ECE Board Exam (April 2005) - Communications

1. Calculate the Antenna power gain for a beamwidth of 10 degrees. A. 20 dB B. 26 dB

C. 2.6 dB D. 2.0 dB

2. Calculate the minimum length of a pair of conductors to be considered a transmission line, if its operating frequency is 800 MHz. A. 37.5 mm C. 37.5 cm B. 375 mm D. 3.75 cm 3.

What is the purpose of the indirectly-heated cathode in a cathode ray tube? A. beam modulation C. beam focusing B. beam production D. beam deflection

4.

The time transfer accuracy used with reference to the Universal Transmitter Mercator Grid is_____. A. UTC C. GMT B. UTMG D. UTM

5. A transmitter operates at frequency 144 MHz. the transmitter is using (a) doubler, two tripler and a quadrupler. Calculate its crystal oscillator frequency. A. 2 KHz C. 2000 MHz (2000 KHZ) B. 3000 KHz D. 3 KHz 6.

Brightness of an image is known as _____. A. Luminance C. Reflectance B. Chrominance D. Radiance

7. The principle of data reduction which says that when reducing a s….. of data into the form of an underlying mode, one should be maximally non-committal with respect to missing data. A. Jaynes maximum entropy principle B. Maximum entropy principle C. Kullback principle of minimum discrimination D. Minimum discrimination principle 8. In a satellite system, Johannes Kepler stated that “the square of the periodic time of orbit is proportional to the cube of the mean distance between the primary and the satellites”. This is also known as _____. A. Kepler’s 3rd Law C. Kepler’s 2nd Law B. Kepler’s 1st Law D. Kepler’s Law of Areas 9. Calculate the time delay in nanosecond introduced by a 100 ft coaxial cable with a dielectric constant of 2.3. A. 230 C. 154 B. 152 D. 15.2 10. The velocity of sound is a function of _____. A. temperature and volume C. medium and temperature B. medium and volume D. medium and velocity 11. The frequency stability of cellular mobile telephone transmitter authorized by NTC for use in the Philippines is _____. A. 3.0 KHz plus or minus 2.0 ppm B. 2.5 KHz plus or minus 2.5 ppm C. 5.2 KHz plus or minus 2.5 ppm D. 5.0 KHz plus or minus 2.0 ppm

12. What height must a satellite be placed above the surface of the earth in order for its rotation to be equal to the earth’s rotation? A. 23,426.4 mi C. 22,426.4 mi B. 27,426.4 mi D. 26,426.4 mi 13. Determine the wavelength of radio waves propagated using a frequency of 30 MHz. A. 15 meters C. 30 meters B. 10 meters D. 9 meters 14. For vertical scanning in a TV system, the field rate is _____ Hz. A. 262 and 1/2 C. 60 B. 30 D. 525 15. The actual data rate for terrestrial digital TV transmission to allow for the addition of synchronizing and error-correction bit is _____. A. 32.28 Mbps C. 48 Mbps B. 8 Mbps D. 64 Mbps 16. According to the NTC memorandum circular, a spectrum user fee of PhP10… per indoor radion station used for Wireless Data Network shall be paid by the Public Telecom Entity (PTE) with a data rate in excess of _____ Mbps. A. 0.64 C. 4.8 B. 0.44 D. 11 17. What are the letter-number designations of carrier and one SB? A. J3E C. A3E B. H3E D. F3E 18. What layer of the Open Systems Interconnection (OSI) model handles the transmission of bits over a communications channel? A. physical layer C. data link layer B. transport layer D. network layer 19. Under R.A. 9292, Electronics Technicians may apply for registration without examination within _____ years, after the effectivity of the Republic Act. A. 7 C. 12 B. 10 D. 5 20. What is the effective height of a broadcast antenna if the voltage induced in the antenna is 2.7 volts and the measured field intensity received in the antenna site is 27 mV/m? A. 29.7 meters C. 72.9 meters B. 100 meters D. 127 meters

21. The IEEE standard used for high speed wireless Ethernet access known as Wi-Fi’s is _____. A. 803.12 B. 803.116

C. 802.116 D. 801.11

22. Medium-Earth Orbit (MEO) satellite operates in the _____ frequency band. A. 2-18 GHz C. 1.2 – 1.66 GHz B. 1.0 – 2.5 GHz D. 6 – 12 GHz 23. Known as the data transfer scheme that used handshaking principle. A. Synchronous data transfer scheme B. Asynchronous data transfer scheme

