grand viva question for ece student

What are different categories of antenna and give an example of each? 1. Different categories of antenna are a re as follows : 1. Wire Antennas - Short Dipole Antenna 2. Microstrip Antennas - Rectangular Microstrip (Patch) ( Patch) Antennas 3. Reflector Antennas - Corner Reflector 4. Travelling Wave Antennas - Helical Antennas 5. Aperture Antennas - Slot Antenna 6. Other Antennas - NFC Antennas 2. What is handover and what are its types? Handover in mobile communication refers to the process of transferring a call from one network cell to another a nother without breaking the call. There are two types of handover which are as follows : Hard Handoff : hard handoff han doff is the process in which the cell connection is disconnected from the previous cell before it is made with the new one. Soft Handoff : It is the process in which a new connection is established first before disconnecting the old one. on e. It is thus more efficient and smart. 3. What is ionospheric bending? When a radio wave travels into the ionospheric layer it experiences refraction due to difference in density. The density of ionospheric layer is rarer than the layer l ayer below which causes the radio wave to be bent away from the normal. Also the radio wave experiences a force from the ions in the ionospheric layer. If incident at the correct c orrect angle the radio wave is completely reflected back to the inner atmosphere due to total internal reflection. This phenomenon is called ionospheric reflection and is used in mobile communication for radio wave propagation also known as ionospheric bending of radio waves. 4. What is CDMA? CDMA stands for Code Division Multiple Access which uses digital format. In CDMA systems several transmissions via the radio interface take place simultaneously on the same frequency bandwidth. band width. User data is combined at the transmitter’s side with a code, then transmitted. tra nsmitted. On air, all

transmission get mixed. At the receiver's side the same code is used as in the transmitter’s side. The code helps the receiver to filter the user information of the transmitter from incoming mixture of all transmissions on the same frequency band and same time. 5. Explain the concept of frequency re-use. The whole of the geographical area is divided into hexagonal shape geometrical area called cell and each cell having its own transceiver. Each BTS (cell site) allocated different band of frequency fr equency or different channel. Each BTS antenna is designed in such a way that i cover cell area in which it is placed with frequency allotted without interfering inter fering other cell signals. The design process of selecting and allocating channel groups for all of the cellular base station within system is called frequency reuse. reus e. 6. Explain Bluetooth. Bluetooth is designed to be a personal area network, where participating entities are mobile and require r equire sporadic communication with others. It is omni directional i.e. it does not have line of sight limitation like infra red does. Ericsson started the work on Bluetooth and named it after the Danish king Harold Biuetooth. Bluetooth operates in the 2.4 GHz area of spectrum and provides a range of 10 metres. It offers transfer speeds of around 720 Kbps. 7. What are GPRS services? GPRS services are defined to fall in one of the two categories : - PTP ( Point to point) - PTM ( Point to Multipoint) Some of the GPRS services are not likely to be provided by network operators during early deployment of GPRS due in part to the phased development of standard. Market demand is another factor affecting the decision of operators regarding regar ding which services to offer first. 8. What are the advantages of CDMA?  Advantages of CDMa are as follows : 1. Frequency diversity : Transmission is spread out over a large bandwidth

due to that less affected by noise. If bandwidth is increased S/N ratio increases, which means noise will be reduced. 2. Multiplication Resistance : Chipping codes used for CDMA not on ly exhibit low correlation but also low autocorrelation. Hence a version of the signal that is delayed by more than tha n one chip interval does not interfere with dominant signal as in other multipath environments. 3. Privacy : Due to spread spectrum is obtained obtain ed by the use of noise like signals, where each user has a unique code, so privacy is inherent. 4. Graceful Degradation. In CDMA, more users access the system simultaneously as compared to FDMa, TDMA. 9. What are the advantages of spread spectrum? SPread spectrum has the following advantages : 1. No crosstalk interference. 2. Better voice quality/data integrity and less static noise. 3. Lowered susceptibility to multipath fading. 4. Inherent security. 5. Co-existence. 6. Longer operating distances. 7. Hard to detect. 8. Hard to intercept or demodulate. 9. Harder to jam than narrow bands. 10. Use of ranging and radar. 10. Explain the steps involved in demodulating a signal. Once the signal is coded, modulated and then sent, the receiver must demodulate the signal. This is usually usua lly done in two steps : 1. Spectrum spreading (e.g., direct sequence or frequency hopping) modulation is removed. 2. The remaining information bearing signal is demodulated by multiplying with a local reference identical in structure and synchronised with received signal. 11. How can a Pseudo Random Noise COde be usable? To be usable for direct d irect sequence spreading, a PN code must meet the following conditions :

