1. Define amplitude modulation?ANS: In amplitude modulation, the amplitude of the carrier signal is varied according to the modulating signal.2. What is the range of carrier used in AM?ANS: 00 Hz to 1500 KHz.3. Which modulation is used for video signals?ANS: Amplitude modulation is used for video signals.4. What are the types of amplitude modulation?ANS: The various types of amplitude modulation are:a) Double Sideband Modulation (DSB-AM)b) Double Sideband Suppressed Carrier Modulation (DSB SC-AM)c) Single Sideband Carrier Modulation(SSB AM)d) Single Sideband Suppressed Carrier Modulation (SSB SC-AM)e) Vestigial Sideband Modulation (VSB AM)5. Define modulation index of AM.ANS: Modulation index indicates the amount of amplitude variation around the un-modulated carrier Modulation index, .M is the peak amplitude value of modulating signal.A is the peak amplitude value of carrier signal.6. What are the advantages of AM?ANS: The AM transmitter and receiver are simple.

7. What are the disadvantages of AM?ANS: AM is more susceptible to noise.8. What are the applications of AM?ANS: Applications of AM:a) AM radio broadcasting. b) AM video transmission.9. What are the types of continuous wave analog modulation?ANS:a) 1.Amplitude modulation b) 2.Angle modulation

10 Define modulation? ANS: Modulation is a process by which some characteristics of high frequency carrier signal is varied in accordance with the instantaneous value of the modulating signal. 11 .What are the types of analog modulation? ANS:1. Amplitude modulation. 2.Angle Modulation 3. Frequency modulation.12.Define depth of modulation. ANS: It is defined as the ratio between message amplitude to that of carrier amplitude. m=Em/Ec13. What are the degrees of modulation? ANS: Under modulation. m1

14 Define modulation index for AM?ANS: It is defined as the ratio of the maximum modulating voltage to the maximum carrier voltage. It is also called as Depth of modulation. It is denoted by m and:m = Vm / Vc15+. What is the relation between total power and carrier power? ANS: Pt = Pc (1 + m)Pt : Total power Pc : Carrier power m :Modulation index

16. What is the bandwidth of AM? ANS: Bandwidth =2fm

FREQUENCY MODULATION

. Define frequency modulation. ANS: 1.Frequency modulation is defined as the process by which the frequency of the carrier wave is varied in accordance with the 2. What do you meant by multi-tone modulation? ANS: Modulation done for the message signal with more than one frequency component is called multitone modulation. 3.What isFrequencyModulation?ANS: Frequency modulation tells information over a carrier using a variation in the frequency.You use this frequently when you are in the car listening to your favorite FM station on the

4.What Are 4GModulationFrequencies?ANS: The 4G modulation frequencies are a range of wireless frequencies used in parallel to transfer data and facilitate voice calls. 4G's modulation frequency band ranges from 2 to 8 GHz

5.What is highfrequencymodulation?ANS: Frequency modulation is a method of impressing an audio frequency signal onto a radio frequency carrier wave, by changing the frequency of the carrier wave in response to the audio

6.What isfrequencymodulation?ANS: The encoding of a carrier wave by variation of its frequency in accordance with an input signal.

7. What do you understand by narrowband FM? ANS: When the modulation index is less than 1, the angle modulated systems are called low index. The bandwidth requirement of low index systems is approximately twice of the modulating signal frequency. Therefore low index systems are called narrowband FM 8. Why Armstrong method of FM is superior to reactance modulator? ANS: Reactance modulator is direct FM, where as Armstrong method is indirect FM. Armstrong method generates FM from PM. Hence crystal oscillators can be used in Armstrong method. Therefore frequency stability is better than reactance modulator. 9. Differentiate between narrow band FM and wideband FM ?ANS: In narrow band FM, the frequency deviation is very small. Hence the frequency spectrum consists of two major sidebands like AM. Other sidebands are negligible and hence they can be neglected. Therefore the bandwidth of narrowband FM is limited only to twice of the highest modulating frequency.10. State Carsons rule of FM bandwidth? ANS: Carsons rule of FM bandwidth is given as, BW = 2( + fm (max)) Here is the maximum frequency deviation and fm (max)) is the maximum signal frequency. 11. What is direct FM? ANS: In this type of angle modulation, the frequency of the carrier is varied directly by the modulating signal. This means; an instantaneous frequency deviation is directly proportional to amplitude of the modulating signal 12. What is indirect FM? ANS: In this type of angle modulation, FM is obtained by phase modulation of the carrier. This means, an instantaneous phase of the carrier directly proportional to amplitude of the modulating signal

