Excel Review Center 1.
2.
Suppose an input signal to a -law compressor has a positive voltage and an amplitude 25% of the maximum possible. Calculate the output volt age as a percentage of the maximum output.
10. A horn antenna antenna has a gain of of 15 dBi at 10 GHz. What is its gain at 15 GHz?
A. B.
11. What is is an ITU-T ITU-T recommendation for Group 3 fax machines?
C. 87.5 m D. 71.3 m *
Local Digital Tandem * Crossbar
100 dB * 86 dB
C. 96 dB D. 76 dB
Induction coil * Varistor Capacitor Compensating coil
An asynchronous communications system uses ASCII at 9600 bps, with eight data bits, one start bit, one stop bit, and no parity bits. C alculate the maximum percent efficiency in this system? A. B. C. D.
9.
75.1 m 71.9 m
What component in the telephone set has the primary function of interfacing the handset to the local loop? A. B. C. D.
8.
C. 927 kHz D. 972 Hz
Two sounds of of 4 W and 10 W powers are produced at ground level at a distance of 10 m and 20 m respectively from a listener. If the ground is level, unobstructed and non-absorbing, what will be the SPL of the sound heard by the listener? A. B.
7.
927 Hz * 729 Hz
What exchange is used to connect between central offices when a direct trunk is not available? A. B. C. D.
6.
Phase distortion * Phase shift Amplitude Frequency
Calculate the length of a quarter-wave monopole antenna for a frequency of 1000 kHz. A. B.
5.
C. 72.5% D. 62.5%
With a CW transmit transmit frequency of 5 GHz, calculate the Doppler frequency seen by a stationary radar when the t arget radial velocity is 100 km/h. A. B.
4.
75.2% * 50.1%
What parameter that most affects transmission of high-speed modem data? A. B. C. D.
3.
EST
100 % 80 % * 90 % 75 %
A telephone, often an 800 toll-free number, which spells something, such as 1-800-LIBRARY is called _______. A. B. C. D.
Vanity line * Specialty line Specialization line Customized line
A. B.
A. B. C. D.
18.5 dB * 28.6 dB
C. 20.1 dB D. 14.5 dB
T.3 T.5 T.6 * T.4
2.71 V/m 2.71 V/m
C. 2.71 mV/m * D. 2.71 kV/m
13. Who coined the computer terms “bit” and “software”? A. B. C. D.
J. Turin J. Turret J. Monty J. Tukey *
14. For the safety and comfort of factory factory workers, the sound-intensity level in a certain factory must remain below 85 dB. What is the maximum sound intensity allowed in this factory? A. B. C. D.
-4
2
3.2 x 10 W/m * -6 2 3.2 x 10 W/m -10 2 3.2 x 10 W/m -3 2 3.2 x 10 W/m
15. Teletex is an ITU-T standard for text and message transmission replacing the Telex. The teletex is ____ times faster than the telex. A. B. C. D.
100 50 * 25 10
16. A microwave microwave radio system uses 256QAM, that is, ther e are 256 possible amplitude and phase combinations. How many bits per symbol does it use? A. B.
3 7
C. 5 D. 8 *
17. In reverberation reverberation chamber method, what what volume of the chamber is r equired if the absorption coefficient is to b e measured at 1000 Hz? 3 3 A. 0.35 m * C. 0.45 m 3 3 B. 0.25 m D. 0.55 m
18. In PCM, PCM, assuming uniform quantization, quantization, what is the signal-to-noise ratio in dB for an 8-bit code word? A. B. C. D.
750 MHz * 900 MHz
C. 750 GHz D. 1800 MHz
20. What is the duty cycle of a radar with a PW of 3 s and a PRT of 6 ms? A. B.
0.05 0.5
C. 0.005 D. 0.0005 *
21. A digital digital transmission has an error -4 9 probability of 10 and is 10 bits long. Calculate the expected number of error bits.
12. Given that that a half-wave dipole dipole has a gain of 2.14 dBi, calculate the electric field strength at a distance of 10 km in free space in the direction of m aximum radiation from a half-wave dipole that is fed, by means of lossless, matched line, by a 15 W transmitter. A. B.