1. Sequence must be built bui lt from 2 levelled numbers. 2. The codes must have sharp autocorrelation peak to enable code synchronization. 3. Codes must have a low cross-correlation value, the lower it is, more are the number of users which can be allowed in the system. 4. The codes should be “balanced” i.e. the difference between ones and zeros in code may only be 1. 12. What are the drawbacks dr awbacks of walsh codes? Walsh codes have the following drawbacks dr awbacks : 1. The codes do not have a single, narrow autocorrelation peak. 2. The spreading is not over o ver the whole bandwidth; instead the energy ener gy is spread over a number of discrete frequency components. 3. Although the full sequence cross correlation is identically zero, this does not hold for a partial sequence cross correlation function. Thus advantage of using orthogonal codes is lost. 4. Orthogonality is also affected by channel properties like multi path. 13. Explain radio environment in building. Building penetration : Building penetration depends on the material used for construction and architecture used. This varies building to building and is based on building construction. Building Height Effect : The signal strength is always a lways higher at top floor and generally floor gain height is about 2.7dB/floor which is not dependent on building construction. Building Floor Reception : The signal isolation between floors in a multi floor building is on the average about 20dB. Within a floor of 150 * 150 feet, the propagation loss due to interior walls, depending on the wall materials is about 20 dB between the strong and the weak areas. 14. List some advantages of GSM. Here are some advantages of GSM : 1. GSM is mature, this maturity means a more stable network with robust features. 2. Less signal deterioration inside buildings. 3. Ability to use repeaters. 4. Talk time is generally higher in GSM phones due to pulse nature of

transmission. 5. The availability of Subscriber Identity Modules allows users to switch networks and handset at will. 6. GSM covers virtually all parts of world so international inter national roaming is not a problem. 15. What are the various types of numbers for network identity? Various types of number for network identity are as follows : 1. MSISDN ( Mobile station ISDN) Number : It is international m obile subscriber number which is normally called mobile number. It is unique worldwide. 2. MSRN ( Mobile Subscriber Routing Number) : MSRN is used during mobile terminate trunk call to provide location of mobile subscriber. 3. HON ( Hand Over Number ) : HON is used for providing information required to transfer call from fr om one B?SC to another BSC or to another a nother MSC. 4. ISMI ( International Mobile Subscriber Identity Number) : Purpose of ISMI is for location update and authentication. au thentication. 5. TMSI ( Temporary Mobile Subscriber Identity ) : TMSI is used instead of IMSI to improve security efficiency of network. 6. IMEI : International Mobile Equipment Identity. Ide ntity. 16. What are the functions of Base Station System ( BSS)? Functions of BSS are as follows : 1. Radio path control. 2. BTS and TC control. 3. Connection establishment with MS-NSS. 4. Mobility management, speech transcoding. 5. Connection of statistical data. 17. What are the parts par ts of Network Management System ( NMS )? Following are the parts par ts of network management system : 1. OMC : Operation and maintenance center - Computerized monitoring center. 2. NMC : Network Management Center - Centralized Centra lized control of a network is done here. 3. OSS : Operation and support supp ort system - Used for supporting activities performed in an OMC and/or and/ or NMC.

18. What are applications of DSP? Some selected applications or digital signal processing that are often encountered in daily life are listed as follows: 1. Telecommunication: Echo cancellation in telephone telephon e networks. 2. Military Radar signal processing 3. Consumer electronics Digital Audio/TV 4. Instrumentation and control 5. Image processing image representation, image compression 6. Speech processing speech analysis methods are used in automatic speech recognition 7. Medicine Medical diagnostic instrumentation such as computerised tomography (CT) 8. Seismology DSP techniques are employed in geophysical exploration for oil and gas. 9. Signal Filtering Removal of unwanted background noise. 19. What is analog-to-digital conversion of signals?  A discrete-time signal is defined by specifying its value only at discrete times, called sampling instants. When the sampled values are quantised and encoded, a digital signal is obtained. A digital signal is obtained from the analog signal by using an analog-to-digital converter. This entire process is referred to as the conversion of signals from analog to digital d igital form. 20. What are the properties of ROC for z-Transform? Properties of the ROC for the z-Transform : 1. X(z) converges uniformly if and only onl y if the ROC of the z-transform X(z) of the sequence includes the unit circle. c ircle. The ROC of X(z) consists of a ring in the z-plane centered about the origin. That is, the ROC of the z-transform of x(n) has values of z for which x(n) r-n is absolutely summable. 2. The ROC does not contain any an y poles. 3. When x(n) is of finite duration du ration then the ROC is the entire z-plane, except possibly z=0 and/or z=infinity. 4. If x(n) is a right sided sequence, seq uence, the ROC will not include infinity. 5. If x(n) is a left sided sequence, seque nce, the ROC will not include z=0. However if x(n)=0 for all n>0, the ROC will include z=0. 6. If x(n) is two sided and if the circle c ircle |z| = r0 is in the ROC, then the ROC

