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Amateur Radio - General > G9 - ANTENNAS AND FEED LINES [4 Exam Questions 4 Groups] > Flashcards

G9 - ANTENNAS AND FEED LINES [4 Exam Questions 4 Groups] Flashcards

1
Q

Which of the following factors determine the characteristic impedance of a parallel conductor antenna feed line?

A. The distance between the centers of the conductors and the radius of the

conductors

B. The distance between the centers of the conductors and the length of the line

C. The radius of the conductors and the frequency of the signal

A

A. The distance between the centers of the conductors and the radius of the

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2
Q

What are the typical characteristic impedances of coaxial cables used for antenna feed lines at amateur stations?

A. 25 and 30 ohms

B. 50 and 75 ohms

C. 80 and 100 ohms

D. 500 and 750 ohms

A

B. 50 and 75 ohms

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3
Q

What is the characteristic impedance of flat ribbon TV type twinlead?

A. 50 ohms

B. 75 ohms

C. 100 ohms

D. 300 ohms

A

D. 300 ohms

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4
Q

What is the reason for the occurrence of reflected power at the point where a feed line connects to an antenna?

A. Operating an antenna at its resonant frequency

B. Using more transmitter power than the antenna can handle

C. A difference between feed-line impedance and antenna feed-point impedance

D. Feeding the antenna with unbalanced feed line

A

C. A difference between feed-line impedance and antenna feed-point impedance

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5
Q

How does the attenuation of coaxial cable change as the frequency of the signal it is carrying increases?

A. It is independent of frequency

B. It increases

C. It decreases

D. It reaches a maximum at approximately 18 MHz

A

B. It increases

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6
Q

In what values are RF feed line losses usually expressed?

A. ohms per 1000 ft

B. dB per 1000 ft

C. ohms per 100 ft

D. dB per 100 ft

A

D. dB per 100 ft

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7
Q

What must be done to prevent standing waves on an antenna feed line?

A. The antenna feed point must be at DC ground potential

B. The feed line must be cut to an odd number of electrical quarter wavelengths long

C. The feed line must be cut to an even number of physical half wavelengths long

D. The antenna feed-point impedance must be matched to the characteristic impedance of the feed line

A

D. The antenna feed-point impedance must be matched to the characteristic impedance of the feed line

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8
Q

If the SWR on an antenna feed line is 5 to 1, and a matching network at the transmitter end of the feed line is adjusted to 1 to 1 SWR, what is the resulting SWR on the feed line?

A. 1 to 1

B. 5 to 1

C. Between 1 to 1 and 5 to 1 depending on the characteristic impedance of the line

D. Between 1 to 1 and 5 to 1 depending on the reflected power at the transmitter

A

B. 5 to 1

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9
Q

What standing wave ratio will result from the connection of a 50-ohm feed line to a non-reactive load having a 200-ohm impedance?

A. 4:1

B. 1:4

C. 2:1

D. 1:2

A

A. 4:1

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10
Q

What standing wave ratio will result from the connection of a 50-ohm feed line to a non-reactive load having a 10-ohm impedance?

A. 2:1

B. 50:1

C. 1:5

D. 5:1

A

D. 5:1

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11
Q

What standing wave ratio will result from the connection of a 50-ohm feed line to a non-reactive load having a 50-ohm impedance?

A. 2:1

B. 1:1

C. 50:50

D. 0:0

A

B. 1:1

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12
Q

What would be the SWR if you feed a vertical antenna that has a 25-ohm feed-point impedance with 50-ohm coaxial cable?

A. 2:1

B. 2.5:1

C. 1.25:1

D. You cannot determine SWR from impedance values

A

A. 2:1

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13
Q

What would be the SWR if you feed an antenna that has a 300-ohm feed-point impedance with 50-ohm coaxial cable?

A. 1.5:1

B. 3:1

C. 6:1

D. You cannot determine SWR from impedance values

A

C. 6:1

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14
Q

What is one disadvantage of a directly fed random-wire antenna?

