General Exam-Antennas and Feed Lines

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rledwith
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General Exam-Antennas and Feed Lines
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2013-07-03 17:09:20
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Amateur Radio General Exam - G9 Question Set - Antennas and Feed Lines
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  1. G9A01 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
    D. The frequency of the signal and the length of the line
    • (A)
    • The characteristic impedance of a parallel-conductor feed line depends on the distance between the conductor centers and the radius of the conductors.
  2. G9A02 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
    • (B)
    • Common coaxial cables used as antenna feed lines have characteristic impedances of 50 or 75 ohms.
  3. G9A03 What is the characteristic impedance of flat ribbon TV type twinlead?
    A. 50 ohms
    B. 75 ohms
    C. 100 ohms
    D. 300 ohms
    • (D)
    • The flat ribbon type of feed line often used with TV antennas has a characteristic impedance of 300 ohms. This feed line is called twin lead.
  4. G9A04 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
    • (C)
    • Whenever power traveling along a feed line encounters a different impedance from the characteristic impedance of the feed line, such as at an antenna, some of the power is reflected back towards the power source. The greater the difference between the feed lines characteristic impedance and the new impedance, the larger the fraction of power that is reflected. 

    Power reflected back 
    from an antenna returns to the transmitter, which in turn reflects the power back towards the antenna. creating a standing wave. When the transmitter and antenna impedances are not matched, less power is transferred to the antenna because of the extra loss incurred as the reflected power travels up and down the feed line.
  5. G9A05 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
    • (B)
    • Feed line loss is greater at higher frequencies. For example, if you were to use the same type of coaxial cable for your 160 meter antenna as for your 2 meter antenna, there would be much more loss at the higher 2 meter frequencies.
  6. G9A06 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
    • (D)
    • RF feed line loss is normally specified in decibels of loss for each 100 feet of line. Loss must also be specified at a certain frequency.
  7. G9A07 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
    • (D)
    • To eliminate reflected power, the antenna impedance must be matched to the characteristic impedance of the feed line. If the impedances are matched, all of the feed line power is transferred to the antenna. The problem with reflected power causing standing waves and raising the feed line SWR is not generally transmitter efficiency but rather the transmitter’s reaction to the high SWR. Modern solid-state transmitters usually have protection circuitry that reduces the power output in the presence of high SWR. (When the SWR is high there are high voltages present that can damage components.) By reducing SWR, the transmitter can operate at maximum power output.
  8. G9A08 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
    • (B)
    • A matching network at the transmitter does not change the SWR on the feed line, so the feed line SWR is still 5:1.
  9. G9A09 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)
    • If a load connected to a feed line is purely resistive, the SWR can be calculated by dividing the line characteristic impedance by the load resistance or vice versa, whichever gives a value greater than one. 200 / 50 = 4:1 SWR.
  10. G9A10 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
    • (D)
    • If a load connected to a feed line is purely resistive, the SWR can be calculated by dividing the line characteristic impedance by the load resistance or vice versa, whichever gives a value greater than one. 50 / 10 = 5:1 SWR.
  11. G9A11 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
    • (B)
    • If a load connected to a feed line is purely resistive, the SWR can be calculated by dividing the line characteristic impedance by the load resistance or vice versa, whichever gives a value greater than one. 50 / 50 = 1:1 SWR.
  12. G9A12 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)
    • If a load connected to a feed line is purely resistive, the SWR can be calculated by dividing the line characteristic impedance by the load resistance or vice versa, whichever gives a value greater than one. 50 / 25 = 2:1 SWR.
  13. G9A13 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
    • (C)
    • If a load connected to a feed line is purely resistive, the SWR can be calculated by dividing the line characteristic impedance by the load resistance or vice versa, whichever gives a value greater than one. 300 / 50 = 6:1 SWR.
  14. G9B01 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
    • (B)
    • A random-wire antenna consist of a wire connected directly to the transmitter at one end. It can be of any length because an antenna tuner is used to match the impedances. It does not require a feed line because the single piece of wire serves as both a feed line and an antenna. It is considered to be a multiband antenna because the antenna tuner will match the impedances for several frequency bands. One significant disadvantage of a random-wire antenna is that you may experience RF “hot spots” in your station because the station equipment and ground system are part of your antenna system!
  15. G9B02 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
    • (D)
    • A ground-plane antenna is often constructed with a ¼-wavelength vertical radiating element and four ¼-wavelength horizontal “radial” wires that form the ground plane. You can change the impedance of a ground-plane antenna by changing the angle of the radials. Bending or sloping the radials downward to about a 45-degree angle will increase the impedance from approximately 35 ohms to approximately 50 ohms,
  16. G9B03 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
    • (B)
    • A ground-plane antenna is often constructed with a ¼-wavelength vertical radiating element and four ¼-wavelength horizontal “radial” wires that form the ground plane. You can change the impedance of a ground-plane antenna by changing the angle of the radials. Bending or sloping the radials downward to about a 45-degree angle will increase the impedance from approximately 35 ohms to approximately 50 ohms, reducing SWR.
