87 lines
5.1 KiB
Markdown
87 lines
5.1 KiB
Markdown
E9C Practical wire antennas; folded dipoles; phased arrays; effects of ground near antennas
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- [[E9C01]] (D)
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What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase? #card
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- [[A.]] Cardioid
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- [[B.]] Omni-directional
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- [[C.]] A figure-eight broadside to the axis of the array
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- [[D.]] A figure-eight oriented along the axis of the array
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- [[E9C02]] (A)
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What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase? #card
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- [[A.]] Cardioid
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- [[B.]] A figure-eight end-fire along the axis of the array
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- [[C.]] A figure-eight broadside to the axis of the array
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- [[D.]] Omni-directional
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- [[E9C03]] (C)
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What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase? #card
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- [[A.]] Omni-directional
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- [[B.]] Cardioid
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- [[C.]] A figure-eight broadside to the axis of the array
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- [[D.]] A figure-eight end-fire along the axis of the array
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- [[E9C04]] (B)
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What happens to the radiation pattern of an unterminated long wire antenna as the wire length is increased? #card
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- [[A.]] Fewer lobes form with the major lobes increasing closer to broadside to the wire
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- [[B.]] Additional lobes form with major lobes increasingly aligned with the axis of the antenna
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- [[C.]] The elevation angle increases, and the front-to-rear ratio decreases
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- [[D.]] The elevation angle increases, while the front-to-rear ratio is unaffected
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- [[E9C05]] (A)
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What is the purpose of feeding an off-center-fed dipole (OCFD) between the center and one end instead of at the midpoint? #card
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- [[A.]] To create a similar feed point impedance on multiple bands
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- [[B.]] To suppress off-center lobes at higher frequencies
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- [[C.]] To resonate the antenna across a wider range of frequencies
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- [[D.]] To reduce common-mode current coupling on the feed line shield
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- [[E9C06]] (B)
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What is the effect of adding a terminating resistor to a rhombic or long-wire antenna? #card
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- [[A.]] It reflects the standing waves on the antenna elements back to the transmitter
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- [[B.]] It changes the radiation pattern from bidirectional to unidirectional
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- [[C.]] It changes the radiation pattern from horizontal to vertical polarization
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- [[D.]] It decreases the ground loss
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- [[E9C07]] (A)
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What is the approximate feed point impedance at the center of a two-wire half-wave folded dipole antenna? #card
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- [[A.]] 300 ohms
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- [[B.]] 72 ohms
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- [[C.]] 50 ohms
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- [[D.]] 450 ohms
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- [[E9C08]] (C)
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What is a folded dipole antenna? #card
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- [[A.]] A dipole one-quarter wavelength long
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- [[B.]] A center-fed dipole with the ends folded down 90 degrees at the midpoint of each side
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- [[C.]] A half-wave dipole with an additional parallel wire connecting its two ends
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- [[D.]] A dipole configured to provide forward gain
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- [[E9C09]] (A)
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Which of the following describes a G5RV antenna? #card
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- [[A.]] A wire antenna center-fed through a specific length of open-wire line connected to a balun and coaxial feed line
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- [[B.]] A multi-band trap antenna
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- [[C.]] A phased array antenna consisting of multiple loops
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- [[D.]] A wide band dipole using shorted coaxial cable for the radiating elements and fed with a 4:1 balun
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- [[E9C10]] (B)
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Which of the following describes a Zepp antenna? #card
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- [[A.]] A horizontal array capable of quickly changing the direction of maximum radiation by changing phasing lines
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- [[B.]] An end-fed half-wavelength dipole
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- [[C.]] An omni-directional antenna commonly used for satellite communications
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- [[D.]] A vertical array capable of quickly changing the direction of maximum radiation by changing phasing lines
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- [[E9C11]] (D)
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How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus soil? #card
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- [[A.]] Radiation at low angles decreases
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- [[B.]] Additional lobes appear at higher elevation angles
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- [[C.]] Separate elevation lobes will combine into a single lobe
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- [[D.]] Radiation at low angles increases
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- [[E9C12]] (C)
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Which of the following describes an extended double Zepp antenna? #card
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- [[A.]] An end-fed full-wave dipole antenna
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- [[B.]] A center-fed 1.5-wavelength dipole antenna
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- [[C.]] A center-fed 1.25-wavelength dipole antenna
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- [[D.]] An end-fed 2-wavelength dipole antenna
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- [[E9C13]] (B)
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How does the radiation pattern of a horizontally polarized antenna vary with increasing height above ground? #card
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- [[A.]] The takeoff angle of the lowest elevation lobe increases
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- [[B.]] The takeoff angle of the lowest elevation lobe decreases
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- [[C.]] The horizontal beamwidth increases
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- [[D.]] The horizontal beamwidth decreases
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- [[E9C14]] (B)
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How does the radiation pattern of a horizontally-polarized antenna mounted above a long slope compare with the same antenna mounted above flat ground? #card
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- [[A.]] The main lobe takeoff angle increases in the downhill direction
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- [[B.]] The main lobe takeoff angle decreases in the downhill direction
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- [[C.]] The horizontal beamwidth decreases in the downhill direction
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- [[D.]] The horizontal beamwidth increases in the uphill direction
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