EST-FINAL EXAM

1. The first stage of a two-stage amplifier has a voltage gain of 10, a 600-ohm input resistor, a 1600-ohm
equivalent noise resistance and a 27-kiloohm output resistor. For the second stage, these values are 25,
81 kiloohms, 10 kiloohms and 1 megaohm respectively. Calculate the equivalent input-noise resistance
of this two-stage amplifier.
A. 2200 ohms C. 2356 ohms
B. 2518 ohms D. 2135 ohms

2. A receiver connected to an antenna whose resistance is 50 ohms has an equivalent noise resistance of
30 ohms. Calculate the receiver’s noise figure in decibels and its equivalent noise temperature.
A. 2.04 dB, 154 K C. 2.04 dB, 174 K
B. 2.04 dB, 164 K D. 2.04 dB, 184 K

3. The tuned circuit of the oscillated in a simple AM transmitter employs a 50-microhenry (50-uH) and a 1-
nanofarad (1-nF) capacitor. If the oscillator output is modulated by audio frequencies up to 10 kHz, what
is the frequency range occupied by the sidebands?
A. 722 to 702 kHz C. 712 to 710 kHz
B. 712 to 702 kHz D. 722 to 702 kHz

4. A certain transmitter radiates 9 kW with the carrier unmodulated, and 10.125 kW when the carrier is
sinusoidally modulated. Calculate the modulation index, percent of modulation. If another sine wave,
corresponding to 40 percent modulation, is transmitted simultaneously, determine the total radiated
power.
A. 0.25, 10.84 kW C. 0.5, 10.84 kW
B. 0.5, 8.64 kW D. 0.25, 9.84 kW

5. The antenna current of an AM broadcast transmitter, modulated to a depth of 40 percent by an audio sine
wave, is 11 A. It increases to 12 A as a result of simultaneous modulation by another audio sine wave.
What is the modulation index due to this second wave?
A. 0.567 C. 0.757
B. 0.643 D. 0.812

6. Calculate the percentage power saving when the carrier and one of the sidebands are suppressed in an
AM wave modulated to a depth of 50 percent?
A. 65.5 % C. 83.3%
B. 76.6 % D. 94.4%

7. In an FM system, when the audio frequency (AF) is 500 Hz and the AF voltage is 2.4 V, the deviation is
4.8 kHz. If the AF is now increased to 7.2 V, what is the new deviation?
A. 14.4 kHz C. 16.6 kHz
B. 15.5 kHz D. 17.7 kHz

For Problems 8 to 10:

FM wave represented by the voltage equation:
v = 12 sin( 6x108t + 5 sin 1250t).

8. Find the carrier and modulating frequencies?

A. 95.5 MHz, 199 Hz C. 92.6 MHz, 169 Hz
B. 199 Hz, 95.5 mHz D. 169 Hz, 92.6 mHz

9. What is the modulation index?

A. 4 C. 6
B. 5 D. 7

10. What power will this FM wave dissipate in a 10-ohm resistor?

A. 1.2 W C. 5.2 W
B. 4.2 W D. 7.2 W

11. In a broadcast superheterodyne receiver having no RF amplifier, the loaded Q of the antenna coupling
circuit (at the input to the mixer) is 100. If the intermediate frequency is 455 kHz. Calculate the image
frequency and its rejection ratio at 1000 kHz.
A. 1910 kHz, 138.6 C. 1910 kHz, 168.3
B. 1810 kHz, 128.6 D. 1810 kHz, 128.6
12. What is the minimum value that the characteristic impedance of an air-dielectric parallel-wire line could
have?
A. 50 ohms C. 83 ohms
B. 75 ohms D. 300 ohms

13. A coaxial cable, having an inner diameter of 0.025 mm and using an insulator with a dielectric constant of
2.56, is to have a characteristic impedance of 2000 ohms. What must be the outer conductor diameter?
A. 209 light years C. 409 light years
B. 309 light years D. 509 light years

