E9 Antennas and Transmission Lines Flashcards
(114 cards)
1
Q
E9A01 (C) What describes an isotropic antenna?
A
C. A theoretical antenna used as a reference for antenna gain
2
Q
E9A02 (D) What antenna has no gain in any direction?
A
D. Isotropic antenna
3
Q
E9A03 (A) Why would one need to know the feed point impedance of an antenna?
A
A. To match impedances in order to minimize standing wave ratio on the transmission line
4
Q
E9A04 (B) Which of the following factors may affect the feed point impedance of an antenna?
A
B. Antenna height, conductor length/diameter ratio and location of nearby conductive objects
5
Q
E9A05 (D) What is included in the total resistance of an antenna system?
A
D. Radiation resistance plus ohmic resistance
6
Q
E9A06 (D) How does the beamwidth of an antenna vary as the gain is increased?
A
D. It decreases
7
Q
E9A07 (A) What is meant by antenna gain?
A
A. The ratio of the radiated signal strength of an antenna in the direction of maximum radiation to that of a reference antenna
8
Q
E9A08 (B) What is meant by antenna bandwidth?
A
B. The frequency range over which an antenna satisfies a performance requirement
9
Q
E9A09 (B) How is antenna efficiency calculated?
A
B. (radiation resistance / total resistance) x 100 per cent
10
Q
E9A10 (A) Which of the following choices is a way to improve the efficiency of a ground-mounted quarter-wave vertical antenna?
A
A. Install a good radial system
11
Q
E9A11 (C) Which of the following factors determines ground losses for a ground-mounted vertical antenna operating in the 3 MHz to 30 MHz range?
A
C. Soil conductivity
12
Q
E9A12 (A) How much gain does an antenna have compared to a 1/2-wavelength dipole when it has 6 dB gain over an isotropic antenna?
A
A. 3.85 dB
13
Q
E9A13 (B) How much gain does an antenna have compared to a 1/2-wavelength dipole when it has 12 dB gain over an isotropic antenna?
A
B. 9.85 dB
14
Q
E9A14 (C) What is meant by the radiation resistance of an antenna?
A
C. The value of a resistance that would dissipate the same amount of power as that radiated from an antenna
15
Q
E9A15 (D) What is the effective radiated power relative to a dipole of a repeater station with 150 watts transmitter power output, 2 dB feed line loss, 2.2 dB duplexer loss, and 7 dBd antenna gain?
A
D. 286 watts
16
Q
E9A16 (A) What is the effective radiated power relative to a dipole of a repeater station with 200 watts transmitter power output, 4 dB feed line loss, 3.2 dB duplexer loss, 0.8 dB circulator loss, and 10 dBd antenna gain?
A
A. 317 watts
17
Q
E9A17 (B) What is the effective radiated power of a repeater station with 200 watts transmitter power output, 2 dB feed line loss, 2.8 dB duplexer loss, 1.2 dB circulator loss, and 7 dBi antenna gain?
A
B. 252 watts
18
Q
E9A18 (C) What term describes station output, taking into account all gains and losses?
A
C. Effective radiated power
19
Q
E9B01 (B) In the antenna radiation pattern shown in Figure E9-1, what is the 3 dB beam-width?
A
B. 50 degrees
20
Q
E9B02 (B) In the antenna radiation pattern shown in Figure E9-1, what is the front-to-back ratio?
A
B. 18 dB
21
Q
E9B03 (B) In the antenna radiation pattern shown in Figure E9-1, what is the front-to-side ratio?
A
B. 14 dB
22
Q
E9B04 (D) What may occur when a directional antenna is operated at different frequencies within the band for which it was designed?
A
D. The gain may change depending on frequency
23
Q
E9B05 (A) What type of antenna pattern over real ground is shown in Figure E9-2?
A
A. Elevation
24
Q
E9B06 (C)
What is the elevation angle of peak response in the antenna radiation pattern shown in Figure E9-2?
A
C. 7.5 degrees
25
E9B07 (C)
How does the total amount of radiation emitted by a directional gain antenna compare with the total amount of radiation emitted from an isotropic antenna, assuming each is driven by the same amount of power?
C. They are the same
26
E9B08 (A)
How can the approximate beam-width in a given plane of a directional antenna be determined?
