EXAM 5 - ELECTRONICS SYSTEMS AND TECHNOLOGY Instruction: Submit your answer sheet (provided) together with this questionnaire to the office for checking.
B. C. D.
Nitrogen Carbon-dioxide Neodymium-YAG
that the bandwidth is 1.0 MHz and the temperature is 20°C, and that the receiver is connected to an antenna with an impedance of 75 Ω.
10. _________ of a frequency band is the entry in the table of frequency allocation of A. 30.3 C. 3.03 a given frequency for the purpose of its B. 303 D. 0.303 use by one or more terrestrial or space The luminous flux emitted by a 60-cd radiocommunication services or the radio 18. What is the modulation rate of the CCITT isotropic light source is concentrated on astronomy service under specified an area of 0.5 m2. What is the illumination V.26 modem? conditions. of the area? A. 56 kbps C. 1200 bauds A. Assignment C. Allocation A. 9.6 lx C. 377 lx B. 1560 cps D. 9600 bauds B. Allotment D. Regulation B. 120 lx D. 1508 lx 19. What is the insertion loss of connector11. In FM, the Carson’s Rule states that the The ultrapure glass used to manufacture type splices for a single mode fiber optics? bandwidth is equal to twice the sum of the optical fibers is approximately _____ pure. modulating frequency and ________. A. 0.51 dB C. 0.31 dB A. 99.9 % C. 99.99 % B. 0.49 dB D. 0.38 dB A. carrier signal B. 99.999 % D. 99.9999 % B. modulating index 20. An object nearer to a converging lens than C. frequency deviation What is the other name for parity? its focal point always has a/an ___ image. D. image frequency A. BCC C. LRC A. inverted C. same size B. VRC D. CRC 12. Which microphone will be damaged if B. smaller D. virtual exposed to high temperature above 52°C? Which one of the following is not a reason 21. Which of the following ITU standards for the use of an earth mat? A. Dynamic C. Crystal describes the interconnection techniques B. Ribbon D. Capacitor between PDNs and PSTNs? A. Impossibility of a good ground 13. What is the guardband between connection. A. V.100 C. V.200 B. Provision of an earth for the antenna. supergroup 18 and supergroup D25? B. V.300 D. V.400
Time Element: 4 hours 1.
2.
3.
4.
5.
C.
Protection of personnel working underneath.
D.
Improvement of the radiation pattern of the antenna.
What one part of the transmitter protects the crystal oscillator from “pulling”? A. B.
6.
C. 0.476 nF D. 0.476 fF
10111111 11111110
C. 00000010 D. 01111111
Noise is primarily A. B. C. D.
9.
0.476 µF 0.476 pF
C. 56 kHz D. 8 kHz
14. If the modulation index of an AM wave is changed from 0 to 1, the transmitted power is A. B. C. D.
unchanged halved doubled increased by 50%
15. Which mode of transmission achieves less than full-duplex but more than halfduplex? A. B.
Full/full duplex Isochronous
C. Echoplex D. Synchronous
high-frequency spikes low-frequency variations random level shifts random frequency variations
Which laser emits light in the visible range of 400 to 700 nm? A.
Argon-ion
16. If the current ratios of the two or more elements must be held 5% and the phase angle to 3°, the antenna is called a A. B. C. D.
22. An object farther from a converging lens than its focal point always has a/an _____ image. A. B.
inverted virtual
C. same size D. smaller size
23. Which of the following is the most widely used balanced modulator?
What is the go-ahead sequence? A. B.
8.
C. Modulator D. Antenna coupler
What is the capacitance of 55 miles #44 copper wire spaced 18 inches? From wire tables, # 44 wire has a radius to 0.10215 in.? A. B.
7.
Buffer amplifier Power amplifier
A. 12 kHz B. 128 kHz
end fire array
A. B. C. D.
Full-wave bridge circuit Balanced bridge modulator Lattice modulator None of these
24. A non-exclusive facility at which the public may, by the payment of appropriate fees, place as well as receive telephone calls or a telegram or other messages. A. B. C. D.
Public Toll Service Station Public Toll Calling Station Public Toll Carrier Station Public Toll Bus Station
critical phased array
broadband array wideband array
17. Calculate the noise figure of the receiver whose RF amplifier has an input resistance of 1000 Ω and an equivalent shot-noise resistance of 2000 Ω, a gain of 25 and a load resistance of 125 kΩ. Given
25. What is a thin springy sheet of bakelite or metal that permits the voice coil in a dynamic loudspeaker to move back and forth along the core of its magnet? A. B.