14. It is required to match a 200-ohm load to a 300-ohm transmission line, to reduce the SWR along the line
to 1. What must be the characteristic impedance of the quarter-wave transformer used for this purpose, if
it is connected to the load?
A. 145 ohms C. 285 ohms
B. 245 ohms D. 290 ohms

15. A (200 + j75)-ohm load is to be matched a 300-ohm line to give SWR = 1. Calculate the reactance of the
stub and the characteristic impedance of the quarter-wave transformer, both connected directly to the
load.
A. -610Ω, 262Ω C. -650Ω, 262Ω
B. -650Ω, 272Ω D. -610Ω, 282Ω

16. A half-wave dipole antenna is capable of radiating 1-kW and has a 2.15-dB gain over an isotropic
antenna. How much power must be delivered to the isotropic (omnidirectional) antenna, to match the
field-strength directional antenna?
A. 1350 W C. 1520 W
B. 1480 W D. 1640 W

17. If an antenna has a field gain (expressed in voltage) of 2, and the transmitter has an overall efficiency of
50 percent (the circuit and transmission line losses) then, if a 1-kW signal is fed to the finals, this will
result in 500 W being fed to the antenna. What is the erp?
A. 1000 W C. 3000 W
B. 2000 W D. 4000 W

18. Calculate the beamwidth between nulls of a 2-m paraboloid reflector used at 6 GHz.
A. 1.75 degrees C. 0.875 degree
B. 3.5 degrees D. 7 degrees

19. A parabolic antenna has a 0.5° beamwidth at 18 GHz. Calculate its gain in dB.
A. 26.5 C. 65.4
B. 50.7 D. 80.7

20. It is desired to build a λ/2 dipole to receive a 100-MHz broadcast. Determine the optimum length of the
dipole.
A. 3 m C. 1.43 m
B. 5.85 m D. 1.5 m
21. Two λ/2 dipoles are separated by 50 km. They are “aligned” for optimum reception. The transmitter feeds
its antenna with 10 W at 144 MHz. Calculate the power received.
A. 2.96 x 10-10 W C. 4.96 x 10-10 W
B. 3.96 x 10-10 W D. 5.96 x 10-10 W
22. Compute the power received at a satellite if the power gain of the transmitting parabolic dish antenna is
30000; the transmitter drives 2kW of power into the antenna at a carrier frequency of 6.21 GHz; the
satellite receiving antenna has a power gain of 30; and the transmission path is 45000 km.
A. 10.9 uW C. 10.9 pW
B. 12.9 uW D. 12.9 pW
23. Calculate the ghost width for a 17-in wide TV screen when a reflected wave results from an object 3/8 mi
“behind” a receiver.
A. 3.21 in C. 2.35 in
B. 4.27 in D. 1.28 in
24. Determine the characteristic impedance of RG-8A/U coaxial cable with D = 0.285 in and d = 0.08 in. It
uses a polyethylene dielectric.
A. 160 ohms C. 150 ohms
B. 50 ohms D. 80 ohms
25. A digital transmission has an error probability of 10-4 and is 109 bits long. Calculate the expected number
of error bits and the BER.
A. 105 , 104 C. 106, 105
4 5
B. 10 , 10 D. 105, 106
26. Determine the number of bits required for a binary code to represent 110 different possibilities.
A. 6 C. 8
B. 7 D. 9

27. A receiver has a 20-dB noise figure (NF), a 1-MHz bandwidth, a +5dBm third-order intercept point, and a
0-dB S/N. Determine its sensitivity.
A. -74 dBm C. -84 dBm
B. -94 dBm D. -104 dBm

28. Determine the worst-case output S/N for a broadcast FM program that has a maximum intelligence
frequency of 5 kHz. The input S/N is 2.
A. 10 C. 30
B. 20 D. 40

29. An FM signal has a center frequency of 100 MHz but is swinging between 100.001 MHz and 99.999 MHz
at a rate of 100 times per second. Determine the intelligence frequency.
A. 100 Hz C. 1000 Hz
B. 2000 Hz D. 500 Hz

