ADAMSON UNIVERSITY COLLEGE OF ENGINEERING ECE DEPARTMENT
TRANSMISSION LINE REVIEWERMULTIPLE CHOICE
REFERENCE: Review Book (2009) by Cuervo Santos Communication System by Blake
Submitted By: Caldejon Ashley Q. Calamucha, Xiareen Taye C. Casantusan, Genielyn
Bernadeth B. Zari, PECE Instructor
TRANSMISSION LINE
a. b. c. d.
Identification: 1. A device for coupling balanced and unbalanced lines. a. Balun b. Transmission Line c. Coaxial Line d. Open-wire Line
Answer: A 6.
Answer: A
2. The ratio between voltage and current on an infinitely long transmission transmission line. a. Balun b. Characteristic Impedance c. Propagation Velocity d. Reflection Coefficient
A transmission line containing concentric conductors. a. Transmission Line b. Quarter-wave Transformer c. Coaxial Line d. Stub Answer: C
4.
A transmission line containing parallel conductors separated by spacers. a. Balun b. Transmission Line c. Coaxial Line d. Open-wire Line Answer: D
5.
The speed at which signals travel down a transmissi t ransmission on line.
A section of transmissi t ransmission on line, electrically a quarter-wavelength in length, that is used to change impedances on a transmission line. a. Propagation Velocity b. Quarter-wave transformer c. Stub d. Smith Chart Answer: B
7.
Answer: B 3.
Propagation Velocity Stub Smith Chart Surge Impedance
The ratio of reflected to incident voltage on a transmission line. a. Smith Chart b. Standing-wave Ratio c. Reflection Coefficient d. Velocity Factor Answer: C
8.
A graphical transmission line calculator. a. Stub b. Velocity Factor c. Reflection coeffi coe fficient cient d. Smith Chart Answer: D
9. The ratio of maximum to minimum voltage on a transmission line. a. Stub b. Balun c. Velocity Factor d. Surge Impedance Answer: A
10. Any pair of conductors used to conduct electrical energy. a. Stub b. Transmission Line c. Balun d. Coaxial Line Answer: B
11. Ratio of the speed of propagation on a line to that of light in free space. a. Balun b. Coaxial Line c. Velocity Factor d. Reflection Coefficient Answer: C
12. Transmission media with some form of conductor that provides a conduit in which electromagnetic signals are contained. a. Transmission line input impedance b. Reflection Coefficient c. Unguided transmission media d. Guided transmission media Answer: D
13. Transport signals using electrical current. a. Copper wires b. Optical fibers c. Stub d. Balun Answer: A
14. Transport signals by propagating electromagnetic waves through a nonconductive material. a. Copper wires
b. Optical fibers c. Stub d. Balun Answer: B
15. Emitted then radiated through air or a vacuum or sometimes water. a. Balun b. Stub c. Unguided signals d. Guided signals Answer: C
16. Transmission media that are wireless systems (i.e., those without a physical conductor) a. Guided transmission media b. Copper wires c. Optical fibers d. Unguided transmission media Answer: D
17. A guided transmission medium and can be any physical facility used to propagate electromagnetic signals between two locations in a communications system. a. Cable transmission medium b. Guided transmission medium c. Unguided transmission medium d. Optical transmission medium Answer: A
18. The most common means of interconnecting devices in local area networks because cable transmission systems are the only transmission medium suitable for the transmission of digital signals.
a. b. c. d.