Vibrator Hypex
C. Diaphragm D. Spider
26. The transistor with the lowest noise figure in the microwave region is a A. B. C. D.
MOSFET Dual-gate MOSFET JFET MESFET
27. What is the estimated medium wind loading in the Philippines for antenna tower design? A. 300 kph B. 200 kph
C. 100 kph D. 250 kph
C. D.
Bridge circuit Constant current source
35. What is a form of amplitude distortion introduced when the positive and negative alternations in the AM modulated signals are not equal? A. B. C. D.
Envelope distortion Spurious emission Carrier shift Johnson noise
36. What protocol is used to connect the other packet switching network?
28. What is the primary disadvantage of FM? A. B. C. D.
Higher cost and complexity Excessive use of spectrum space Noise susceptibility Lower efficiency
A. B.
X.75 X.50
C. X.25 D. X.10
37. What polarization is employed in AM broadcasting?
D.
44. The square of the thermal noise voltage generated by a resistor is proportional to A. B. C. D.
A. B. C. D.
Space segment occupant Space segment lessee Space occupant Space segment player
30. To find the characteristic impedance of a coaxial cable, measurements are made with (a) the far end open circuited and (b) far end short circuited, the corresponding readings being a) Ro = 3 Ω and Xc = 55 Ω, capacitive b) Rs = 10 Ω and XL = 90 Ω, inductive What is the characteristic impedance, Z0, of the line? A. B.
75.7 – j2.0 Ω 87.5 – j5 Ω
C. 70.7 + j1.19 Ω D. 70.7 – j1.97 Ω
31. What is the most important specification of loudspeakers and microphones? A. B. C. D.
Frequency response Field strength Power density Gain
32. What is known as the frequency of a free vibration? A. B. C. D.
Resonant frequency Natural frequency Center frequency Normal frequency
33. What is usually used to demodulate SSB or CW signal? A. B.
PLL Ratio detector
C. BFO D. All of these
34. What is the principal circuit in the popular 1496/1596 IC balanced modulator? A. B.
Differential amplifier Rectifier
A. B.
Horizontal Circular
C. Vertical D. Omnidirectional
38. One of the sources of errors of GPS signal is ionospheric effect which contributes _____ of error. A. ± 5 m B. ± 10 m
C. ± 2.5 m D. ± 3 m
39. In the phasing method of SSB generation, one sideband is canceled out due to A. B. C. D.
phase shifting sharp selectivity carrier suppression phase inversion
40. The purpose why an RF amplifier is operated under linear class-B conditions (as opposed to class-C) is to A. B. C. D.
generate only even harmonics generate only odd harmonics increase the efficiency amplify an AM signal
41. A rectangular waveguide has dimensions of 3 cm x 5 cm. What is the dominant mode cut-off frequency? A. B.
2 GHz 2.5 GHz
C. 3 GHz D. 3.5 GHz
42. Echo suppressors are used on all communications system when the round trip propagation time exceeds how many milliseconds? A. B.
50 ms 100 ms
C. 30 ms D. 1 ms
43. Identify an electronic device, not specifically designed for the purpose, which can be used as a phase detector. A. B. C.
Wien bridge Colpitts oscillator Balanced modulator
its resistance its temperature the bandwidth over which it is measured all of the above
45. What modulation is used by asynchronous data? A. B.
QPSK PSK
C. FSK D. QAM
46. How to make the antenna efficiency of an HF grounded vertical antenna comparable to that of a half-wave antenna? A.
29. Any entity authorized by NTC to lease space segment capacity.
Butterworth filter
B. C. D.
By installing a good ground radial system By isolating the coax shield from ground By shortening the vertical By lengthening the vertical
47. Waveguide becomes compulsory above what frequency? A. B.
Above 3 GHz At 300 MHz
C. Above 10 kHz D. Above 10 GHz
48. What multi-channel digital surround sound format used for both commercial/theatrical and consumer grade applications typically uses 384 or 448 kbit/s (overall)? A. Dolby 5.1 B. SDDS 5.1
C. DTS 5.1 D. AC-3
49. How does the bandwidth of the transmitted signal affect selective fading? A. B. C. D.
It is more pronounced at narrow bandwidths It is equally pronounced at both narrow and wide bandwidths It is more pronounced at wide bandwidths The receiver bandwidth determines the selective fading