A. It must be longer than 1 wavelength

B. You may experience RF burns when touching metal objects in your station

C. It produces only vertically polarized radiation

D. It is not effective on the higher HF bands

A

B. You may experience RF burns when touching metal objects in your station

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15
Q

What is an advantage of downward sloping radials on a quarter wave ground-plane antenna?

A. They lower the radiation angle

B. They bring the feed-point impedance closer to 300 ohms

C. They increase the radiation angle

D. They bring the feed-point impedance closer to 50 ohms

A

D. They bring the feed-point impedance closer to 50 ohms

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16
Q

What happens to the feed-point impedance of a ground-plane antenna when its radials are changed from horizontal to downward-sloping?

A. It decreases

B. It increases

C. It stays the same

D. It reaches a maximum at an angle of 45 degrees

A

B. It increases

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17
Q

What is the low angle azimuthal radiation pattern of an ideal half-wavelength dipole antenna installed 1/2 wavelength high and parallel to the Earth?

A. It is a figure-eight at right angles to the antenna

B. It is a figure-eight off both ends of the antenna

C. It is a circle (equal radiation in all directions)

D. It has a pair of lobes on one side of the antenna and a single lobe on the other side

A

A. It is a figure-eight at right angles to the antenna

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18
Q

How does antenna height affect the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna?

A. If the antenna is too high, the pattern becomes unpredictable

B. Antenna height has no effect on the pattern

C. If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional

D. If the antenna is less than 1/2 wavelength high, radiation off the ends of the wire is eliminated

A

C. If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional

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19
Q

Where should the radial wires of a ground-mounted vertical antenna system be placed?

A. As high as possible above the ground

B. Parallel to the antenna element

C. On the surface or buried a few inches below the ground

D. At the top of the antenna

A

C. On the surface or buried a few inches below the ground

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20
Q

How does the feed-point impedance of a 1/2 wave dipole antenna change as the antenna is lowered from 1/4 wave above ground?

A. It steadily increases

B. It steadily decreases

C. It peaks at about 1/8 wavelength above ground

D. It is unaffected by the height above ground

A

B. It steadily decreases

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21
Q

How does the feed-point impedance of a 1/2 wave dipole change as the feed-point location is moved from the center toward the ends?

A. It steadily increases

B. It steadily decreases

C. It peaks at about 1/8 wavelength from the end

D. It is unaffected by the location of the feed point

A

A. It steadily increases

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22
Q

Which of the following is an advantage of a horizontally polarized as compared to vertically polarized HF antenna?

A. Lower ground reflection losses

B. Lower feed-point impedance

C. Shorter Radials

D. Lower radiation resistance

A

A. Lower ground reflection losses

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23
Q

What is the approximate length for a 1/2-wave dipole antenna cut for 14.250 MHz?

A. 8 feet

B. 16 feet

C. 24 feet

D. 32 feet

A

D. 32 feet

24
Q

What is the approximate length for a 1/2-wave dipole antenna cut for 3.550 MHz?

A. 42 feet

B. 84 feet

C. 131 feet

D. 263 feet

A

C. 131 feet

25
Q

What is the approximate length for a 1/4-wave vertical antenna cut for 28.5 MHz?

A. 8 feet

B. 11 feet

C. 16 feet

D. 21 feet

A

A. 8 feet

26
Q

Which of the following would increase the bandwidth of a Yagi antenna?

A. Larger diameter elements

B. Closer element spacing

C. Loading coils in series with the element

D. Tapered-diameter elements

A

A. Larger diameter elements

27
Q

What is the approximate length of the driven element of a Yagi antenna?

A. 1/4 wavelength

B. 1/2 wavelength

C. 3/4 wavelength

D. 1 wavelength

A

B. 1/2 wavelength

28
Q

Which statement about a three-element, single-band Yagi antenna is true?

A. The reflector is normally the shortest parasitic element

B. The director is normally the shortest parasitic element

C. The driven element is the longest parasitic element

D. Low feed-point impedance increases bandwidth

A

B. The director is normally the shortest parasitic element

29
Q

Which statement about a three-element; single-band Yagi antenna is true?

A. The reflector is normally the longest parasitic element

B. The director is normally the longest parasitic element

C. The reflector is normally the shortest parasitic element

D. All of the elements must be the same length

A

A. The reflector is normally the longest parasitic element

30
Q

How does increasing boom length and adding directors affect a Yagi antenna?

A. Gain increases

B. Beamwidth increases

C. Weight decreases

D. Wind load decreases

A

A. Gain increases

31
Q

Which of the following is a reason why a Yagi antenna is often used for radio communications on the 20 meter band?

A. It provides excellent omnidirectional coverage in the horizontal plane

B. It is smaller, less expensive and easier to erect than a dipole or vertical antenna

C. It helps reduce interference from other stations to the side or behind the antenna

D. It provides the highest possible angle of radiation for the HF bands

A

C. It helps reduce interference from other stations to the side or behind the antenna

32
Q

What does “front-to-back ratio” mean in reference to a Yagi antenna?

A. The number of directors versus the number of reflectors

B. The relative position of the driven element with respect to the reflectors and directors

C. The power radiated in the major radiation lobe compared to the power radiated in exactly the opposite direction

D. The ratio of forward gain to dipole gain

A

C. The power radiated in the major radiation lobe compared to the power radiated in exactly the opposite direction

33
Q

What is meant by the “main lobe” of a directive antenna?

A. The magnitude of the maximum vertical angle of radiation

B. The point of maximum current in a radiating antenna element

C. The maximum voltage standing wave point on a radiating element

D. The direction of maximum radiated field strength from the antenna

A

D. The direction of maximum radiated field strength from the antenna

34
Q

What is the approximate maximum theoretical forward gain of a three element, single-band Yagi antenna?

A. 9.7 dBi

B. 9.7 dBd

C. 5.4 times the gain of a dipole

D. All of these choices are correct

A

A. 9.7 dBi

35
Q

Which of the following is a Yagi antenna design variable that could be adjusted to optimize forward gain, front-to-back ratio, or SWR bandwidth?

A. The physical length of the boom

B. The number of elements on the boom

C. The spacing of each element along the boom

D. All of these choices are correct

A

D. All of these choices are correct

36
Q

What is the purpose of a gamma match used with Yagi antennas?

A. To match the relatively low feed-point impedance to 50 ohms

B. To match the relatively high feed-point impedance to 50 ohms

C. To increase the front to back ratio

D. To increase the main lobe gain

A

A. To match the relatively low feed-point impedance to 50 ohms

37
Q

Which of the following is an advantage of using a gamma match for impedance matching of a Yagi antenna to 50-ohm coax feed line?

A. It does not require that the elements be insulated from the boom

B. It does not require any inductors or capacitors

C. It is useful for matching multiband antennas

D. All of these choices are correct

A

A. It does not require that the elements be insulated from the boom

38
Q

Approximately how long is each side of a quad antenna driven element?

A. 1/4 wavelength

B. 1/2 wavelength

C. 3/4 wavelength

D. 1 wavelength

A

A. 1/4 wavelength

39
Q

How does the forward gain of a two-element quad antenna compare to the forward gain of a three-element Yagi antenna?

A. About 2/3 as much

B. About the same

C. About 1.5 times as much

D. About twice as much

A

B. About the same

40
Q

Approximately how long is each side of a quad antenna reflector element?

A. Slightly less than 1/4 wavelength

B. Slightly more than 1/4 wavelength

C. Slightly less than 1/2 wavelength

D. Slightly more than 1/2 wavelength

A

B. Slightly more than 1/4 wavelength

41
Q

How does the gain of a two-element delta-loop beam compare to the gain of a two-element quad antenna?

A. 3 dB higher

B. 3 dB lower

C. 2.54 dB higher

D. About the same

A

D. About the same

42
Q

Approximately how long is each leg of a symmetrical delta-loop antenna?

A. 1/4 wavelength

B. 1/3 wavelength

C. 1/2 wavelength

D. 2/3 wavelength

A

B. 1/3 wavelength

43
Q

What happens when the feed point of a quad antenna is changed from the center of either horizontal wire to the center of either vertical wire?

A. The polarization of the radiated signal changes from horizontal to vertical

B. The polarization of the radiated signal changes from vertical to horizontal

C. The direction of the main lobe is reversed

D. The radiated signal changes to an omnidirectional pattern

A

A. The polarization of the radiated signal changes from horizontal to vertical

44
Q

What configuration of the loops of a two-element quad antenna must be used for the antenna to operate as a beam antenna, assuming one of the elements is used as a reflector?

A. The driven element must be fed with a balun transformer

B. The driven element must be open-circuited on the side opposite the feed point

C. The reflector element must be approximately 5% shorter than the driven element

D. The reflector element must be approximately 5% longer than the driven element

A

D. The reflector element must be approximately 5% longer than the driven element

45
Q

How does the gain of two 3-element horizontally polarized Yagi antennas spaced vertically 1/2 wavelength apart typically compare to the gain of a single 3-element Yagi?

A. Approximately 1.5 dB higher

B. Approximately 3 dB higher

C. Approximately 6 dB higher

D. Approximately 9 dB higher

A

B. Approximately 3 dB higher

46
Q

What does the term “NVIS” mean as related to antennas?

A. Nearly Vertical Inductance System

B. Non-Visible Installation Specification

C. Non-Varying Impedance Smoothing

D. Near Vertical Incidence Sky wave

A

D. Near Vertical Incidence Sky wave

47
Q

Which of the following is an advantage of an NVIS antenna?

A. Low vertical angle radiation for working stations out to ranges of several thousand kilometers

B. High vertical angle radiation for working stations within a radius of a few hundred kilometers

C. High forward gain

D. All of these choices are correct

A

B. High vertical angle radiation for working stations within a radius of a few hundred kilometers

48
Q

At what height above ground is an NVIS antenna typically installed?

A. As close to one-half wave as possible

B. As close to one wavelength as possible

C. Height is not critical as long as it is significantly more than 1/2 wavelength

D. Between 1/10 and 1/4 wavelength

A

D. Between 1/10 and 1/4 wavelength

49
Q

What is the primary purpose of antenna traps?

A. To permit multiband operation

B. To notch spurious frequencies

C. To provide balanced feed-point impedance

D. To prevent out of band operation

A

A. To permit multiband operation

50
Q

What is the advantage of vertical stacking of horizontally polarized Yagi antennas?

A. Allows quick selection of vertical or horizontal polarization

B. Allows simultaneous vertical and horizontal polarization

C. Narrows the main lobe in azimuth

D. Narrows the main lobe in elevation

A

D. Narrows the main lobe in elevation

51
Q

Which of the following is an advantage of a log periodic antenna?

A. Wide bandwidth

B. Higher gain per element than a Yagi antenna

C. Harmonic suppression

D. Polarization diversity

A

A. Wide bandwidth

52
Q

Which of the following describes a log periodic antenna?

A. Length and spacing of the elements increases logarithmically from one end of the boom to the other

B. Impedance varies periodically as a function of frequency

C. Gain varies logarithmically as a function of frequency

D. SWR varies periodically as a function of boom length

A

A. Length and spacing of the elements increases logarithmically from one end of the boom to the other

53
Q

Why is a Beverage antenna not used for transmitting?

A. Its impedance is too low for effective matching

B. It has high losses compared to other types of antennas

C. It has poor directivity

D. All of these choices are correct

A

B. It has high losses compared to other types of antennas

54
Q

Which of the following is an application for a Beverage antenna?

A. Directional transmitting for low HF bands

B. Directional receiving for low HF bands

C. Portable direction finding at higher HF frequencies

D. Portable direction finding at lower HF frequencies

A

B. Directional receiving for low HF bands

55
Q

Which of the following describes a Beverage antenna?

A. A vertical antenna constructed from beverage cans

B. A broad-band mobile antenna

C. A helical antenna for space reception

D. A very long and low directional receiving antenna

A

D. A very long and low directional receiving antenna

56
Q

Which of the following is a disadvantage of multiband antennas?

A. They present low impedance on all design frequencies

B. They must be used with an antenna tuner

C. They must be fed with open wire line

D. They have poor harmonic rejection

A

D. They have poor harmonic rejection

Amateur Radio - General (10 decks)

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