BSECE Board Examination Reviewer in Communications Engineering Transmission Lines 1.(Nov 1998) What determines the velocity factor in transmission line? a) The termination impedance b) The center conductor resistivity c) Dielectrics in the line d) The termination impedance 2.A transmission line has a capacitance of 25 pF / ft. and an inductance of 0.15 mH / ft. Determine the characteristic impedance of the line. a) 100 W b) 75 W c) 77.5 W d) 50 W 3.In a waveguide, the TE mode means that the: a) none of the above b) magnetic field is perpendicular to the direction of wave propagation c) magnetic and electric field are perpendicular to each other d) electric field is perpendicular to the direction of wave propagation 4.(Nov 1998) Determine the dB gain of a receiving antenna which delivers a microvolt signal to a transmission line over that of an antenna that delivers a 2 microvolt signal under identical circumstances. a) 3 dB b) 10 dB c) 8 dB d) 6 dB
5.How many cycles of a 1MHz wave can a 6-mile transmission line accommodate? a) 16.67 cycles b) 32.26 cycles c) 6 cycles d) 60 cycles 6.Power loss due to increased effective resistance of a conductor at microwave frequencies due to skin effect. a) Conduction Loss b) Dielectric Loss c) Radiation Loss d) Corona 7.What is the cut-off wavelength of a 6-cm x 3-cm waveguide? Assume the dominant mode of operation. a) 20 cm b) 18 cm c) 15 cm d) 12 cm 8.The ratio of incident and reflected voltage waves representing transmission and reflection coefficients used to characterize a linear microwave device. a) Z Parameter b) Y Parameter c) S Parameter d) H Parameter 9.What is the longest wavelength that a 2.5-cm wide waveguide will support in the dominant mode (m = 1)? a) 3 cm b) 5 cm c) 6 cm d) 1 cm 10.Who developed the Smith Chart? a) James N. Smith b) Philip S. Chart c) Philip H. Smith d) Gunn Chart
11.What is the effect of standing waves on a transmission line? a) increase in the power fed to antenna b) a cooler operating line c) prevention of arcing d) decrease in the power fed to antenna 12.The _____ is a measure of the mismatch between a load and the transmission line. a) Return Loss b) SWR c) Phase-shift constant d) reflection coefficient 13.A very low-loss coaxial transmission line has 30 pF / ft. of distributed capacitance and 75 nH / ft. of inductance. What is its characteristic impedance?
a) 75 Ω b) 100 Ω c) 72.5 Ω d) 50 Ω 14.What is meant by SWR of a transmission line? a) Short Wave Receiver b) Slope Waveguide Relation c) Sitting Wave Ratio d) Standing Wave Ratio 15.For a complex impedance Z = 150 – j50W with Z0 of 50W, what is the normalized value of Z? a) 15 – j5 Ohms b) 3 – j1 Ohms c) 3 – j1 d) 15 – j5 Ohms 16.What is the impedance of most waveguide? a) 300 ohms b) 75 ohms c) 600 ohms d) 50 ohms
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BSECE Board Examination Reviewer in Communications Engineering Transmission Lines 17.(Nov 1997) The outer conductor of a coaxial transmission line is always grounded at the a) output only b) input only c) point of high SWR d) input and output 18.An open circuit line greater than wavelenght/4 but less than wavelenght/2 in length will exhibit _____ reactance. a) capacitive b) minimum c) inductive d) maximum 19.(Nov 1997) An electronic equipment used to measure standing wave ratio. a) Altimeter b) Multimeter c) Reflectometer d) Wavemeter 20.What is a short (< l/4) length of transmission line, shorted at one end and attached at the appropriate distance from the load for the purpose of matching a complex load to the transmission line? a) quarter-wave transformer b) stub c) balun d) network