A. Note the two points where the signal strength of the antenna is 3 dB less than maximum and compute the angular difference
27
E9B09 (B)
What type of computer program technique is commonly used for modeling antennas?
B. Method of Moments
28
E9B10 (A)
What is the principle of a Method of Moments analysis?
A. A wire is modeled as a series of segments, each having a uniform value of current
29
E9B11 (C)
What is a disadvantage of decreasing the number of wire segments in an antenna model below the guideline of 10 segments per half-wavelength?
C. The computed feed point impedance may be incorrect
30
E9B12 (D)
What is the far field of an antenna?
D. The region where the shape of the antenna pattern is independent of distance
31
E9B13 (B)
What does the abbreviation NEC stand for when applied to antenna modeling programs?
B. Numerical Electromagnetic Code
32
E9B14 (D)
What type of information can be obtained by submitting the details of a proposed new antenna to a modeling program?
A. SWR vs frequency charts
B. Polar plots of the far field elevation and azimuth patterns
C. Antenna gain
D. All of these choices are correct
33
E9B15 (B)
What is the front-to-back ratio of the radiation pattern shown in Figure E9-2?
B. 28 dB
34
E9B16 (A)
How many elevation lobes appear in the forward direction of the antenna radiation pattern shown in Figure E9-2?
A. 4
35
E9C01 (D)
What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase?
D. A figure-8 oriented along the axis of the array
36
E9C02 (A)
What is the radiation pattern of two 1/4 wavelength vertical antennas spaced 1/4 wavelength apart and fed 90 degrees out of phase?
A. Cardioid
37
E9C03 (C)
What is the radiation pattern of two 1/4 wavelength vertical antennas spaced a 1/2 wavelength apart and fed in phase?
C. A Figure-8 broadside to the axis of the array
38
E9C04 (B)
What happens to the radiation pattern of an unterminated long wire antenna as the wire length is increased?
B. The lobes align more in the direction of the wire
39
E9C05 (A)
What is an OCFD antenna?
A. A dipole feed approximately 1/3 the way from one end with a 4:1 balun to provide multiband operation
40
E9C06 (B)
What is the effect of a terminating resistor on a rhombic antenna?
B. It changes the radiation pattern from bidirectional to unidirectional
41
E9C07 (A)
What is the approximate feed point impedance at the center of a two-wire folded dipole antenna?
A. 300 ohms
42
E9C08 (C)
What is a folded dipole antenna?
C. A dipole consisting of one wavelength of wire forming a very thin loop
43
E9C09 (A)
What is a G5RV antenna?
A. A multi-band dipole antenna fed with coax and a balun through a selected length of open wire transmission line
44
E9C10 (B)
Which of the following describes a Zepp antenna?
B. An end fed dipole antenna
45
E9C11 (D)
How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus rocky ground?
D. The low-angle radiation increases
46
E9C12 (C)
Which of the following describes an extended double Zepp antenna?
C. A center fed 1.25 wavelength antenna (two 5/8 wave elements in phase)
47
E9C13 (C)
What is the main effect of placing a vertical antenna over an imperfect ground?
C. It reduces low-angle radiation
48
E9C14 (B)
How does the performance of a horizontally polarized antenna mounted on the side of a hill compare with the same antenna mounted on flat ground?
B. The main lobe takeoff angle decreases in the downhill direction
49
E9C15 (B)
How does the radiation pattern of a horizontally polarized 3-element beam antenna vary with its height above ground?
B. The main lobe takeoff angle decreases with increasing height
50
E9D01 (C)
How does the gain of an ideal parabolic dish antenna change when the operating frequency is doubled?
C. Gain increases by 6 dB
51
E9D02 (C)
How can linearly polarized Yagi antennas be used to produce circular polarization?
C. Arrange two Yagis perpendicular to each other with the driven elements at the same point on the boom fed 90 degrees out of phase
52
E9D03 (A)
Where should a high Q loading coil be placed to minimize losses in a shortened
A. Near the center of the vertical radiator
53
E9D04 (C)
Why should an HF mobile antenna loading coil have a high ratio of reactance to resistance?
C. To minimize losses
54
E9D05 (A)
What is a disadvantage of using a multiband trapped antenna?
A. It might radiate harmonics
55
E9D06 (B)
What happens to the bandwidth of an antenna as it is shortened through the use of loading coils?