30. A 2.5 MHz carrier is modulated by a music signal that has a frequency components ranging from 100 Hz
to 5 kHz. What is the range of frequencies generated for the upper sideband?
A. 2.5 MHz to 2.505 MHz
B. 2.495 MHz ro 2.505 MHz
C. 2.5001 MHz to 2.505 MHz
D. 2.495 MHz to 2.499 MHz

31. An AM broadcast station operates at its maximum allowed output power of 80W at a percent modulation
of 60%. What is the upper sideband power?
A. 6.1 watts C. 9.23 watts
B. 7.2 watts D. 12.2 watts

32. Determine the side frequency voltage if the modulation index is 70% and the carrier amplitude is 50V.
A. 25 C. 75
B. 17.5 D. 50

33. Determine the phase-shift represented by a 75 ns delay of a 4 MHz signal to a 75-ft cable with a
dielectric constant of 2.3
A. 108 degrees C. 52 degrees
B. 4.8 degrees D. 250 degrees
34. By how much should two antennas be separated for space diversity in the 11 GHz band?
A. 5.5 m C. 9.5m
B. 7.5m D. 11.5m
35. The refractive indices of core and cladding materials of a step index fiber are 1.48 and 1.45, respectively.
Calculate the fractional indices change.
A. 0.0002 C. 0.02
B. 0.002 D 0.2
36. How long does it take to dial the number 784-3745 using pulse dialing with .5s inter digit time?
A. 6.5s C. 6.8s
B. 7.2s D. 12.5s
37. Compute the bit rate for a 2000 baud 16-QAM signal.
A. 8000 bps C. 2000 bps
B. 4000 bps D. 500 bps
38. Given a bandwidth of 6000 Hz for an ASK signal, what is the baud rate?
A. 3000 Hz C. 12000 Hz
B. 2000 Hz D. 6000 Hz
39. A radiolink receiver has a noise figure of 8dB and an IF bandwidth of 12 MHz. What is the FM
improvement threshold in dBW?
A. -115.21 dBW C. -123.21 dBW
B. -125.21 dBW D. -199.21 dBW
40. A LOS microwave radiolink requires an antenna with a 32-dB gain. The link operates at 6 GHz. What
diameter of parabolic dish is required? Assume an aperture efficiency of 55%.
A. 1.8 ft C. 2.8 ft
B. 2.0 ft D. 3.4 ft
41. A transmission line operating at 125 MHz has Z0 = 40Ω, α = 0.02 (Np/m), and β = 0.75 rad/m. Find the
line parameter L.
A. 38.2 nH/m C. 38.2 uH/m
B. 42.5 nH/m D. 42.5 uH/m
42. A Satellite receiving system includes a dish antenna ( Teq = 35 K) connected via a coupling network (Teq=
40 K) to a microwave receiver (Teq=52 K referred to its input). What is the noise power to the receiver’s
input over a 1-MHz frequency range?
A. 1.75 x 10-15W C. 1.15 x 10-15W
-12
B. 1.75 x 10 W D. 1.15 x 10-12W

43. For a total capacity of 36 Mbps and 64-QAM of digital modulation, what is the ideal RF bandwidth?
A. 4MHz C. 6 MHz
B. 5 MHz D. 7MHz
44. Find the velocity of a satellite in a circular orbit 500 km above the earth’s surface
A. 76 km/s C. 7.6 km/s
B. 76 m/s D. 7.6 km/s2
45. Calculate the length of the path to a geostationary satellite from an earth station where the angle of
elevation is 30°.
A. 36,000 km C. 39,000 km
B. 36,000 mi D. 39,000 mi
46. A dipole antenna has a radiation resistance of 67 ohms and a loss resistance of 5 ohms, measured at the
feedpoint. Calculate the efficiency
A. 90% C. 92%
B. 91% D. 93%
47. What is the phase velocity of a rectangular waveguide with a wall separation of 3 cm and a desired
frequency of operation of 6 GHz?
A. 3.45 x 108 m/s C. 4.53 x 108 m/s
8
B. 4.35 x 10 m/s D. 5.43 x 108 m/s

48. A fiber is rated as having a bandwidth-distance product of 500MHz-km. Find its dispersion in ns/km.
A. 1 ns/km C. 3 ns/km
B. 2 ns/km D. 4 ns/km