50. What is the phase delay of an 800 Hz voice signal if the phase shift is 15 degrees? A. B.
52 µsec 83.33 µsec
C. 1.25 µsec D. 26 µsec
51. What is the minimum number of turns a helix antenna must have? A. B.
3 4
C. 5 D. 6
52. Sound waves travel in water at what speed? A. B.
12.4 miles/sec 186,000 ft/sec
C. 5,000 ft/sec D. 3,141 ft/sec
53. What is the CCITT recommendation for a preparation of loss plan, a variable loss plans and a fixed loss plan? A. B.
G.133 G.132
C. G.141 D. G.122
54. What is the diameter of a copper wire to be used in a 16 km loop with a dc loop resistance of 100 ohms/km? A. B.
0.838 mm 1.626 mm
C. 0.432 mm D. 2.159 mm
55. What is the overall Eb/No for a satellite with an up-link Eb/No of 14 dB and a downlink Eb/No of 18 Db? A. B.
12.5 1.25
C. 12.5 dB D. 1.25 dB
56. What is the core diameter of step-index multimode optical fiber? A. B.
0.02 nm 2 nm
C. 0.2 nm D. 0.002 nm
57. What kind of cell is appropriate for load management, fast moving mobiles and low-usage areas? A. B.
Pico cells Nano cells
C. Micro cells D. Umbrella cells
58. What is the proper procedure for suppressing electrical noise in a mobile station? A. B. C. D.
Apply shielding and filtering where necessary Insulate all plain sheet metal surfaces from each other Apply anti-static spray liberally to all nonmetallic Install filter capacitors in series with all dc wiring
59. When light strikes a flat polished end of a fiber, it produces a loss of what percent? A. B.
14 % 10 %
C. 4 % D. 1 %
60. MPEG-2 is more formally known as international standard ___________. A. B. C. D.
ISO/IEC 13818-3 ISO/IEC 13818-4 ISO/IEC 13818-2 ISO/IEC 13818-1
61. What is the orbital location of the Philippine Mabuhay Satellite in the geostationary orbit?
A. B. C. D.
120 degrees east longitude 146 degrees east longitude 158 degrees east longitude 160 degrees east longitude
70. An increase in transmitter power from 25 W to 30 W will cause the antenna current to increase from 700 mA to
A. 800 mA C. 750 mA 62. Dolby Digital is the common version B. 767 mA D. 840 mA containing up to 6 total channels of sound, with 5 channels for normal-range 71. Bass response is speakers (Right front, Center, Left Front, Right Rear and Left Rear) and one A. maximum high frequency response channel for the subwoofer. It is otherwise B. emphasizing the high audio known as ____. frequencies C. bypassing high audio frequencies A. AC-3 C. AC-1 D. bypassing low audio frequencies B. AC-2 D. AC-4 72. Standard tariff for flat rate telephone 63. As of August 2006 the GPS system used service beyond the normal flat rate in that a satellite constellation of ____ active area. Block II/IIA/IIR/IIR-M satellites in intermediate circular orbits. A. WATS C. OTLP B. TIP D. DTWX A. 29 C. 24 B. 26 D. 30 73. What is the expected critical frequency for a 120 mm thick brick wall? Assume a longitudinal wave velocity in brick of 64. What is the expected lifespan of the 2350m/s and that the velocity of sound in Philippine Mabuhay Satellite? air is 330 m/s. A. 15 years C. 20 years A. 114.5 Hz C. 214.5 Hz B. 10 years D. 12 years B. 314.5 Hz D. 414.5 Hz 65. What concept is used to analyze interference by obstacles near the path of 74. What INTELSAT satellite used the first FDMA demand-assignment system a radio beam? developed by COMSAT for satellites? A. Fresnel zone concept B. Frenzel zone concept A. Intelsat III C. Intelsat V B. Intelsat IV D. Intelsat VI C. Huygens’ concept D. Ray theory concept 75. Not more than ________ digits make up 66. How strong interference from one an international telephone number as recommended by CCITT REC. E. 161. particular station can be eliminated? A. B. C.
By using noise limiters By using squelch circuits By using negative feedback
D.
By using wave traps in the antenna circuitry
67. What is the power loss of a telephone hybrid? A. 1 dB B. 3 dB
C. 2 dB D. 6 dB
68. Which of the following is considered as an indirect method of generating FM? A. B. C. D.
Reactance modulator Balanced modulator Varactor diode modulator Armstrong system
69. What type of microphone operates on the principle that the electrical resistance of carbon granules varies as the pressure on the granules vary? A. B.
Dynamic Carbon
C. Crystal D. Ribbon-type
A. B.
8 11
C. 10 D. 12
76. What are unidirectional amplifiers having 20-25 decibel gain that are placed about 75 km apart used to compensate for losses along the telephone line? A. B. C. D.