B. It is decreased
56
E9D07 (D)
What is an advantage of using top loading in a shortened HF vertical antenna?
D. Improved radiation efficiency
57
E9D08 (B)
What happens as the Q of an antenna increases?
B. SWR bandwidth decreases
58
E9D09 (D)
What is the function of a loading coil used as part of an HF mobile antenna?
D. To cancel capacitive reactance
59
E9D10 (B)
What happens to feed point impedance at the base of a fixed length HF mobile antenna as the frequency of operation is lowered?
B. The radiation resistance decreases and the capacitive reactance increases
60
E9D11 (B)
Which of the following types of conductors would be best for minimizing losses in a station's RF ground system?
B. A wide flat copper strap
61
E9D12 (C)
Which of the following would provide the best RF ground for your station?
C. An electrically short connection to3 or 4 interconnected ground rods driven into the Earth
62
E9D13 (B)
What usually occurs if a Yagi antenna is designed solely for maximum forward gain?
B. The front-to-back ratio decreases
63
E9E01 (B)
What system matches a higher impedance transmission line to a lower impedance antenna by connecting the line to the driven element in two places spaced a fraction of a wavelength each side of element center?
B. The delta matching system
64
E9E02 (A)
What is the name of an antenna matching system that matches an unbalanced feed line to an antenna by feeding the driven element both at the center of the element and at a fraction of a wavelength to one side of center?
A. The gamma match
65
E9E03 (D)
What is the name of the matching system that uses a section of transmission line connected in parallel with the feed line at or near the feed point?
D. The stub match
66
E9E04 (B)
What is the purpose of the series capacitor in a gamma-type antenna matching network?
B. To cancel the inductive reactance of the matching network
67
E9E05 (A)
How must the driven element in a 3-element Yagi be tuned to use a hairpin matching system?
A. The driven element reactance must be capacitive
68
E9E06 (C)
What is the equivalent lumped-constant network for a hairpin matching system of a
3-element Yagi?
C. A shunt inductor
69
E9E07 (B)
What term best describes the interactions at the load end of a mismatched transmission line?
B. Reflection coefficient
70
E9E08 (D)
Which of the following measurements is characteristic of a mismatched transmission line?
D. An SWR greater than 1:1
71
E9E09 (C)
Which of these matching systems is an effective method of connecting a 50 ohm coaxial cable feed line to a grounded tower so it can be used as a vertical antenna?
C. Gamma match
72
E9E10 (C)
Which of these choices is an effective way to match an antenna with a 100 ohm feed point impedance to a 50 ohm coaxial cable feed line?
C. Insert a 1/4-wavelength piece of 75 ohm coaxial cable transmission line in series
73
E9E11 (B)
What is an effective way of matching a feed line to a VHF or UHF antenna when the impedances of both the antenna and feed line are unknown?
B. Use the universal stub matching technique
74
E9E12 (A)
What is the primary purpose of a phasing line when used with an antenna having multiple driven elements?
A. It ensures that each driven element operates in concert with the others to create the desired antenna pattern
75
E9E13 (C)
What is a use for a Wilkinson divider?
C. It is used to divide power equally between two 50 ohm loads while maintaining 50 ohm input impedance
76
E9F01 (D)
What is the velocity factor of a transmission line?
D. The velocity of the wave in the transmission line divided by the velocity of light in a vacuum
77
E9F02 (C)
Which of the following determines the velocity factor of a transmission line?
C. Dielectric materials used in the line
78
E9F03 (D)
Why is the physical length of a coaxial cable transmission line shorter than its electrical length?
D. Electrical signals move more slowly in a coaxial cable than in air
79
E9F04 (B)
What is the typical velocity factor for a coaxial cable with solid polyethylene dielectric?
B. 0.66
80
E9F05 (C)
What is the approximate physical length of a solid polyethylene dielectric coaxial transmission line that is electrically one-quarter wavelength long at 14.1 MHz?
C. 3.5 meters
81
E9F06 (C)
What is the approximate physical length of an air-insulated, parallel conductor transmission line that is electrically one-half wavelength long at 14.10 MHz?
C. 10 meters
82
E9F07 (A)
How does ladder line compare to small-diameter coaxial cable such as RG-58 at 50 MHz?
A. Lower loss
83
E9F08 (A)
What is the term for the ratio of the actual speed at which a signal travels through a transmission line to the speed of light in a vacuum?
