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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.
| 801. |
In a FM signal, the modulation index increases, then the power |
| A. | increases |
| B. | decreases |
| C. | remains constant |
| D. | none of the above |
| Answer» D. none of the above | |
| 802. |
A band limited signal is sampled at the Nyquist rate. The signal can be recovered by passing the samples through |
| A. | an RC filter |
| B. | an envelope detector |
| C. | a PPL |
| D. | an ideal low pass filter with the appropriate bandwidth |
| Answer» E. | |
| 803. |
Which of the following is the digital system? |
| A. | PWM |
| B. | PAM |
| C. | PPM |
| D. | PCM |
| Answer» E. | |
| 804. |
A tape recorder and deck are entirely similar. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 805. |
The circuit of figure give an output which is |
| A. | a frequency modulated signal |
| B. | an amplitude modulated signal |
| C. | a phase modulated signal |
| D. | none of the above |
| Answer» B. an amplitude modulated signal | |
| 806. |
Consider the following reasons for using antenna coupler To prevent illegal radiation of spurious frequenciesTo tune out reactive components of antenna impedanceTo 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 | |
| 807. |
The highest modulation frequencies typically used in FM broadcast is |
| A. | 5 kHz |
| B. | 10 kHz |
| C. | 15 kHz |
| D. | 25 kHz |
| Answer» D. 25 kHz | |
| 808. |
In a CD the channel separation is |
| A. | 1 μm |
| B. | 1.6 μm |
| C. | 2.5μm |
| D. | 4 μm |
| Answer» C. 2.5Œºm | |
| 809. |
Audio-signal modulates a 125 MHz carrier, causing a frequency deviation of 5 kHz. The bandwidth of the narrowband FM signal is __________ kHz. |
| A. | 10 |
| B. | 8 |
| C. | 9 |
| D. | 20 |
| Answer» D. 20 | |
| 810. |
Waveform shown in figure is that for |
| A. | FM |
| B. | PCM |
| C. | AM-DSB |
| D. | AM-SSB |
| Answer» D. AM-SSB | |
| 811. |
Consider the following Generation of SSB signalsDesign of minimum phase type filtersRepresentation of band pass signals Which of the above applications is Hilbert transform used? |
| A. | 1 only |
| B. | 1, 2 and 3 |
| C. | 1, 2 only |
| D. | 1 and 3 |
| Answer» C. 1, 2 only | |
| 812. |
Earth's curvature affects the effective height of antenna. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 813. |
In telephone systems, load is expressed in the unit of |
| A. | erlangs |
| B. | decibels |
| C. | bells |
| D. | watts |
| Answer» B. decibels | |
| 814. |
In FM, increased depth of modulation increases |
| A. | modulation |
| B. | modulation index |
| C. | bandwidth |
| D. | all of the above |
| Answer» E. | |
| 815. |
Noise with uniform power spectral density of N0ω/Hz is passed through a filter H(ω) = 2 exp (-J ω ty) followed by an ideal low pass filter of bandwidth B Hz. The output noise power in watts is |
| A. | 2 N0B |
| B. | 4 N0B |
| C. | 8 N0B |
| D. | 16 N0B |
| Answer» C. 8 N0B | |
| 816. |
During playback the take up reel is |
| A. | in clockwise motion |
| B. | in anticlockwise motion |
| C. | either clockwise or anticlockwise motion |
| D. | none of the above |
| Answer» C. either clockwise or anticlockwise motion | |
| 817. |
In which of the following schemes are several channels interleaved and transmitted together? |
| A. | TDM |
| B. | FDM |
| C. | group |
| D. | subgroup |
| Answer» C. group | |
| 818. |
In an AM transmitter after the modulation stage, class C amplifier |
| A. | can be used |
| B. | cannot be used |
| C. | may be used, but it has no use |
| D. | can't be determine to use |
| Answer» C. may be used, but it has no use | |
| 819. |
A (75 - j 50) Ω load is connected to a coaxial line of Z0 = 75 Ω at 10 GHz. The best method of matching consists of using |
| A. | a capacitance at some specific distance from load |
| B. | a short circuited stub at some specific distance from load |
| C. | an inductance at load |
