10 2-18.   Electrically charged particles that affect the propagation of radio waves are found in what atmospheric layer? 1.   Troposphere 2.   Ionosphere 3.   Chronosphere 4.   Stratosphere 2-19.   Most weather phenomena take place in which of the following region of the atmosphere? 1.   Troposphere 2.   Ionosphere 3.   Chronosphere 4.   Stratosphere 2-20.   Radio wave propagation has the least effect because of its constancy on which of the following atmospheric layers? 1.   Troposphere 2.   Ionosphere 3.   Chronosphere 4.   Stratosphere 2-21.   Long range, surface-wave communications are best achieved when the signal is transmitted over seawater with (a) what polarization at (b) what relative frequency? 1.   (a) Vertical (b) Low 2.   (a) Vertical (b) High 3.   (a) Horizontal (b) High 4.   (a) Horizontal (b) Low 2-22.   The Navy’s long-range vlf broadcasts are possible because of the advantages of which of the following types of propagation? 1.   Diffraction 2.   Ionospheric refraction 3.   Repeated reflection and refraction 4.   Both 2 and 3 above 2-23.   A space wave (a) is primarily a result of refraction in what atmospheric layer and (b) extends approximately what distance beyond the horizon? 1.   (a) Ionosphere (b) One-tenth farther 2.   (a) Ionosphere (b) One-third farther 3.   (a) Troposphere (b) One-third farther 4.   (a) Troposphere (b) One-tenth farther 2-24.   The signal of a space wave is sometimes significantly reduced at the receiving site because of which of the following interactions? 1.   Space-wave refraction 2.   Space-wave reflections 3.   Ground-wave diffraction 4.   Ground-wave reflections 2-25.   For long-range communications in the hf band, which of the following types of waves is most satisfactory? 1.   Sky wave 2.   Space wave 3.   Surface wave 4.   Reflected ground wave 2-26.   Ionization in the atmosphere is produced chiefly by which of the following types of radiation? 1.   Alpha radiation 2.   Cosmic radiation 3.   Infrared radiation 4.   Ultraviolet radiation 2-27.   Ultraviolet waves of higher frequencies produce ionized layers at what relative altitude(s)? 1.   Lower 2.   Higher 3.   Both 1 and 2 above