Qualitative treatment only)

ASSIGNMENT- UNIT3

  1. Draw the basic block diagram of feedback amplifier and explain each block in detail. 10M.
  2. What is the effect of negative feedback on input and output impedances of a voltage series feedback amplifier? Give necessary expressions.
  3. Write a short note about RC Phase Shift Oscillator.

 Short Answer questions:

  1. What is meant by feedback?
  2. What is tank circuit? How it is used in oscillators?
  3. State Barkhausen’s criterion.
  4. Differentiate positive feedback with negative feedback.
  5. If open loop voltage gain of feedback amplifier is 200 and feedback factor is 1/5 then find
  6. Gain with negative feedback.
  7. BW with negative feedback if open loop BW is 100 KHz.
  8. What are the advantages of negative feedback?
  9. What is the effect of negative feedback on bandwidth?
  10. Explain how gain stability is improved by negative feedback?
  11. Draw block diagrams of voltage- series and current- shunt feedback topologies?
  12. What are four topologies of feedback amplifiers?
  13. What is positive feedback .Give the advantage of positive feedback?
  14. Write the definition of oscillator?
  15. Differentiate oscillators with the frequency of operation?
  16. Draw under damped over damped and un-damped oscillatory signals.
  17. .In the forward path of an oscillator, two amplifiers of equal gain are cascaded. If the feedback path transfer function is 1/81, find the gain of each amplifier.

Long Answer questions:

  1. What is the effect of negative feedback on input and output impedances in voltage-series feedback amplifier give necessary expressions?
  2. Derive the general equation for LC oscillator circuits used in oscillators.
  3. Distinguish between positive feedback and negative feedback in amplifiers. State the advantages of negative feedback in amplifiers.
  4. Draw the circuit diagram of Hartley’s oscillator and explain its operation in detail. Derive the expression for frequency of oscillation.
  5. Draw the circuit diagram of Colpitt’s oscillator and explain its operation in detail. Derive the expression for frequency of oscillation.
  6. What is the effect of negative feedback on Bandwidth give explanation with necessary equations?
  7. Write in detail about four topologies of feedback amplifiers and compare the topologies in terms of gain, BW, input impedance and output impedance.
  8. Write the working operation of the following circuits and derive the expression of frequency of oscillation. i. RC-Phase shift oscillator. ii. Wein-bridge oscillator. iii. Crystal oscillator.
  9. Draw a neat circuit diagram of an RC phase shift oscillator using BJT and explain its working principle
  10. A Hartley oscillator is designed with L1=2mH, L2=20mH, and a variable capacitance. Determine the range of capacitance value, if the frequency of oscillation is varied between 950 kHz and 2050 kHz.

ALL THE BEST

Prepared by       P.Lakshmi Prasanna

 

 

Basic Electronics Important Questions-Unit 2 (FAQ)

UNIT-2

ASSIGNMENT- UNIT2(CO2)

  1. Draw the h-parameter equivalent model of transistor in CE configuration and define the four h- parameters.
  2. Explain the construction of JFET (either n-channel or p-channel).
  3. Explain the current components of a BJT in detail with a neat sketch.

 

Short Answer Questions:

  1. Write the differences between JFET and BJT.
  2. What are three possible configurations of BJT?
  3. Define α, β and γ of a BJT write the relationship between them.
  4. What are three possible regions of a transistor (write about cut-off, active and saturation regions).
  5. What is base width modulation?
  6. Define four h-parameters of transistor. And draw general h-parameter model of a BJT.
  7. Define the following
  8. Bandwidth of an amplifier.
  9. Gain or amplification factor.
  10. Compare CE, CB and CC transistors.( in terms of input resistance, o/p resistance, current gain, voltage gain, phase shift and applications).
  11. What are the advantages of FET over BJT?
  12. Why FET is more preferable than BJT?
  13. How FET is known as uni polar device ? how do you compare FET with BJT?
  14. Why FET is called as voltage controlled device?
  15. What are the parameters of FET?
  16. What are the three possible configurations of FET?
  17. Give the relationship between gm , rd and µ.
  18. Draw the equivalent circuit diagram of FET in CS configuration.
  19. Why BJT is called as Current controlled device.
  20. Draw transfer and output characteristics of FET.
  21. Draw the symbols of NPN transistor,n channel FET and SCR.
  22. If the emitter of a transistor is open will there be any collector current.

Long Answer Questions:

  1. What is CB configuration? Draw the input and output characteristics of CB transistor. Explain in detail.
  2. Define α and β of a transistor and derive the relationship between them.
  3. Explain the current components of BJT in detail.
  4. Explain how transistor is working as an amplifier?
  5. Explain the working of CE amplifier with a neat circuit diagram. Derive expression for input resistance, and current gain using h parameter equivalent circuit.
  6. Draw the hybrid equivalent circuit of an NPN BJT in CE configuration. Derive expressions for Av, Ai, Ri,
  7. Calculate the values of Ic and Ib, for a transistor with α=.99,Ico=5µA,Ib=20µA.
  8. Draw a simple inverter circuit and explain its operation.
  9. Draw the h-parameter model of CE transistor and explain how h-parameters are calculated from CE characteristics.
  10. Explain the construction and working of FET (either n-channel or p-channel).
  11. Draw output and transfer characteristics of FET explain the working of /FET through them.
  12. Derive the relationship between gm, rd and µ.
  13. Write the comparisons between FET and BJT.
  14. How FET is working as an amplifier?
  15. Explain the working operation of NPN and PNP transistors.
  16. Explain various operation regions of a transistor in detail.
  17. What is CE configuration? Draw the input and output characteristics of CB transistor. Explain in detail.
  18. What is CC configuration? Draw the input and output characteristics of CB transistor. Explain in detail.
  19. What are the disadvantages of BJT? Why FET is preferred over BJT? Give the applications of FET.
  20. Explain the working of JFET And explain the parameters of JFET.

 

 

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Basic Electronics Important Questions -Unit-1 (FAQ)

Basic Electronics Important questions  –Unit-1

Note: Read the questions in the following order   i. Assignment questions ii. Class test  iii. Expected questions iv.  Tutorials For every unit.

 Unit1:

ASSIGNMENT- UNIT 1 

  1.  Explain the working of Bridge rectifier in detail with a neat circuit diagram and derive the expression for ripple factor and efficiency. 10M.
  2. Explain the working of PN-junction diode in detail in forward and reverse bias conditions. 10M.
  3. A 230v, 60 Hz voltage is applied to the primary of a step down center tapped transformer of a FWR with turns ratio 5:1 is connected to a load resistance of 1 KΩ i. i. Determine voltage across the load. ii. DC current through the load. If there is a resistance of 100Ω for the transformer secondary and diode forward Resistance is given as 10Ω.

