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MCQOPTIONS
This section includes 1362 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics & Communication Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 101. |
If e = 10 cos (2π x 10⁸t + 20 cos 2π 10³t). The bandwidth is |
| A. | 10⁸ Hz |
| B. | 42 kHz |
| C. | 21 kHz |
| D. | 10⁸ ± 10³ Hz |
| Answer» C. 21 kHz | |
| 102. |
In the absence of noise, if C is channel capacity in bits/s, δf is channel bandwidth in Hz and N is number of coding levels. Then |
| A. | C = log₂ N |
| B. | C = (δf) log₂ N |
| C. | C = 2 (δf) log₂ N |
| D. | C = 0.5 (δf) log₂ N |
| Answer» D. C = 0.5 (δf) log₂ N | |
| 103. |
In telephone systems the relation between load ρ, number of calls initiated during a specified interval λ and average duration of a call (h) is |
| A. | ρ = λh |
| B. | ρ = λh² |
| C. | λ = ρh |
| D. | h = λρ |
| Answer» B. ρ = λh² | |
| 104. |
If carrier modulated by a digital bit stream had one of the possible phases of 0°, 90°, 180°, 270°, then the modulation is called. |
| A. | BPSK |
| B. | QPSK |
| C. | QAM |
| D. | MSK |
| Answer» C. QAM | |
| 105. |
A source has two symbols x1 and x2 with probabilities pi and pr. If a new source with four symbols is generated from the above source, the new symbol probabilities will be (∈ is a number such that 0 < ∈ < 1) |
| A. | p1, p2, p1, p2 |
| B. | p1, p1, p2, p2 |
| C. | (1 - ∈)p1, (1 - ∈) p2, p1, p2 |
| D. | p1/4, p2/4, p1/4, p2/4 |
| Answer» D. p1/4, p2/4, p1/4, p2/4 | |
| 106. |
Tuned voltage amplifiers are not used |
| A. | in public address systems |
| B. | in radio receivers |
| C. | in television receivers for sound signals |
| D. | in television receivers for video signals |
| Answer» B. in radio receivers | |
| 107. |
When ωm is the modulation frequency in frequency modulation, the modulation index is proportional to |
| A. | ωm |
| B. | ω²m |
| C. | 1/ωm |
| D. | 1/ω²m |
| Answer» D. 1/ω²m | |
| 108. |
An FM signal has modulating frequency fm and maximum frequency deviation of δ. The bandwidth will be nearly equal to |
| A. | δ |
| B. | 2 δ |
| C. | 2fm δ |
| D. | fm δ |
| Answer» C. 2fm δ | |
| 109. |
The equation v(t) = A cos [ωct + φ(t)] where A and ωc are constant and φ(t) is a function of base signal represents 1. Phase modulation2. Amplitude modulation3. Angle modulation4. Frequency modulation Which of the above are true? |
| A. | 3 only |
| B. | 1, 3 and 4 |
| C. | 1, 2, 3, 4 |
| D. | 3 and 4 only |
| Answer» C. 1, 2, 3, 4 | |
| 110. |
Consider the following statements as regards communication receiver 1. Variable sensitivity is used to eliminate selective fading2. A product demodulator can be used to receive Morse code3. The noise limiter cuts off receiver output during a noise pulse4. Double conversion is used to improve image rejection Which of the above statements are correct? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 3 |
| C. | 2, 3, 4 |
| D. | 1, 3, 4 |
| Answer» D. 1, 3, 4 | |
| 111. |
When a signal is quantized such that the step size S is small in comparison with the peak to peak range of the signal, the mean square quantization error is equal to |
| A. | S² |
| B. | S²/2 |
| C. | S²/6 |
| D. | S²/12 |
| Answer» E. | |
| 112. |
In FM reception, amplitude disturbances due to static change |
| A. | reduce the signal frequencies |
| B. | increase the signal frequencies |
| C. | disturb the signal frequencies |
| D. | do not affect the signal frequencies |
| Answer» E. | |
| 113. |
Consider the following reasons for using antenna coupler 1. To prevent illegal radiation of spurious frequencies2. To tune out reactive components of antenna impedance3. To have correct value of load impedance for transmitter Which of the above are correct? |