Cable transmission medium Cable transmission systems Transmission Line Balun
Answer: B
19. A metallic conductor system used to transfer electrical energy from one point to another using electrical current flow. a. Copper wire b. Optical fiber c. Transmission Line d. Cable Answer: C
20. Type of transmission where one conductor carries the signal, and the other conductor is the return path. a. Unbalanced transmission lines b. Regular transmission lines c. Irregular transmission lines d. Balanced signal transmission Answer: D
21. Type of transmission where one wire is at ground potential, whereas the other wire is at signal potential. a. Unbalanced signal transmission b. Balanced signal transmission c. Regular signal transmission d. Irregular signal transmission Answer: A
22. Most common type of balun is __________. a. Cable balun b. Narrowband balun c. Shield
d. Stub Answer: B
23. Comprised of two or more metallic conductors. a. Series-wire transmission lines b. Open-wire transmission lines c. Parallel-wire transmission lines d. Closed-wire transmission lines Answer: C
24. Nonconductive insulating material. a. Metal b. Twin lead c. Silver d. Dielectric Answer: D
25. Consist of two parallel wires, closely spaced and separated by air. a. Open-wire transmission lines b. Closed-wire transmission lines c. Series-wire transmission lines d. Parallel-wire transmission lines Answer: A
26. Essentially the same with open-wire transmission line except that the spacers between the two conductors are replaced with a continuous solid dielectric that ensures uniform spacing along the entire cable. a. Open-wire transmission lines b. Twin lead c. Closed-wire transmission lines d. Parallel-wire transmission lines Answer: B
27. Formed by twisting two insulated conductors around each other and often stranded in units, and the units are then cabled into cores containing up to 3000 pairs of wire. a. Open-wire transmission lines b. Parallel-wire transmission lines c. Twisted-pair transmission lines d. Twin lead
Answer: B 31.
Often used for high data transmission rates to reduce losses and isolate transmission paths. a. Plenum b. Stub c. Coaxial cables d. Optical fibers Answer: C
Answer: C
28. Consists of two copper wires where each wire is separately encapsulated in PVC insulation. a. Shielded wire b. Shielded twisted pair c. Stranded wire d. Unshielded twisted pair cable
32.
A coaxial cable with one layer of foil insulation and one layer of braided shielding is referred to as ____ shielded. a. Single b. Triple c. Quadruple d. Dual
Answer: D Answer: D
29. A parallel two-wire transmission line consisting of two copper conductors separated by a solid dielectric material. a. Shielded-twisted pair cable b. Unshielded-twisted pair cable c. Shielded wire d. Stranded wire
33.
Consists of two layers of foil insulation and two layers of braided metal shielding. a. Quad shielding b. Dual shielding c. Single shielding d. Triple shielding Answer: A
Answer: A 30.
The name given to the area between the ceiling and the roof in a singlestory-building or between the ceiling and the floor of the next higher level in a multistory building. a. Stub b. Plenum c. Wire d. Platinum
34.
Relatively expensive to manufacture, and to minimize losses, the air insulator must be relatively free of moisture. a. Water-filled coaxial cables b. Rigid air-filled coaxial cables c. Optical fibers d. Shielded wires Answer: B
Used to express the attenuation and the phase shift per unit length of a transmission line. a. Reflection coefficient b. Velocity constant c. Propagation constant d. Velocity factor
d. Shielded wire
35.
Answer: C 36.
Other name for propagation constant. a. Reflection coefficient b. Velocity constant c. Velocity factor d. Propagation coefficient Answer: D
37.
Defined as the ratio of the actual velocity of propagation of an electromagnetic wave through a given medium to the velocity of propagation through a vacuum. a. Velocity factor b. Reflection coefficient c. Propagation coefficient d. Stub Answer: A
38.
Other name for velocity factor a. Propagation factor b. Velocity constant c. Propagation value d. Propagation constant Answer: B
39.
The relative permittivity of a material. a. Velocity b. Acceleration constant c. Dielectric constant
Answer: C 40.
The ratio of the ac resistance to the dc resistance of a conductor is called __________ ratio. a. Capacitor b. Diode c. LED d. Resistance Answer: D
41.
Also directly proportional to frequency. a. Radiation loss b. Radiance loss c. Copper loss d. Capacitor loss Answer: A
42.
Occurs whenever a connection is made to or form a transmission line or when two sections of transmission line are connected together. a. Radiation loss b. Coupling loss c. Capacitor loss d. Resistance loss Answer: B
43.