Short Answer Questions:

  1. Write the expression of diode current equation and explain each term in detail.
  2. Define cut in or threshold voltage of a diode. Give the values of Vof Si and Ge diode.
  3. Write the differences between Extrinsic and Intrinsic semiconductors.
  4. What are P-type and N-type semiconductors?
  5. Write in detail about Drift and Diffusion currents.
  6. Draw the Energy Band Diagrams of an insulator, semiconductor, Conductor.
  7. Write the differences between insulators, conductors and semi conductors.
  8. Define the following   a. Mobility b. Conductivity  c. Mass Action law. d.Fermi level in semi conductors.
  9. Draw the diagrams for Fermi-level in Intrinsic, N-type and P-type semi conductors and write the formula for EF in the above two cases.
  10. Define Hall Effect and write the uses or applications of Hall Effect.
  11. What properties of semi conductor are defined from Hall Effect?
  12. What is a diode and write the applications of Diode.
  13. Draw the VI-Characteristics of a diode. And calculate Static and Dynamic resistances from the characteristics.
  14. Write about diffusion and Transition capacitances of a diode.
  15. Define avalanche breakdown and zener breakdown.
  16. What is avalanche effect and zener effect?
  17. What is a rectifier? Differentiate between Half Wave Rectifier and Full Wave Rectifier.
  18. Draw the equivalent circuit of practical Diode under forward bias and Reverse Bias.
  19. Draw the equivalent circuit of ideal Diode under forward bias and Reverse Bias.
  20. Define Peak Inverse Voltage (PIV) of a diode in a rectifier circuit. Write the PIV values in HWR, FWR and Bridge Rectifier.
  21. Define the following i. Ripple factor       ii. Regulation or Percentage of Regulation. iii. From factor and peak factor. iv. Efficiency of a rectifier  v. RMS value and average value of voltage or current wave in half wave rectifier.
  22. Write the applications of Zener Diode.
  23. Explain how Zener diode works as a regulator.
  24. What is the concentration of holes in Si crystals having donor concentration of 1.4 x 1024/m3 when the intrinsic carrier concentration is 1.4 x 1018/m3 ? Find the ratio of electron to hole concentration.
  25. Problems on motilities of n-type and p-type semiconductors.
  26. An n-type Ge crystal has a current density of 100A/m2. The crystal has a resistivity of 0.5 Ω-m and electron mobility of 0.4 m2/V-s. Calculate the drift velocity and the time taken by the electron to travel 10 micrometer in the crystal. Assume q= 1.6 x 10-19
  27. Problems on Fermi levels.
  28. Problems on diode current equation in forward bias and reverse bias.
  29. Write the advantages of full wave and bridge rectifiers over half wave rectifier.

Long Answer Questions:

  1. Define Hall Effect. Derive the expression for Hall voltage and hall coefficient and explain the uses of Hall Effect.
  2. Derive the expression for transition and diffusion capacitances of a diode.
  3. Explain the working of Zener Diode as a regulator.
  4. Derive the expression for ripple factor and efficiency of a Half Wave rectifier and full wave rectifier.
  5. Derive the expression for ripple factor and efficiency of a bridge rectifier.
  6. Compare half wave rectifier, FWR and Bridge rectifier in terms of (ripple factor, percentage of regulation, efficiency, PIV, from factor and peak factor etc…… read the comparison table in text book).
  7. How will you find the dynamic and static resistance of the diode using a graph?
  8. What is an ideal diode? How can it be represented as a switch? Draw the equivalent circuit and its characteristics.
  9. Draw the VI-Characteristics of a PN junction diode in forward and reverse biased conditions. Define forward resistance and reverse resistances and explain how they can be obtained from the characteristics.
  10. Draw the circuit diagram of a half wave rectifier and explain its operation with wave forms.
  11. Draw the circuit diagram of bridge rectifier and explain its operation with wave forms.
  12. Draw the circuit diagram of a full wave rectifier and explain its operation with wave forms. What is its advantage over half wave rectifier?
  13. What is static resistance of the diode? How will you find the dynamic resistance?
  14. Explain the zener and avalanche thermal breakdown mechanisms. What will be their thermal coefficients?
  15. How is a PN junction formed? Draw the circuit diagram of PN-Junction diode in forward bias and reverse bias. Explain its operation and give VI-characteristics.
  16. What is a rectifier? Draw the circuit diagram for bridge rectifier with LC-filter and explain its operation.
  17. Explain bridge wave rectifier with circuit diagram and output wave forms. Find      i. RMS value of current.   ii. Ripple factor.  iii. TUF   iv. Efficiency   v. Peak factor.
  18. Explain avalanche breakdown and zener breakdown in PN diode.
  19. Derive the expression for ripple factor of a FWR (or HWR/ Bridge) with shunt capacitance filter.
  20. Derive the expression for ripple factor of a FWR (or HWR/ Bridge) with series inductance filter.
  21. Derive the expression for ripple factor of a FWR (or HWR/ bridge) with LC π section filter.
  22. Derive an expression for current in a diode.
  23. Compare drift and diffusion currents.

 Tutorial -1 Questions

  1. A Full Wave Rectifier has a Secondary Voltage of 230V from one-end of the transformer to ground. then calculate i. DC load Current. ii. RMS value of output current. If diode has a resistance of 10Ω and the resistance of secondary winding is negligible. Given RL=5KΩ.
  2. Find the conductivity of P-type semi conductor, if the concentration of holes is 4.2X1022atoms/m3 and mobility of holes is 1800 Cm2/V.
  3. Write the expression for Hall voltage and find Hall voltage if the Magnetic field strength of 1000 Wb/m2 where the current flowing through the semi conducting material is 9A. Width of semi conducting material is 2m with resistivity of 100 Mhos-m. Also find the Hall coefficient?
  1. Write a short note on P-type and N-type semi conductors.

 

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Digital Modulation schemes Viva Questions

ASK Generation & Detection:

  1. Define ASK. Write the practical applications of ASK.
  2. Draw the waveforms of ASK scheme.
  3. Draw the Phasor diagrams of ASK.
  4. Write the equation of ASK wave.
  5. What are the applications of ASK?
  6. What are the advantages and disadvantages of ASK?
  7. Write the expression for Probability of error of ASK.
  8. What is the BW of ASK?
  9. Draw the signal constellation diagram of ASK.
  10. Draw the block diagram of ASK generator. Explain its working.
  11. Draw the block diagram of coherent ASK demodulator. Explain its working.
  12. Draw the block diagram of non-coherent ASK demodulator. Explain its working.
  13. How ASK is different from AM?
  14. If bit rate is 10µsec then calculate the band width of ASK.
  15. Which is the efficient modulation scheme among ASK and PSK give the reason.
  16. Write the relation between complementary error function and Q-Function.
  17. Write the Pe of ASK in terms of Q function.
  18. What is meant by Signal space diagram?
  19. A source generates three symbols with probability 0.25,0.25 and 0.5 at a rate of 3000 symbols/sec Assuming the symbols are generated independently from the source the most efficient source encoder would have average bit rate of——————————.

FSK Generation & Detection:

  1. Define FSK. Write the practical applications of FSK.
  2. Draw the waveforms of FSK scheme.
  3. Draw the Phasor diagrams of FSK.
  4. Write the equation of FSK wave.
  5. What are the advantages and disadvantages of FSK?
  6. Write the expression for Probability of error of FSK.
  7. What is the BW of FSK?
  8. List some applications of FSK.
  9. Draw the block diagram of FSK generator and explain its working.
  10. Draw the block diagram of coherent FSK demodulator and explain its working.
  11. Draw the block diagram of non-coherent FSK demodulator and explain its working.
  12. Show that FSK is inferior to PSK by 3dB for a given probability of error.
  13. Define digital modulation schemes.
  14. Identify the differences between Pass band and Base band Communication.
  15. What is a matched filter?
  16. What are the properties of matched filter?
  17. What is MSK? What is the need for Minimum Shift Keying?
  18. For the given 8 bit data 10111010 draw the FSK output waveform.
  19. Draw the constellation diagram of FSK.
  20. What will happen if the same frequency is used for both the carriers?
  21. Draw FM signal and FSK signal differentiate those two signals.
  22. What are the applications of FM?
  23. How FSK is different from FM?
  24. Write the probability of error expression of FSK in-terms of Q function.
  25. Write the relation between complementary error function and Q-Function.
  26. Among FSK and PSK which is the most efficient scheme and why?

