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FCC GENERAL Exam Question Pool. Subelement 3BI. Antennas and Feedlines. ? Questions. --------------------------------------------------- 3BI 1.3 C Why is a Yagi antenna often used for radio communications on the 20-meter wavelength 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 discriminates against interference from other stations off to the side or behind D. It provides the highest possible angle of radiation for the HF bands 3BI 1.7 D What method is best suited to match an unbalanced coaxial feed line to a Yagi antenna? A. "T" match B. Delta match C. Hairpin match D. Gamma match 3BI 1.9 A How can the bandwidth of a parasitic beam antenna be increased? A. Use larger diameter elements B. Use closer element spacing C. Use traps on the elements D. Use tapered-diameter elements 3BI 2.1 C How much gain over a half-wave dipole can a two-element cubical quad antenna provide? A. Approximately 0.6 dB B. Approximately 2 dB C. Approximately 6 dB D. Approximately 12 dB 3BI 3.1 B How long is each side of a cubical quad antenna driven element for 21.4-MHz? A. 1.17 feet B. 11.7 feet C. 47 feet D. 469 feet 3BI 3.2 B How long is each side of a cubical quad antenna driven element for 14.3-MHz? A. 1.75 feet B. 17.6 feet C. 23.4 feet D. 70.3 feet 3BI 3.3 B How long is each side of a cubical quad antenna reflector element for 29.6-MHz? A. 8.23 feet B. 8.7 feet C. 9.7 feet D. 34.8 feet 3BI 3.4 C How long is each leg of a symmetrical delta loop antenna driven element for 28.7-MHz? A. 8.75 feet B. 11.32 feet C. 11.7 feet D. 35 feet 3BI 3.5 C How long is each leg of a symmetrical delta loop antenna driven element for 24.9-M Hz? A. 10.09 feet B. 13.05 feet C. 13.45 feet D. 40.36 feet 3BI 3.6 C How long is each leg of a symmetrical delta loop antenna reflector element for 14.1-MHz? A. 18.26 feet B. 23.76 feet C. 24.35 feet D. 73.05 feet 3BI 3.7 B How long is the driven element of a Yagi antenna for 14.0-MHz? A. Approximately 17 feet B. Approximately 33 feet C. Approximately 35 feet D. Approximately 66 feet 3BI 3.8 B How long is the director element of a Yagi antenna for 21.1-MHz? A. Approximately 42 feet B. Approximately 21 feet C. Approximately 17 feet D. Approximately 10.5 feet 3BI 3.9 C How long is the reflector element of a Yagi antenna for 28.1-MHz? A. Approximately 8.75 feet B. Approximately 16.6 feet C. Approximately 17.5 feet D. Approximately 35 feet 3BI 5.1 D What is the feed-point impedance for a half-wavelength dipole HF antenna suspended horizontally one-quarter wavelength or more above the ground? A. Approximately 50 ohms, resistive B. Approximately 73 ohms, resistive and inductive C. Approximately 50 ohms, resistive and capacitive D. Approximately 73 ohms, resistive 3BI 5.2 B What is the feed-point impedance of a quarter-wavelength vertical HF antenna with a horizontal ground plane? A. Approximately 18 ohms B. Approximately 36 ohms C. Approximately 52 ohms D. Approximately 72 ohms 3BI 5.3 D What is an advantage of downward sloping radials on a ground- plane antenna? A. Sloping the radials downward lowers the radiation angle B. Sloping the radials downward brings the feed-point impedance close to 300 ohms C. Sloping the radials downward allows rainwater to run off the antenna D. Sloping the radials downward brings the feed-point impedance closer to 50 ohms 3BI 5.4 B What happens to the feed-point impedance of a ground-plane antenna when the radials slope downward from the base of the antenna? A. The feed-point impedance decreases B. The feed-point impedance increases C. The feed-point impedance stays the same D. The feed-point impedance becomes purely capacitive 3BI 6.1 C Compared to a dipole antenna, what are the directional radiation characteristics of a cubical quad HF antenna? A. The quad has more directivity in the horizontal plane but less directivity in the vertical plane B. The quad has less directivity in the horizontal plane but more directivity in the vertical plane C. The quad has more directivity in both horizontal and vertical planes D. The quad has less directivity in both horizontal and vertical planes 3BI 6.2 A What is the radiation pattern of an ideal half-wavelength dipole HF antenna? A. If it is installed parallel to the earth, it radiates well in a figure-eight pattern at right angles to the antenna wire B. If it is installed parallel to the earth, it radiates well in a figure-eight pattern off both ends of the antenna wire C. If it is installed parallel to the earth, it radiates equally well in all directions D. If it is installed parallel to the earth, the pattern will have two lobes on one side of the antenna wire, and one larger lobe on the other side 3BI 6.3 B How does proximity to the ground affect the radiation pattern of a horizontal dipole HF antenna? A. If the antenna is too far from the ground, the pattern becomes unpredictable B. If the antenna is less than one-half wavelength from the ground, reflected radio waves from the ground distort the radiation pattern of the antenna C. A dipole antenna's radiation pattern is unaffected by its distance to the ground D. If the antenna is less than one-half wavelength from the ground, radiation off the ends of the wire is reduced 3BI 6.4 C What does the term antenna front-to-back ratio mean? 