  17. G9B04 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 ½-wavelength dipole antenna ½ wavelength or more above the ground radiates its signals in a bi-directional fashion with maximum radiation at a 90º angle to the antenna. This is called a “figure 8” radiation pattern. If the antenna is placed less than 1/2 wavelength above the ground, reflections from the ground will cause more of the antenna’s signal to be radiated at high vertical angles and the pattern becomes omnidirectional.
  18. G9B05 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
    • (C)
    • As height is reduced below 1/2 wavelength the antenna pattern becomes almost omnidirectional, sending signals nearly equally in all compass directions.
  19. G9B06 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
    • (C)
    • In most installations, ground conductivity is inadequate to serve as the antenna’s ground plane, so an artificial ground screen must be made from wires placed along the ground near the base of the antenna. These radials are usually ¼ wavelength or longer. Depending on ground conductivity, 8, 16, 32 or more radials may be required to form an effective ground. The radial wires of a ground-mounted vertical antenna should be placed on the ground surface or buried a few inches below the surface.
  20. G9B07 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
    • (B)
    • As the antenna is lowered below ¼ wavelength above ground, the impedance steadily decreases to a very low value when placed directly on the ground.
  21. G9B08 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)
    • The center of a ½-wavelength dipole is the location of the lowest feed point impedance, approximately 72 ohms in free space. At the ends of the dipole, feed point impedance is several thousand ohms. In between, feed point impedance increases steadily as the feed point is moved from the center towards the ends of the antenna.
  22. G9B09 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)
    • The signals from a horizontally polarized antenna have lower losses when reflecting from the ground. This is because the horizontal polarization of the wave induces currents that flow along the surface of the ground. Vertical polarization tends to induce currents that flow vertically in the ground, where losses are higher.Radio waves reflecting from the ground have lower losses when the polarization of the wave is parallel to the ground. That is, when the waves are horizontally polarized. Because the reflected waves combine with the direct waves (not reflected) to make up the antenna’s radiation pattern, lower reflection loss results ¡n stronger signal strength.Ground-mounted vertical antennas, however, are able to generate stronger signals at low angles of radiation than horizontally polarized antennas at low heights. This means they are often preferred for DX contacts on the lower HF bands where it is impractical to raise horizontally polarized antennas to the height necessary for strong low-angle signals.
  23. G9B10 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
    • (D)
    • In free space, ½ wavelength in feet equals 492 divided by frequency in MHz. If you cut a piece of wire that length, however, you’ll find it is too long to resonate at the desired frequency. A resonant ½-wave dipole made of ordinary wire will be shorter than the free-space wavelength for several reasons. First, the physical thickness of the wire makes it look a bit longer electrically than it is physically. The lower the length-to-diameter (l/d) ratio of the wire, the shorter it will be when it is resonant. Second, the dipole’s height above ground also affects its resonant frequency. In addition, nearby conductors, insulation on the wire, the means by which the wire is secured to the insulators and to the feed line also affect the resonant length. For these reasons, a single universal formula for dipole length, such as the common 468/f, is not very useful. You should be start with a length near the free-space length and be prepared to trim the dipole to resonance using an SWR meter or antenna analyzer. The exam only requires that you identify an approximate resonant length for a dipole. Use the free-space length, calculated as 492 / f (in MHz), and select the closest choice. In this case, length (feet) = 492 / 14.250 = 34.5 feet, so select the closest value; 32 feet
  24. G9B11 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
    • (C)
    • In free space, ½ wavelength in feet equals 492 divided by frequency in MHz. If you cut a piece of wire that length, however, you’ll find it is too long to resonate at the desired frequency. A resonant ½-wave dipole made of ordinary wire will be shorter than the free-space wavelength for several reasons. First, the physical thickness of the wire makes it look a bit longer electrically than it is physically. The lower the length-to-diameter (l/d) ratio of the wire, the shorter it will be when it is resonant. Second, the dipole’s height above ground also affects its resonant frequency. In addition, nearby conductors, insulation on the wire, the means by which the wire is secured to the insulators and to the feed line also affect the resonant length. For these reasons, a single universal formula for dipole length, such as the common 468/f, is not very useful. You should be start with a length near the free-space length and be prepared to trim the dipole to resonance using an SWR meter or antenna analyzer. The exam only requires that you identify an approximate resonant length for a dipole. Use the free-space length, calculated as 492 / f (in MHz), and select the closest choice. In this case, length (feet) = 492 / 3.550 = 139 ft. The closest value is 131 feet.