A luminous discharge that occurs between the two conductors of a transmission line when the difference of potential between them exceeds the breakdown voltage of the dielectric insulator. a. Radiation loss b. Coupling loss c. Corona
d. Copper loss Answer: C 44.
A transmission line with no reflected power. a. Coaxial transmission line b. Optical transmission line c. Copper transmission line d. Nonresonant line Answer: D
45.
Other name for nonresonant line. a. Flat b. Round c. Coupled d. Single Answer: A
46.
Defined as the ratio of the maximum voltage to the minimum voltage or the maximum current to the minimum current of a standing wave on a transmission line. a. Round-wave ratio b. Standing-wave ratio c. Single-wave ratio d. Double-wave ratio Answer: B
47.
SWR stands for: a. Shorted Wave Radiation b. Sine Wave Response c. Shorted Wire Region d. none of the above
47.
TDR stands for: a. Total Distance of Reflection b. Time-Domain Reflectometer c. Time-Domain Response d. Transmission Delay Ratio ANS: B 48.
An example of an unbalanced line is: a. a coaxial cable b. 300-ohm twin-lead TV cable c. an open-wire-line cable d. all of the above ANS: A 49.
When analyzing a transmission line, its inductance and capacitance are considered to be: a. lumped b. distributed c. equal reactances d. ideal elements ANS: B 50.
As frequency increases, the resistance of a wire: a. increases b. decreases c. stays the same d. changes periodically ANS: A 51.
ANS: D
The effect of frequency on the resistance of a wire is called: a. I 2 R loss b. the Ohmic effect c. the skin effect
d.there is no such effect
d. none of the above
ANS: C
ANS: D
51.
56.
As frequency increases, the loss in a cable's dielectric: a. increases b. decreases c. stays the same d. there is no loss in a dielectric
The velocity factor of a cable depends mostly on: a. the wire resistance b. the dielectric constant c. the inductance per foot d. all of the above
ANS: A
ANS: B
52.
57.
The characteristic impedance o f a cable depends on: a. the resistance per foot o f the wire used b. the resistance per foot and the inductance per foot c. the resistance per foot and the capacitance per foot d. the inductance per foot and the capacitance per foot ANS: D
A positive voltage pulse sent down a transmission line terminated in a shortcircuit: a. would reflect as a positive pulse b. would reflect as a negative pulse c. would reflect as a positive pulse followed by a negative pulse d. would not reflect at all ANS: B
For best matching, the load on a cable should be: a. lower than Z 0 b. higher than Z 0 c. equal to Z 0 d. 50 ohms
A positive voltage pulse sent down a transmission line terminated with its characteristic impedance: a. would reflect as a positive pulse b. would reflect as a negative pulse c. would reflect as a positive pulse followed by a negative pulse d. would not reflect at all
ANS: C
ANS: D
55.
59.
54.
The characteristic impedance of a cable: a. increases with length b. increases with frequency c. increases with voltage
58.
A positive voltage-pulse sent down a transmission line terminated in an opencircuit: a. would reflect as a positive pulse
b. would reflect as a negative pulse c. would reflect as a positive pulse followed by a negative pulse d. would not reflect at all ANS: A The optimum value for SWR is: a. zero b. one c. as large as possible d. there is no optimum value
ANS: C 64.
A Smith Chart is used to calculate: a. transmission line impedances b. propagation velocity c. optimum length of a transmission line d. transmission line losses
60.
ANS: B 61.
A non-optimum value for SWR will cause: a. standing waves b. loss of power to load c. higher voltage peaks on cable d. all of the above ANS: D 62.
VSWR stands for: a. variable SWR b. vacuum SWR c. voltage SWR d. none of the above ANS: C 63.
The impedance "looking into" a matched line: a. is infinite b. is zero c. is the characteristic impedance
ANS: A 65.
Compared to a 300-ohm line, the loss of a 50-ohm cable carrying the same power: a. would be less b. would be more c. would be the same d. cannot be compared ANS: B 66.