22.If a transmission line is terminated with a resistance equal to its characteristic impedance a) the standing wave ratio will be minimum b) the input impedance will be twice the terminating resistance c) the reflection coefficient will be unity d) the line loss will be maximum 23.In a waveguide, the TM mode means that the: a) electric field is perpendicular to the direction of wave propagation b) magnetic and electric fields are perpendicular to each other c) none of the above d) magnetic field is perpendicular to the direction of wave propagation 24.How can SWR be minimized? a) using filters b) using limiter c) using Smith Chart d) using stubs 25.In a transmission line, the characteristic impedance equals _____. a) Zoc/Zsc
b) √ZocZsc c) Zsc/Zoc
21.(Apr 1997) To couple a coaxial line to parallel line, it is better to use a _____. a) directional coupler b) balun c) slotted line d) quarter-wave transformer
d) √Zsc/Zoc 26.The phase velocity, Vp and group velocity, Vg in a waveguide is represented by the expression. a) Vp = C/Vg b) C = (Vp)(Vg) c) C = (VpVg)1/2 d) Vg = C2Vp
27.When does a transmission line terminated in a short look like a short to the source? a) at less than l / 2 b) at quarter-wavelength c) at less than l / 4 d) at half-wavelength 28.(Mar 1996)When a transmission line uses ground return, it is called a (n) _____ line. a) ungrouped b) unbalanced c) balanced d) grounded 29.(Mar 1996) Termination means a) load connected to the output end of the transmission line b) looking back impedance of a line with no load c) result of cutting both ends of a conductor d) result of disconnecting a line from a transmitter 30.(Nov 1998) A transmission line consisting of two conductors that have equal resistance per unit length. a) Open-wire line b) Balanced line c) Coaxial line d) Unbalanced line 31.(Nov 1997) Coaxial lines are used on those systems operating _____. a) at 300 MHz b) above 10 kHz c) below 2 GHz d) above 10 GHz 32.(Nov 1998)Which of the following determines the characteristics of a transmission line? a) Physical dimensions b) Length c) Inductance d) Capacitance
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BSECE Board Examination Reviewer in Communications Engineering Transmission Lines 33.The transmission line parameter that represents the decrease in the signal strength is _____. a) reflection coefficient b) propagation constant c) attenuation constant d) phase-shift constant 34.What is the voltage reflection coefficient for a 75-
Ω line with a terminating impedance of 50 Ω? a) b) c) d)
-0.5 0.5 -0.2 0.2
35.(Nov 1998) What is the meaning of the term velocity factor of a transmission line? a) The velocity of the wave on the transmission line multiplied by the velocity of the wave of light in vacuum b) The ratio of the characteristic impedance of the line to the terminating impedance c) The index of shielding for coaxial cable d) The velocity of the waves on the transmission line divided by the velocity of light in a vacuum 36.A waveguide can considered as a _____. a) LPF b) BPF c) HPF d) BRF
be
37.A 5-GHz signal is to be propagated along a waveguide with a width of 3 cm. What is the largest value of m that can be accommodated by the waveguide? (0 correct answers) a) m = 2 b) m = 0 c) m = 1 d) m = 3
38.Why is impedance matching of a transmission line to the antenna important? a) for maximum power transfer b) for minimum time delay c) for maximum efficiency d) for greater energy transformation 39.Would it be possible to produce a 70-W twin lead? a) depends on the load b) can not be answered c) yes d) no 40.A type of transmission line consisting of an inner conductor surrounded by, but insulated from an outer conductor. a) strip line b) Micro strip line c) Coaxial cable d) balanced line 41.A type of semiconductor bolometer is called _____. a) Optocoupler b) Thermistor c) Galvanometer d) Thyristor 42.(Mar 1996) What quarterwave transformer will match a 100 W line to an antenna whose value is 175W? a) 150 Ohms b) 132.29 Ohms c) 137.5 Ohms d) 16.58 Ohms 43.What is the distance between a voltage maximum and adjacent current maximum on a transmission line with standing waves? a) wavelength/4 b) wavelength/2 c) wavelength/8 d) wavelength
44.(Nov 1996) Which tester is used to measure SWR? a) Spectrum analyzer b) Reflectometer c) Oscilloscope d) Multimeter 45.How wide must waveguide be? a) over wavelength/2 b) over wavelength/4 c) less than wavelength/4 d) less than wavelength/2