A. B.
49.8 dB * 48.9 dB 94.8 dB 84.9 dB
19. Calculate the operating frequency for a helical antenna that consists of 10 turns with a spacing of 10 cm and a diameter of 12.7 cm.
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5
A. 10 * 6 B. 10
4
C. 10 3 D. 10
22. Calculate also also the BER of the above above problem. 4
A. 10 * 3 B. 10
6
C. 10 5 D. 10
23. A Yagi antenna has a gain of 10 dBi and a front-to-back ratio of 15 dB. It is located 15 km from a transmitter with an ERP of 100 kW at a frequency of 10 MHz. The antenna is connected to a receiver via a matched feedline with a loss of 2 dB. Calculat e the signal power supplied to the receiver if the antenna is pointed directly toward the transmitt ing antenna. A. B.
26.2 W 26.2 mW *
C. 26.2 kW D. 26.2 W
24. What refers refers to a mobile station identifier sent over the air interf ace and is assigned dynamically by the network t o the mobile station? A. B. C. D.
Transient Mobile Station Identifier Virtual Mobile Station Identifier Host Mobile Station Identifier Temporary Mobile Station Identifier *
25. A type of emission is is produced when when an amplitude modulated transmitter is modulated by a facsimile signal. A. B. C. D.
A3F F3F A3C * F3C
26. Calculate the maximum range of a deep-space radar operating at 2.5 GHz and using a peak pulse power of 25 MW. The antenna diameter is 64 m, the 2 target cross section 1 m and, because a maser amplifier is us ed, the receiver noise figure is only 1.1. Furthermore, because of the low PRF to allow the pulses to return from long dist ances (and thus the wide pulses us ed), the receiver bandwidth is only 5 kHz. A. B. C. D.
13700 km 123700 km 132700 km * 132500 km
27. Which type of micr ophone operates on the principle that the electric al resistance of carbon granules varies as the pressure on the granules vary? A. B. C. D.
Dynamic Crystal Carbon * Ribbon-type
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28. In FM fax, the frequencies for black and white are _______ respectively. A. B. C. D.
1500 and 2300 Hz * 2300 and 1500 Hz 1300 an 2400 Hz 1070 and 1270 Hz
29. Calculate the required via net loss for a satellite link with a one-way delay of 250 ms. A. 250 dB C. 50.4 dB * B. 40.5 dB D. 25 dB 30. Group 3 fax uses which modulation? A. B. C. D.
QAM * FSK Vestigial sideband AM FM
31. A radar transmitter uses a magnetron to generate pulses with a power level of 1 MW. The pulses have a duration of 2 s and the pulse repetition rate is 5 00 Hz. The magnetron has an efficiency of 60%. Calculate the duty cycle of the tube. A. B.
0.01 0.0001
42 to 52 Vdc - 42 to - 52 Vdc * 24 to 64 Vdc - 24 to - 64 Vdc
C. 20 mm D. 30 mm
60 kbps * 30 kbps
C. 120 kbps D. 15 kbps
41. Which theory states that light wave behaves as if it is consists of many tiny particles?
42. What is the dB SPL of an auditorium with contemporary music? 80 - 95 85 - 90 95 - 100 * 100 - 105
C. 6.84 GHz D. 6.05 GHz
What is the frequency band of DECT? 1.88 – 1.90 1.68 – 1.70 1.48 – 1.50 1.28 – 1.30
C. 15.8 D. 20.1
Alfecon * Mafecon Delcon Isial
Frequency response * Field strength Power density Gain
A. B.
GHz * GHz GHz GHz
2 3.5 *
C. 1.75 D. 7
46. Calculate also the gain of the paraboloid reflector in the above problem. A. B.
9600 * 960
C. 96000 D. 96
47. What is true about iDEN (Integrated Dispatch Enhanced Network)? I.
It can support at least two handset voices. II. It uses PSTN connection-numeric paging. III. It works also on 1.5 GHz. IV. It uses data and fax transmission. A. B. C. D.