A balanced load can be connected to an unbalanced cable: a. directly b. by using a filter c. by using a "balun" d. cannot be connected ANS: C 67.
On a Smith Chart, you "normalize" the impedance by: a. assuming it to be zero b. dividing it by 2p c. multiplying it by 2p d. dividing it by Z 0 ANS: D 68.
d. 50 ohms
The radius of the circle you draw on a Smith Chart represents: a. the voltage
b. the current c. the impedance d. none of the above ANS: D 69.
The center of the Smith Chart always represents: a. zero b. one c. the characteristic impedance d. none of the above ANS: C 70.
A TDR is commonly used to: a. measure the characteristic impedance of a cable b. find the position of a defect in a cable c. replace a slotted-line d. all of the above ANS: B
II. PROBLEM SOLVING 71.A
parallel-wire line spaced at 1.27 cm has a diameter of 0.21 cm. What is the characteristic impedance? a. b. c.
a.
14.7
b. c. d.
14.8 14.9 15.1
Solution:
304
303 301
Zo= Zo=
d. 300
ln (
ln (
)
)
Zo = 14.7
Solution:
Zo = 276 log Zo = 276 log
74.
In an improperly loaded transmission line, determine the power reflected from the load if the incident power at the load is 500 W and the reflection coefficient is 0.71.
Zo= 298.8 § 300 a.
72.
In a coaxial line if the inner diameter is 0.51 cm and the center conductor has a diameter of 0.22 cm. What is the characteristic impedance?
c. 50.4
d. 50.5
Zo= 138 log
Zo= 138 log ( Zo= 50.4 73.
b. 252.06 c. 253.4 d. 254 Solution: 2 Pref = t Pinc 2 Pref = (0.71) (500) Pref = 252.05
a. 50.1 b. 50.2
Solution:
252.05
75.
)
A stripline is formed using a multilayer board (dielectric constant =2). The center track is 0.15 inch wide and 0.005 inch thick and the PC board first- layer thickness is 0.05 inch thick., with an overall board thickness of twice the single layer. What is its characteristic impedance?
In wire communications system,calculate the return loss in dB, if the load impedance is 600 ohms and the characteristics impedance of the line is 300 ohms. a. 9.60 b. 9.56 c.
9.54
d. 9.52 Solution: Return Loss (dB)= 20 log(
)
Return Loss (dB)= 20 log( Return Loss (dB)= 20 log(
Zo=
)
72.4
78.
Determine the impedance of a balanced 2-wire with unequal diameters d1 = 12 mm and d2= 10mm. The spacing between wires is 30mm.
)
Return Loss (dB) = 9.54dB 76.
The VSWR on a loss- free line of 50 ohm characteristic impedance is 4.2. Determine the value of the purely resistive load impedance which is known to be larger than 50 ohms.
a.
35.56M
b. c. d.
35.57M 35.55M 35.58M
Solution: a. 211 b.
Zo =
210
Zo =
c. 209 d. 208
N = [ (
N = [ (
A microstrip lie is formed using a 0.095 inch thick PC board (dielectric constant = 1.8) with a bottom grounds plane and a single 0.15 inch wide, 0.008 inch thick track on the top. What is its characteristic impedance?
c.
72.4
d.
72.2
a. 1.56 mS/m 1.23 mS/m
Solution:
ln (
ln (
)
G= )
)±(
) ± ((
)±(
)] )]
For a parallel-wire line, determine the conductance if the conductivity is 200 x10 6 S/m and the conductor diameter is 12 mm. The conductor spacing is 10mm.
G=
Zo=
)±(
c. 1.76 mS/m d. 1.89mS/m
72.6
Zo=
79.
b.
72.8
N= 13.98
77.
a. b.
Where,
RL = (VSWR)(Zo) RL= (4.2)(50) RL= 210
Solution:
Zo= 35.36 M
Solution: VSWR =
G= 1.23 mS/m
80.