PAM1. What are the different pulse modulation techniques?ANS: Pulse amplitude modulation (PAM), Pulse width modulation (PWM), Pulse position modulation (PPM).2. What is the role of pulse in pulse modulation techniques?ANS: In pulse modulation techniques, pulse train is used as the carrier. 3. Define PAM.ANS: In PAM, amplitude of the pulse is proportional to the amplitude of modulating signal. The width and position of the pulse remain unchanged.4. What is the relation between PAM and sampling operation?ANS: PAM and sampling are the same.5. What are the types of PAM?ANS: Naturally sampled PAM, Ideally sampled PAM, Sample and hold PAM.6. Define naturally sampled PAM signal?ANS: The original shape of the input signal is retained on the top of the pulses.7. Define sample and hold PAM? ANS: The previous sample value is retained till the next sampling instant.8. Define flat top sampled PAM?ANS: The top of the pulse in flat top sampled PAM remains constant.9. What are the drawbacks of PAM?ANS: Drawbacks of PAM:a) The bandwidth needed for PAM signal is very large. b) The power requirement varies from pulse to pulse. c) The interference of noise is maximum.10. What are the applications of PAM?ANS: Used for short distance baseband communication.

PPM

1. What are the advantages and disadvantages of PPM? ANS: 1.Advantages of PPM: Power requirement for each and every pulses are the same only. 2. Disadvantages of PPM: Synchronization between the transmitter and receiver is needed. Bandwidth requirement is larger comparing with PAM. 2.. What are the applications of PPM?ANS: Short distance synchronous communication.3.. What are the types of PWM?ANS: a. Trailing edge modulationb. Leading edge modulationc. Leading-Trailing edge modulation4.Pulse Position Modulation (PPM)?ANS: In this variation of the modulation process the modulating signal alters the position of the pulse from its normal centre position. The position of the pulse is proportional to the instantaneous amplitude of the modulating signal.

PWM

QUESTION-ANSWER:1. What is the other name for PWM?ANS: Pulse duration modulation.2. Define PWM?ANS: In PWM, width of the pulse depends on the amplitude of the input signal. The amplitude and position of the pulse remains constant.3. What are the advantages and disadvantages of PWM?ANS: Advantages of PWM: a) Noise interference is lessb) No need of synchronization between transmitter and receiver. Disadvantages of PWM: a) Power requirement varies from pulse to pulseb) Bandwidth requirement is more than PAM.4. What are the applications of PWM?ANS: PWM is used to generate PPM.5. Define PPM.ANS: In PPM, the position of the pulse depends on the amplitude of the modulating signal. The amplitude and width of the pulse remains constant.6. What are the advantages and disadvantages of PPM?ANS:1.Advantages of PPM: Power requirement for each and every pulses are the same only. 2.Disadvantages of PPM: Synchronization between the transmitter and receiver is needed. Bandwidth requirement is larger comparing with PAM. 7. What are the applications of PPM?ANS: Short distance synchronous communication.8. What are the types of PWM?ANS: a. Trailing edge modulationb. Leading edge modulationc. Leading- Trailing edge modulation DELTA MODULATION AND DPSK1. Mention the merits of DPCM.ANS:1. Bandwidth requirement of DPCM is less compared to PCM.2. Quantization error is reduced because of prediction filter3. Numbers of bits used to represent one sample value are also reduced compared to PCM.2. What is the main difference in DPCM and DM?ANS: DM encodes the input sample by one bit. It sends the information about + or -, ie step rise or fall. DPCM can have more than one bit of encoding the sample. It sends the information about difference between actual sample value and the predicted sample value.3. How the message can be recovered from PAM?The message can be recovered from PAM by passing the PAM signal through reconstruction filter integrates amplitude of PAM pulses. Amplitude reconstruction signal is done to remove amplitude discontinuities due to pulses.4.What is the need ofdeltamodulation?ANS: if you are talking about a plane then its to set new modes unpromising if you will.