a
46.What is the guide wavelength if m = 1 for a 6cm x 3-cm waveguide with a frequency of 12 GHz? a) 4.5 cm b) 5 cm c) 2.55 cm d) 2 cm 47.(Mar 1996) Characteristic impedance of a transmission line is the impedance measured at the _____ when its length is infinite. a) midsection b) output c) shorted end of the line d) input 48.What is the dominant mode in a rectangular waveguide? a) TE02 b) TM11 c) TM01 d) TE10 49.For an ideal transmission line, the best possible conductor to use is _____. a) Iron b) Silver c) Gold d) Copper
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BSECE Board Examination Reviewer in Communications Engineering Transmission Lines 50.(Apr 1998) Referred to as a ferrite device that can be used in lieu of a duplexer to isolate a microwave transmitter and receiver when both are connected to the same antenna. a) Isolator b) Coupler c) Circulator d) Diode 51.What is impedance of lossless line wavelength/4? a) Z0 b) infinity c) 0 d) complex
the input a shorted of length
52.Does minimum or maximum VSWR indicate best matching of antenna to transmission line? a) either a or b b) minimum c) either a nor b d) maximum 53.What is the main frequency determining element of a klystron? a) resonant cavity b) accelerating voltage c) repeller voltage d) mode of operation 54.The mode at which a waveguide operates is determined by the: a) shape of the waveguide b) method used to couple the signal into the waveguide c) length of the waveguide d) impedance of the waveguide 55.When does a transmission line have an SWR equal to 1? a) ZL = a b) ZL = Z0 c) ZL = 0 d) G = 1
56.For a parallel-resonant circuit, a l / 4 stub must be _____ at the ends. a) shorted b) open c) complex d) loaded 57.(Nov 1996) In a transmission line, if the maximum current to minimum current ratio is 2:1, what is the ratio of the maximum voltage to minimum voltage? a) 1:2 b) 1:4 c) 2:1 d) 4:1 58.What is the length in centimetres of a quarterwave stub, in free space at 4 GHz? a) 19 m b) 18.75 m c) 19 cm d) 1.875 cm 59.(Nov 1998) Best choice of transmission line component to couple a coaxial line to a parallel wire line. a) Balun b) Directional coupler c) Shorting d) Slotted line 60.A matching stub should be placed _____. a) midway between load and transmitter b) nearest to the load c) nearest to transmitter d) anywhere 61.What would be the SWR of a transmission line if power is being delivered to a 100- Ω load by a line with a characteristic impedance of 50 W? a) 4 b) 2 c) 5.5 d) 3
62.A quarter-wave stub shorted at the end has high impedance: a) at the shorted end b) wavelength/4 back from the short c) wavelength/2 back from the short d) at the center 63.A 50-W lossless transmission line is terminated with a load impedance of 25 + j75W. What is the input impedance at a distance of 0.5l from the load? a) 15.5 + j31.6W Ohms b) 30 +j15W Ohms c) 50 Ohms d) 25 + j75W Ohms 64.(Mar 1996) The characteristic impedance of a transmission line does not depend upon its ______. a) length b) conductor diameter c) conductor spacing d) conductor radius 65.A 300-W line is terminated is a load impedance of 100 + j200W. What is the reflection coefficient for this line? a) 0.85<212.1° b) 0.632<108° c) 0.35<61.5° d) 0.75<120° 66.A flat transmission line delivers 5 kW at 10 A. What is its impedance? a) 50 Ohms b) 20 Ohms c) 200 Ohms d) 500 Ohms
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BSECE Board Examination Reviewer in Communications Engineering Transmission Lines 67.What must be the ratio of outer conductor diameter to center conductor diameter, for a 75- Ω Teflon coaxial transmission line? a) 4.8 b) 6.12 c) 4 d) 3.2 68.A type of transmission line where the two conductors carry equal current. a) unbalanced b) balanced c) strip line d) waveguide 69.A waveguide acts as a _____. a) LPF b) Resonator c) HPF d) BRF 70.(Mar 1996) To connect coaxial line to a parallel-wire, _____ is the best to use. a) balun b) directional coupler c) slotted line d) quarter-wave transformer 71.One of the following microwave diodes is suitable for very low-power oscillators only. a) IMPATT b) Tunnel c) TWT d) LSA 72.Which of the following is not a microwave vacuum tube? a) BWO b) Gunn c) Klystron d) Magnetron 73.What is meant voltage node? a) high impedance b) voltage minima c) current minima d) voltage maxima