 

PSK Generation & Detection:

  1. Define PSK. Write the practical applications of PSK.
  2. Draw the waveforms of PSK scheme.
  3. Draw the signal space diagram of PSK.
  4. Write the equation of PSK wave.
  5. What are the applications of PSK?
  6. What are the advantages and disadvantages of PSK?
  7. Write the expression for Probability of error of PSK in terms of erfc()
  8. Write the expression for Probability of error of PSK in terms Q().
  9. Write the difference between erf(x) and erfc(x)..
  10. What is the BW of PSK?
  11. What are antipodal signals?
  12. Give the equation for average probability of symbol error for coherent binary PSK.
  13. Explain how QPSK differs from PSK in terms of transmission bandwidth and bit information it carries.
  14. What are the advantages of M-ary modulation scheme?
  15. Draw the constellation diagram for QPSK.
  16. Compare FSK and PSK.
  17. What do we infer from constellation diagrams of various modulation schemes?
  18. Draw the block diagram of PSK generator. Explain its working.
  19. Draw the block diagram of coherent PSK detector. Explain its working.
  20. How non coherent PSK is advantageous over coherent PSK?
  21. Other name of Non-coherent PSK is———–.
  22. Write the expression for a Gaussian function———————.

 

DPSK Generation & Detection:

  1. Define DPSK.
  2. Draw the waveforms of DPSK scheme.
  3. Write the equation of DPSK.
  4. What are the applications of DPSK?
  5. What are the advantages and disadvantages of DPSK?
  6. Write the expression for Probability of error of DPSK.
  7. What is the BW of DPSK?
  8. What are the applications of DPSK?
  9. Draw the DPSK system and explain its working.
  10. If the input sequence to a DPSK modulator is 10011100 write the following sequences, Deferentially encoded sequence if previous bit is 0 And the phase of the encoded sequence.
  11. The capacity of a band limited AWGN channel in terms of KBPS if the average received signal to noise power spectral density is 1000 and the BW is approximately infinite is…………..
  12. For error free channel conditional probability is ————-.
  13. The modulation technique that provides minimum probability of error is———-.

QPSK Generation & Detection:

  1. Define QPSK.
  2. Draw the waveforms of QPSK scheme.
  3. Draw the Phasor diagrams of QPSK.
  4. Write the equation of QPSK wave.
  5. What are the applications of QPSK?
  6. What are the advantages and disadvantages of QPSK?
  7. Write the expression for Probability of error of QPSK.
  8. Draw the block diagram of QPSK modulator. Explain its working.
  9. Draw the block diagram of coherent QPSK de modulator. Explain its working.
  10. Write the table for four di-bits with phases used in a QPSK modulation scheme.
  11. Write the equation of QPSK wave.
  12. What is the BW of QPSK?
  13. What are the applications of QPSK?
  14. Draw the constellation diagram for QPSK.
  15. In Minimum Shift Keying the relation between the signal frequencies and bit rate are————.
  16. A pulse for is passed through a matched filter then the impulse response of matched filter is—————————.
  17. A lossless channel means—————–.
  18. A distortion less channel means————————-.
  19. Write the channel matrix for a Binary symmetric channel——————–.

Losses in fibre optics:

  1. Define Transmission loss of Optical fibre?
  2. What are various losses in fibre optics?
  3. What are step index graded index optical fibers?

Data Formats:

  1. Compare NRZ-I and NRZ- L.
  2. What is the use of data formatting?
  3. Compare NRZ and biphase encoding.
  4. What is the relationship between quantization levels and number of bits in a code word?
  5. Give the advantages of Manchester encoding.
  6. Assume a data stream is made of ten 0s. Encode this stream using the following encoding schemes.
  7. How much change can you find for each scheme? a)NRZ b)RZ c)Bi phase
  1. List out the merits & demerits of each data formats.
  2. Represent the given data 11010100 in Manchester encoding and NRZ –M scheme.

Delta Modulation and Demodulation Viva Questions

Delta Modulation & Demodulation:

  1. What is Delta Modulation?
  2. A message signal m(t) has a BW of 1KHz and exhibits a maximum rate of change of change of 2 Volts/sec the signal is sampled at a sampling frequency of 20 KHz and Quantized using a delta modulator the minimum step size to avoid slope overload is———-
  3. Which type of Quantization is used in DM?
  4. What are two types of quantization errors?
  5. What is granular noise?
  6. What is slope overload distortion?
  7. Draw the block diagram of Delta Modulation system.
  8. What are the advantages and disadvantages of DM system?
  9. What happens to the output signal if the variation of the message signal is
  • greater than the step size
  • less than the step size
  1. What is the advantage of delta modulation over PCM?
  2. Compare DPCM, PCM& Delta modulation.
  3. How to reduce the quantization noise that occurs in DM?
  4. A band pass signal has a spectral range that extends from 20 to 82 KHz. Find the acceptable sampling frequency.
  1. Find the Fourier series expansion of an Impulse train.
  2. Mention the applications of DM.
  3. Write the condition to eliminate Slope over load distortion in Delta Modulation for a single tone message signal.
  4. Write the condition to eliminate Slope over load distortion in Delta Modulation for some arbitrary signal.
  5. We chose oversampling in DM system. True or False?
  6. How DPCM is different from DM?
  7. Draw the waveforms of DM demodulation and Demodulation.
  8. Differentiate Coherent and Non coherent modulation schemes.
  9. Explain the working DM system.
  10. Draw the Wave forms and explain two distortions in DM system.

Pulse Code Modulation Viva Questions

Pulse Code Modulation:

  1. What is PCM? Does PCM come under Digital Modulation technique?
  2. What are the applications of PCM?
  3. What is the need for Regenerative repeaters in PCM?
  4. Draw the block diagram of PCM system.
  5. Define µ-law and A-law. And draw the characteristics of two laws.
  6. What is meant by Quantization?
  7. Differentiate Uniform and Non uniform Quantization techniques.
  8. What is meant by companding in PCM?
  9. What are the advantages and disadvantages of PCM?
  10. What is the difference between ADC & PCM?
  11. Name some ADC circuits?
  12. Which ADC is fastest ADC circuit?
  13. What is slope overload distortion?
  14. Draw the waveforms of PCM modulation and demodulation.
  15. State sampling theorem.
  16. What is aliasing?
  17. Give the expression for aliasing error and the bound for aliasing error.
  18. What is quantization?
  19. What are the various steps involved in A/D conversion.
  20. Define step size.
  21. What is the importance of regenerative repeater?
  22. List out the three basic functions of regenerative repeater.
  23. What is companding?
  24. Write the mean square quantization error if the step size is S.
  25. What is a mid tread Quantizer?
  26. What is a mid rise Quantizer?
  27. What do you mean by quantizing process?
  28. What will happen when sampling rate is greater than Nyquist rate?
  29. What will happen when sampling rate is less than Nyquist rate?
  30. Find the A/D Converter output for input DC voltage of 3.6V.
  31. In digital telephony, (a) what kind of modulation is used? (b)Give the typical sampling rate, output data rate and speech signal Bandwidth.
  32. Mention some applications of PCM.
  33. What is the function of Sample and Hold circuit?
  34. Write the expression for SNR in decibels of a PCM system.
  35. For a DAC the required resolution is 25mv and the total input is 5V. the number of bits required would be——————————————.