5.What isdeltamodulation?ANS: A pulse-modulation technique in whicha continuous signalis converted into6. What is the reason to use delta modulation?ANS: Data rate and bandwidth required are more in PCM. So delta modulation is used.7. How many bits are transmitted per sample in DM?ANS: Only one bit per sample is transmitted in DM.8. What are the two types of errors present in DM?ANS: Slope over load distortion and granular noise.5. Define slope overload distortion with an illustrative waveform?ANS: When the slope of the input signal is larger than the slope of staircase waveform, the staircase waveform cant follow the input signal variations. This error is known as slope overload distortion. 6. Define granular noise with an illustrative waveform?ANS: When the slope of the input signal is smaller than the slope of staircase waveform the granular noise occurs.7. How to reduce the slope overload distortion?ANS: The slope overload distortion can be minimized by increasing the step size of the quantiser.8. How to reduce the granular noise?ANS: This noise can be controlled by decreasing the step size of the quantized.9. Explain the operation of DM.ANS: In delta modulation present sample value is compared with the previous sample value. If present sample value is greater than previous sample value, then 1 is transmitted. If present sample value is less than previous sample value, then 0 is transmitted.

ASK

QUESTION ANSWER:1. ASK isa) Amplitude shift keyingb)Amplitude shift keyboardc)Amplitudeshine keyingd) none of theseANS: A2.In general, networks designed to transmit primarily computer data are likely to be ________, wile networks designed to transmit voice data are likely to be ________.a. slow, fastb. digital, analogc. level 1, level 2d. direct, indirecte. numeric, musicalAnswers: b3.Digital computer data can be transmitted over a traditional telephone network by using a special device called a:a. digitizerb. analog converterc. protocol converterd. modeme. codecAnswers: d 4.Which of the following is not a key advantage of digital transmission?a. It is more secure.b. It is simpler to integrate voice, video, and data on the same circuit.c. It permits minimum transmission rates.d. It produces fewer errors.e. It is more efficient.Answers: c 5.Most newer long distance telephone circuits built by the common carriers over the past decade use:a. digital transmissionb. copper wirec. analog transmissiond. infrared linkinge. spread spectrum transmissionAnswers: a6.Analog is also called:a. basebandb. broadbandc. loudnessd. asynchronouse. synchronousAnswers: b7.Digital is also called:a. basebandb. broadbandc. asynchronousd. synchronouse. pitchAnswers: a8.In which of the following systems is data represented by measurements on a continuous scale?a. analogb. digitalc. asynchronousd. synchronouse. integratedAnswers: a9.In which of the following systems is data represented by the transmission of discrete signals over a transmission channel?a. analogb. broadbandc. digitald. integratede. synchronousAnswers: c10._____________ is not a form of modulation used to transform digital data into analog signals.a. amplitude shift keyingb. statistical time divisionc. amplitude modulationd. frequency modulatione. phase modulationAnswers: b, 11.AM stands for:a. Analog Modemb. Anomaly Multiplexingc. Asynchronous Modemd. Amplitude Modulatione. Analytical ModemAnswers: d12.In which type of modulation is a 1 distinguished from a 0 by the number of waves transmitted in the same unit of time?a. bandwidth modulationb. amplitude modulationc. frequency modulationd. phase modulatione. codec modulationAnswers: c13.____________ is a modulation technique that combines amplitude and phase modulation to send four bits per wave, or symbol.a. time division multiplexingb. pulse code modulationc. synchronous digital line controld. quadrature amplitude modulatione. baseband signalingAnswers: d14.On-off keying is the modulation scheme used for the majority of optical-fiber communication systems. This scheme is an example of ____________________.a. binary frequency shift keyingb. binary phase shift keyingc. binary continuous-phase frequency shift keyingd. binary amplitude shift keyingAnswers: dASK