| D. | a short circuited stub at load |
| Answer» E. | |
| 820. |
If fs be the signal frequency and fi be the intermediate frequency then image frequency is given by |
| A. | fs + fi |
| B. | fs ± fi |
| C. | fs ± 2fi |
| D. | fs + 2fi |
| Answer» E. | |
| 821. |
Which of the following statement about modulation is correct? |
| A. | It avoid use of antennas |
| B. | It reduces bandwidth |
| C. | It ensures transmission over long distances |
| D. | It combines different transmissions |
| Answer» D. It combines different transmissions | |
| 822. |
In a plate modulated class C amplifier, the peak supply voltage is V. The maximum plate-cathode voltage can be |
| A. | 1 V |
| B. | 1.5 V |
| C. | 2.5 V |
| D. | 4 V |
| Answer» B. 1.5 V | |
| 823. |
In a CE amplifier connection, the emitter is at ground potential for |
| A. | AC quantities |
| B. | DC quantities |
| C. | all quantities |
| D. | none of the quantities |
| Answer» B. DC quantities | |
| 824. |
Noise can be measured by |
| A. | D.C. voltmeter |
| B. | A.C. voltmeter |
| C. | either of the above |
| D. | none of the above |
| Answer» C. either of the above | |
| 825. |
In PCM, the information lies |
| A. | in one or two properties of the pulse |
| B. | in absence of pulse |
| C. | in presence of pulse |
| D. | in presence or absence of pulse |
| Answer» E. | |
| 826. |
Which of the following radio waves are not reflected by ionosphere? |
| A. | Waves above 1 kHz |
| B. | Waves above 1 MHz |
| C. | Waves above 10 MHz |
| D. | Waves above 30 MHz |
| Answer» E. | |
| 827. |
If Eb, the energy per bit of a binary digital signal is 10-6 watt sec. and the one sided power spectral density of the white noise N0 = 10-5 W/Hz, then the output SNR of the matched filter is |
| A. | 26 dB |
| B. | 10 dB |
| C. | 20 dB |
| D. | 13 dB |
| Answer» E. | |
| 828. |
Consider the following applications/ advantages of radar beacons navigationtarget identificationaccurate tracking of enemy targetslarge increase in maximum range Which of the above are correct? |
| A. | 1, 2, 3, 4 |
| B. | 1, 2, 4 |
| C. | 1, 2 |
| D. | 2, 3, 4 |
| Answer» C. 1, 2 | |
| 829. |
Assertion (A): SSB systems generally have duplex operationReason (R): SSB systems are generally used in two way communication. |
| 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» C. A is correct but R is wrong | |
| 830. |
If carrier is modulated by a digital bit stream having one of the possible phases of 0°, 90°, 180°, and 270°, then modulation is called |
| A. | BPSK |
| B. | QPSK |
| C. | QAM |
| D. | MSK |
| Answer» C. QAM | |
| 831. |
Consider the following statements as regards communication receiver Variable sensitivity is used to eliminate selective fadingA product demodulator can be used to receive Morse codeThe noise limiter cuts off receiver output during a noise pulseDouble 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 | |
| 832. |
If F(ω) is Fourier transform of f(t), then Fourier transform of f(t) cos2 ωct is |
| A. | F(ω) + [F(ω + 2ωc) + F(ω - 2ωc)] |
| B. | F(ω) + [F(ω + 2ωc) + F(ω - 2ωc)] |
| C. | F(ω) - [F(ω + 2ωc) + F(ω - 2ωc)] |
| D. | F(ω) - [F(ω + 2ωc) + F(ω - 2ωc)] |
| Answer» B. F(œâ) + [F(œâ + 2œâc) + F(œâ - 2œâc)] | |
| 833. |
A communication channel disturbed by additive white, Gaussian noise has a bandwidth of 4 kHz and SNR of 15. The highest transmission rate that this channel can support (in k bits/sec) is |
| A. | 16 |
| B. | 1.6 |
| C. | 3.2 |
| D. | 60 |
| Answer» B. 1.6 | |
| 834. |
An antenna is 30 metre high. The frequency is 1 MHz. The radiation resistance is about |
| A. | 1500 Ω |
| B. | 150 Ω |
| C. | 15 Ω |
| D. | 1.5 Ω |
| Answer» D. 1.5 Œ© | |
| 835. |
If the amplitude of the voltage is kept constant, but its frequency is raised to 6 kHz, the new deviation will be for the modulation index is, if fm = 500 Hz, Δf = 2.25 |
| A. | 6 kHz |
| B. | 12 kHz |
| C. | 27 kHz |
| D. | 54 kHz |