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 power radiated in the major radiation lobe compared to the power radiated 90 degrees away from that direction 3BI 6.5 D What effect upon the radiation pattern of an HF dipole antenna will a slightly smaller parasitic parallel element located a few feet away in the same horizontal plane have? A. The radiation pattern will not change appreciably B. A major lobe will develop in the horizontal plane, parallel to the two elements C. A major lobe will develop in the vertical plane, away from the ground D. If the spacing is greater than 0.1 wavelength, a major lobe will develop in the horizontal plane to the side of the driven element toward the parasitic element 3BI 6.6 C What is the meaning of the term main lobe as used in reference to a directional antenna? A. The direction of least radiation from an antenna B. The point of maximum current in a radiating antenna element C. The direction of maximum radiated field strength from a radiating antenna D. The maximum voltage standing wave point on a radiating element 3BI 7.1 A Upon what does the characteristic impedance of a parallel-conductor antenna feed line depend? 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 3BI 7.2 B What is the characteristic impedance of various coaxial cables commonly used for antenna feed lines at amateur stations? A. Around 25 and 30 ohms B. Around 50 and 75 ohms C. Around 80 and 100 ohms D. Around 500 and 750 ohms 3BI 7.3 A What effect, if any, does the length of a coaxial cable have upon its characteristic impedance? A. The length has no effect on the characteristic impedance B. The length affects the characteristic impedance primarily above 144 MHz C. The length affects the characteristic impedance primarily below 144 MHz D. The length affects the characteristic impedance at any frequency 3BI 7.4 D What is the characteristic impedance of flat-ribbon TV-type twinlead? A. 50 ohms B. 75 ohms C. 100 ohms D. 300 ohms 3BI 8.4 C What is the cause of power being reflected back down an antenna feed line? 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 3BI 9.3 A What will be the standing wave ratio when a 50 ohm feed line is connected to a resonant antenna having a 200 ohm feed-point impedance? A. 4:1 B. 1:4 C. 2:1 D. 1:2 3BI 9.4 D What will be the standing wave ratio when a 50 ohm feed line is connected to a resonant antenna having a 10 ohm feed-point impedance? A. 2:1 B. 50:1 C. 1:5 D. 5:1 3BI 9.5 C What will be the standing wave ratio when a 50 ohm feed line is connected to a resonant antenna having a 50 ohm feed-point impedance? A. 2:1 B. 50:50 C. 1:1 D. 0:0 3BI 11.1 C How does the characteristic impedance of a coaxial cable affect the amount of attenuation to the RF signal passing through it? A. The attenuation is affected more by the characteristic impedance at frequencies above 144 MHz than at frequencies below 144 MHz B. The attenuation is affected less by the characteristic impedance at frequencies above 144 MHz than at frequencies below 144 MHz C. The attenuation related to the characteristic impedance is about the same at all amateur frequencies below 1.5 GHz D. The difference in attenuation depends on the emission type in use 3BI 11.2 A How does the amount of attenuation to a 2 meter signal passing through a coaxial cable differ from that to a 160 meter signal? A. The attenuation is greater at 2 meters B. The attenuation is less at 2 meters C. The attenuation is the same at both frequencies D. The difference in attenuation depends on the emission type in use 3BI 11.4 D What is the effect on its attenuation when flat-ribbon TV-type twinlead is wet? A. Attenuation decreases slightly B. Attenuation remains the same C. Attenuation decreases sharply D. Attenuation increases 3BI 11.7 B Why might silicone grease or automotive car wax be applied to flat-ribbon TV-type twinlead? A. To reduce "skin effect" losses on the conductors B. To reduce the buildup of dirt and moisture on the feed line C. To increase the velocity factor of the feed line D. To help dissipate heat during high-SWR operation 3BI 11.8 D In what values are RF feed line losses usually expressed? A. Bels/1000 ft B. dB/1000 ft C. Bels/100 ft D. dB/100 ft 3BI 11.10 D As the operating frequency increases, what happens to the dielectric losses in a feed line? A. The losses decrease B. The losses decrease to zero C. The losses remain the same D. The losses increase 3BI 11.12 A As the operating frequency decreases, what happens to the dielectric losses in a feed line? A. The losses decrease B. The losses increase C. The losses remain the same D. The losses become infinite 3BI 12.1 D What condition must be satisfied to prevent standing waves of voltage and current on an antenna feed line? A. The antenna feed point must be at DC ground potential B. The feed line must be an odd number of electrical quarter wavelengths long C. The feed line must be 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 3BI 12.2 A How is an inductively-coupled matching network used in an antenna system consisting of a center-fed resonant dipole and coaxial feed line? A. An inductively coupled matching network is not normally used in a resonant antenna system B. An inductively coupled matching network is used to increase the SWR to an acceptable level C. An inductively coupled matching network can be used to match the unbalanced condition at the transmitter output to the balanced condition required by the coaxial line D. An inductively coupled matching network can be used at the antenna feed point to tune out the radiation resistance 3BI 12.5 D What is an antenna-transmission line mismatch? A. A condition where the feed-point impedance of the antenna does not equal the output impedance of the transmitter B. A condition where the output impedance of the transmitter does not equal the characteristic impedance of the feed line C. A condition where a half-wavelength antenna is being fed with a transmission line of some length other than one-quarter wavelength at the operating frequency D. A condition where the characteristic impedance of the feed line does not equal the feed-point impedance of the antenna -------------------------------------------------- End of Subelement 3BI.