 

Digital Communications Quiz unit-3

Digital Communications Unit-3 Quiz with Solutions

UNIT3

QUIZ3[CO3]

  1. The number of Parity check bits in an (n, k) Linear Block codes are (    b      )      a.n                b. (n-k)                       c.  (n+k)                       d. k
  2. The Hamming Weight of the following code words 10011101 & 00111100 is      (   c   ) 2M.                                                                                                                                       a. None of these      b. 4, 5              c.5, 4                           d.3,4
  3. A cyclic code can be generated using———————— and A block can be generated using——————-.(   c   )                                  a.Generator matrix & Generator polynomial.                                                          b.Generator matrix & Generator matrix.                                                            c.Generator polynomial & Generator matrix.                                                            d.None of the above.
  4. The rate of a Block code is the ratio of(    c     )                                                                a.Message length to Block length.                 b.Block length to message length.  c.Message weight to Block length.                 d.None of the mentioned.
  5. The syndrome in LBC is calculated using , where Y represents received code word   (     a       ) 2M                                                                                                                      a. S= Y HT          b. S = YH                    c. S= YT H                  d. S= YT HT
  6.  A non-Zero value of Syndrome in a Block code represents ( b    ) 2M.                  a.No error during transmission.     b.An error occurred during transmission.   c.Both a and  b                                         d.None of the above.
  7. The transmitted code word(X) in an LBC can be obtained from received code word( Y) by using the equation (  a   ), where E represents error vector.              a. X= E + Y           b.  X = X.Y                  c. X= E.Y                    d. X= X/Y

Basic Electronics Lab Viva Questions

Experiment wise viva questions Basic Electronics Lab

PN-Junction Diode:

  1. What is a diode?
  2. What are the applications of diode?
  3. Draw the symbol of PN junction diode and mark anode and cathode.
  4. Define threshold voltage or cut in voltage of a diode.
  5. define dynamic and static resistances of a diode.
  6. Cut-in voltage of Si diode is…………………
  7. Cut-in voltage of Ge diode is…………………
  8. Draw the VI characteristics of PN junction diode.
  9. What is forward bias of a junction diode? Explain with circuit diagram.
  10. What is reverse bias of a junction diode? Explain with circuit diagram.
  11. Define space charge or Depleted region of a diode?
  12. Explain the working operation of a junction diode in forward and reverse bias.
  13. p type material means………….. Give some examples of N-type materials
  14. n type material means…………Give some examples of P-type materials
  15. Ideal diode acts as short circuit under forward bias. Or draw the equivalent circuit of ideal diode in forward bias.
  16. Ideal diode acts as open circuit under reverse bias. Or draw the equivalent circuit of ideal diode in reverse bias.
  17. Draw the equivalent circuit of practical diode in forward bias and reverse bias.
  18. What are the differences between avalanche and Zener break down.
  19. What are intrinsic and extrinsic impurities?
  20. Differentiate a conductor, semiconductor and dielectric material.
  21. Write the diode current equation.

 Zener Diode:

  1. What is Zener diode? Define how it is different from ordinary PN diode.
  2. What are the applications of Zener diode?
  3. Draw the symbol of Zener diode and mark anode and cathode.
  4. Define Zener breakdown.
  5. What is the Zener breakdown voltage value———–.
  6. How Zener diode is acting as a voltage regulator?
  7. What is the cut-in voltage of a Zener diode————.
  8. Draw the equivalent circuit of Zener diode?
  9. Zener diode operates in reverse bias? Why?
  10. Explain avalanche multiplication in detail.
  11. Explain Zener multiplication in detail.
  12. Give two differences between avalanche and Zener multiplication.

Half Wave rectifier and Full wave Rectifier (same questions are valid for FWR)

  1. What is a rectifier? How diode is used as a rectifier?
  2. Define ripple factor?
  3. What is the need for filter at the output of a rectifier?
  4. What is percentage of regulation?
  5. Give the ripple factor values for HWR and FWR (read comparison table between HWR and FWR).
  6. What is the efficiency of HWR and FWR? Give values.
  7. What are the advantages of FWR over HWR?
  8. What are the disadvantages of HWR?
  9. What are the drawbacks of FWR?
  10. Define PIV of a diode.
  11. PIV of HWR and FWR are………..
  12. why we need rectifiers?
  13. where we use rectifiers ?
  14. what are the differences between rectifier and converter?

CE/CB characteristics:

  1. Draw the symbol of transistor.
  2. Draw pnp and npn transistor symbols.
  3. What are three configurations of a BJT?
  4. Draw the circuits of CE, CB and CC configurations.
  5. What is CE or Grounded Emitter configuration?
  6. What is CB or Grounded Base configuration?
  7. What is CC or Grounded Collector configuration?
  8. What are input and output characteristics of BJT?
  9. Draw input and output characteristics of CE configuration.
  10. Draw input and output characteristics of CB configuration.
  11. What are the applications of CE and CB transistors?
  12. Comparison table of CE, CB and CC configurations in terms of input resistance, output resistance, voltage gain, current gain and applications.
  13. What are the three terminals of a transistor?
  14. Define doping levels of emitter, base and collector.
  15. Define early effect in CB transistor.
  16. The majority carriers in pnp transistor are………..
  17. The majority carriers in npn transistor are………..
  18. Why BJT is called as bipolar device?
  19. Is BJT a uni polar or bipolar device?
  20. What are the applications of transistors?
  21. what is the phase difference between input and output waveforms of CE transistor( ans: 180o)
  22. What is the phase difference between input and output waveforms of CB transistor ( ans: 0o or 360o).
  23. Why NPN transistor is preferred over PNP transistor?
  24. Why CE is preferred over other combinations in voltage amplifiers?
  25. Define saturation, cutoff, active regions of a transistor?
  26. What is cutoff region of operation of a transistor?
  27. Read about comparison tables of Si, Ge transistors for active cutoff and cutin and saturation voltages.

JFET:

  1. What is FET or JFET?
  2. What are the differences between BJT and FET?
  3. Why BJT is called as Current controlled device?
  4. Why FET is called as Voltage controlled device?
  5. Draw the symbol of FET?
  6. Symbols of N-channel and p channel FETs.
  7. Differences between N- channel and P- channel FET’s?
  8. Draw the input or output characteristics of JFET?
  9. What are the meanings of source drain and gate?
  10. What are the applications of FET?
  11. What are the advantages of FET over BJT?
  12. Draw h-parameter model of a BJT in CE/CB configurations?
  13. Define pinchoff voltage of a FET?
  14. Explain about linear saturation and breakdown regions of CE/CB output characteristics?
  15. Explain about linear saturation and breakdown regions from drain or output characteristics of JFET
  16. Define 4 h-parameters of BJT in CE configuration?
  17. Draw the equivalent circuit of FET?
  18. define µ, gm­ , rd in FET? what is the relation between those three parameters?
  19. define trans conductance and drain resistance of FET?
  20. The input resistance of a JFET is very high in Mega ohms.
  21. Working of JFET.
  22. Applications of JFET.