QUESTION ANSWER :1. What is the difference between PSK and FSK?ANS: In PSK, phase of the carrier is switched according to input bit sequence. In FSK frequency of the carrier is switched according to input bit sequence. FSK needs double of the bandwidth of PSK.2. What is meant by coherent ASK?ANS: In coherent ASK, correlation receiver is used to detect the signal. Locally generated carrier is correlated with incoming ASK signal. The locally generated carrier is in exact phase with the transmitted carrier. Coherent ASK is also called as synchronous ASK.3. What is the major advantage of coherent PSK over coherent ASK?ANS: ASK is on-off signalling, where as the modulated carrier is continuously transmitted in PSK. Hence peak power requirement is more ASK, whereas it is reduced in case of PSK.4. Explain the model of bandpass digital data transmission system?ANS: The bandpass digital data transmission system consists of source, encoder and modulator in the transmitter. Similarly receiver, decoder and destination form the transmitter.9. What is baseband signal receiver?ANS: A baseband signal receiver increases the signal to noiseratio at the instant of sampling. This reduces the probability of error. The baseband signal receiver is also called optimum receiver.10. What is matched filter?ANS: The matched filter is a baseband signal receiver, which works in presence of white Gaussian noise. The impulse response of the matched response of the matched filter is matched to the shape pf the input signal.11. What is the value of maximum signal to noise ratio of the matched filter? When it becomes maximum?ANS: Maximum signal to noise ratio is the ratio of energy to psd of white noise. i.e., max = E/ (N0/2)This maximum value occurs at the end of bit duration i.e. Tb.

PSKQUESTION ANSWER:1. What is the need for BER? ANS: Bit error Rate is the empirical record of Systems actual bit error performance. 2. What isPhaseShiftKeying (PSK)?ANS.PSK (PhaseShiftKeying) is a way to transmit data digitally. Thephaseof the transmitted signal carries the data. Phase-shift keying(PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave).3.What is 8phaseshiftkeying?ANS.8phaseshiftkeyingis a complex form ofdigital modulationby altering a sine wave and a cosine wave:shiftingtheirphase.4.What isphase-shiftkeying?ANS.A form ofphasemodulation in which the modulating functionshiftsthe instantaneousphaseof the modulated wave between predetermined discrete values5.What Is aPhaseShifton an Amp?ANS. The electronic components in amplifier circuits contribute significantly tophaseshift. Reactive components, such as capacitors and inductors, respond differently to voltage and current signals Source.6.What isstaggered quadraturephase-shiftkeying?ANS. Staggered quadraturephase-shiftkeying(SQPSK), also known as offset quadraturephase-shiftkeying(OQPSK), is a method ofphase-shiftkeying(PSK) in which the signal carrier-wavephasetransition is always 90 degrees.

QPSKQUESTION ANSWER:1. Give the equation for average probability of symbol error for coherent binary PSK. ANS. Average probability of signal error, Pe = 1 / 2 erfc Eb / No 2. Define QPSK. ANS. QPSK is Quadriphase shift keying. In QPSK the phase of the carrier takes on one of the four equally spaced values Such as /4 , 3 /4, 5 /4 and 7 /4. 3. Define Dibit. ANS. dibits 10, 00, 01 & 11.4. Define Information Capacity? ANS. Information capacity represents the number of independent symbols that can be carried in the system for a given time. 5. What is the unit of information capacity? ANS. Unit is bits per second 6. Why digital amplitude modulation is commonly called ON Off Keying? ANS. Carrier is either in ON or Off state so it is called as On Off Keying. 7. Why digital amplitude modulation is called as continuous wave modulation? ANS. When the carrier is being transmitted it has constant amplitude, constant frequency and constant phase. 8.Define Bit rate? ANS. The rate of change at the input to the modulator is called bit rate and is expressed in bits per second. 9.Define Baud? ANS. Baud is the rate of change and is equal to the reciprocal of one signaling element. 10.Define Phase reversal keying? ANS. Since Phase of the output carrier shifts between two phases PSK is also called as Phase reversal keying.11.What is Offset QPSK? ANS. IT is a modified form of QPSK where the bit waveforms on the I and Q channels are offset or phase shifted in phase from each other one by one half of a bit time. 12. What is eight phase PSK? ANS. Eight Phase PSK (8-PSK) is an M-ary encoding technique where M=8. 13.What is the need of maximum distance code? ANS. It is used to reduce the number of transmission errors. 14.What is Quad bits? ANS. A 16 bit PSK modulator acts on the incoming data in groups of four bit is called Quad bits. 15.Define DPSK? ANS. DPSK is the difference between two successive signaling element rather than the absolute phase. 16.What is the need for BER? ANS. Bit error Rate is the empirical record of Systems actual bit error performance.