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FCC EXTRA Exam Question Pool. Subelement 4BI. Antennas and Feedlines. 4 Questions. --------------------------------------------------- 4BI 1A1 A What is an isotropic radiator? A. A hypothetical, omnidirectional antenna B. In the northern hemisphere, an antenna whose directive pattern is constant in southern directions C. An antenna high enough in the air that its directive pattern is substantially unaffected by the ground beneath it D. An antenna whose directive pattern is substantially unaffected by the spacing of the elements 4BI 1B1 A When is it useful to refer to an isotropic radiator? A. When comparing the gains of directional antennas B. When testing a transmission line for for standing wave ratio C. When (in the northern hemisphere) directing the transmission in a southerly direction D. When using a dummy load to tune a transmitter 4BI 1B2 D What theoretical reference antenna provides a comparison for antenna measurements? A. Quarter-wave vertical B. Yagi C. Bobtail curtain D. Isotropic radiator 4BI 1B3 B What purpose does an isotropic radiator serve? A. It is used to compare signal strengths (at a distant point) of different transmitters B. It is used as a reference for antenna gain measurements C. It is used as a dummy load for tuning transmitters D. It is used to measure the standing wave-wave-ratio on a transmission line 4BI 1B4 B How much gain does a 1/2-wavelength dipole have over an isotropic radiator? A. About 1.5 dB B. About 2.1 dB C. About 3.0 dB D. About 6.0 dB 4BI 1B5 A How much gain does an antenna have over a 1/2-wavelength dipole when it has 6 dB gain over an isotropic radiator? A. About 3.9 dB B. About 6.0 dB C. About 8.1 dB D. About 10.0 dB 4BI 1B6 B How much gain does an antenna have over a 1/2-wavelength dipole when it has 12 dB gain over an isotropic radiator? A. About 6.1 dB B. About 9.9 dB C. About 12.0 dB D. About 14.1 dB 4BI 1C1 D What is the antenna pattern for an isotropic radiator? A. A figure-8 B. A unidirectional cardioid C. A parabola D. A sphere 4BI 1C2 D What type of directivity pattern does an isotropic radiator have? A. A figure-8 B. A unidirectional cardioid C. A parabola D. A sphere 4BI 2A1 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? A. Unidirectional cardioid B. Omnidirectional C. Figure-8 broadside to the antennas D. Figure-8 end-fire in line with the antennas 4BI 2A2 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. Unidirectional cardioid B. Figure-8 end-fire C. Figure-8 broadside D. Omnidirectional 4BI 2A3 C What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/2 wavelength apart and fed in phase? A. Omnidirectional B. Cardioid unidirectional C. Figure-8 broadside to the antennas D. Figure-8 end-fire in line with the antennas 4BI 2A4 C How far apart should two 1/4 wavelength vertical antennas be spaced in order to produce a figure-8 pattern that is broadside to the plane of the verticals when fed in phase? A. 1/8 wavelength B. 1/4 wavelength C. 1/2 wavelength D. 1 wavelength 4BI 2A5 A How many 1/2 wavelengths apart should two 1/4 wavelength vertical antennas be spaced to produce a figure-8 pattern that is in line with the vertical antennas when they are fed 180 degrees out of phase? A. One half wavelength apart B. Two half wavelengths apart C. Three half wavelengths apart D. Four half wavelengths apart 4BI 2A6 D What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/4 wavelength apart and fed 180 degrees out of phase? A. Omnidirectional B. Cardioid unidirectional C. Figure-8 broadside to the antennas D. Figure-8 end-fire in line with the antennas 4BI 2A7 D What is the radiation pattern for two 1/4-wavelength vertical antennas spaced 1/8 wavelength apart and fed 180 degrees out of phase? A. Omnidirectional B. Cardioid unidirectional C. Figure-8 broadside to the antennas D. Figure-8 end-fire in line with the antennas 4BI 2A8 A What is the radiation pattern for two 1/4-wavelength vertical antennas spaced 1/8 wavelength apart and fed in phase? A. Omnidirectional B. Cardioid unidirectional C. Figure-8 broadside to the antennas D. Figure-8 end-fire in line with the antennas 4BI 2A9 B What is the radiation pattern for two 1/4 wavelength vertical antennas spaced 1/4 wavelength apart and fed in phase? A. Substantially unidirectional B. Elliptical C. Cardioid unidirectional D. Figure-8 end-fire in line with the antennas 4BI 3A1 B What is a resonant rhombic antenna? A. A unidirectional antenna, each of whose sides is equal to half a wavelength and which is terminated in a resistance equal to its characteristic impedance B. A bidirectional antenna open at the end opposite that to which the transmission line is connected