 

Operational Amplifier:

 

  1. What is Operational Amplifier?
  2. What are the ideal characteristics of Op-amp?
  3. What are the applications of op-amp?
  4. What is inverting amplifier?
  5. What is non inverting amplifier?
  6. What is meant by open loop and closed loop op-amp?
  7. Identify the feedback resistor in inverting and non inverting amplifiers (ans:Rf).
  8. What are the advantages of op-amp over feedback amplifiers?
  9. Define slew rate?
  10. Draw circuits of integrator and differentiator using op-amp
  11. Draw adder and subtractor circuits using op-amp.
  12. What is virtual ground in op-amp circuits?
  13. What is open loop gain of an ideal op amp?

Oscillators:

RC Phase Shift Oscillator:

  1. Mention the two conditions required for oscillations in RC phase shift oscillator?
  2. Give the formula for frequency of oscillations in RC phase shift oscillator?
  3. The phase produced by a single RC network is RC phase shift oscillator?
  4. RC phase shift oscillator uses positive feedback or negative feedback?
  5. The phase produced by basic amplifier circuit in RC phase shift oscillator is?
  6. What is the difference between damped oscillations and un damped oscillations?
  7. What are the applications of RC phase shift oscillator?
  8. How many resistors and capacitors are used in RC phase shift feedback network?
  9. How the Barkhausen’s criterion is satisfied in RC phase shift oscillator
  10. Mention the basic reason for any oscillations?
  11. What is meant by Barkhausen’s criterion?
  12. Audio frequency range is————
  13. RC phase shift oscillator is ——–
  14. Oscillator is a circuit operates on internal input power supply yes or no?
  15. Define an oscillator?
  16. Oscillator did not take any external input yes or no?
  17. Type of feedback used in oscillators is——-
  18. Radio frequency range is———–
  19. Show that single RC section provides a phase shift of 60 degrees.
  20. Positive feedback causes instability yes or no?
  21. In oscillators loop gain must be————–
  22. In oscillators the overall phase shift produced by the circuit is————
  23. Feedback gain 𝛽 must be less than———–

 COLPITTS AND HARTLEY’S OSCILLATORS:

  1. What are the advantages of hartley’s and colpitts oscillators over RC phase shift oscillator?
  2. Applications of Colpitts and Hartleys oscillators are—–.
  3. Colpitts oscr uses ———- in its feedback network.
  4. Hartleys oscr uses ———–in its feedback network.
  5. Define mutual inductance—–
  6. colpitts and hartleys ocsillators are used at ———— frequencies.
  7. Give the formula for frequency of oscillations in Colpitts oscillator.
  8. Give the formula for frequency of oscillations in Hartley’s oscillator?

SINGLE STAGE CE AMPLIFIER:

  1. What is the phase difference between input and output waveforms of a CE amplifier?
  2. What type of biasing is used in the given circuit?
  3. What is the effect of emitter bypass capacitor on frequency response of a CE amplifier?
  4. What is the effect or importance of coupling capacitor?
  5. Why source resistance Rs is used in the input side?
  6. What are the different regions of operation of a BJT?
  7. The phase difference of input and output in CB amplifier?
  8. CE amplifier is voltage or current amplifier?
  9. Draw the equivalent h-parameter model of a CE amplifier?
  10. Why NPN transistor is preferred over PNP transistor?
  11. What is the effect of bypass capacitor over stability of the CE amplifier?
  12. The CE amplifier is in voltage divider bias or in fixed bias configuration?
  13. The values of hfe,hie,hoe and hre in CE configuration are—————-.
  14. hfe,hie,hoe and hre are called as——————–.
  15. What do you mean by loading effect?
  16. What are the practical applications of single stage CE amplifier?
  17. How do you know the amplifier is single stage CE amplifier?
  18. Why this circuit is called RC coupled amplifier?
  19. What is the operating point in CE amplifier from the design specifications?
  20. Quiescent conditions means——–
  21. D.C conditions are for———
  22. What is the relationship between collector current and base current?
  23. Does β and hfe are one and the same?
  24. Why coupling capacitor Cb is connected in reverse (-,+) at the input side and Cc is connected in forward(+,-) at the output side?
  25. How do u know a transistor is working in cut off region?
  26. Write VBE(active),VBE(sat),VBE(cutoff) values of a Si and Ge transistors
  27. Transistor meaning is———
  28. Define frequency response of a CE amplifier?
  29. Define voltage gain of a CE amplifier?
  30. Units of gain as a ratio are———-
  31. Units of gain in logarithim is———
  32. Magnitude response and frequency response are one and the same say yes or no?
  33. Define bandwidth?
  34. What are 3 dB frequencies?
  35. Define cutoff frequencies?
  36. BW is approximately equal to fH justify?
  37. Gain is constant in————-
  38. Semi logarithmic graph is linear or non linear graph?
  39. Stability factor is a function of—–
  40. In the circuit R1 and R2 are used for——–
  41. The feedback type that Re and Ce introduces in the circuit is———–(Ans: negative feedback).
  42. Negative feedback increases stability yes or no(Ans:yes).
  43. CB amplifier provides more band width than CE amplifier justify?

 

Note: Read advantages and disadvantages and applications of every experiment.

 ALL THE BEST 

 Prepared by   P.Lakshmi Prasanna

 

 

 

 

 

 

 

 

 

 

Computer Networks Routing Algorithms

ROUTING ALGORITHMS

Routing Algorithm:- The Algorithm that manages the Routing Tables and makes the Routing Decisions is called Routing Algorithm.

Implementation of Connection – Oriented Network layer Service:-

  • In this service the subnet is called Virtual Circuit Subnet.
  • A path from Source Router to Destination Router is established before sending any packets. That Router is used for all traffic flowing over that connection.

Ex:- A Telephone System.

  • When connection is released, the virtual circuit is also terminated.

Let us see an example, The figure shows the routing using Virtual Circuit subnet, In this Host H1 wants to send packets to H2

lp

 

lop

Now H1 will establishes a connection1 with Host H2 whenever packet comes from host H1 , we use connection 1 with identifier as 1. i.e, from routing table of A , a packet is coming from H1 , identifier is 1 then use the outgoing router C with identifier 1 .

Similarly for H3 use identifier as 2. This is called as lable Switching .

The comparison between these connection oriented and connection less services or Virtual circuit or data gram subnets is given in the table.

 

Electronics Circuits Lab Viva questions

ELECTRONIC CIRCUITS LAB VIVA QUESTIONS

 CLIPPERS:

  1. What are the applications of clippers?
  2. Diode cut in voltage value for si and Ge diodes?
  3. Why the output of the clipper is taken in d.c mode?
  4. Other names of clippers are—— –.
  5. Voice frequency range is——– –.
  6. Positive peak clipper means
  7. Negative peak clipper means
  8. Positive base and negative base clippers means
  9. What is the difference between clipping and clamping operations?
  10. And the working procedures of each clipping circuit
  11. How clippers are applicable in noise reduction in audio applications?
  12. Draw the output waveforms of different clippers with different input and reference voltages—–
  13. Why clippers are called as diode clippers?
  14. What is the difference between slicing and clipping of a voltage waveform?
  15. Clippers comes under linear or non linear wave shaping?
  16. Explain linear and nonlinear wave shaping meanings?
  17. Names some linear and non linear wave shaping circuits?
  18. Define diode threshold and cutin voltages?
  19. An ideal diode acts as———– under forward
  20. An ideal diode acts as———— under reverse
  21. Practical diode equivalent circuit in forward bias——–
  22. Practical diode equivalent circuit in reverse bias——–
  23. Draw diode d.c characteristics.