will consist of a ring in the z-plane that includes the circle |z|=r0. 7. If X(z) is rational, then the ROC extends to t o infinity, i.e. the ROC is bounded by poles. 8. If x(n) is causal, then the ROC includes z=infinity. 9. If x(n) is anti- causal, trhen the t he ROC includes z=0.

DIGITAL QUESTIONS AND ANSWERS

Ques 1. Explain about setup time and hold time, what will happen if there is setup time and hold tine violation, how to overcome this?  Ans.. For Synchronous flip-flops, we have special requirements for the inputs Ans with respect to clock signal input there are Setup Time: Minimum time Period during which data must be stable before the clock makes a valid transition. E.g. for a positive edge triggered flip-flop having a setup time of 2ns so input data should be Stable Stable for 2ns before the clock makes a valid transaction from zero to one. Hold Time: Minimum time period during which data must be stable after the clock has made a valid transition. E.g. for a posedge triggered flip-flop, with a hold time of 1 ns. Input Data (i.e. R and S in the case of RS flip-flop) flip-flo p) should be stable for at least 1 ns after clock has made transition from 0 to 1 Hold time is the amount of time after the clock edge that same input signal has to be held before changing it to make sure it is sensed properly at the clock edge. Whenever there are setup and hold time violations in any flip-flop, it enters a state where its output is unpredictable: this state is known as metastable state (quasi stable state); at the end of metastable state, the flipflop settles down to either ‘1’ or ‘0’. This whole process is known as metastability Ques 2. What is difference difference between latch and flip-flop?  Ans. The main difference between latch and FF is that latches are level sensitive while FF is edge sensitive. They both require the use of clock signal and are used in sequential logic. For a latch, the output tracks the input when the clock signal is high, so as long as the clock is logic 1, the output can change if the input also changes. FF on the other hand, will store the input only when there is a rising/falling edge of the clock. Latch is sensitive to glitches on enable pin, whereas flip-flop is immune to glitches. Latches take fewer

gates (also less power) to implement than flip-flops. Latches are faster than flip-flops. Ques 3 Given only two xor gates one one must function as buffer and another as inverter? Ans Tie Ans  Tie one of o f xor gates input to 1 it will act as inverter. Tie one of xor gates input to 0 it will act as buffer. Ques 4 Difference between Mealy and Moore state machine?  Ans   Mealy and Moore models are the basic models of state machines. A Ans state machine which uses only Entry Actions, so that its output depends on the state, is called a Moore model. A state machine which uses only Input  Actions, so that the output depends on the state and also also on inputs, is called a Mealy model. The models selected will influence a design but there are no general indications as to which model is better. Choice of a model depends on the application, execution means (for instance, hardware systems are usually best realized as Moore models) and personal preferences of a designer or programmer. Mealy machine has outputs that depend on the state and input (thus, the FSM has the output written on edges) Moore machine has outputs that depend depe nd on state only (thus, the FSM has the output o utput written in the state itself.  Advantages and Disadvantages Disadvantag es In Mealy as the output variable is a function both input in put and state, changes of state of the state variables will be delayed with respect to changes of signal level in the input variables, there are a re possibilities of glitches appearing in the output variables. Moore overcomes glitches as output dependent on only states and not the input signal level. All of the concepts can be applied to Moore-model state machines because any Moore state machine can be implemented as a Mealy state machine, although the converse is not true. Moore machine: the outputs are properties of states themselves… which means that you get the output after the machine reaches a particular state, or to get some output your machine has to be taken to a state which provides you the output. The outputs are held until you go to some other state Mealy machine: Mealy machines give you outputs instantly, that is immediately upon receiving input, but the output out put is not held after that clock cycle. Ques 5 Difference between one hot and binary binary encoding?  Ans. Common Ans.  Common classifications used to describe the state encoding of an FSM are Binary (or highly encoded) and One hot.A binary-encoded FSM design only requires as many flip-flops as are needed to uniquely encode the number of states in the state machine. The actual number of flip-flops