A. B. C. D.
II, III and IV * I, II and IV III I, II, III and IV
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76 kHz * 76 Hz 76 MHz 76 mHz
49. A device that connects 2 data terminal equipment (DTE) directly by emulating the physical connections of a d ata communications equipment (DCE) A. B. C. D.
Short haul modem Null modem * X.25 device Smart modem
50. Single sideband reduced carrier emission type. A. B. C. D.
H3E R3E * J3E B8E
51. What is the audio frequency range? 20 kHz to 20 MHz 0 Hz to 20 kHz 300 Hz to 400 Hz 20 Hz to 20 kHz *
52. An MTI radar operates at 5 GHz, with a pulse repetition frequency of 800 pps. Calculate the lowest three blind speeds (km/h) of this radar. A. B. C. D.
43. What is the uplink receiver frequency if the downlink transmitter is on channel 4 (3.84 GHz)?
A. B. C. D.
48. What is the frequency of a 2-cm sound wave in sea water at 25 C?
A. B. C. D.
A. Huygen’s theory B. Wave theory of light C. Nyquist theory D. Quantum theory *
45. Calculate the beamwidth between nulls of a 2-m paraboloid reflector used at 6 GHz.
37. The most important specification of loudspeakers and microphones. A. B. C. D.
A. B.
44.
36. What do you call an alloy of iron, silicon and aluminum used for video heads in video recorders and players? A. B. C. D.
20 cm * 30 cm
A. 6.065 GHz * B. 6.65 GHz
Blip * Flip Blink Spot
16.7 * 19.7
C. 100 W D. 75 W
40. The North American analog cellular radio system uses FM with channels 30 kHz wide. Suppose such a channel were used for digital c ommunication. If the available signal-to-noise ratio is 20 dB, calculate the maximum theor etical bit rate using a two-level code.
A. B. C. D.
35. An anechoic chamber is 5m in length. How far is this in wavelength at 1 GHz? A. B.
A. B.
-9
34. The telephone set is p owered by the central office on the ring side at A. B. C. D.
50 W * 25 W
39. Calculate the length of a five-eights wavelength antenna for a c ellular phone operating about 900 MHz.
4.17 x 10 W -14 4.17 x 10 W * -6 4.17 x 10 W -12 4.17 x 10 W
33. _____ is a white streak or speck that appears momentarily on a TV scr een during playback of a videotape caused by dropouts. A. B. C. D.
A. B.
C. 0.1 D. 0.001 *
32. Calculate the minimum receivable signal in a radar receiver which has an IF bandwidth of 1.5 MHz and a 9-dB noise figure. A. B. C. D.
38. Calculate the average power when peak power = 1 kW, PW = 3 s and rest time = 1997 s.
172.8, 345.6, 518.4 * 173.2, 354.6, 581.4 127.8, 354.6, 518.4 137.8, 435.6, 815.4
53. Asynchronous transmission has lowspeed transmission of less than ____ kbps. A. B. C. D.
2.4 * 4.8 3.6 128
54. Calculate the gain, with respect to an isotropic antenna, of a half-w ave dipole with an efficiency of 90% that is placed one-quarter-wavelength from a plane reflector that reflects 100% of the signal striking it. A. B. C. D.
7.68 dBi * 7.86 dBi 8.76 dBi 8.67 dBi
55. What is the average insertion loss of fusion splice in fiber optics? A. B. C. D.
0.09 dB * 0.9 dB 0.19 dB 0.009 dB
56. How many simultaneous calls does a DECT radio transceiver can assess at any given time? A. B. C. D.
120 * 240 480 960
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Excel Review Center 57.
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The basic European TDM telephone signal combines 30 voice channels with 2 signaling channels that have the s ame data rate as the voice c hannels. The sampling rate is 8 kHz and there are 8 bits per sample for each voice channel. Calculate the total bit rate for this signal. A. B.
