26 4-20.   For ground-wave transmissions, what type of polarization is required? 1.  Vertical 2.  Spherical 3.  Elliptical 4.  Horizontal 4-21.   For high-frequency operation, which of the following antenna polarization patterns is preferred? 1.  Vertically polarized 2.  Spherically polarized 3.  Elliptically polarized 4.  Horizontally polarized 4-22.   Omnidirectional transmission is obtained from which of the following antennas? 1.  Elliptically polarized 2.  Horizontal half-wave 3.  Vertical half-wave 4.  Each of the above 4-23.   With an antenna height of 40 feet and a transmitter frequency of 90 megahertz, which of the following antenna radiation patterns is best for transmitting over bodies of water? 1.  Vertically polarized 2.  Spherically polarized 3.  Elliptically polarized 4.  Horizontally polarized 4-24.   To select a desired signal and discriminate against interfering signals from strong vhf and uhf broadcast transmissions, which of the following actions should you take? 1.  Increase receiver gain 2.  Make the transmitting antenna bi- directional 3.  Use a vertically polarized receiving antenna 4.  Use narrowly directional arrays as receiving antennas 4-25.   A vertically mounted transmission line is LEAST affected by which of the following antenna radiation patterns? 1.  Vertically polarized 2.  Spherically polarized 3.  Horizontally polarized 4.  Elliptically polarized 4-26.   An antenna with which of the following radiation resistance values will exhibit reduced efficiency? 1.    39 ohms 2.    82 ohms 3.  107 ohms 4.  150 ohms 4-27.   An isotropic radiator radiates energy in which of the following patterns? 1.  Vertical 2.  Bi-directional 3.  Unidirectional 4.  Omnidirectional 4-28.   An ordinary flashlight is an example of what type of radiator? 1.  Isotropic 2.  Polarized 3.  Anisotropic 4.  Stroboscopic THIS SPACE LEFT BLANK INTENTIONALLY.