required is equal to the ceiling of the log-base-2 of the number of states in the FSM.A one hot FSM design requires a flip-flop for each state in the design and only one flip-flop (the flip-flop representing the current or “hot” state) is set at a time in a one hot FSM design. For a state machine with 9- 16 states, a binary FSM only requires 4 flip-flops while a one hot FSM requires a flip-flop for ea ch state in the design FPGA vendors frequently recommend using a one hot state encoding style because flip-flops are plentiful in an FPGA and the combinational logic required to implement a one hot FSM design is typically smaller than most binary encoding styles. Since FPGA performance is typically related to the combinational logic size of the FPGA design, one hot FSMs typically run faster than a binary encoded FSM with larger combinational logic log ic blocks Ques 6 How to achieve 180 degree exact phase shift?  Ans. a) DCM an inbuilt resource in most of FPGA can be configured to get 180 degree phase shift. b) BUFGDS that is differential signaling buffers which are also inbuilt resource of most of FPGA can be used. Digital Electronics Solved Questions Ques 7 What is significance of RAS and CAS in SDRAM?  Ans. SDRAM receives its address command in two address words. It uses a multiplex scheme to save input pins. The first address addr ess word is latched into the DRAM chip with the row address strobe (RAS). Following the RAS command is the column address strobe (CAS) for latching the second address word. Shortly after the RAS and CAS strobes, the stored data is valid for reading. Ques 8 Tell some of applications of buffer?  Ans. a) They are used to introduce small delays. b) They are used to eliminate cross talk caused due to inter electrode capacitance due to close routing. c) They are used to support high fan-out, e.g.: bufg 9) Give two ways of converting a two input NAND gate to an inverter? a) Short the 2 inputs of the NAND gate and apply the single input to it. b) Connect the output to one of the input and the other to the input signal. Ques 10. Why is most interrupts active low?  Ans. This answers why most signals are ar e active low if you consider the transistor level of a module, active low means the capacitor in the output terminal gets charged or discharged based on low to high and high to low transition respectively. When it goes from high to low it depends on the pull down resistor that pulls it down and it is relatively easy for the output

capacitance to discharge rather than charging. Hence people prefer using active low signals.

Electronics Interview Questions 609916

1. What is Electronic? The study and use of electrical devices that operate by controlling the flow of electrons or other electrically charged particles.

2. What is communication? Communication means transferring a signal from the t ransmitter which passes through a medium then the output is obtained at the receiver. (or)communication says as transferring transferring of message from one place to another place called communication.

3. Different types of communications communications? ? Explain. Analog and digital communication. As a technology, analog is the process of taking an audio or video signal (the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s. Digital signals are immune to noise, quality of transmission and reception is good, components used in digital communication can be produced with high precision and power consumption is also very less l ess when compared with analog signals. si gnals.

4. What is sampling? The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.

5. State sampling theorem. It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is equal to or greater than twice the cut off frequency and the minimum sampling rate is known as the Nyquist rate.

6. What is cut-off frequency? f requency? The frequency at which the response is -3dB with respect to the maximum response.

7. What is pass band? Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.

8. What is stop band? A stopband is a band of frequencies, between specified l imits, in which a circuit, such as a filter or telephone circuit, does not l et signals through, or the attenuation is above the required stopband attenuation level.

9. Explain RF? Radio frequency (RF) is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves. Since most of this range i s beyond the vibration rate that most mechanical systems can respond to, RF usually refers to oscillations in electrical circuits or electromagnetic radiation.

10. What is modulation? And where it is utilized? Modulation is the process of varying some characteristic of a periodic wave with an external signals. Radio communication superimposes this information bearing signal onto a carrier signal. These high frequency carrier signals can be transmitted over the air easily and are capable of travelling long distances. The characteristics (amplitude, (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the information bearing signal. Modulation is utilized to send an information i nformation bearing signal over long distances.

11. What is demodulation? Demodulation is the act of removing the modulation from an analog signal to get the original baseband signal back. Demodulating is necessary because the receiver system receives a modulated signal with specific characteristics and it needs to turn it to baseband.

