Exam 11 July 2018, questions PDF

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Communication Systems - Section 7                         

Communication Systems - Section 1 Communication Systems - Section 2 Communication Systems - Section 3 Communication Systems - Section 4 Communication Systems - Section 5 Communication Systems - Section 6 Communication Systems - Section 7 Communication Systems - Section 8 Communication Systems - Section 9 Communication Systems - Section 10 Communication Systems - Section 11 Communication Systems - Section 12 Communication Systems - Section 13 Communication Systems - Section 14 Communication Systems - Section 15 Communication Systems - Section 16 Communication Systems - Section 17 Communication Systems - Section 18 Communication Systems - Section 19 Communication Systems - Section 20 Communication Systems - Section 21 Communication Systems - Section 22 Communication Systems - Section 23 Communication Systems - Section 24 Communication Systems - Section 25

1. Consider the following test signal patterns 1. 2. 3. 4. 5.

Ramp Grill Grey shades Sine pulse Picture line up generating equipment

Which of the above are used in TV studios? A.All B.1, 2 and 3 only C.1, 2 and 5 only D.2, 3, 4 and 5 only Answer: Option A

Explanation: All these are standard test signals used in TV studios. View Answer Discuss in Forum Workspace Report 2. If aspect ratio is and number of lines in each frame is 625, the number of picture elements in one frame is A.

x 625

B.

(625)2 C.6252 D.

(625)2

Answer: Option B Explanation:

Since there are 625 lines in one frame, the number of picture elements is

.

View Answer Discuss in Forum Workspace Report 3. Indicate the false statement: If SWR on a transmission line is infinite, the line is terminated in A.open circuit B.short circuit C.pure reactance D.complex impedance Answer: Option D Explanation: If line is OC or SC or terminated in pure reactance, SWR is 1. View Answer Discuss in Forum Workspace Report

4. In TV signals colour burst is used A.to maintain colour sequence B.to ensure I and Q phase correctly C.to synchronise colours D.for interlacing of horizontal lines Answer: Option B Explanation: Colour burst consists of a short train of about 10 cycles sent to the receiver along with synchronous signals. It ensures I and Q phase correctly. View Answer Discuss in Forum Workspace Report 5. The resonant frequency of an RF amplifier is 1 MHz and its bandwidth is 10 kHz. The Q factor will be A.10 B.100 C.0.01 D.0.1 Answer: Option B Explanation:

. View Answer Discuss in Forum Workspace Report 6. The total number of pulses in a TV remote control is A.14 B.12 C.10 D.8

Answer: Option A Explanation: The 14 pulses are preliminary pulse, start pulse, stop pulse and 11 other pulses. View Answer Discuss in Forum Workspace Report 7. Which camera tube has highest sensitivity and very wide spectral response? A.Vidicon B.Plumbicon C.New vicon D.Saticon Answer: Option C Explanation: New vicon has very high sensitivity and very wide spectral response which extends well into infrared region. View Answer Discuss in Forum Workspace Report 8. Assertion (A): A Smith chart can be used for a number of calculations of a transmission line Reason (R): Smith chart is basically a polar impedance diagram. 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: Option B Explanation: Smith chart is a convenient tool for transmission line design and analysis. View Answer Discuss in Forum Workspace Report 9. A computer monitor uses 180 W in normal operation and 20 W in sleep mode. The computer

is on all the 24 hours but is in sleep mode for 18 hours a days. The energy units saved in 30 days are A.0.54 units B.86.4 units C.2.88 units D.4.8 units Answer: Option B Explanation:

. View Answer Discuss in Forum Workspace Report 10. Consider the following functions 1. 2. 3. 4.

It detects the AM video carrier IF so as to produce the video signal It produces and separates out the inter carrier sound IF of 5.5 MHz It amplifies the video signal It amplifies the audio signal

The video detector in a colour TV performs which of the above functions A 1, 2 and 3 . B.1, 2, 3 and 4 C.1 and 2 D 1, 2 and 4 . Answer: Option C Explanation: Video detector does not amplify any signal. View Answer Discuss in Forum Workspace Report 11. Which of the following antennas is circularly polarized? A Yagi-Uda

. B.Parabolic reflector C.Small circular loop D Helical . Answer: Option D Explanation: The helical antenna is circularly polarized, i.e., its polarization is evenly divided between vertical and horizontal components. View Answer Discuss in Forum Workspace Report 12. In colour TV system the colour sub carrier frequency is 4.43 MHz. A True . B.False Answer: Option B Explanation: Video monitor does not have RF tuner and IF amplifier stages. View Answer Discuss in Forum Workspace Report 13. A transmitter power of 5 W is increased by 20 dB. The effective radiated power is A 5W . B.100 W C.25 W D 500 W . Answer: Option D Explanation:

or P = 500 W. View Answer Discuss in Forum Workspace Report 14. The percentage saving in power of 100% modulated suppressed carrier AM signal is A 100 . B.75 C.66.6 D 50 . Answer: Option C Explanation: m = 1,

if carrier is suppressed then

. View Answer Discuss in Forum Workspace Report 15. The maximum distance between television transmission and receiving antennas for reasonably good reception should be A less than 20 km . B.less than 100 km C.less than 500 km D less than 1000 km .