| A. | 1, 2, 3 |
| B. | 1, 2 |
| C. | 1 only |
| D. | 2, 3 |
| Answer» B. 1, 2 | |
| 114. |
For a given data rate, the bandwidth βp of a BPSK signal and the bandwidth β₀ of the OOK signal are related as |
| A. | βp = β₀/2 |
| B. | βp = 2β₀ |
| C. | βp = 3β₀/4 |
| D. | βp = β₀ |
| Answer» E. | |
| 115. |
Which one of the following frequency bands is allocated by ITU (International Telecomm. Union) for DBS - (Direct Broadcast service) also referred as DTH - (Direct to Home service)? |
| A. | 14/12 GHz |
| B. | 6/4 GHz |
| C. | 2/1 GHz |
| D. | 42/40 GHz |
| Answer» C. 2/1 GHz | |
| 116. |
A device has two resistances 300 Ω and 200 Ω respectively. The noise voltages due to these two resistance calculated separately are 5.38 μV and 4.38 μV respectively. When both of them are used together, the noise voltage will be |
| A. | 9.76 V |
| B. | 1 μV |
| C. | 23.56 μV |
| D. | 6.94 μV |
| Answer» E. | |
| 117. |
Consider the following statements as regards SAW filter 1. The centre frequency is determined by the pitch of IDT comb shaped electrodes2. The response can be modified shaping the overlap of comb electrodes3. The response is maximum when acoustic wave has its wavelength equal to pitch4. When a number of identical electrodes are arranged at the same pitch, the frequency characteristics of the filter is expressed by (sin x)/x Which of the above statements are correct? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 3 only |
| C. | 1, 2, 4 only |
| D. | 2, 3, 4 only |
| Answer» D. 2, 3, 4 only | |
| 118. |
If e = 10 sin(10⁸ t + 3 sin 10⁴ t) then carrier frequency is |
| A. | 0.159 MHz |
| B. | 1.59 MHz |
| C. | 15.9 MHz |
| D. | 159 MHz |
| Answer» D. 159 MHz | |
| 119. |
Consider the following statements as regards pulse repetition frequency 1. Pulse interval should be as large as possible so that a pulse returns before next pulse is transmitted2. Greater the number of pulses reflected from a target, greater is the probability of distinguishing it from the noise Which of the above are correct? |
| A. | 1 only |
| B. | 2 only |
| C. | both 1 and 2 |
| D. | neither 1 nor 2 |
| Answer» D. neither 1 nor 2 | |
| 120. |
If the bandwidth is increased by 2, the γFM γAM (where γ is the ratio of SNR of output to SNR at input, FM is frequency modulation and AM is amplitude modulation) is increased by a factor of |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 6 |
| Answer» D. 6 | |
| 121. |
An angle modulated signal is expressed by fa(t) = cos (2 x 10⁸ πt) + 75 sin (2 x 10³ πt). The peak frequency deviation of the carrier is |
| A. | 1 kHz |
| B. | 7.5 kHz |
| C. | 75 kHz |
| D. | 100 MHz |
| Answer» D. 100 MHz | |
| 122. |
Consider the following:1. A signal f(t) and its Hilbert transform fh(t) have the same energy density spectrum2. A signal f(t) and its Hilbert transform, fh(t) have the same auto correlation function3. A signal f(t) and its Hilbert transform are mutually orthogonal Which of the above are true? |
| A. | 1, 2 and 3 |
| B. | 1 and 2 only |
| C. | 1 only |
| D. | 2 and 3 only |
| Answer» B. 1 and 2 only | |
| 123. |
Some possible disadvantages of high level modulation in TV transmitters are 1. Video monitor has to supply high video voltages upto several hundred volts into highly capacitive loads drawing high current at video frequencies2. The grid modulated stage presents a varying load to its driver3. The linearity and high video driving power present design problems Out of above which are true? |
| A. | 1 only |
| B. | 1 and 2 only |
| C. | 1, 2 and 3 |
| D. | 2 and 3 only |
| Answer» D. 2 and 3 only | |
| 124. |