12. Name the modulation techniques. For Analog modulation--AM, SSB, FM, PM and SM Digital modulation--OOK, FSK, ASK, Psk, QAM, MSK, CPM, PPM, TCM, OFDM

13. Explain AM and FM.

AM-Amplitude modulation is a type of modulation where the ampli tude of the carrier signal is varied in accordance with the information bearing signal. FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the information bearing signal.

14. Where do we use AM and FM? AM is used for video signals for example TV. Ranges from 535 to 1705 kHz. FM is used for audio signals for example Radio. Ranges from 88 t o 108 MHz.

15. What is a base station? Base station is a radio receiver/transmitter that serves as the hub of the local wireless network, and may also be the gateway between a wired network and the wireless network.

16. How many satellites are required to cover the earth? 3 satellites are required to cover the entire earth, which is placed at 120 degree to each other. The life span of the satelli te is about 15 years.

17. What is a repeater? A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other side of a n obstruction, so that the signal can cover longer distances without degradation.

18. What is an Amplifier? An electronic device or electrical circuit that is used to boost (amplify) the power, voltage or current of an applied signal.

19. Example for negative feedback and positive feedback? Example for

ve feedback is ---Amplifiers And for +ve feedback is

 Oscillators

20. What is Oscillator? An oscillator is a circuit that creates a waveform output from a direct current input. The two main types of oscillator oscill ator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while relaxation oscillators have waveforms with sharp changes.

21. What is an Integrated Circuit?

An integrated circuit (IC), also called a microchip, is an electronic circuit etched onto a silicon chip. Their main advantages are low cost, low power, high performance, and very small size.

22. What is crosstalk? Crosstalk is a form of interference caused by signals in nearby conductors. The most common example is hearing an unwanted conversation on the telephone. Crosstalk can also occur in radios, televisions, networking equipment, and even electric guitars.

23. What is resistor? A resistor is a two-terminal electronic component that opposes an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR.

25. What is inductor? An inductor is a passive electrical device employed in electrical circuits for its property of inductance. An inductor can take many forms.

26. What is conductor? A substance, body, or device that readily conducts heat, electricity, sound, etc. Copper is a good conductor of electricity.

27. What is a semi conductor? A semiconductor is a solid material that has electrical conductivity in between that of a conductor and that of an insulator(An Insulator is a material that resists the flow of electric current. It is an object intended to support or separate electrical conductors without passing current through itself); it can vary over that wide range either permanently or dynamically.

28. What is diode? In electronics, a diode is a two-terminal device. Diodes have two acti ve electrodes between which the signal of interest may flow, and most are used for their unidirectional current property.

29. What is transistor? In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. The transistor is the fundamental building block of computers, and all

other modern electronic devices. Some transistors are packaged individually but most are found in integrated circuits

30. What is op-amp? An operational amplifier, often called an op-amp , is a DC-coupled high-gain electronic voltage amplifier with differential inputs[1] and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation.

31. What is a feedback? Feedback is a process whereby some proportion of the output signal of a system is passed (fed back) to the input. This is often used to control the dynamic behaviour of the system.

32. Advantages of negative feedback over positive feedback. Much attention has been given by researchers to negative feedback processes, because negative feedback processes lead systems towards equilibrium states. Positive feedback reinforces a given tendency of a system and can lead a system away from equilibrium states, possibly causing quite unexpected results.

33. What is Barkhausen criteria? Barkhausen criteria, without which you will not know which conditions, are to be satisfied for oscillations. Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the product of the transfer gain of the amplifier and the magnitude of t he feedback factor of the feedback network ( the magnitude of the loop gain ) are less than unity . The condition of unity loop gain -A? = 1 is called the Barkhause Barkhausen n criterion. This condition implies that A?= 1and that the phase of - A? is zero.

34. What is CDMA, TDMA, FDMA? Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. An analogy to the problem of multi ple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different directions (spatial division). In CDMA, they would speak different languages. People speaking the

same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but onl y users associated with a particular code can understand each other.

35. explain different types of feedback Types of feedback: Negative feedback: This tends to reduce output (but in amplifiers, stabilizes and linearizes operation). Negative feedback feeds part of a system's output, inverted, into the system's input; generally with the result that fluctuations are attenuated. Positive feedback: This tends to increase output. Positive feedback, sometimes referred to as "cumulative causation", is a feedback loop system in which the system responds to perturbation (A perturbation means a system, is an alteration of function, induced by external or internal mechanisms) in the same direction as the perturbation. In contrast, a system that responds to the perturbation in the opposite di rection is called a negative feedback system. Bipolar feedback: which can either increase or decrease output.