What is the characteristic impedance of an open-line with conductors 4mm in diameter separated by 15 mm?
2.3 ,an inner conductor of 1 mm diameter and an outer conductor of diameter 5 mm? a. 64 b.65.9 c. 63.6
d.67.9 a.
241. 52
b. 242.66 c. 243.62 d. 244 Solution: Zo = Zo =
Solution: Zo=
log
log
Zo= 241.52
Zo=
log
log
Zo= 63.6
83.
Calculate the velocity factor of a coaxial cable used as a transmission line, with the characteristic impedance of 50 , capacitance is 40 pF/m and inductance equal to 50H/m.
81.
The Forward power in a transmission line is 150 W and reverse power is 20 W. Calculate the SWR on the line.
c. d.
b. 23.36 x106 m/s
2.15
a.
b.
4.2.1
c. 24.36 x106 m/s
2.13 .2.12
Solution: SWR =
SWR =
6
a. 22.36 x10 m/s
d. 25.36 x106 m/s
Solution:
SWR = 2.15
Vp = c Vf
Vf=
=
Vf= 0.0745 82.
What is the characteristic impedance o f a coaxial cable using a so lid polyethylene dielectric having a relative permeability of
Where :
Vp=
=
Vp=22.36x 84.
m/sa
What is the characteristic impedance of a coaxial cable using solid polyethylene dielectric having a relative permeability of 2.3, an inner conductor of 1mm diameter and an outer conductor of diameter 5mm?
a.11.10ft b. 11.08ft c. 11.07ft
d. 11.05ft
Solution: a. 4.25ft.
=
b. 4.26ft. c. 4.24ft.
=
d. 4.23ft.
= 6.75 m
Solution: =
Length =
=
= 3.375 m
= 11.07 ft.
= 5.175m = 16.974 ft
86.
Length = =
What is the actual length in feet of onequarter wavelength of a coax with a velocity factor of 0.68 at 30 MHz?
Length = 4.24 ft.
a. 5.576 ft
b. 5.577 ft 85.
What is the actual length in feet of onehalf wavelength of a coax with velocity factor of 0.63 at 28 MHz?
c. 5.578 ft d. 5.579 ft
Solution: = = =
= 6.8 m = 22.33 ft.
Length = = 11.16ft
= 6.8m
89.
What is the actual length in feet of a one quarter wavelength of a coax with a velocity factor of 0.695 at 42 MHz?
Length = = 1.7 m = 5.576 ft 87.
What is the actual length in feet of a one half wavelength of a coax with a velocity factor of 0.61 at 27 MHz? a.
a. b.
4.05ft
c.
4.07ft
d.
4.08
4.06ft
Solution:
11.12ft.
=
b. 11.13ft. c. 11.14ft. d. 11.15ft.
=
Solution: =
=
= 4.96 m= 16.28 ft
Length = = 4.07ft
= 6.78 m= 22.23 ft
Length = = 11.12 ft. 88.
What is the actual length in feet of a one half wavelength of a coax with a velocity factor of 0.59 at 26Mhz?
90. An amplifier with 20 dB ga in is connected to another with 10dB gain by means of a transmission line with a loss of 4dB if a signal with a power level of -14 dB were applied to the system, calculate the power output. a.13 dBm b.12 dBm
a. 11.20ft b. 11.19ft c. 11.17ft
c.11 dBm d. 10 dBm
d. 11.16ft
Solution: =
Solution: Po(dBm)= Pi(dBm) + GT(dBm) ± LT(dBm) Po(dBm)= -14(dBm) + (20+10)(dBm) ± (4)(dBm) Po= 12 dBm
91. An attenuator has a loss of 26 dB. If a power of 3W is applied to the attenuator, find the output power. a. b. c.
mW 7. 51mW 7.53 mW
7. 50
D a.
d. 7.54 mW
L(dB)= 10 log
Pout =
Pout =
Zo=
Zo=
92. What would be the approximate series impedance of a quarter- wave matching line used to match a 600 ohms feed to 70 ohms antenna? 204.94
b. 204.95 c. 204.96 d. 204.97
Zo¶ = Zo¶ =
D1=D2 = 2.5 cm
Pout= 7. 54 mW
Solution:
100
b. 101 c. 102 d. 103 Solution: For d<< D1 D2
Solution:
a.