C. DMA data transfer scheme D. Uninterrupted data transfer scheme 24. What is the delay time for satellite transmissions from earth transmitter to earth receiver. A. 5000 ms C. 500 ms B. 50 ms D. 500 us 25. The normal design limitation of a telephone loop is its value of 1 resistance Rz, the maximum value of Rloop must not exceed _____. A. 5400 ohms C. 2300 ohms B. 1300 ohms D. 2800 ohms 26. A microwave communications uses plane reflectors as passive repeaters. The diameter of the parabolic antenna is 18 ft while the effective is 310 ft. Determine the reflector coupling factor. A. 0.76 C. 0.92 B. 0.906 D. 0.706 27. Calculate the approximate height of a GEO satellite using Kepler law (A = 42241.0979, P = 0.9972) A. 34,416.40 Km C. 36,000 Km B. 35,790 Km D. 421,164 Km 28. In Satellite Communications, satellites using frequencies between GHz uplink and 17-20 GHz downlink are known to be operating in _____ band. A. Ka C. x B. Ku D. v 29. Determine the bandwidth efficiency of a 16 QAM modulator using input rate. A. 4 Mbps C. 5 Mbps B. 2 Mbps D. 3 Mbps 30. Determine the shot noise for a diode with a forward bias of 1…. A 110 KHz bandwidth. (q = 1.6x10 raised to minus 19 C) A. 0.006 uArms C. 0.004 uArms B. 0.005 uArms D. 0.007 uArms 31. The relative permittivity of silicon is _____. A. 11.7 C. 1.18 B. 1.17 D. 11.8

32. A third generation Wireless technology known to deliver broadband data speed to mobile communication device is _____. A. EDGE B. Bluetooth

C. WiFi D. GPRS

33. Which among the IEEE standards, refers to the global specifications of Wireless LAN? A. 802.3 C. 802.11x B. 802.14 D. 802.11b 34. In telecommunications, short haul connection refers to a connection exceeding _____ kilometers. A. 200 C. 250 B. 150 D. 300 35. A satellite communication system uses SPADE. The digital modulation technique used in SPADE is _____. A. QPSK C. 8 QAM B. 16 QAM D. BPSK

36. One of the following is NOT a system specification for third generation wireless system. A. TD/CDMA C. CDMA 2000 B. WCDMA D. IMT 2000 37. The meaning of MP3 is _____. A. Motion Picture Production, layer 3 B. Motion Picture Experts Group 1, Audio Player 3 C. Music Production layer 3 D. Music Production level 3 38. A receiver produces a noise power of 250 mW with no signal. The output increases to 5W when the signal is applied. Calculate the (S+N)/N power ration in dB. A. 13 C. 13.22 B. 10 D. 20 39. A non-coherent light source for optical communications system. A. ILD C. LED B. PIN Diode D. APD 40. One of the following is NOT classified as a Customer Premises Equipment (CPE) by the NTC. A. Automatic Teller Machine B. VSAT C. Videophone Terminal Equipment D. ISDN Terminal Equipment 41. Bluetooth Wireless Technology uses _____ technique to produce the spreading function of spectrum signals. A. Hybrid Direct-sequence C. hybrid-frequency hopping B. direct sequence D. frequency hopping 42. Calculate the maximum theoretical data rate for one satellite transponder used for binary data transmissions. A. 36 Mbps C. 144 Mbps B. 72 Mbps D. 64 Mbps 43. The tunnel diode _____. A. has a tiny hole through its center to facilitate tunneling B. uses a high doping level to provide a narrow junction C. works by quantum tunneling exhibited by gallium arsenide D. is joint-contact diode with high reverse resistance 44. What is the characteristic impedance of a basic parallel-wire line, its diameter is 0.023 inches with spacing of 0.14 inches apart, if it uses a dielectric material made of coNtinuous polyvinyn chloride? A. 238.7 ohms C. 234 khms B. 99 ohms D. 188 ohms (PVK = 3.4)(ans = 162.4) http://www.asiinstr.com/technical-Dielectric%20Constants.htm 45. A transistor amplifier has a measured S/N power of 70 at its`input 21 at its output. Determine the noase figure of the transistor. A. 5.1 dB C. 52 dB B. 51>2 dB D. 5.2 dB 46. Crosstalk in telephony, refers to the unwanted coupling between signal paths and contributu to noise in the telephone recdiver."Calculate crosstalk coupling loss in dBx (one unit of crosstalk iN dB ábov% reference coupling) if the c2osstalk soupling4is 20 dBx.

A. 60 B. 70

C. 80 D. 90

47. The critiCal maximum5value of the external incident angle for which light will propagate in the fiber is known as __________. A. acceptance"angle B. critical angle C. inter.al inciden4 angle D. crktical internal incile~t angle 48. For an 8 PSK modulavion with an input data rate equal to 10 MHz, carrier frmquejcy of 70 MHz, determine the bit rate in the hi-ph channel. A. 5 Mbps C. 3.33 Mbps B. 20 Mbps D. 10 Mbps ﾍ 49. In data0communic!tions, network, coaxial cab|e “RG 11” u3ed for type of applicatiof? A. IBM 3270 compuTer terminals B. Thick Ethernet C. Cable TV Systems D. Thin Ethernet 50. CalcUlate the peak enveloqe power of a single sideband (SSB) transmitter that produces a peak-to-pea+ voltage of 240 volts across a 100 ohms antenna load. A. 144 W C. 72 W B. 20 W D. 24 W 51. A digital transmission has an error of probability of 10 raised tO minus 5 power, and is 1000 million bits long. Calculate th% exp… error rate )BER). A. 500 C. 100,000 B. 5 billion D. 10.000 52. The best Terrain between antennas is _____- which will prevent re

. effects on the hop. A. rocky B. plain and flev

C. forested D. water surface

53. Best descriptIon of a collinear !nd broadside !ntenna radiation C. Bidirectional C. Perfdct Circle B. Omnidirectional D* Unidirectional 54. The Rules `nd Rggulation governing CATV systems in |he Philippines defines the specified zone of a TV broadcast station to be the area extending ______ km from reberence point in the community to which the station is licensed or authorized. A. 56 km C. 72 km B. 75 km D. 60 km 55. What is the carrier frequency of an FM station with a channel number 300? A. 101.1 MHz C. 107.9 MHz B. 107.5 MHz D. 99.5 MHz 56. The velocity of sound in dry air medium is 331.45 m/s. Calculate the velocity if there is an increase of temperature equal to 10 degrees Centigrade. A. 341.52 m/s C. 332.52 m/s B. 337.52 m/s D. 332 m/s 57. The input current in a matched transmission line is 50 mA while the current is 2 mA. The line is 1 mile long. Calculate the attenuation coefficient in dB per meters. A. 0.01738 C. 0.00279 B. 0.002 D. 27.96 58. Determine the maximum quantization error for an 8-bit linear sign-magnitude PCM code for a maximum decoded voltage of 1.27 Vp. A. 0.05 V C. 0.005 V B. 0.001 V D. 0.01 V 59. One of the following statements is false, regarding making the.. (IL?) very high. A. the image rejection will be very good. B. There is no need to make the local oscillator extremely stable. C. Tracking will be greatly improved. D. The selectivity will be poor. 60. Another name used for optical density is ______. A. light density C. light flux B. flux density D. radiant flux 61. The hue 180 degrees out of phase with red is _______. A. cyan C. blue B. green D. yellow 62. The composite video signal of TV is composed of the following s… A. camera signal with blanking pulses B. camera signal with blanking and sync C. blanking signal, horizontal and vertical synchronizing signal D. camera signal, horizontal and vertical synchronizing signal 63. In analog CMTS (AMPS), the narrowband control channel using 395 voice channels is channel ________. A. 12 C. 25