  25. G9B12 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)
    • In free space, ½ wavelength in feet equals 492 divided by frequency in MHz. If you cut a piece of wire that length, however, you’ll find it is too long to resonate at the desired frequency. A resonant ½-wave dipole made of ordinary wire will be shorter than the free-space wavelength for several reasons. First, the physical thickness of the wire makes it look a bit longer electrically than it is physically. The lower the length-to-diameter (l/d) ratio of the wire, the shorter it will be when it is resonant. Second, the dipole’s height above ground also affects its resonant frequency. In addition, nearby conductors, insulation on the wire, the means by which the wire is secured to the insulators and to the feed line also affect the resonant length. For these reasons, a single universal formula for dipole length, such as the common 468/f, is not very useful. You should be start with a length near the free-space length and be prepared to trim the dipole to resonance using an SWR meter or antenna analyzer. The exam only requires that you identify an approximate resonant length for a dipole. Use the free-space length, calculated as 492 / f (in MHz), and select the closest choice. In this case, a 1/4-wavelength antenna would be half as long as a 1/2-wavelength antenna, so calculate length (feet) = 246 / 28.5 = 8.6 ft. The closest value is 8 feet.
  26. G9C01 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)
    • Using larger diameter elements can increase the SWR bandwidth of a parasitic beam antenna, such as a Yagi antenna. The exact length of the elements becomes less critical when larger diameter elements are used.
  27. G9C02 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
    • (B)
    • A Yagi antenna consists of a driven element that is close to 1/2 wavelength long with one or more parasitic elements that help direct the radiated energy in one direction. Directors are parasitic elements that are mounted along the antenna's supporting boom in the preferred direction of radiation and reflectors are mounted in the opposite direction.
  28. G9C03 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
    • (B)
    • In a typical three-element Yagi, the director is 95% the length of the driven element and is placed at the front of the driven element in the direction signals are to be transmitted and received. The reflector element is 105% of the length of the driven element and is placed to the rear. The director is normally the shortest element of a Yagi antenna.
  29. G9C04 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)
    • In a typical three-element Yagi, the director is 95% the length of the driven element and is placed at the front of the driven element in the direction signals are to be transmitted and received. The reflector element is 105% of the length of the driven element and is placed to the rear. The director is normally the shortest element of a Yagi antenna.
  30. G9C05 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)
    • As the boom length of a Yagi is increased and more elements are added, the directivity or gain of the antenna increases. Directivity has an advantage in that it concentrates the transmitted and received signals in the intended direction more than in other directions, thus minimizing interference and improving the signal-to-noise ratio of received signals.
  31. G9C06 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
    • (C)
    • A Yagi antenna provides gain or directivity. Directivity has an advantage in that it concentrates the transmitted and received signals in the intended direction more than in other directions. Directivity applies to receiving as well as transmitting, so the antenna picks up signals better from the desired direction and rejects signals coming from the sides or back of the antenna. This minimizes interference from stations in other directions. This is one important reason for using a Yagi antenna for HF operation, such as on the 20 meter band.
  32. G9C07 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
    • (C)
    • Using a directional antenna helps reduce interference in that it sends the signal in the intended direction rather than off to the side or behind. Most of the radiated signal is sent in the desired direction. This is called the major lobe of the antenna’s radiation pattern. A much smaller amount of the signal is radiated in other directions. If you measure the power radiated at the peak of the major lobe (or in the desired direction) and compare that with the power radiated in the exactly opposite direction, that is the antenna’s “front-to-back ratio.”
  33. G9C08 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
    • (D)
    • A Yagi antenna radiates most of the signal in one direction. This is called the major lobe of the antenna’s radiation pattern. A much smaller amount of the signal is radiated in other directions.
  34. G9C09 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)
    • The maximum theoretical gain of a three-element Yagi antenna is 9.7 dBi. dBi means “decibels with respect to an isotropic antenna." An isotropic antenna is one that radiates equally in all possible directions.
  35. G9C10 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
    • (D)
    • All of these choices affect a Yagi antenna’s forward gain, front-to-back ratio, and SWR bandwidth. As you might imagine, adjusting an antenna design for the desired combination of these three important parameters can be a complicated procedure. Computer modeling programs greatly simplify this process.
  36. G9C11 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 gamma match transforms the relatively low feed point impedance of a Yagi’s driven element (typically 25 ohms or less) to 50 ohms to match the characteristic impedance of common coaxial feed lines.
  37. G9C12 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)
    • One major advantage of the gamma match is that the driven element does not have to be insulated from the antenna’s boom. This simplifies mounting the element and leads to a sturdier antenna.
  38. G9C13 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)
    • All of the elements of a quad antenna are square-shaped loops. The entire driven element of a quad antenna is approximately a full wavelength, so each of the element’s four sides is approximately 1/4 wavelength long.