D
Zo= 99.23 Zo= 100
94. What is the characteristic impedance of a single wire with diameter d =0.25 mm placed at the center between grounded parallel planes separated by 1mm apart? The wire is held by a material with a velocity factor of 0.75. a. b. c.
= 204.94
93. What is impedance of a ba lance 4-wire with a diameter of 0.25 cm and spaced 2.5 cm apart using an insulator with a dielectric constant of 2.56?
ohms 77 ohms 74 ohms 76
d. 75 ohms
Solution:
For
Zo=
Zo=
G=
Zo= 75 ohms
G=
Where d = 0.25 mm h= 1 mm
G= 2.76 x 10-9 S/m
Where
= Vf = 0.75
95. What is the phase coe fficient of a transmission line at the frequency of 10MHz if the velocity of propagation is 2.5 x 108 m/s? a.0.23 rad/m
97. What is the input impedance o f a transmission line if its characteristic impedance is 300ohms and the load is 600 ohms? Assume a quarter wavelength section only
b.0.25 rad/m
c.0.24 rad/m d. 0.26 rad/m
a. 180 ohms b. 170 ohms c. 160 ohms
Solution:
d. 150 ohms
Solution:
For l=
a.
2.76 x 10
-9
-9
S/m
b. 2.77 x 10 S/m -9 c. 2.78 x 10 S/m d. 2.79 x 10 -9 S/m Solution:
)
line,
Zin= (
= 0.25 rad/m 96. Determine the conductance o f a two wire open line with the following parameters: D = 4inches ; d= 1in and = 2.6 x10 8 -m.
Zin= Zo (
) =
98. Determine the standing wave ratio of a 300 ohms line whose load is 400 +j 150 ohms. a. 1.68 b.
1.67
c. 1.66 d. 1.65 Solution:
SWR =
and the capacitance is 75 pf/m. A. 1.015 µh B. 2.250 µh C. 1.025µh D. 2.450 µh Solution:
= 0.25 < 44.22 SWR =
Zo =
2
= 1.67
L = Zo C 2 -12 L = (52) (75x10 ) L = 203 nH/m L = 203 nH/m (5 meter) L = 1.015µH
99. What proportion of the incident is reflected back from the loadfor a 75ohms line terminated with Zl = 50-j25 ohms? a. b.
7.82
% 7.83%
c.
7.84%
d.
7.85%
Zo =
/
log ( )
log
Zo = 298 /<0
101.An open wire line with a 2mm diameter each separated by 12mm. Calculate the char impedance. A. 298 B. 250 C. 300 D. 450 Solution: Zo =
Solution:
= 7.84%
100.Find the inductance of a meter length transmission line if the characteristic impedance is 52 ohms
102.A coaxial cable with inner diameter of 3mm and an outer diameter of 9mm. Determine the characteristic impedance if the dielectric is polyethylene having r = 2.3 A. 43.4 B. 50.2 C. 32.6 D. 47.7
Solution: Zo =
log ( )
Zo =
log ( )
Zo = 43.4
103.A coaxial transmission line uses Teflon as a dielectric (r = 2.1). What is the propagation velocity of the signal? A. 207x106 m/s B. 301x106 m/s C. 245x106 m/s D. 195x106 m/s Solution: Vf = Vf =
Vf = 0.69 Vp = VfC Vp = 0.69 ( 3x108 ) Vp = 207x106 m/s 104.A 530 Mhz signal is propagat ing along a RG 8/u coaxial cable with a velocity factor 0.66. If a 75 degrees phase shift is needed, what is the length of the transmission line? A. 7.8 cm B. 8.5 cm C. 5.3 cm D. 6.7 cm Solution: Vp = VfC Vp = 0.66 ( 300x106 ) Vp = 198x106 m/s = = =
L = 7.8 cm
SWR =
= 1.5
107.A generator sends a 250 W of power down a line. If the SWR of the line is 2.5, determine the power absorbed by the load. A. 204.1 W B. 304.1 W C. 404.1 W D.504.1 W Solution:
PL =
=
Pref = 2.8125 W PL = Pinc ± Pref PL = 5W ± 2.8125W PL = 2.1875W