B. 30

D. 21

64. A frequency modulation system requires a signal-to-noise ratio at the detector output. The modulating frequency is 2 kHz and deviation is 50 kHz. Determine the required minimum S/N at the input. A. 120 dB C. 80 dB B. 25 dB D. 83.3 dB 65. Which of the following is contained in a fiber optic transmitter? A. an output circuit B. light detector C. fiber-to-detector connector D. light source 66. In a PLL frequency demodulator, this information or the modulating signal is the _____ signal. A. phase-shift C. VCO B. error D. input 67. A satellite earth station designed to receive satellite signals. Such stations may be used to receive data, such as stock market prices or new-wire service or television programs. A. transmit-receive earth station B. receive only earth station C. receive-only satellite earth station D. transmit-only earth station 68. A typical separation distance between satellites in a geostational orbit is 183.3 miles. In terms of degrees, it is equivalent to ______ degrees. A. 7 C. 4 B. 6 D. 5 69. What is the cut-off frequency of a rectangular waveguide that has width of 0.6 m and a height of 0.36 m? A. 0.9845 GHz C. 9.8425 MHz B. 9842.5 KHz D. 9842.5 MHz 70. For an earth station transmitter with an output power of 10 kW, a back-off loss of 3 dB, a total branching and feeder loss of 4 dB, transmit aftenna gain of 40 dB, determine the EIRP. A. 73 dBW C. 44 dBW B. 37 dBW D. 70 dBW 71. At 0 degsee elevation, a geostationary satellite can cover a maximum of ______ percent of the garth’s surface. A. 66 C. 46 B. 42.5 D. 33.33 72. hat is the common u0-#onverter and down-converter IF? A. 36 MHz C. 70 MHz B. 40 MHz D. 500 MHz 73. Luminance signals are adjusted to match the brightness sensa|ion of human vision for color television. Thus is _______. A. 29% red, 59% green, and 12% blue B. 30% red, 59% green, and 11% blue C. 29% red, 60 green, and 11% blue D. 30% red, 58% green, and 12% blue 74. The National Telecommunications Commission (NTC), requires -anual installation of Navigational Satellite Aids Equipment, particularly, NAVTEX receiver and EPIRB equipment to passenger anf General C… Vessels engaged in coastwise trade with a gross tonnage of _______.

A. 120

C

150M B. 80

D. 100

. . . . 87. In a spread-spectrum frequency hopping system, a ________ circuit selects frequency modulated by the synthesizer. A. frequency synthesizer C. PSN code generator B. FSK oscillator D. frequency shifter 88. Which is the most positive element in the electron guin of TV receivers? A. screen grid C. 1st anode B. 2nd anode D. control grid 89. A signal which varies between three levels. A. Alternate mark inversion B. RZ

C. Bipolar code D. NRZ

90. An object nearer to a converging lens than its focal point always a/an _______ image. A. the same size C. virtual B. inverted D. smaller 91. The radio transceiver in the SRRS in the Philippines has a maximum transmitted output power of _________. A. 4 W C. 3 W B. 5 W D. 6 W 92. What synchronizes the horizontal line of the TV picture tube? A. HSC C. HFC B. HAFC D. HAC 93. The ratio of the separation distance between two co-channel cell, the cell radius is known as co-channel _________. A. reduction interference ratio B. interference ratio C. interference reduction factor D. reduction ratio 94. What causes a herringbone pattern in facsimile? A. noise B. crosstalk C. phase jitter D. single-frequency interference 95. A rectangular waveguide has the following cross sectional dimension width is 0.8 in., while the height is 0.6 in., as fed by a coaxial at 12 GHz frequency. Calculate the cut-off wavelength. A. 3.05 cm C. 1.44 cm B. 4.06 cm D. 5.08 cm 96. In FDM, how many voice band channels are there in a jumbo group? A. 7200 C. 10,800 B. 3600 D. 1000 97. Using NTSC standard, what is the aural carrier frequency of UHF TV channel 28? A. 558.75 MHz C. 553.75 MHz

B. 559.75 MHz

D. 555.25 MHz

98. A parametric amplifier must be cooled _______. A. to provide better amplification B. to be operational because it cannot operate at room temperature C. to improve the noise performance D. to increase the bandwidth 99. Which of the following frequencies is wrong? A. 60 Hz for vertical sync and scanning B. 15,750 Hz for horizontal sync scanning C. 31,500 Hz for equalizing pulses and serrations in the vertical sync pulse D. 31,000 Hz for the vertical scanning frequency 100. An optic fiber is made of glass with a refractive index of 1.54, and clad with another glass with refractive index of 1.50. Launching takes place from air. Calculate the numerical aperture of the fiber. A. 0.352 C. 0.0352 B. 0.00352 D. 3.52