49. A CDMA mobile measures the signal strength from the base as -100dBm. What should the mobile
transmitter power be set to as a first approximation.
A. 450 mW C. 250 mW
B. 350 mW D. 150 mW

50. In ionosphere incidence angle is 60°. The maximum usable frequency fm is equal to
A. 2fc
B. fc
C. 0.5 fc
D. sqrt. 3 x fc

51. A cordless telephone using separate frequencies for transmission in base and portable units is known as
A. duplex arrangement C. either (a) or (b)
B. half duplex arrangement D. neither (a) or (b)

52. For attenuation of high frequencies we should use

A. shunt capacitance C. inductance
B. series capacitance D. inductance

53. A modem is classified as low speed if data rate handled is

A. upto 100 bps C. upto 400 bps
B. upto 250 bps D. upto 600 bps

54. VSB modulation is preferred in TV because

A. it reduces the bandwidth requirement to half
B. it avoids phase distortion at low frequencies
 C. it results in better reception
D. none of the above

55. A woofer should be fed from the input through a

A. low pass filter C. band pass filter
B. high pass filter D. band stop filter

56. The colour subcarrier and sidebands produced by its modulation with the chrominance signals are
accommodated in the standard channel width by the process of
A. frequency adjustment C. frequency changing
B. frequency interleaving D. frequency changing

57. In FM signal with a modulation index mf is passed through a frequency tripler. The wave in the output of
the tripler will have a modulation index of
A. mf C. mf/3
B. 3mf D. mf/9

58. In colour TV receiver, varactor diode is used for

A. Detection C. tuning
B. Rectification D. both (a) and (b)

59. The number of noise sources in a BJT are

A. 3 C. 1
B. 2 D. 4

60. Energy content of atmospheric noise

A. does not depend on frequency
B. decreases as frequency is increased
C. increases as frequency is increased
D. either (a) or (c) depending on the temperature

61. A 400 W carrier is amplitude modulated with m = 0.75. The total power in AM is
A. 400 W
B. 512 W
C. 588 W
D. 650 W

62. Non-coherently detection is not possible for

A. PSK
B. ASK
C. FSK
D. both (a) and (c)

63. Tracking of extra terrestrial objects requires

A. high transmitting power
B. very sensitive receiver
C. fully steerable antenna
D. all of the above

64. Assertion (A): Free space does not interfere with normal radiation and propagation of radio waves
Reason (R): Free space has no magnetic or gravitational fields.
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

65. In radar systems PRF stands for

A. Power Return Factor
B. Pulse Return Factor
C. Pulse Repetition Frequency
D. Pulse Response Factor

66. As the frequency increases, the absorption of ground wave by earth's surface
A. decreases
B. increases
C. remains the same
 D. either (a) or (c)

67. The velocity of sound waves in air

A. is constant at all temperatures
B. varies directly as temperature
C. varies inversely as absolute temperature
D. varies directly as square root of absolute temperature

68. The range of a cordless telephone is about

A. 1000 m
B. 500 m
C. 100 m
D. 10 m

69. An earth mat for a communication tower consists of

A. one or two radials extending from base of tower at a depth of about 5 cm below ground
B. a large number of radials extending from base of tower at a depth of about 3 m
C. a large number of radials extending from base of tower at a depth of about 30 cm
D. none of the above

70. The rate at which information can be carried through a communication channel depends on
A. carrier frequency
B. bandwidth
C. transmission loss
D. transmitted power

71. In standing wave pattern on a transmission line

A. voltage and current nodes coincide
B. voltage and current antinodes coincide
C. voltage nodes and current antinodes as well as current nodes and voltage antinodes coincide
D. both (a) and (b)

72. Frequency shift keying is used mostly in

A. Telegraphy
B. Telephony
C. satellite communication
D. radio transmission

73. It is desired that transmission line and load should match for a range of frequencies. The best method is
A. to use a balun
B. to use a single stub of adjustable position
C. to use a double stub
D. to use a broad band amplifier