36. What are the main divisions of power system? The generating system,transmission system,and distribution system

37. What is Instrumentation Amplifier (IA) and what are all the advantag advantages? es? An instrumentation amplifier is a differential op-amp circuit providing high input i mpedances with ease of gain adjustment by varying a single resistor.

38. What is meant by impedance diagram. The equivalent circuit of all the components of the power system are drawn and they are interconnected is called impedance diagram.

39. What is the need for load flow flo w study. The load flow study of a power system is essential to decide the best operation existing system and for planning the future expansion of the system. It i s also essential for designing the power system.

40. What is the need for base values? The components of power system may operate at different voltage and power levels. It will be convenient for analysis of power system if the volt age, power, current ratings of the components of the power system is expressed with referance to a common value called base value.

Analog Communication 1. What is Sampling? What is Sampling Theorem? Ans: Sampling Ans:  Sampling is defined as the process in which an analog signals are converted into digital signals. It signals. It means that a continuous time signal is converted into a discrete time signal.

 Analog Communication notes

Sampling Theorem is defined as : ’The :  ’The continuous time signal that can be represented in its samples and recovered back if the sampling frequency (fs) is greater than the maximum frequency of the signal (fm) that is fs >2fm’. 2. Define PAM and write down its drawbacks? Ans: Pulse Pulse Amplitude  Amplitude Modulation is the process by which the amplitude of the regularly spaced pulses varies according to the the amplitude of the modulating signal. The drawbacks are: a. Since the amplitude of the pulses a. Since pulses varies therefore the peak peak power of the modulating s/g is much greater. b. The b.  The bandwidth required for transmitting is greater since the amplitude varies. 3. What is Modulation? What happens in over modulation?  Ans: Modulation Modulation is  is defined as the process in which some characteristics of the signal called carrier is varied according to the modulating or baseband signal. For example – Amplitude Modulation, Phase Modulation, Modulation, Frequency Modulation. In case of over modulation, the modulation index is greater than one and envelope distortion occurs. 4. What do you mean by Nyquist rate? rate?  Ans: In case of Nyquist rate, the sampling frequency is equal equal to the maximum maximum frequency of the signal and therefore therefore the successive cycles of the spectrum does not overlap. 5. What do you mean by FM and classify FM? Ans: Frequency Modulation can Modulation can be defined as the frequency of the carrier (wc) is varied acc. to the modulating signal about an unmodulated frequency. FM are of 2 types: a. Narrowband FM a. Narrowband b. Wideband b.  Wideband FM 6. What is under sampling? Ans: Under Ans:  Under sampling is also known as aliasing effect  in  in which the the sampling frequency is less than the maximum frequency of the signal and therefore the successi successive ve cycles of the spectrum overlap. 7. State the advantages of superheterodyn superheterodyning? ing? Ans: The Ans:  The advantages are: a. High a.  High selectivity and sensitivity. sensitivity. b. No change in Bandwidth that is bandwidth remains same all over the operating range. c. High c.  High adjacent channel rejection. 8. What is multiplexing? Name the types of multiplexing multiplexing? ? Ans: Multiplexing  is   is defined as the process in which a number of message signals are combined together to form composite signals so that they can be transmitted through the common channel. The two types of multiplexing are: a. Frequency Division Multiplexing: Multiplexing : In this technique, fixed frequency bands are allotted to every user in the complete channel bandwidth. Such frequency is allotted to user on a continuous basis. b. Time Division Multiplexing Multiplexing::  When the pulse is present for the short time duration and most of the time their is no signal present in-between them than this free space between the two pulses can occupied by the pulses from other channels. This is known as Time Division Multiplexing. 9. What is Amplitude Modulation? Ans: Amplitude Ans:  Amplitude Modulation Modulation is  is defined as the process in which the instantaneous value of the amplitude of the carrier is varied according to the amplitude of the modulating or base band signal. 10. How can be aliasing be avoided? Ans: Aliasing Ans:  Aliasing can be avoided avoided if:

a. Sampling frequency must be greater than the frequency of the modulating signal. a. Sampling b. The b.  The frequency should be band limited to maximum frequency of the signal(fm) Htz. c. If c.  If pre-alias filter is used.