CLAMPERS:

  1.  Define clamping operation? And how it is different from clippers?
  2. What are the other names of clampers?
  3. Difference between clipping and clamping circuits
  4. Why capacitors are used in clampers?
  5. What are different types of clampers?
  6. Working Operation of each clamper circuit
  7. Practical applications of clampers are
  8. What happens in the output waveform if the polarity of capacitor is changed in the clampers
  9. Capacitor acts as———- for D.C input
  10. Capacitor acts as————- for A.C
  11. Fully charged capacitor acts as——– –.
  12. What do u mean by transient and steady state response of a clamper?
  13. DC restorers are used in CRO’s yes or no
  14. DC inserter means————
  15. Voltage or amplitude slicers means———–
  16. Voltage or amplitude limiters means———– –.
  17. Explain the operation of positive peak clamper?
  18. What is the working principle of a capacitor/
  19. Output waveforms of clampers with different input and different reference voltages—
  20. The voltage across a capacitor remains———— once the capacitor is fully

SINGLE STAGE CE AMPLIFIER:

  1. What is the phase difference between input and output wave forms of a CE amplifier?
  2. What type of biasing is used in the given circuit?
  3. What is the effect of emitter bypass capacitor on frequency response of a CE amplifier?
  4. What is the effect or importance of coupling capacitor?
  5. Why source resistance Rs is used in the input side?
  6. What are the different regions of operation of a BJT?
  7. The phase difference of input and output in CB amplifier?
  8. CE amplifier is voltage or current amplifier?
  9. Draw the equivalent h-parameter model of a CE amplifier?
  10. Why NPN transistor is preferred over PNP transistor?
  11. What is the effect of bypass capacitor over stability of the CE amplifier?
  12. The CE amplifier is in voltage divider bias or in fixed bias configuration?
  13. The values of hfe,hie,hoe and hre in CE configuration are———– –.
  14. hfe,hie,hoe and hre are called as————— –.
  15. What do you mean by loading effect?
  16. What are the practical applications of single stage CE amplifier?
  17. How do you know the amplifier is single stage CE amplifier?
  18. Why this circuit is called RC coupled amplifier?
  19. What is the operating point in CE amplifier from the design specifications?
  20. Quiescent conditions means——–
  21. C conditions are for———
  22. What is the relationship between collector current and base current?
  23. Does β and hfe are one and the same?
  24. Why coupling capacitor Cb is connected in reverse (-,+) at the input side and    Cc is connected in forward(+,-) at the output side?
  25. How do u know a transistor is working in cut off region?
  26. Write VBE(active),VBE(sat),VBE(cutoff) values of a Si and Ge transistors
  27. Transistor meaning is———
  28. Define frequency response of a CE amplifier?
  29. Define voltage gain of a CE amplifier?
  30. Units of gain as a ratio are———-
  31. Units of gain in logarithim is———
  32. Magnitude response and frequency response are one and the same say yes or no?
  33. Define bandwidth ?
  34. What are 3 dB frequencies?
  35. Define cutoff frequencies?
  36. BW is approximately equal to fH justify?
  37. Gain is constant in————-
  38. Semi logarithmic graph is linear or non linear graph?
  39. Stability factor is a function of—–
  40. In the circuit R1 and R2 are used for——–
  41. The feedback type that Re and Ce introduces in the circuit is———–(Ans: negativefeedback).
  42. Negative feedback increases stability yes or no(Ans:yes).
  43. CB amplifier provides more band width than CE amplifier justify?

TWO STAGE RC COUPLED CE AMPLIFIER:

  1. What is the need for cascading in amplifiers?
  2. Why do we need two stage CE amplifier?
  3. Why this circuit is called two stage CE amplifier?
  4. What is the relationship between gain and bandwidth?
  5. Cascading of number of stages in amplifiers increases——— –.
  6. Cascading of number of stages linear amplifiers decreases—– –.
  7. Why do we use a coupling capacitor between two stages?
  8. Why RC coupling is preferred in Audio frequency range?
  9. Explain various types of capacitors?
  10. What do you mean by loading effect? How to avoid it?
  11. Identify the stages of the amplifier?
  12. CE-CE combination is called as———-
  13. Cascade configuration means——
  14. What is the overall gain of two satge amplifier—–
  15. Is two stage amplifier is a multistage amplifier or not?
  16. Why this circuit is called RC coupled amplifier?
  17. Does CB-CB combination is possible?
  18. CE-CC combination is known as——-
  19. CB-CC combination is called as——–
  20. There exist an inverse proportionality between gain and BW yes or no?

VOLTAGE SERIES FEEDBACK AMPLIFIERS:

  1. What do u mean by feedback?
  2. What are the two types of feedback?
  3. What are the advantages of negative feedback over positive feedback?
  4. Voltage series feedback means?
  5. Input of a voltage series combination is———–
  6. Output of a voltage series combination is———–
  7. For voltage series amplifier Ri , Ro,gain and BW changes as——-
  8. How does u know the feedback is voltage series in the given circuit?
  9. What are different types of feedback topologies?
  10. Applications of voltage series amplifier?
  11. What is the difference between two stage and voltage series amplifier?
  12. Which is the best topology among four?
  13. How feedback amplifiers are different from ordinary amplifiers?
  14. Define feedback gain?

RC PHASE SHIFT OSCILLATOR:

  1.  Mention the conditions for oscillations in RC phase shift oscillator?
  2. Give the formula for frequency of oscillations in RC phase shift oscillator?
  3. The phase produced by a single RC network is RC phase shift oscillator?
  4. RC phase shift oscillator uses positive feedback or negative feedback?
  5. The phase produced by basic amplifier circuit in RC phase shift oscillator is?
  6. What is the difference between damped oscillations un damped oscillations?
  7. What are the applications of RC phase shift oscillator?
  8. How many resistors and capacitors are used in RC phase shift feedback network?
  9. How the Barkhausen’s criterion is satisfied in RC phase shift oscillator
  10. Mention the basic reason for any oscillations?
  11. What is meant by Barkhausen’s criterion?
  12. Audio frequency range is————
  13. RC phase shift oscillator is ——–
  14. Oscillator is a circuit operates on internal input power supply yes or no?
  15. Define an oscillator?
  16. Oscillator did not take any external input yes or no?
  17. Type of feedback used in oscillators is——-
  18. Radio frequency range is———–
  19. Show that single RC section provides a phase shift of 60
  20. Positive feedback causes instability yes or no?
  21. In oscillators loop gain must be————–
  22. In oscillators And overall phase shift produced by the circuit is————
  23. Feedback gain 𝛽 must be less than———–

COLPITTS AND HARTLEY’S OSCILLATORS:

  1. What are the advantages of hartley’s and colpitts oscillators over RC phase shift oscillator?
  2. Applications of C and H oscillators are—–.
  3. C oscillator uses—- as feedback network.
  4. H oscillator uses—– as feedback
  5. Define mutual inductance—–
  6. These are used at———–

MEASUREMENT OF IMPEDANCES:

  1. Differentiate symmetrical and asymmetrical networks?
  2. Define image impedance?
  3. Define characteristic or nominal impedance?
  4. Theoretical Calculations of open circuit and short circuit impedances for all the
  5. What is the significance of image impedance?
  6. Is there any difference between image and inverse impedance?
  7. Why char impedance is called as nominal impedance?
  8. Does char impedance and image impedance are same yes or no?