106.A transmitter sends a 5W of power to a 75 line. Suppose the transmitter and the line is matched but the load is not. Determine the power absorbed by the load if the coefficient of reflection is 0. 75. A. 2.1875 W B. 3.1875 W C. 4.1875 W D. 5.1875 W Solution:
PL =
0.374m
L = 0.374 (
105.Calculate the SWR of the line is the 75 and is terminated by 50 A. 1.5 B. 1.6 C. 1.7 D. 1.8 Solution:
Pinc
250W
PL = 204.1W ) = 0.078cm
108.A 75 characteristic impedance transmission line is terminated in by
the load impedance of 120. Determine the input impedance looking into the line 1m long, if the line has a velocity factor of 0.9 and operates at a frequency of 50Mhz. A. 34.4-j12.2 B. 34.4+j12.2 C. 44.4-j12.2 D. 44.4+j12.2 Solution: = =
=
= 5.4m
(360°) = 66.67 °
Zin = Zo
Zin =
Zin = 34.4 ± j12.2
109.A parallel tuned circuit is to be constructed from a shorted section of parallel wire line. If the operating frequency is 2.4 Ghz and the dielectric used is polyethylene, what is the length of the shorted section? A. 2.06 cm B. 3.06 cm C. 4.06 cm D. 5.06 cm Solution: Vf = Vf =
L=
L = 50m
L = 1.5 dB
)
)
L = 0.173 Pout = Pin e-2 L -2 (0.1 73) Pout = 150 e Pout = 106.2 W
111.TDR equipment receives a signal 250 ns after the test signal had been transmitted. If the discontinuity of the line is found 35m from the test point, what is the velocity factor of the line? A. 0.933 B. 1.933 C. 2.933 D. 3.933 Solution: d=
=
Vf =
= 0.66
Vp = VfC Vp = 0.66 (300x106) = 198x106 m/s =
110.The transmitter has an output power of 150W. Suppose the line is 50m long and perfectly matched with a loss of 3 db/100m, how much power is received in the antenna? A. 106.2 W B. 206.2 W C. 306.2 W D. 406.2 W Solution:
=
=
L = 2.0625 cm
= 0.0825m
Vf =
Vf = 0.933 112.The line has 97% velocity factor. If two minima are located 30cm apart, determine the frequency. A. 485 Mhz B. 585 Mhz C. 685 Mhz
D. 785 Mhz Solution: = 2 (30cm) = 60cm f= f=
f = 485 MHz
113.The power incident in the line is 200W. Assuming the reflected power is 15W, what is the SWR of the line? A. 1.75 B. 2.75 C. 3.75 D.4.75 Solution:
SWR = SWR =
SWR = 1.75
114.A transmission line 90m long has a characteristic impedance of 75. The line is connected through a 15V dc source and 75 source resistance at time t=0. What is the voltage across the input immediately after t=0? A. 7.5V B. 8.5V C. 9.5 V D. 10.5 V Solution: Vin =
=
= 7.5 V
115.A transmission line 90m long has a
characteristic impedance of 75. The line is connected through a 15V dc source and 75 source resistance at time t=0. The voltage across the input end changes to 10V, with the same polarity as before, at time t=1.5µs. What is the resistance that terminates the lines? A. 150 B. 250 C. 350 D. 450 Solution: V10 =
)Vs
=
R=
=1+
R=
= 150
116.A parallel wire transmission line has an inductance of 120 nH/m and a characteristic impedance of 320. Calculate the capacitance of the line. A. 1.17 pF/m B. 2.17 pF/m C. 3.17 pF/m D. 4.17 pF/m Solution: Zo = C=
=
C = 1.17 pF/m 117.A radio frequency 50 transmission line is connected to a coil with internal resistance of 20 and inductive resistance of 5 at a frequency of 10Mhz. The line is to be matched to the load by means of