VF repeaters Loading coils Loop extenders Echo suppressors
77. To generate an SSB or DSB signal one must use a circuit known as A. B. C. D.
filter modulator ring modulator balanced modulator reactance modulator
78. What is the gain, in dB of a helical antenna with diameter of λ/3, 10 turns at pitch of λ/4, used at 100 MHz? A. B.
16 31.4
C. 41.1 D. 1.25
79. A carrier is phase modulated by a test 87. What causes material dispersion? tone. If the amplitude and the frequency of the tone are both doubled, the amount of A. Wavelength dependence of the index the deviation is of refraction. B. Wavelength independence of the A. doubled C. unchanged index of refraction. B. halved D. multiplied by 4 C. Dependence of the propagation constant on the mode number. 80. A quarterwave transformer is connected to D. Independence of the propagation a parallel wire line in order to match the constant on the mode number. line to a load of 1000 Ω. The transformer has a characteristic impedance of 316.23 88. The term used to refer to the reduction of receiver gain caused by the signal of a Ω. The distance between centers is 4 nearby station transmitter in the same inches. What is the percentage reduction frequency band? in the diameter of the line? A. B.
85 % 86 %
C. 83 % D. 90 %
81. The term “pulling” refers to A. B. C. D.
the change of the crystal oscillator frequency by loading one half-cycle operation of a pushpull amplifier loading on the transmitter caused by the antenna connection reduction of the power supply terminal voltage as the transmitter is keyed
82. A transmitter operating at 30 MHz with 4 W output is connected via 10 m of RG8A/u cable to an antenna that has an input resistance of 300 Ω. Find the reflection coefficient. A. B.
0.71 0.97
C. 0.77 D. 0.76
83. Store-and-forward multiple-access network. A. B. C. D.
ARPANET ALOHA PRNET Packet switching
84. What device measures the internal open circuit voltage of an equivalent noise generator having an impedance of 600 Ω and delivering noise power to a 600 Ω load? A. B.
Psophometer Reflectometer
C. Barometer D. Voltmeter
85. The dielectric constants of materials commonly used in transmission lines range from about A. B.
1.2 to 2.8 3.5 to 5.2
C. 2.8 to 3.5 D. 1.0 to 1.2
86. Hall construction and internal finishes affect the final sound quality _______. A. B.
poorly significantly
C. mildly D. badly
A. B. C. D.
Quieting Cross-modulation interference Squelch gain rollback Desensitizing
89. A certain machine with a slightly out-ofbalance motor rotating at 1800/min is fixed on a perfectly elastic mount with a static compression of 2.50 mm. Calculate the resonant frequency of mount. A. B.
10 Hz 30 Hz
C. 20 Hz D. 40 Hz
90. What stages are common to both AM and FM receivers? A. B. C. D.
Tuner, local oscillator, detector, AF amplifier RF amplifier, mixer, IF amplifier, AF amplifier Local oscillator, RF amplifier, frequency discriminator, detector Tuner, IF amp, detector, AF amp
91. Calculate the lowest resonant frequency for a brick partition 120mm thick, 4m by 2m in area with longitudinal wave velocity of 2350 m/s. (Assume that it is supported at its edges.) A. B.
10 Hz 30 Hz
C. 20 Hz D. 40 Hz
A. B.
12,013.02 10,239.01
C. 15,014.01 D. 20,345.91
94. The effective lineal dimension of the passive is 2 m in the direction in which the beamwidth is to be measured. Determine that beamwidth of the fully illuminated passive used at 4 GHz. A. B.
1.5° 2.2°
C. 2.0° D. 3.0°
95. In microwave communications, what is the non-diversity probability of outage for a given path with an assigned fade margin of 45 dB? Assume a path length of 10 km and an operating frequency of 4 GHz. A. B.
1.9 x 10-9 1.9 x 10-5
C. 1.9 x 10-8 D. 1.9 x 10-11
96. What radio blackout condition is described as weak or minor degradation of HF radio communication on the sunlit side and occasional loss of radio contact? A. B.
R1 R2
C. R0 D. R3
97. Which of the following predicts that rf energy decays exponentially when it encounters a conductive medium? A. B. C. D.
Fresnel’s equation Hertz’s equation Maxwell’s equation Appleton’s theory
98. For monoaural sound reproduction, which audio frequency is preferred? A. B.
160 to 8000 Hz 16 to 15000 Hz
C. 20 to 2000 Hz D. 300 to 3000 Hz
99. What is a recent weighting which is used for measuring audible sound in the presence of ultrasound? A. B.
U-weighting C-weighting
C. A-weighting D. B-weighting
100. For two different sounds, the combined level cannot be more than ____ dB above 92. Determine the quality factor (Q) of an SSB the higher of the two sound levels. filter with the following characteristics: the carrier or center frequency = 1709 kHz; A. 3 C. 12 dB suppression of the unwanted sideband B. 6 D. 9 = 30 dB. <<< END >>> Submit not later than August 2, 2008 93. In microwave communications, what is the separation requirement for optimum operation between two antennas in space diversity system operating in 6 GHz? Assume a path length of 25 miles. A. B.
15.31 m 23.15 m
C. 44.76 m D. 31.68 m