and with each side approximately equal to one wavelength C. An antenna with an LC network at each vertex (other than that to which the transmission line is connected) tuned to resonate at the operating frequency D. A high-frequency antenna, each of whose sides contains traps for changing the resonance to match the band in use 4BI 3B1 A What is a nonresonant rhombic antenna? A. A unidirectional antenna terminated in a resistance equal to its characteristic impedance B. An open-ended bidirectional antenna C. An antenna resonant at approximately double the frequency of the intended band of operation D. A horizontal triangular antenna consisting of two adjacent sides and the long diagonal of a resonant rhombic antenna 4BI 3B2 A What are the advantages of a nonresonant rhombic antenna? A. Wide frequency range, high gain and high front-to-back ratio B. High front-to-back ratio, compact size and high gain C. Unidirectional radiation pattern, high gain and compact size D. Bidirectional radiation pattern, high gain and wide frequency range 4BI 3B3 D What are the disadvantages of a nonresonant rhombic antenna? A. It requires a large area for proper installation and has a narrow bandwidth B. It requires a large area for proper installation and has a low front-to-back ratio C. It requires a large amount of aluminum tubing and has a low front-to-back ratio D. It requires a large area and four sturdy supports for proper installation 4BI 3B4 D What is the characteristic impedance at the input of a nonresonant rhombic antenna? A. 50 to 55 ohms B. 70 to 75 ohms C. 300 to 350 ohms D. 700 to 800 ohms 4BI 3C1 B What is the effect of a terminating resistor on a rhombic antenna? A. It reflects the standing waves on the antenna elements back to the transmitter B. It changes the radiation pattern from essentially bidirectional to essentially unidirectional C. It changes the radiation pattern from horizontal to vertical polarization D. It decreases the ground loss 4BI 3C2 C What should be the value of the terminating resistor on a rhombic antenna? A. About 50 ohms B. About 75 ohms C. About 800 ohms D. About 1800 ohms 4BI 4A1 A What factors determine the receiving antenna gain required at an amateur station in earth operation? A. Height, transmitter power and antennas of satellite B. Length of transmission line and impedance match between receiver and transmission line C. Preamplifier location on transmission line and presence or absence of RF amplifier stages D. Height of earth antenna and satellite orbit 4BI 4A2 A What factors determine the EIRP required by an amateur station in earth operation? A. Satellite antennas and height, satellite receiver sensitivity B. Path loss, earth antenna gain, signal-to-noise ratio C. Satellite transmitter power and orientation of ground receiving antenna D. Elevation of satellite above horizon, signal-to-noise ratio, satellite transmitter power 4BI 4A3 B What factors determine the EIRP required by an amateur station in telecommand operation? A. Path loss, earth antenna gain, signal-to-noise ratio B. Satellite antennas and height, satellite receiver sensitivity C. Satellite transmitter power and orientation of ground receiving antenna D. Elevation of satellite above horizon, signal-to-noise ratio, satellite transmitter power 4BI 4A4 C How does the gain of a parabolic dish type antenna change when the operating frequency is doubled? A. Gain does not change B. Gain is multiplied by 0.707 C. Gain increases 6 dB D. Gain increases 3 dB 4BI 4B1 D What happens to the beamwidth of an antenna as the gain is increased? A. The beamwidth increases geometrically as the gain is increased B. The beamwidth increases arithmetically as the gain is increased C. The beamwidth is essentially unaffected by the gain of the antenna D. The beamwidth decreases as the gain is increased 4BI 4B2 B What is the beamwidth of a symmetrical pattern antenna with a gain of 20 dB as compared to an isotropic radiator? A. 10.1 degrees B. 20.3 degrees C. 45.0 degrees D. 60.9 degrees 4BI 4B3 B What is the beamwidth of a symmetrical pattern antenna with a gain of 30 dB as compared to an isotropic radiator? A. 3.2 degrees B. 6.4 degrees C. 37 degrees D. 60.4 degrees 4BI 4B4 C What is the beamwidth of a symmetrical pattern antenna with a gain of 15 dB as compared to an isotropic radiator? A. 72 degrees B. 52 degrees C. 36.1 degrees D. 3.61 degrees 4BI 4B5 D What is the beamwidth of a symmetrical pattern antenna with a gain of 12 dB as compared to an isotropic radiator? A. 34.8 degrees B. 45.0 degrees C. 58.0 degrees D. 51.0 degrees 4BI 4C1 C How is circular polarization produced using linearly-polarized antennas? A. Stack two Yagis, fed 90 degrees out of phase, to