74. Consider the following statements

1. The amplitude of an FM wave is constant

2. FM is more immune to noise than AM
3. FM broadcasts operate in upper VHF and UHF frequency ranges
4. 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

75. Which of the following is taken as reference antenna for directive gain?
A. Half wave dipole
B. Elementary doublet
C. Isotropic
D. Infinitesimal dipole
76. Which of the following types of noise assumes greater importance at high frequencies?
A. Transit time noise
B. Shot noise
C. Impulse noise
D. Random noise

77. In transistor radio receivers the number of IF amplifier stages are

A. 1
B. 2
C. 4
D. 6

78. To relay outdoor remotely located live programs, TV transmitter use

A. microwave links
B. coaxial cable link
C. open wire link
D. either (b) or (c)

79. Assertion (A): A balun is an RF impedance matching transformer.

Reason (R): Sometimes a booster amplifier is used with a TV set.
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

80. Fields are said to be circularly polarised if their magnitudes are

A. equal and they are in phase
B. equal but they differ in phase by ± 90°
C. unequal and differ in phase by ± 90°
D. unequal but are in phase
81. CATV stands for
A. Common Antenna Television
B. Community Antenna Television
C. Cable Antenna Television
D. Channel Antenna Television

82. Household tape recorders use

A. separate motor for each operation
B. only one motor for all operations
C. one motor for capstan and another for take up reel
D. a total of 3 motors

83. Assertion (A): A composite video signal has synchronising pulses.

Reason (R): It is necessary to synchronise the scanning process in the transmitter and receiver.
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

84. 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

85. Assertion (A): In standing wave pattern, the nodes and anti nodes are separated by half wave-length
Reason (R): When line is terminated in resistance RL, the standing wave ratio is SWR = Z0/RL or RL/Z0
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
86. An FM signal with a deviation is passes through the mixer, and has its frequency reduced five fold. The
deviation in the output of the mixer is
A. Δ
B. 5Δ
C. Δ/5
D. Indeterminant
87. FSK is a system involving
A. pulse modulation
B. frequency modulation
C. amplitude modulation
D. phase modulation
88. In FM, as bandwidth increases
A. distortion increases
B. distortion decreases
C. distortion remains unaffected
D. all

89. Microwave link repeaters are typically 50 km apart in TV transmission due to

A. atmosphere attenuation
B. output power tube limitations
C. attenuation of surface wave
D. earth's curvature

90. Radiation resistance of an antenna is a

A. dc resistance
B. ac resistance
C. either (a) or (b)
D. none of the above

91. Which of the following statement regarding single-sideband (SSB) transmission is not correct?
A. In such transmission only or sideband is transmitted, leaving of the other sideband and the
carrier
B. It has gained general acceptance of use in home-entertainment equipment
C. It is generally reserved for point-to-point communication
D. It is generally reserved for point-to-point communication

92. For demodulating PCM; it is first converted into

A. PDM
B. PPM
C. PWM
D. PAM

93. One of the advantages of base modulation over collector modulation in a class C transistor amplifier is
A. higher efficiency
B. more linear operation
C. more power output per transistor
D. lesser requirement of modulating power

94. 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

95. For a short dipole having an effective length less than half the wavelength the radiation resistance is
A. proportional to length
B. proportional to square root of length
C. proportional to square of length
D. none of the above

96. In a low level amplitude modulated system, the amplifier modulated stage must be
A. class C
 B. linear
C. non linear
D. harmonic

97. A noise can be represented as superposition of spectral components. When this noise is passed through
a narrow band filter, the output of filter should look like
A. Sinusoidal
B. rectangular
C. triangular
D. none of the above

98. In a single sideband suppressed carrier AM system, the modulation index is changed from 0 to 1, the
power content of the signal
A. will be quarter
B. will be doubled
C. will increase by 50 percent
D. will increase by 25 percent

99. Neper is
A. larger than a decibel
B. smaller than decibel
C. equal to 1 decibel
D. none of the above

100. Which of following digital modulation technique?

A. ASK
B. FSK
C. PSK
D. All