1.544 Mbps 3.152 Mbps
C. 2.048 Mbps* D. 6.072 Mbps
58. What is the horizontal beamwidth of a pyramidal horn antenna if its width is one wavelength? A. B.
80 * 90
C. 75 D. 60
59. Most commercial satellite activity occurs in which band(s)? A. B. C. D.
L C and Ku * X S and P
2000 W * 500 W
C. 4000 W D. 1000 W
61. The bandwidth of U600 mastergroup is A. B. C. D.
2250 kHz 2728 kHz 2520 kHz * 2278 kHz
62. In satellite communications, what is the height of a satellite from the earth’s surface if the sidereal period is 20 hours? A. B. C. D.
14.0 dB 12.5
C. 14.5 dB * D. 14.5
64. A satellite transmitter operates at 4 GHz with an antenna gain of 40 dBi. The receiver 40,000 km away has an antenna gain of 50 dBi. If the transmitter has a power of 8 W , find (ignoring feedline losses and mismatch) the E IRP in dBW. A. B.
50 dBW 49 dBW *
C. 69 dBw D. 30 dBW
65. If an antenna has a length of 0.125 then what is the radiation resistance? A. B. C. D.
12.34 * 11.13 11.23 12.67
65,536 * 75,125
C. 66,456 D. 56,138
67. T-1 carrier service has _______ digital bit rate. A. B. C. D.
1.544 Mbps * 2048 Mbps 1.644 Mbps 9600 kbps
68. What is the velocity of sound in dry air when the temperature change is 15 degree Celsius? A. B.
340.6 m/s * 330.15 m/s
A. B.
56 dB * 76 dB
C. 345.12 m/s D. 344.7 m/s
C. 46 dB D. 36 dB
70. One of the reasons why FDM is being replaced by TDM A. B. C. D.
There is more time than frequency If is difficult to place channels side by side Noise is amplified with voice when an FDM system is used * Most available frequencies have been used
71. A transmitter with a power output of 100 W is connected to a dipole antenna with a radiation resistance of 70 and an ohmic resistance of 2 . How much power is radiated into space? A. B.
97.2 W * 92.7 W
A. B.
1.78 kHz * 1.68 kHz
C. 97.2 kW D. 92.7 kW
C. 1.87 kHz D. 1.58 kHz
73. A type of distortion a facsimile produces when it becomes out of synchronization. A. B. C. D.
Pincushion Barrel Skewing * Fattening
74. Which optical detector is used when high sensitivity and bandwidth are required? A. B. C. D.
PMT * APD PIN Phototransistor
75. Digital modulation is superior to analog modulation in the sense that: A.
B.
C. D.
Analog signals have discrete states, while digital ones vary continuously Digital signals resemble noise less than analog ones *
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Digital signals are easier to use with FM Digital signals have greater bandwidth
76. What parameter of light detector determines the range or syst em length that can be achieved f or a given wavelength? A. B. C. D.
72. What is the Doppler shift in frequency caused by a vehicle moving t owards a radar at 96 kph if t he radar is operated at 10 GHz?
31,022.5 km * 31,200.4 km 31,302.4 km 31,489.2 km
63. The sound intensity received from the nearby jet plane is 12.6 W/m2 and that from another jet plane some dist ance away is 0.45 W/m2. Find the relative loudness of the two. A. B.
A. B.
69. What is the signal-to-noise ratio in a PCM system with 512 quantizing levels using uniform quantization?
60. 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 transmiss ion 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. B.
66. Determine the number of levels in a compact disc audio system if the number of bits per sample is 16.
Transit time Spectral response * Dark current Responsitivity
77. Which theorem sets the limit on the maximum capacity of a channel with a given noise level? A. B. C. D.
Nyquist theorem Hartley theorem Shannon-Hartley theorem * Shannon theorem
78. Lightning rods must be mounted a top structure not less than ________ above the highest point. A. B. C. D.
10 cm 20 cm 30 cm * 40 cm
79. What sound intensity corresponds to a sound-intensity level of 50 dB? A. B. C. D.
-6
2
1 x 10 W/m -7 2 1 x 10 W/m * -8 2 1 x 10 W/m -5 2 1 x 10 W/m
80. AWG # 26 has a typical loss of A. B. C. D.
0.21 dB/1000 ft. 0.32 dB/1000 ft. 0.41 dB/1000 ft. 0.51 dB/1000 ft. *
81. OSI consists of how many layers of interconnection. A. B. C. D.
3 5 7 * 9
82. Calculate the maximum range of a radar system which operates at 3 cm with a peak pulse power of 500 kW, if its -13 minimum receivable power is 10 W, 2 the capture area of its antenna is 5 m , and the radar cross-sectional area of the 2 target is 20 m . A. B.