Answer: Option B Explanation: Television transmission is governed by line of sight distance which is about 100 km or less. View Answer Discuss in Forum Workspace Report 16. Assertion (A): EM waves are attenuated as they travel outward from a source Reason (R): Both field intensity and power density follow inverse square law. 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: Option A Explanation: As per inverse square law, power is inversely proportional to square of distance. View Answer Discuss in Forum Workspace Report 17. The frequency response of a microphone means A bandwidth of frequencies having output with in ± 1 dB of the output at 1000 Hz . B.bandwidth of frequencies having output with in ± 3 dB of the output at 1000 Hz C.bandwidth of frequencies having output with in ± 1 dB of the output at 500 Hz D bandwidth of frequencies having output with in ± 3 dB of the output at 500 Hz . Answer: Option A Explanation: 100 Hz is taken as standard for specifying the output. View Answer Discuss in Forum Workspace Report

18. Graphic equaliser system in stereophonic systems generally have A 3 or 4 bands . B.1 band C.more than 8 bands D large number of bands . Answer: Option A Explanation: Stereo systems have 3 or 4 bands at 300 Hz, 1000 Hz, 10000 Hz etc. in graphic equaliser system. View Answer Discuss in Forum Workspace Report 19. An amplifier operating over a frequency range of 18 to 20 MHz has 10 kΩ input resistance. At a temperature of 27° C, the noise voltage at input of amplifier is (Boltzman constant k = 1.38 x 10-23 J/K) A 18.2 μV . B.182 μV C.16.2 μV D 162 μV . Answer: Option A Explanation: Using Equation Va = (4 x 1.38 x 10-23 x 300 x 2 x 106 x 104)0.5 = 18.2 x 10-6 V. View Answer Discuss in Forum Workspace Report 20. Some sources of TV programs are 1. TV camera 2. Telecine 3. VTR

4. External signal Which of the above are actually present in a TV studio? A 1, 2, 3 and 4 . B.1, 2, 3 C.1 and 3 D 1 2 and 4 . Answer: Option A Explanation: All these are present. View Answer Discuss in Forum Workspace Report 21. Two sinusoidal signals of same amplitude and frequencies 10 kHz and 10.1 kHz are added together. The combined signal is given to an ideal frequency detector. The output of the detector is A 0.1 kHz sinusoidal . B.10.1 kHz sinusoidal C.a linear function D a constant . Answer: Option B Explanation: Y(t) = A cos (2p x 104 t) + A cos (2p x 10.1 x 103 t) when passed through high pass filter, Output will be A cos (2p x 10.1 x 103 t) only. View Answer Discuss in Forum Workspace Report 22. In Vidicon camera tube, the resistance of photoconductive material on the target plate A is constant

. B.is more in darkness and less in brightness C.is more in brightness but less in darkness and brightness D may be more or less in darkness and brightness . Answer: Option B Explanation: Light dependent resistor (LDR) has high resistance in darkness and low resistance in brightness. View Answer Discuss in Forum Workspace Report 23. 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) D . Answer: Option B Explanation: Available power is PG and is spread over 4 nd2. View Answer Discuss in Forum Workspace Report 24. The percentage saving in power of 100% modulated suppressed carrier AM signal is A 100 . B.75 C.66.6 D 50 . Answer: Option C

Explanation: Pc = 400 W, m = 0.75

View Answer Discuss in Forum Workspace Report 25. Which of the following are useful in comparing the noise performance of receivers? 1. 2. 3. 4.

Input noise voltage Noise figure Noise resistance Noise temperature

Select answer as per the following codes: A 1, 2 and 3 . B.1, 3 and 4 C.2, 3, 4 D 1, 2, 4 . Answer: Option C Explanation: Noise figure, noise resistance and noise temperature are useful quantities. Input noise voltage alone is not sufficient unless gain of amplifier stages is also known. View Answer Discuss in Forum Workspace Report 26. Compact discs use A magnetic recording and retrieval . B.optical recording and retrieval C.optical recording but magnetic retrieval D magnetic recording but optical retrieval .