| Answer» D. 54 kHz | |
| 836. |
A signal x(t) = 100 cos (24p x 103t) is ideally sampled with a sampling period of 50 μ sec and then passed through an ideal low pass filter with cut off frequency of 15 kHz Which of the following frequencies are present at the filter output? |
| A. | 12 kHz only |
| B. | 8 kHz only |
| C. | 12 kHz and 9 kHz |
| D. | 12 kHz and 8 kHz |
| Answer» E. | |
| 837. |
A high pulse repetition frequency in a radar |
| A. | increases the maximum range |
| B. | decreases the maximum range |
| C. | has no effect on the maximum range |
| D. | either (a) or (b) depending on other factors |
| Answer» D. either (a) or (b) depending on other factors | |
| 838. |
Consider the following A signal f(t) and its Hilbert transform fh(t) have the same energy density spectrumA signal f(t) and its Hilbert transform, fh(t) have the same auto correlation functionA 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 | |
| 839. |
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 (Œ¥f) log2 N | |
| 840. |
What is typical bandwidths of a 2-wire telephone line? |
| A. | 300 Hz to 3.4 kHz |
| B. | 20 Hz to 4 kHz |
| C. | dc to 4 kHz |
| D. | 20 Hz to 20 kHz |
| Answer» B. 20 Hz to 4 kHz | |
| 841. |
In a satellite transponder the power amplifier feeds power P to the transmitting antenna of gain G. If distance of earth is d, the power flux density is |
| A. | PG/d |
| B. | PG/4pd2 |
| C. | P/G(4pd2) |
| Answer» C. P/G(4pd2) | |
| 842. |
In a superheterodyne receiver, having no RF amplifier, the IF is 455 kHz. The image frequency at 1000 kHz is |
| A. | 1455 kHz |
| B. | 545 kHz |
| C. | 1910 kHz |
| D. | 90 kHz |
| Answer» C. 1910 kHz | |
| 843. |
The characteristics of H and V sync pulses in a colour TV receiver are H sync, pulses are narrow and have frequency of 15625 HzV sync, pulses are much wider and have frequency of 50 HzH and V pulses have almost the same size but frequencies of 15625 and 50 Hz respectivelyV sync, pulses are very narrow but H sync, pulses are wide and their frequencies are 15625 Hz and 50 Hz respectively Which of the above are correct? |
| A. | 1 and 2 only |
| B. | 1 only |
| C. | 3 only |
| D. | 4 only |
| Answer» B. 1 only | |
| 844. |
The efficiency of a horn speaker is about |
| A. | 0.1 |
| B. | 0.4 |
| C. | 0.6 |
| D. | 0.8 |
| Answer» C. 0.6 | |
| 845. |
For an antenna of height ht metres, the radio horizon is equal to |
| A. | 4ht metres |
| B. | 4ht km |
| C. | 2.5ht km |
| D. | 2.5ht metres |
| Answer» C. 2.5ht km | |
| 846. |
During transmission over a communication channel, bit errors occur independently with probability P. If a block of n bits is transmitted, the probability of at most one bit error is equal to |
| A. | 1 - (1 - P)n |
| B. | P + (n - 1) (1 - P) |
| C. | nP (1 - P)n - 1 |
| D. | (1 - P)n + nP (1 - P)n - 1 |
| Answer» B. P + (n - 1) (1 - P) | |
| 847. |
In a channel voice coder, the outputs of sixteen 20 Hz low pass filters are sampled, multiplexed and A/D converted. If sampling is at 40 samples/second and 3 bits/sample represents each voltage sample, the bit rate is about |
| A. | 1.9 k bits/sec |
| B. | 0.95 k bits/sec |
| C. | 3.8 k bits/sec |
| D. | 7.6 k bits/sec |
| Answer» B. 0.95 k bits/sec | |
| 848. |
In VCR, the chrominance signal's frequency is |
| A. | up converted during recording and down converted during playback |
| B. | down converted during recording and up converted during playback |
| C. | not changed during recording and playback |
| D. | any of the above depending on VCR system |
| Answer» C. not changed during recording and playback | |
| 849. |
A trinitron colour picture tube uses |
| A. | three electron guns |
| B. | one electron gun |
| C. | one electron gun with three separate in line cathodes |
| D. | none of the above |
| Answer» D. none of the above | |
| 850. |
Which is a digital coding technique? |
| A. | PCM |
| B. | DM |
| C. | DPCM |
| D. | All |
| Answer» E. | |