13
2-48. What effect can the sporadic-E layer have
on the propagation of sky waves?
1. Causes multipath interference
2. Permits long distance communications
at unusually high frequencies
3. Permits short-distance communications
in the normal skip zone
4. Each of the above
2-49. A sudden and intense burst of ultraviolet
light is especially disruptive to
communications in which of the following
frequency bands?
1. Hf
2. Mf
3. Lf
4. Vlf
2-50. The density of what ionosphere layer
increases because of a violent eruption on
the surface of the sun?
1. D
2. E
3.
F1
4.
F2
2-51. Which irregular variation in ionospheric
conditions can cause a waiting period of
several days before communications
return to normal?
1. Sporadic E
2. Ionospheric storms
3. Sudden ionospheric disturbance
4. Each of the above
2-52. For a radio wave entering the atmosphere
of the earth at a given angle, the highest
frequency at which refraction will occur is
known by which of the following terms?
1. Usable frequency
2. Refraction frequency
3. Maximum usable frequency
4. Optimum working frequency
2-53. The most consistent communications can
be expected at which of the following
frequencies?
1. Critical frequency
2. Maximum usable frequency
3. Maximum working frequency
4. Optimum working frequency
2-54. If the optimum working frequency for a
communications link is 4,250 kHz, what is
the approximate maximum usable
frequency?
1. 4,500 kHz
2. 5,000 kHz
3. 5,500 kHz
4. 6,000 kHz
2-55. In determining the success of radio
transmission, which of the following
factors is the LEAST predictable?
1. Antenna capabilities
2. Weather conditions along the path of
communication
3. Density of ionized layers
4. Presence of ionized layers
2-56. At frequencies above 100 MHz, the
greatest attenuation of rf energy from
raindrops is caused by which of the
following factors?
1. Ducting
2. Heat loss
3. Scattering
4. Absorption
2-57. Under certain conditions, such as ducting,
line-of-sight radio waves often propagate
for distances far beyond their normal
ranges because of which of the following
factors?
1. Low cloud masses
2. Ionospheric storms
3. Temperature inversions
4. Frequency fluctuations