Answer: Option B Explanation: CD uses optical recording and retrieval. View Answer Discuss in Forum Workspace Report 27. A carrier is phase modulated (PM) with frequency deviation of 10 kHz by a single tone frequency of 1 kHz. If the single tone frequency is increased to 2 kHz, assuming that phase deviation remains unchanged, the bandwidth of the PM signal is A 21 kHz . B.22 kHz C.42 kHz D 44 kHz . Answer: Option D Explanation: Frequency deviation = 10 kHz, fm = 1 kHz 2(fm + Df) Bandwidth = 22 kHz 2(10 + 1)

22 kHz

fm is doubled Hence 22 x 2

44 kHz bandwidth.

View Answer Discuss in Forum Workspace Report 28. In a communication receiver, a squelch circuit is normally inserted A before detector . B.after detector C.before mixer

D after power amplifier . Answer: Option B Explanation: Squelch, i.e., muting is added after detector to suppress noise when no carrier is present at input. View Answer Discuss in Forum Workspace Report 29. 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: Option D Explanation: Depending on which logic is used. View Answer Discuss in Forum Workspace Report 30. A carrier is simultaneously modulated by two sine waves having modulation indices of 0.4 and 0.3. The total modulation index will be A 0.1 . B.0.7 C.0.5 D 0.35 . Answer: Option C Explanation:

m1= 0.4, m2 = 0.3 . . View Answer Discuss in Forum Workspace Report 31. A 1000 kHz carrier is simultaneously modulated by 300 Hz and 2 kHz audio sine wave. Which of the following frequencies will not be present in the output? A 998 kHz . B.999.7 kHz C.1000.3 kHz D 700 kHz . Answer: Option D Explanation: 1000 ± 0.3 and 1000 ± 2 kHz will be present. View Answer Discuss in Forum Workspace Report 32. SWR for a transmission line is infinity when the load is 1. 2. 3. 4.

Short circuit Complex impedance Open circuit Pure reactance

Of the above statements: A 1, 3, 4 are correct . B.1 and 3 are correct C.2, 3, 4 are correct D 1, 2, 4 are correct . Answer: Option B Explanation:

SWR is infinite if |rv| = 1. View Answer Discuss in Forum Workspace Report 33. The discone antenna is A used in UHF range . B.circularly polarized C.used in radar D used as a direction finding antenna . Answer: Option A Explanation: Discone antenna is a combination of disc and cone. It is omnidirectional and is used in VHF and UHF range especially at airports. View Answer Discuss in Forum Workspace Report 34. The direction of pick up in a CD is A linear from centre towards edge . B.linear from edge to centre C.nonlinear from centre to edge D nonlinear from edge to center . Answer: Option A Explanation: It is linear from centre to edge. View Answer Discuss in Forum Workspace Report 35. 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: Option D Explanation: A short-circuited stub placed at a suitable distance from load provides best matching. View Answer Discuss in Forum Workspace Report 36. In PCM the amplitude levels are transmitted in a 7 unit code. Sampling frequency is 10 kHz. The bandwidth should be A 5 kHz . B.35 kHz C.70 kHz D 5 MHz . Answer: Option B Explanation: Bandwidth = (10 x 7) = 35 kHz. View Answer Discuss in Forum Workspace Report 37. In colour television V and U signals are A same as I and Q signal . B.same as R - Y and B - Y C.modified I and Q signal D modified R - Y and B - Y .

Answer: Option D Explanation: U = 0.493 (B - Y) and V = 0.877 (R - Y). View Answer Discuss in Forum Workspace Report 38. Which of the following has highest power gain? A CE . B.CC C.CB D CB or CC . Answer: Option A Explanation: CE connection has good current and voltage gain. Therefore power gain is very high. View Answer Discuss in Forum Workspace Report 39. Two messages m1, and m2 have a probability of 0.5 each. The entropy is A 0.25 . B.0.5 C.0.75 D 1 . Answer: Option D Explanation: Entropy = 0.5 log2 2 + 0.5 log2 2 = 1. View Answer Discuss in Forum Workspace Report

40. A TV receiver is 40 cm wide and 30 cm high. The EHT supply required is about A 2kV . B.20 kV C.53 kV D 10 W . Answer: Option B Explanation:

and EHT supply is 1 kV per diagonal inch. View Answer Discuss in Forum Workspace Report 41. An AM signal is detected using an envelope detector, the carrier frequency and modulating signal frequency are 1 MHz and 2 kHz respectively. An appropriate value for the time constant of the envelope detector is A 500 μ sec . B.20 μ sec C.0.2 μ sec D 1 μ sec . Answer: Option B Explanation: In envelope detector, for proper detection

10-6 ≤ RC ≤ 250 μ sec. Only 20 m sec satisfies the condition. View Answer Discuss in Forum Workspace Report