Consider the following statements as regards IF in radio receivers 1. If IF is too high, poor selectivity and poor adjacent channel rejection could result2. If IF is high, tracking difficulties increase3. A very low IF makes selectivity too sharp4. As IF is decreased, image frequency rejection becomes better Which of the above are correct? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 3 |
| C. | 2, 3, 4 |
| D. | 1, 3, 4 |
| Answer» C. 2, 3, 4 | |
| 125. |
For a resistance of about 15 kΩ operating in a frequency range of a few MHz, the noise voltage is in the range of |
| A. | a few μV |
| B. | about 100 μV |
| C. | a few μV |
| D. | a few volts |
| Answer» E. | |
| 126. |
Consider the following statements about advantages of phase discriminator over slope detector 1. Fewer tuned circuits2. Greater limiting3. Better linearity4. Easy alignment Which of the above are true? |
| A. | 1, 2, 3, 4 |
| B. | 2, 3, 4 |
| C. | 1, 2, 3 |
| D. | 1, 3, 4 |
| Answer» E. | |
| 127. |
If a line is terminated in characteristic impedance Z₀, the input impedance measured at the input will be |
| A. | Z₀ |
| B. | Z₀/2 |
| C. | Zero |
| D. | infinite |
| Answer» B. Z₀/2 | |
| 128. |
An AM wave is given by s(t)AM = 20 (1 + 0.5 cos 10³t + 0.3 cos 10⁴ t cos 10⁶ t) the modulation index of the envelope is |
| A. | 0.5 |
| B. | 0.58 |
| C. | 0.3 |
| D. | 0.8 |
| Answer» C. 0.3 | |
| 129. |
The Hilbert transform of cos ω₁t + sin ω₂t is |
| A. | sin ω₁t + cos ω₂t |
| B. | sin ω₁t - cos ω₂t |
| C. | cos ω₁t - cos ω₂t |
| D. | - sin ω₁t + cos ω₂t |
| Answer» C. cos ω₁t - cos ω₂t | |
| 130. |
In a system an input resistance of 20 kΩ causes a noise voltage of 15μV. If two such input resistances each of 20 kΩ are used in parallel, the total noise voltage will be about |
| A. | 15 μV |
| B. | 30 μV |
| C. | 7.5 μV |
| D. | 10.6 μV |
| Answer» E. | |
| 131. |
FM broadcast is done using |
| A. | medium waves |
| B. | short waves |
| C. | VHF and UHF waves |
| D. | microwaves |
| Answer» D. microwaves | |
| 132. |
If velocity of sound waves in air at 0°C is 330 m/s, the velocity at 40°C is about |
| A. | 330 m/s |
| B. | 334 m/s |
| C. | 353 m/s |
| D. | 380 m/s |
| Answer» D. 380 m/s | |
| 133. |
Consider the following statements 1. The amplitude of an FM wave is constant2. FM is more immune to noise than AM3. FM broadcasts operate in upper VHF and UHF frequency ranges4.FM transmitting and receiving equipments are simpler as compared to AM transmitting and receiving equipments Which of the above are correct? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 3 |
| C. | 2, 3, 4 |
| D. | 1, 3, 4 |
| Answer» C. 2, 3, 4 | |
| 134. |
In the FM wave described by equation v = 15 sin (4 x 10⁸ t + 3 sin 1100 t), the maximum frequency deviation is |
| A. | 175 Hz |
| B. | 525 Hz |
| C. | 3 Hz |
| D. | 58.33 Hz |
| Answer» C. 3 Hz | |
| 135. |
Consider the draw backs 1. Slope overload2. Serration noise3. Granular noise Which of these draw backs does Delta modulation have? |
| A. | 1 and 2 only |
| B. | 2 and 3 only |
| C. | 1 and 3 only |
| D. | 1, 2, 3 |
| Answer» D. 1, 2, 3 | |
| 136. |
Consider the following differences between QPSK and MSK 1. The side lobes in MSK are relatively much smaller in comparison to the main lobe2. The spectrum of MSK has a main centre lobe which is 1.5 times as wide as the main lobe of QPSK3. The waveforms of both MSK and QPSK exhibit phase continuity Which of the above statements are correct? |
| A. | 1 only |
| B. | 1 and 2 only |
| C. | 1, 2 and 3 |
| D. | 2 and 3 only |
| Answer» C. 1, 2 and 3 | |
| 137. |
In a phase discriminator fc, is the IF to which primary circuit is tuned. Consider the following statements: The primary and secondary voltages are 1. exactly 90° out of phase when input frequency is fc2. more than 90° out of phase when input frequency is higher than fc3. less than 90° out of phase when input frequency is lower than fc Which of the above statements is correct? |