by
a
74.What is the name of the microwave transmission line that is used with printed circuits? a) coax b) microstrip c) ferrite loop d) waveguide 75.The use of stub-matching network eliminates standing waves on _____. a) transmitter side of stub b) both sides of stubs c) all of the above d) load side to stub 76.Two 2-mm-diameter wires held 6 cm apart center-tocenter has a characteristic impedance of _____. (0 correct answers) a) 75 Ohms b) 250 Ohms c) 491 Ohms d) 500 Ohms 77.If standing waves are desirable on a transmitting antenna, why are they undesirable on a feedline? a) it decreases the length b) it limits the life of the antenna c) it increases power loss d) it shortens the feeding life 78.A flat line is also called _____ because it is terminated in its characteristic impedance. a) Capacitive b) Non-resonant c) Resonant d) Inductive 79.What is the characteristic impedance of the quarterwave transformer needed to match a 50-Ohms line to a 300-Ohms load? a) 122 200 Ohms b) Ohms c) 312Ohms d) Ohms
80.In a coaxial cable, the characteristic impedance depends on the diameter of a) inner conductor b) both a and d c) none of the above d) outer conductor 81.(Apr 1997) Distance travelled by a wave in the time of one cycle. a) Crest b) Wavelength c) Frequency d) Hop
82.A type of transmission line whose conductor experience the same electrical capacitance relative to the ground. a) Strip Line b) Waveguide c) Balanced Line d) Coax 83.The characteristic impedance will _____, if the spacing between the wires of a balanced transmission line is increased. a) none of the above b) increase c) decrease d) remain the same 84.Find the input impedance, in ohms, for a 50- Ω lossless transmission line, 3.5l long, if
the load is 20 + j75 Ω. a) 7 + j8 Ω b) 20 + j75 Ω c) 6.25 – j12.5 Ω d) 12.5 – j6.25 Ω 85.(Apr 1997) A single conductor running from the transmitter to the antenna. a) RG-8 / U b) Single line wire c) Microstrip d) Twin-lead
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BSECE Board Examination Reviewer in Communications Engineering Transmission Lines 86.(Mar 1996) Transmission lines are either balanced or unbalanced with respect to _____. a) ground b) input c) positive terminal d) negative terminal 87.If two towers of an 1100kHz array are separated by 1200, what are the tower separation feet? a) 412 b) 321 c) 298 d) 48 88.Skin effect describes the tendency of: a) ac conductors to carry the circuit current on their surface b) both a nor c c) dc conductors to carry the circuit current on their surface d) both a and c 89.(Apr 1998) A major and basic advantage for the used of a klystron. a) High power b) Lesser noise c) Efficiency d) Cheaper 90.A transmission line capable of handling highpowered signal is _____. a) coax b) waveguide c) micro strip line d) stripline 91.What physical length corresponds to 0.25wavekerh at 500 MHz for cable with a propagation velocity of 0.68C? a) 0.102 m b) 0.102 m What is the SWR for a 100-W characteristic line and a 300-W load? c) 1.02 m d) 2.01 m
92.(Nov 1998) Which of the following is not a common transmission line impedance? a) 120 ohms b) 50 ohms c) 650 ohms d) 75 ohms 93.When does an open transmission line look a short to the source? a) at half-wavelength b) at less than l / 4 c) at quarter-wavelength d) at less then l / 5 94.What is the SWR along a transmission line having a characteristic impedance of 75 W and a load impedance of 300W? a) 4 b) 0.5 c) 2 d) 0.25 95.What is the SWR for a 100-Ohms characteristic line and a 300-Ohms load? a) 0.33 b) 3 c) 2 d) 4 96.(Mar 1996) What is the velocity factor of non-foam dielectric 50 or 75 ohm flexible coaxial cable such as RG 8, 11, 58, and 59? a) 0.10 b) 0.66 c) 2.70 d) 0.30 97.(Apr 1998) Referred to the dielectric constant of a transmission line material. a) Inductance and capacitance b) Velocity factor c) Characteristic impedance d) Propagation velocity