42. For signal amplitude modulated to a depth of 100% by a sinusoidal signal, power is A same as that of unmodulated carrier . B.twice the power of unmodulated carrier C. D .

times the power of unmodulated carrier times the power of unmodulated carrier

Answer: Option C Explanation: When m = pt = 1.5 Pc View Answer Discuss in Forum Workspace Report 43. If transmitted power is 10 kW, the field strength at a distance d is 50 mV/m. If transmitted power is reduced to 2.5 kW, the field strength at the same point will be A 25 mV/m . B.12.5 mV/m C.6.25 mV/m D 3.125 mV/m . Answer: Option A Explanation: E ∝ Pt . View Answer Discuss in Forum Workspace Report 44. Some features of advanced mobile phone service are 1. To provide telephone communication to a large number of telephone users within the

area of a metropolitan only 2. To use minimum amount of frequency spectrum 3. To permit hand held as well as vehicle operation of telephone

Which of the above are true? A 1 and 2 only . B.1, 2, 3 C.1 and 3 only D 2 and 3 only . Answer: Option B Explanation: All the three features are necessary. View Answer Discuss in Forum Workspace Report 45. The carrier frequency will be if L = 50 µH and C = 1 nF. A 512 . B.612 kHz C.712 kHz D 812 kHz . Answer: Option C Explanation: L = 50 µH, C = 1 nF

. View Answer Discuss in Forum Workspace Report 46. Three point tracking is achieved with A double conversion . B.padder capacitor C.double spotting D variable selectivity .

Answer: Option B Explanation: To obtain three point tracking a capacitor is connected in series with local oscillator coil. This capacitor is called padder capacitor. View Answer Discuss in Forum Workspace Report 47. In TV transmitter, visual exciter may consist of 1. 2. 3. 4. 5.

Video processing unit Visual modulator VSB filter Delay equaliser Frequency converter

Which of the above are actually a part of visual exciter? A 1, 2 and 3 . B.2, 3 and 4 C.1, 2, 3 and 4 D 1, 2, 3, 4 and 5 . Answer: Option D Explanation: All these are part of visual exciter. View Answer Discuss in Forum Workspace Report 48. The positive peak of an AM wave is 16 V and the minimum value is 4 V Assuming single tone modulation, the modulation index is A 0.6 . B.0.25 C.4 D 0.36 .

Answer: Option A Explanation:

Average value = 10 V and

.

View Answer Discuss in Forum Workspace Report 49. In a circuit the value of resistor is made four times. The noise voltage generated by this resistance will A be doubled . B.be increased four times C.remain the same D become half . Answer: Option A Explanation: Noise voltage ∝ R. View Answer Discuss in Forum Workspace Report 50. A resistor of 10 kΩ has an rms noise voltage of 1 mV under a certain set of conditions. A resistor of 20 kΩ under the same conditions will have an rms noise voltage of A 1 mV . B.2 mV C.1.414 mV D 4 mV . Answer: Option C Explanation: i ∝ R.

View Answer Discuss in Forum Workspace Report

Communication Systems - Section 8                         

Communication Systems - Section 1 Communication Systems - Section 2 Communication Systems - Section 3 Communication Systems - Section 4 Communication Systems - Section 5 Communication Systems - Section 6 Communication Systems - Section 7 Communication Systems - Section 8 Communication Systems - Section 9 Communication Systems - Section 10 Communication Systems - Section 11 Communication Systems - Section 12 Communication Systems - Section 13 Communication Systems - Section 14 Communication Systems - Section 15 Communication Systems - Section 16 Communication Systems - Section 17 Communication Systems - Section 18 Communication Systems - Section 19 Communication Systems - Section 20 Communication Systems - Section 21 Communication Systems - Section 22 Communication Systems - Section 23 Communication Systems - Section 24 Communication Systems - Section 25

1. In a satellite system circular polarization is to be obtained. The antenna used is A.parabolic B.horn C.log periodic D.helical Answer: Option D Explanation: Helical antenna produces a circularly polarized radiation if its two components are at right angles and are equal. It is very commonly used in radio telemetry. View Answer Discuss in Forum Workspace Report

2. A horizontal output stage is cutoff for retrace and 40% of trace. If time for each horizontal line is 64 μs and retrace time is 12 μs, the transistor is conducting for about A.64 μs B.6.4 μs C.31 μs D.3.1 μs Answer: Option C Explanation:

Total time for each horizontal line =

.

Time for trace = 64 - 12 = 52 μs. Time for which transistor is not conducting = 12 + 0.4 x 52 = 32.8 ms. Time for which transistor is conducting = 64 - 32.8 = 31 μs. View Answer Discuss in Forum Workspace Report 3. A TV remote control works on the principle of A.pulse code m...