CONSTANT –K-LOW PASS FILTER:

  1. Define a filter?
  2. What is the difference between ordinary LPF and constant –k-LPF?
  3. Why this filter is called as constant-k-low pass filter?
  4. What does u mean by a LPF?
  5. Draw the gain characteristics of ideal and practical Low pass filters?
  6. Define attenuation? units of attenuation are——
  7. Gain and attenuation are——-
  8. Define cut off frequency of a constant k low pass filter?
  9. Draw the attenuation characteristic and explain that graph?
  10. Draw the output voltage vs frequency curve and explain it?’
  11. What are the applications of constant-k low pass filter?
  12. Advantages and disadvantages of constant k low pass filter?

M-DERIVED HIGH PASS FILTER:

  1. Define high pass filter?
  2. Define the constant m?
  3. How m derived filter is different from ordinary HPF?
  4. Why we will go for m derived filters?
  5. Draw the model graphs of m derived HPF and explain?
  6. Applications of m derived HPF?
  7. Advantages and disadvantages of m derived HPF?
  8. Define infinity frequency and cut off frequency?
  9. Are these filters are passive filters or active filters?

NOTE: read applications and advantages and disadvantages for all the circuits.

analog communications lab viva questions

EXPERIMENT WISE VIVA QUESTIONS ANALOG COMMUNICATION LAB

Amplitude Modulation:

  1. What is meant by Modulation? What is the need for modulation?
  2. What are different types of analog modulation techniques?
  3. What are the other names of message signal? What are the other names of carrier signal?
  4. Write the equation of AM signal and explain each parameter in that equation?
  5. Define Amplitude Modulation? Define modulation depth or modulation index?
  6. What is the range of Audio frequency signals? What is the range of Radio frequency signal?
  7. What are the applications of Amplitude modulation?
  8. How many generation methods are there to generate an AM wave? What are the methods of demodulation of an AM wave?
  9. Explain the operation of diode detector circuit?
  10. Write the formula for modulation index? Differentiate under, over and perfect modulation in AM?
  11. As the amplitude of message signal increases, modulation index increases or decreases?
  12. Define single tone modulation? In laboratory type of AM is single tone modulation or not?
  13. Draw the frequency spectrum of AM wave?
  14. If modulation index is 100%, calculate the ratio of total power to carrier power of an AM wave?
  15. If µ=1 in an AM wave what is the amount of power saving in an AM wave? What is the band width of an AM wave?
  16. Explain the operation of AM modulator? Explain the operation of 8038 circuit in AM modulator?
  17. Explain the procedure of Amplitude modulation? What is the significance of Emax and Emin points in AM wave?
  18. Plot message, carrier and AM signals?
  19. What is meant by envelope detector?
  20. The frequency of AM wave follows — (message signal frequency or carrier frequency)?
  21. The amplitude of AM wave at fc +fm is— and The amplitude of AM wave at fc -fm is—–
  22. In amplitude modulation the amplitude of ——— is changing with respect to ——
  23. Envelope of AM signal follows————– (message signal/ carrier signal)?
  24. What are the advantages and disadvantages of AM?
  25. How demodulated signal differs from original signal in AM?
  26. The two important distortions that can appear in the demodulated output of an envelope detector are————– and—————————- –.
  27. Differentiate high-level and low-level modulations in AM?
  28. What is trapezoidal rule?

Balanced Modulator:

  1. What are the disadvantages of AM?
  2. Most of the power in AM spectrum is carried by ————
  3. Define DSBSC modulation?
  4. How DSBSC is more efficient than AM in terms power saving, explain?
  5. What is meant by frequency response?
  6. Draw the magnitude response or amplitude spectrum of DSBSC signal?
  7. The signal generated by balanced modulator is———–
  8. Draw the wave form of DSBSC wave and AM wave, and differentiate those two waveforms?
  9. Give the equation of DSBSC signal?
  10. What are the generation methods of DSBSC?
  11. What are the demodulation methods of DSBSC?
  12. What is the bandwidth of DSBSC signal?
  13. Define Costas loop and it’s operation?
  14. Amount of power saving in DSBSC signal is————
  15. Coherent detection means?
  16. Give the practical applications of balanced modulator?
  17. Explain the operation of product modulator?
  18. Why the circuit is called balanced modulator?
  19. If the circuit is operating in balanced state, the modulation index value is——- –.
  20. Explain the working procedure of 1496 IC for the generation of DSBSC wave?
  21. As message signal amplitude increases, carrier suppression in dB’s ———
  22. Plot message, carrier and DSBSC waves and explain each wave clearly.
  23. How do you differentiate modulation by demodulation?
  24. Explain the significance of local oscillator frequency in modulators and in
  25. Differentiate synchronous and non synchronous detection techniques in analog modulators?
  26. The phase shift at zero crossings in DSBSC wave is——- –.
  27. What is Quadrature carrier multiplexing?
  28. How DSBSC is different from SSB?

Frequency Modulation:

  1. Define Frequency modulation? How it is different from phase modulation?
  2. Write equation of FM wave, explain each parameter in it?
  3. Draw the amplitude spectrum of FM wave?
  4. Give the Carson’s rule in FM?
  5. Define modulation index β, frequency deviation?
  6. Differentiate Narrow band FM with Wide band FM?
  7. Explain the FM operation using 8308IC?
  8. Draw message, carrier and FM waves and explain each wave clearly?
  9. Explain the methods for generation of FM and its demodulation?
  10. How FM wave is different from PM wave?
  11. Give the practical applications of FM?
  12. State advantages and disadvantages of FM?
  13. The range of speech signals is——— –.
  14. Type of Modulation used in radios is——- –.
  15. Type of modulation used for voice signals in T.V — and for video signals in V is—- –.
  16. Noise immunity is more in which analog modulation technique———– –.
  17. FM is more robust to noise compared to AM, why?
  18. Carson’s rule is for———- –.
  19. In commercial FM broadcasting, the audio frequency range handled is only up to—- –.
  20. The transmission band width required for commercial FM broadcasting is——– –.
  21. Define Hilbert transform?
  22. Explain capture effect in FM broadcasting?

Pre-emphasis and De-emphasis:

  1. Define pre-emphasis and De-emphasis processes in
  2. Why Pre-emphasis is used at Transmitter of FM and de-emphasis at FM receiver?
  3. Draw the pre-emphasis circuit and explain its working in detail?
  4. Draw de-emphasis circuit and explain its working in detail?
  5. Draw the frequency response characteristics of pre-emphasis and de-emphasis explain each one in detail?
  6. Calculate the cut-off frequencies of pre-emphasis and de-emphasis circuits practically
  7. Pre-emphasis circuit operation is similar to——— –.
  8. De-emphasis circuit operation is similar to——— –.
  9. What is the necessity of boosting up high frequencies in frequency modulation communication system?
  10. Define 3dB frequencies?