  39. G9C14 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
    • (B)
    • A two-element quad (or delta loop) antenna has about the same gain as a three-element Yagi.
  40. G9C15 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
    • (B)
    • All of the elements of a quad antenna are square-shaped loops. The reflector element of a quad antenna is slightly more than a full wavelength (about 5% longer), so each of the four sides is slightly longer than 1/4 wavelength.
  41. G9C16 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
    • (D)
    • Like the quad antenna, a delta-loop antenna uses loop elements that are approximately one wavelength long. The difference is that delta loop elements are triangle-shaped loops, rather than square. The gain of a delta loop is about the same as a quad antenna when the number of elements and spacing are the same.
  42. G9C17 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
    • (B)
    • A delta-loop antenna has a driven element that is a triangle-shaped loop. It also uses a triangle-shaped loop reflector and sometimes one or more directors. The entire driven element of a delta-loop antenna is approximately a full wavelength, so each of the 3 sides is approximately 1/3 wavelength long.
  43. G9C18 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)
    • The polarization of signals radiated by a vertically-oriented 1-wavelength loop is determined by where the feed point is located. If the feed point is located at the top or bottom of the loop, the polarization of the radiated signal is horizontal. If the feed point is located on either side of the loop, the polarization of the radiated signal is vertical.
  44. G9C19 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
    • (D)
    • All of the elements of a quad antenna are square-shaped loops. The reflector element of a quad antenna is slightly more than a full wavelength (about 5% longer), so each of the four sides is slightly longer than 1/4 wavelength.
  45. G9C20 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
    • (B)
    • “Stacking” two Yagis the proper distance apart combines their signals so that the forward gain of the resulting array is doubled, a gain of 3 dB.
  46. G9D01 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
    • (D)
    • NVIS, or Near Vertical Incidence Skywave, refers to a communications system that uses low, horizontally polarized antennas such as dipoles that radiate most of their signal at high vertical angles. These signals are then reflected back to Earth in a region centered on the antenna. NVIS allows stations to communicate within the skip zone for lower-angle sky wave propagation.
  47. G9D02 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
    • (B)
    • NVIS, or Near Vertical Incidence Skywave, refers to a communications system that uses low, horizontally polarized antennas such as dipoles that radiate most of their signal at high vertical angles. These signals are then reflected back to Earth in a region centered on the antenna. NVIS allows stations to communicate within the skip zone for lower-angle sky wave propagation.
  48. G9D03 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
    • (D)
    • NVIS must be mounted close to the ground so that the radiated signal is maximized at high vertical angles.
  49. G9D04 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)
    • Traps consist of parallel LC circuits that act as electrical switches to isolate sections of the antenna at their resonant frequencies. At other frequencies, traps act as inductance or capacitance. This changes the antenna’s “electrical length” automatically, allowing it to operate on two or more bands.
  50. G9D05 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
    • (D)
    • The increase in gain for a vertical stack of Yagi antennas results from narrowing the vertical width of the main or major lobe of a single antenna’s radiation pattern. The narrower lobe results in stronger received signals and less received noise at angles away from the peak of the main lobe.
  51. G9D06 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 log periodic antenna is designed to provide consistent gain and feed point impedance over a wide frequency range.
  52. G9D07 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)
    • The name “log-periodic” refers to the ratio of length and spacing between adjacent elements of the antenna. By designing the antenna entirely in terms of ratios, the antenna’s performance becomes independent of frequency over a wide range
  53. G9D08 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
    • (B)
    • The Beverage antenna is used for receiving because it rejects noise and signals from unwanted directions, increasing the received signal-to-noise ratio for better copying ability. It is not used for transmitting because it is quite inefficient compared to most transmitting antennas.
  54. G9D09 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
    • (B)
    • Beverage antennas are most effective at frequencies of 7 MHz and below. This includes the amateur MF 160 meter band, as well as the lower HF bands of 80, 60, and 40 meters.
  55. G9D10 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
    • (D)
    • The typical Beverage antenna consists of a wire 1 wavelength or more long, supported from 6 to 10 feet above ground. It is terminated with a 300 to 1000-ohm resistor connected to a ground rod at the end of the antenna in the direction of preferred reception. It is highly directional, rejecting noise and signals from unwanted directions.
  56. G9D11 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
    • (D)
    • Multiband antennas by definition are designed to radiate well on several frequencies. Most HF amateur bands are harmonically-related, meaning their frequencies are integral multiples of each other--3.5, 7, 14, 21, and 28 MHz. While this is convenient in that one antenna can be used on separate bands, harmonics of a fundamental signal on, for example 7 MHz, will be radiated well by a multiband antenna on 14, 21, and 28 MHz.

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