98.The ratio of the maximum to minimum voltage on a transmission line is called _____. a) Smax b) Reflection Coefficient c) SWR d) Propagation Constant 99.The aspect ratio of a standard rectangular waveguide is _____. a) 1:2 b) 4:3 c) 3:4 d) 2:1 100.A type of transmission line used in gamma match. a) strip line b) twin-lead c) micro strip line d) coaxial 101.A shorted transmission line less than l / 4 in length will exhibit _____ reactance. a) capacitive b) inductive c) minimum d) maximum 102.The cut-off frequency in a waveguide signifies a) longer wave will not propagate significantly b) the frequency at which no transmission takes place c) the dimension of the waveguide d) all of the above 103.Which of the following is not a method of coupling into or out of a waveguide? a) Probe b) Loop c) Holes d) Slot
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BSECE Board Examination Reviewer in Communications Engineering Transmission Lines 104.Name a use for a circular waveguide. a) FM receiver b) telephony c) TV transmitter d) radar 105.(Nov 1997) A convenient method of determining antenna impedance. a) Smith Chart b) Reactance circle c) Trial and error d) Stub matching 106.What type of coupling is used between helical resonators? a) loop b) probe c) mechanical d) slot 107.What is the phase shift corresponding to wavelenght/4 in standing wave pattern? a) 180° b) 40° c) 0° d) 90° 108.For a transmission line giving a maximum rms voltage reading of 50 V at one point and a minimum rms voltage reading 25 V at another point. What is the VSWR of the line? a) 2 b) 4 c) 5 d) 1 109.What should be the SWR into a dummy antenna? a) a b) 1:2 c) 0 d) 1:1
110.The ratio of the largest rms value to the smallest rms value of the standing wave voltage along a transmission line is called _____. a) attenuation constant b) propagation constant c) SWR d) reflection coefficient 111.Indicate the false statement. The SWR on a transmission line is infinity: the line is terminated in a (n) a) pure reactance b) open circuit c) complex impedance d) short circuit 112.(Nov 1996) Transmission line must be matched to the load to a) reduce the load current b) transfer maximum current to the load c) transfer maximum power to the load d) transfer maximum voltage to the load 113.(Apr 1997) What is the impedance in ohms of a transformer marked 25 V, 4 W, when the secondary is correctly loaded? a) 165 Ohms b) 150 Ohms c) 156 Ohms d) 160 Ohms 114.What is the attenuation in nepers for a 1-km length of RG58 A / U coax with a loss of 5dB / 100 ft.? a) 86.86 Np b) 68.68 Np c) 18.88 Np d) 8 Np 115.A wire conductor experiences the following characteristics: a) b and b) Resistance increases with wire length
c) Resistance increases with a decrease in wire diameter d) none of these 116.What is the function of a resistive pyramid or vane at the end of a waveguide section? a) reflector b) dummy load c) termination d) absorber 117.(Nov 1996) Energy that has neither been radiated into space nor completely transmitted. a) Standing waves b) Captured waves c) Incident waves d) Modulated waves 118.(Nov 1996) Transmission lines when connected to antenna have a) resistive load whose resistance is less than characteristic impedance b) capacitive load c) resistive load at the resonant frequency d) resistive load whose resistance is greater than the characteristic impedance of the line 119.What is the characteristic impedance of twin lead? a) 600 W b) 50 W c) 300 W d) 70 W 120.(Nov 1996) The standing wave ratio is equal to _____ if the load is properly matched with the transmission line. a) 10 b) 50 c) 1 d) 2
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ARVIN