686 km * 686 nmi
C. 686 mi D. 686 m
83. What antenna radiates equally in all directions? A. B. C. D.
Vertical antenna Isotropic antenna * Horizontal antenna Dipole antenna
84. A certain antenna has a gain of 7 dB with respect to an is otropic radiator. What is the effective area if it operates at 200 MHz? A. B.
2
0.897 m * 2 0.798 m
2
C. 0.978 m 2 D. 0.879 m
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85. The bandwidth of a fax signal is kept narrow by: A. B. C. D.
Sending the data at a slow rate of speed * Limiting the image resolution Limiting the range of shades sent Using pulse modulation
86. The noise from an airplane engine 100 m from an observer is f ound to have an intensity of 45 dB. W hat will be the intensity when the plane flies overhead at an altitude of 1 km? A. B.
25 dB * 15 dB
C. 52 dB D. 35 dB
87. An advantage of fiber optics over cable communications is: A. B. C. D.
More sensitivity to noise Improved antenna efficiency Higher RF output Simpler and easier maintenance *
88. What is the data rate of the ISDN Basic access B channel? A. B. C. D.
32 kbps 64 kbps * 144 kbps 192 kbps
95. A certain antenna has a gain of 7 dB with respect to an isotropic radiator. What is the effective area if it operates at 200 MHz? A. B.
2
0.897 m * 2 0798 m
2
C. 0.987 m 2 D. 0.115 m
96. The deviation for voice FM signals is usually: A. B. C. D.
Plus-or-minus 3 kHz Plus-or-minus 5kHz * Plus-or-minus 6 kHz Plus-or-minus 10 kHz
97. Suppose a composite video signal with a baseband frequency range from dc t o 4 MHz is transmitted by linear PCM, using eight bits per sample and a sampling rate of 10 MHz. What would be the maximum signal-to-noise r atio in dB? A. B.
49.9 dB * 35 dB
C. 60.1 dB D. 75.2 dB
98. The advantage of using top loading in a shortened HF vertical antenna is A. B. C. D.
lower quality factor greater structural strength higher losses improved radiation efficiency *
89. What is the unit of responsitivity? A. B. C. D.
99. An AM receiver can be used to demodulate FM by means of:
Ampere/volt Ampere/watt * Watt/ampere Volt/ampere
90. Calculate the length of a practical halfwave dipole for a frequency of 15 MHz. A. B.
10.5 m 9.5 m *
C. 8.5 m D. 7.5 m
91. Wideband FM is preferable to narrowband FM for music tr ansmission because: A. B. C. D.
Lower frequencies are heard better Spectrum space is conserved The fidelity is better * No! Narrowband FM is better for music
A. B. C. D.
Envelope detection Product detection Slope detection * Pulse detection
100. A continuously variable signal is recovered from a signal having discr ete states by: A. B. C. D.
A ratio detector A D/A converter * A product detector An envelope detector < < < Nothing Follows > > >
92. What is the gain of the Hertzian dipole over isotropic antenna? A. B. C. D.
1.64 dB 2.15 dB 1.76 dB * 1.55 dB
93. In acoustics, what is the resonant frequency of a Helmholtz r esonator whose cavity volume is 1.5 m3 and a radius of 5 cm? A. B. C. D.
13.56 Hz * 15.36 Hz 11.24 Hz 12.19 Hz
94. The input terminal impedance at the center of a folded dipole antenna is A. B. C. D.
72 300 * 50 73
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