| A. | 1 only |
| B. | 1 and 2 |
| C. | 1, 2 and 3 |
| D. | 2 and 3 |
| Answer» B. 1 and 2 | |
| 138. |
A line has L = 0.8 µH/m and C = 32 pF/m. Z0 = |
| A. | 6000 |
| B. | 600 |
| C. | 158 |
| D. | 15.8 |
| Answer» D. 15.8 | |
| 139. |
Consider the following statement: The radar pulse must be flat topped to 1. allow accurate range measurement2. allow good minimum range3. prevent frequency changes in magnetron4. make the returned echoes easier to distinguish from noise. Which of the above are correct? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 3 |
| C. | 1, 2 |
| D. | 1, 3, 4 |
| Answer» C. 1, 2 | |
| 140. |
Some advantages of optical fibre cables are 1. small diameter2. Immunity to cross talk and EM interference3. Laser and LED modulation methods lend themselves ideally to digital operation Which of the above are correct? |
| A. | 1 only |
| B. | 1 and 2 |
| C. | 1, 2, 3 |
| D. | 2, 3 |
| Answer» D. 2, 3 | |
| 141. |
Consider the following statements as regards advantages of CCD sensors as camera pick up tube 1. High sensitivity2. Good spectral response3. Image lag absent Out of the above which are correct |
| A. | 1, 2, 3 |
| B. | 1, and 2 only |
| C. | 1 and 3 only |
| D. | 2 and 3 only |
| Answer» B. 1, and 2 only | |
| 142. |
An FM signal with a deviation δ is passed through a mixer, and has its frequency reduced 5 fold. The deviation in the output of the mixer is |
| A. | 5/δ |
| B. | Intermediate |
| C. | δ/5 |
| D. | δ |
| Answer» E. | |
| 143. |
If a source of information generates messages at the rate of r messages per second and H is entropy, the information rate is |
| A. | H/r |
| B. | 1/rH |
| C. | rH |
| D. | r/H |
| Answer» D. r/H | |
| 144. |
If e = 10 sin(10⁸ t + 3 sin 10³ t) then the modulation index is |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 4 |
| Answer» D. 4 | |
| 145. |
Which of the following form of angle modulation, If e = 10 sin(10⁸ t + 3 sin 10⁴ t) |
| A. | AM |
| B. | FM |
| C. | AM or FM |
| D. | AM or PCM |
| Answer» C. AM or FM | |
| 146. |
Consider the following statements as regards BPSK and QPSK: 1. In BPSK we deal individually with each bit of duration Tb2. In QPSK we lump two bits to form a symbol3. In both BPSK and QPSK signal changes occur at bit rate4. In QPSK the symbol can have any one of four possible values Which of the above statements are correct? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 3 |
| C. | 1, 2, 4 |
| D. | 2, 3, 4 |
| Answer» D. 2, 3, 4 | |
| 147. |
Convolution of x(t + 5) with impulse function δ(t - 7) is equal to |
| A. | x(t - 2) |
| B. | x(t + 12) |
| C. | x(t - 12) |
| D. | (t + 2) |
| Answer» B. x(t + 12) | |
| 148. |
Assertion (A): If a carrier is modulated by three sine waves and m₁, m₂, m₃ are the modulation indices, the total modulation index mt is mt = (m₁² + m₂² + m₃²)^0.5Reason (R): An AM, higher the level of modulation, lower is the audio power required to produce modulation. |
| A. | Both A and R are correct and R is correct explanation of A |
| B. | Both A and R are correct but R is not correct explanation of A |
| C. | A is correct but R is wrong |
| D. | A is wrong but R is correct |
| Answer» D. A is wrong but R is correct | |
| 149. |
A source is radiating power equally in all directions. If source power is P, the power density at distance d is |
| A. | P/4πd² |
| B. | P/2πd² |
| C. | P/d² |
| D. | P/4πd |
| Answer» B. P/2πd² | |
| 150. |
An angle modulated signal is given by s(t) = cos 2π (2 x 10⁶t + 30 sin 150t + 40 cos 150t). The maximum frequency and phase deviations of s(t) are |
| A. | 10.5 kHz, 140π rad |
| B. | 6 kHz and 80π rad |
| C. | 10.5 kHz, 100π rad |
| D. | 7.5 kHz, 100π rad |
| Answer» E. | |