Sampling and reconstruction:

  1. Define sampling theorem? What is the need for sampling?
  2. What are the necessary and sufficient condition for sampling and reconstruction of a signal?
  3. Define Nyquist rate and Nyquist interval in sampling theorem?
  4. If message frequency is 2 KHz and sampling frequency is 2 KHz,4 KHz, 8 KHz and 16 KHz in each case the number of samples are—————————– –.
  5. What are different types of sampling techniques?
  6. What was the effect on sampled signal if fs < 2 fm ?
  7. Draw the amplitude spectrum of sampled signal if fs < 2 fm, fs =2 fm, fs > 2 fm.
  8. What is aliasing effect in sampling? How to avoid it?
  9. Why do we use pre-filtering in sampling?
  10. What do you mean by reconstruction of sampling theorem?
  11. What are the types of filters used in reconstruction?
  12. Define sample and hold process?
  13. Differentiate second order, fourth order and sixth order low pass filters in reconstruction process.
  14. Explain the sampling and reconstruction process in detail by using the trainer
  15. Define band pass sampling?
  16. How sampling is different from PAM?
  17. Define a continuous time signal or an analog signal. Give some examples of analog signals.
  18. Define a discrete time signal. Give some examples of discrete
  19. What is the difference between discrete and a digital signal?
  20. Define a digital signal? Give some
  21. What is the need for converting a continuous signal into a discrete
  22. Explain about zero-order hold circuit.
  23. How to convert an analog signal into digital signals?

Digital signal processors operates———— as inputs.As the number of samples increases, the reconstruction of original signal becomes?

Pulse Amplitude Modulation:

  1. What is the basic principle of PAM?
  2. Name some Pulse Modulation techniques?
  3. Define PAM?
  4. How PAM is different from AM?
  5. Can we produce a PAM signal using a sampling circuit?
  6. Differentiate PAM output with sampling output?
  7. Does PAM come under Analog modulation technique or Digital Modulation technique?
  8. What is the Bandwidth of PAM?
  9. Compare BW of PAM and AM?
  10. Draw waveforms of PAM. explain each one briefly.
  11. What are the advantages of PAM over AM?
  12. What are the advantages and Disadvantages of PAM?
  13. Explain the working procedure PAM kit?
  14. Can we use PAM technique in TDM?
  15. Differentiate uni-polar and bi-polar PAM.
  16. What do you mean by zero order holding? And draw the circuit diagram of zero-order hold circuits?
  17. What are the drawbacks of PAM?
  18. Explain the working of PAM demodulation circuit?
  19. Define Flat-Top sampling?
  20. Draw the circuit diagram of Flat-Top Sampled circuit?
  21. What was the roll off characteristics of sinc pulse?

    Pulse Width Modulation (PWM):

    1. Define PWM?
    2. Differentiate PWM, PAM and PPM?
    3. Name the applications of Mono-stable multivibrator?
    4. What is a Multivibrator?
    5. Differentiate Monostable, Bi stable and Astable Multivibrators?
    6. How a Monostable Multivibrator produces a PWM signal?
    7. What are the other names of PWM?
    8. Define Pulse Duration Modulation?
    9. What is Pulse Time Modulation?
    10. Draw PAM and PWM signals and each one in detail.
    11. Draw PWM signal with respect to message signal?
    12. In PWM —————- of Pulse carrier signal is changing with respect to message signal.
    13. Explain the operation of PWM circuit.
    14. 555 timer in Monostable mode produces————.
    15. 555 timer in Astable mode produces——————.
    16. What are the advantages of PWM over PAM?
    17. What is the difference between PWM and FM?
    18. Which type of noise is affecting the amplitude of PWM signal?
    19. Which system is more immune to noise (PWM or PAM)?
    20. What are the disadvantages of PWM?
    21. What are the applications of PWM?
    22. Band Width of PWM is—————-.
    23. Band width of PAM is—————-.

      Pulse Position Modulation (PPM):

      1. Define PPM?
      2. The information is conveyed by ————- of Pulses in PPM.
      3. In PWM information is conveyed by————— of pulses.
      4. In PAM information is conveyed by————— of pulses.
      5. What are the advantages and disadvantages of PPM?
      6. Compare PPM with Phase Modulation.
      7. PAM is similar to————————–.
      8. PWM is similar to————————–.
      9. PPM is similar to————————–.
      10. Differentiate Analog Modulation Techniques with Pulse Modulation Techniques.
      11. What are the applications of PPM?
      12. Draw PPM signal with respect to message signal.
      13. Draw PPM signal with respect to PWM signal.
      14. Explain the operation of PPM Modulator?

        Phase Locked Loop (PLL):

        1. What are the applications of PLL?
        2. Why this circuit is called Phase Locked Loop?
        3. What are the three components of PLL circuitry?
        4. Explain the operation of PLL by using a Block Diagram?
        5. Define free-running frequency?
        6. Define Lock range and Capture range of a PLL?
        7. What is meant by Frequency synthesizer?
        8. Why PLL is used in FM Receivers/
        9. How PLL is used in FSK demodulation circuits?
        10. What do you mean by Lock state in a PLL?
        11. What is meant by Pull in time in PLL?
        12. Phase Detector or Phase Comparator is used for ——————.
        13. Why VCO is used in feedback loop of PLL?
        14. What are the input and Output signals of a VCO in a PLL?
        15. What are the advantages and Disadvantages of PLL?
        16. Why Lock range is greater than Capture range in a PLL?

          Time Division Multiplexing (TDM):

          1. Define the concept of Time Division Multiplexing?
          2. Differentiate Multiplexing and Sampling?
          3. What are the different types of Multiplexing Techniques?
          4. Does TDM come under analog Multiplexing or Digital Multiplexing?
          5. Define a frame in a TDM?
          6. Why synchronization is required in TDM?
          7. Why multiplexing is required?
          8. What do you mean by inter-leaving gaps in TDM frame?
          9. If two signals of frequencies 2KHz and 4 KHz are multiplexed in time –domain then draw TDM signal
            1. Without inter-leaving gap.
            2. with inter-leaving gap of 10 ms.
          10. What are the advantages and Disadvantages of TDM?
          11. Differentiate TDM with FDM?
          12. What are the advantages of TDM over FDM?
          13. Explain the operation of TDM using trainer kit used.
          14. Synchronous TDM means?

            Additional Questions:

            1. What is a filter?
            2. Differentiate Active and Passive Filters?
            3. Why LPF is used in Demodulation Circuits?
            4. Why pre-filtering is required in sampling?
            5. Anti-aliasing is achieved by using———– in Sampling Circuits?
            6. Define Single-tone modulation in AM and FM?
            7. Why FM receivers are more immune to AM receivers?
            8. BW of Narrow band FM is ——————.
            9. BW of AM is ———————————-.
            10. How to calculate Image frequency of a Radio Receiver?
            11. Define Power Spectral Density.
            12. Define AWGN noise.
            13. Define SNR.
            14. Where do we use Hilbert Transform?
            15. Over modulation in AM means….
            16. What is µ value when AM wave is similar to DSBSC wave?

           

         

       

     

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