A. Velocity factor
84
E9F09 (B)
What is the approximate physical length of a solid polyethylene dielectric coaxial transmission line that is electrically one-quarter wavelength long at 7.2 MHz?
B. 6.9 meters
85
E9F10 (C)
What impedance does a 1/8 wavelength transmission line present to a generator when the line is shorted at the far end?
C. An inductive reactance
86
E9F11 (C)
What impedance does a 1/8 wavelength transmission line present to a generator when the line is open at the far end?
C. A capacitive reactance
87
E9F12 (D)
What impedance does a 1/4 wavelength transmission line present to a generator when the line is open at the far end?
D. Very low impedance
88
E9F13 (A)
What impedance does a 1/4 wavelength transmission line present to a generator when the line is shorted at the far end?
A. Very high impedance
89
E9F14 (B)
What impedance does a 1/2 wavelength transmission line present to a generator when the line is shorted at the far end?
B. Very low impedance
90
E9F15 (A)
What impedance does a 1/2 wavelength transmission line present to a generator when the line is open at the far end?
A. Very high impedance
91
E9F16 (D)
Which of the following is a significant difference between foam dielectric coaxial cable and solid dielectric cable, assuming all other parameters are the same?
A. Foam dielectric has lower safe operating voltage limits
B. Foam dielectric has lower loss per unit of length
C. Foam dielectric has higher velocity factor
D. All of these choices are correct
92
E9G01 (A)
Which of the following can be calculated using a Smith chart?
A. Impedance along transmission lines
93
E9G02 (B)
What type of coordinate system is used in a Smith chart?
B. Resistance circles and reactance arcs
94
E9G03 (C)
Which of the following is often determined using a Smith chart?
C. Impedance and SWR values in transmission lines
95
E9G04 (C)
What are the two families of circles and arcs that make up a Smith chart?
C. Resistance and reactance
96
E9G05 (A)
What type of chart is shown in Figure E9-3?
A. Smith chart
97
E9G06 (B)
On the Smith chart shown in Figure E9-3, what is the name for the large outer circle on which the reactance arcs terminate?
B. Reactance axis
98
E9G07 (D)
On the Smith chart shown in Figure E9-3, what is the only straight line shown?
D. The resistance axis
99
E9G08 (C)
What is the process of normalization with regard to a Smith chart?
C. Reassigning impedance values with regard to the prime center
100
E9G09 (A)
What third family of circles is often added to a Smith chart during the process of solving problems?
A. Standing wave ratio circles
101
E9G10 (D)
What do the arcs on a Smith chart represent?
D. Points with constant reactance
102
E9G11 (B)
How are the wavelength scales on a Smith chart calibrated?
B. In fractions of transmission line electrical wavelength
103
E9H01 (D)
When constructing a Beverage antenna, which of the following factors should be included in the design to achieve good performance at the desired frequency?
D. It should be one or more wavelengths long
104
E9H02 (A)
Which is generally true for low band (160 meter and 80 meter) receiving antennas?
A. Atmospheric noise is so high that gain over a dipole is not important
105
E9H03 DELETED February 1, 2016
E9H03 DELETED February 1, 2016
106
E9H04 (B)
What is an advantage of using a shielded loop antenna for direction finding?
B. It is electro statically balanced against ground, giving better nulls
107
E9H05 (A)
What is the main drawback of a wire-loop antenna for direction finding?
A. It has a bidirectional pattern
108
E9H06 (C)
What is the triangulation method of direction finding?
C. Antenna headings from several different receiving locations are used to locate the signal source
109
E9H07 (D)
Why is it advisable to use an RF attenuator on a receiver being used for direction finding?
D. It prevents receiver overload which could make it difficult to determine peaks or nulls
110
E9H08 (A)
What is the function of a sense antenna?
A. It modifies the pattern of a DF antenna array to provide a null in one direction
111
E9H09 (C)
Which of the following describes the construction of a receiving loop antenna?
C. One or more turns of wire wound in the shape of a large open coil
112
E9H10 (D)
How can the output voltage of a multiple turn receiving loop antenna be increased?
D. By increasing either the number of wire turns in the loop or the area of the loop structure or both
113
E9H11 (B)
What characteristic of a cardioid pattern antenna is useful for direction finding?
B. A very sharp single null
114