form an array with the respective elements in parallel planes B. Stack two Yagis, fed in phase, to form an array with the respective elements in parallel planes C. Arrange two Yagis perpendicular to each other, with the driven elements in the same plane, and fed 90 degrees out of phase D. Arrange two Yagis perpendicular to each other, with the driven elements in the same plane, and fed in phase 4BI 4C2 C Why does an antenna system for earth operation (for communications through a satellite) need to have rotators for both azimuth and elevation control? A. In order to point the antenna above the horizon to avoid terrestrial interference B. Satellite antennas require two rotators because they are so large and heavy C. In order to track the satellite as it orbits the earth D. The elevation rotator points the antenna at the satellite and the azimuth rotator changes the antenna polarization 4BI 5.1 B What term describes a method used to match a high-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 on each side of the driven element center? A. The gamma matching system B. The delta matching system C. The omega matching system D. The stub matching system 4BI 5.2 A What term describes an unbalanced feed system in which the driven element is fed both at the center of that element and a fraction of a wavelength to one side of center? A. The gamma matching system B. The delta matching system C. The omega matching system D. The stub matching system 4BI 5.3 D What term describes a method of antenna impedance matching that uses a short section of transmission line connected to the antenna feed line near the antenna and perpendicular to the feed line? A. The gamma matching system B. The delta matching system C. The omega matching system D. The stub matching system 4BI 5.4 B What should be the approximate capacitance of the resonating capacitor in a gamma matching circuit on a 1/2 wavelength dipole antenna for the 20-meter wavelength band? A. 70 pF B. 140 pF C. 200 pF D. 0.2 pF 4BI 5.5 A What should be the approximate capacitance of the resonating capacitor in a gamma matching circuit on a 1/2 wavelength dipole antenna for the 10-meter wavelength band? A. 70 pF B. 140 pF C. 200 pF D. 0.2 pF 4BI 6A1 C What kind of impedance does a 1/8-wavelength transmission line present to a generator when the line is shorted at the far end? A. A capacitive reactance B. The same as the characteristic impedance of the line C. An inductive reactance D. The same as the input impedance to the final generator stage 4BI 6A2 C What kind of impedance does a 1/8-wavelength transmission line present to a generator when the line is open at the far end? A. The same as the characteristic impedance of the line B. An inductive reactance C. A capacitive reactance D. The same as the input impedance to the final generator stage 4BI 6B1 A What kind of impedance does a 1/4-wavelength transmission line present to a generator when the line is shorted at the far end? A. A very high impedance B. A very low impedance C. The same as the characteristic impedance of the transmission line D. The same as the generator output impedance 4BI 6B2 B What kind of impedance does a 1/4-wavelength transmission line present to a generator when the line is open at the far end? A. A very high impedance B. A very low impedance C. The same as the characteristic impedance of the line D. The same as the input impedance to the final generator stage 4BI 6C1 C What kind of impedance does a 3/8-wavelength transmission line present to a generator when the line is shorted at the far end? A. The same as the characteristic impedance of the line B. An inductive reactance C. A capacitive reactance D. The same as the input impedance to the final generator stage 4BI 6C2 C What kind of impedance does a 3/8-wavelength transmission line present to a generator when the line is open at the far end? A. A capacitive reactance B. The same as the characteristic impedance of the line C. An inductive reactance D. The same as the input impedance to the final generator stage 4BI 6D1 B What kind of impedance does a 1/2-wavelength transmission line present to a generator when the line is shorted at the far end? A. A very high impedance B. A very low impedance C. The same as the characteristic impedance of the line D. The same as the output impedance of the generator 4BI 6D2 A What kind of impedance does a 1/2-wavelength transmission line present to a generator when the line is open at the far end? A. A very high impedance B. A very low impedance C. The same as the characteristic impedance of the line D. The same as the output impedance of the generator -------------------------------------------------- End of Subelement 4BI.