a quarter-wave line and a stub that are connected across the load. Calculate the characteristic impedance of the quarter-wave transformer. A. 32.6 B. 42.6 C. 52.6 D. 63.6 Solution:
YL =
=
matched, determine the current which flows into the line. A. 100 mA B. 200 mA C. 300 mA D. 400 mA Solution: Is = Is =
= (47 ±j12) mS
YL = GL = 47 mS ZL = ZL = Zo = Zo =
Is = 100mA
= 21.3
= 32.6
118.An open-wire line has a 3mm diameter separated 6mm from each other by an dielectric. Calculate the characteristic impedance of the line. A. 166 B. 266 C. 366 D. 466 Solution: Zo = Zo =
120. A certain instrument measures the input impedance of a line and gave a reading of 1200 ohms when its far-end terminals open circuited and 300 ohms when it is short circuited. Calculate the characteristic impedance of the line. a.500 b.600
c.700 d.800
log ( )
log
Zo = 166
Solution:
119.A radio frequency coaxial transmission line has a characteristic impedance of 50 and is connected across the terminals of a signal generator, line and the load are
121. A transmission line has an inductance of 253 nH/m and a capacitance of 56 pF/m. If the physical length of the line is 1.5 m,
calculate its electrical length at a frequency of 265 MHz.
c.166 d.167
a.3/2
Solution: b. 1/2
c. 4/2 d. 5/2
Solution:
Electrical length = 1.5 m (
123. The reflected current at the load of a mismatched line is 3 mA. If the reflection coefficient of the load is 0.7, what is the incident current?
)
Electrical length = 1.5
Electrical length = 3/2
a. 4.5 b.4.4 c.4.3
d.4.2 122. A radio-frequency transmission line has a capacitance of 46.8 pF/m and a phase constant of 30° /m. Determine the inductance of the line at a frequency of 30 MHz. a. 164 b.165
Solution:
c.57%
d.58%
Solution:
124. A radio frequency transmission lines has a characteristic impedance of 75 ohms. If the line is terminated by an aer ial with an input impedance of 72 ohms, calculate the SWR of the line.
a. 1.01
b.1.02
125. A lossless transmission line is connected to a 10 ohms load. If the SWR=5, calculate the percentage of the incident power that is dissipated in the load.
b.56%
d.1.04
a.55%
c.1.03
Solution:
126. The reflection coefficient on a lossfree line of 72 ohms characteristic impedance is 60%. Calculate the load impedance (purely resistive) and which is smaller than 72 ohms. a.17 b.18
c.19 d.20 Solution:
1.6
127. A radio frequency 50 ohms transmission line is connected to a coil with internal resistance of 20 ohms and induct ive reactance of 5 ohms at a frequency of 10 MHz. The line is to be matched to the load by means of a quarter-wave line and a stub that are connected across the load. Calculate the reactance of the stub.
128. A lossless line has a 75 ohms characteristic impedance and is connected to 50 ohms load. If the sending current of 1 mA flows into the line. Calculate the power reflected from the load. a.1 b.1 c.3
d.4 Solution:
a.83.2
b.83.3
c.83.4
d.83.5
Solution:
129. A loss-free line transmission line has an inductance of 263.2 nH/m and a capacitance of 46.8 pF/m. If the generator produces a sinusoidal voltage at 3 MHz of 2
V peak, determine the phase change if the line is 3 m long. a. 11.34 b.11.35 c.11.36 d.11.37 Solution:
Phase change at 3 meters long:
