B-007-04: Ionospheric absorption, causes and variation, fading, phase shift, Faraday rotation
B-007-04-01:
What effect does the D region of the ionosphere have on lower frequency HF signals in the daytime?
It absorbs the signals
It bends the radio waves out into space
It refracts the radio waves back to earth
It has little or no effect on 80-metre radio waves
B-007-04-02:
What causes the ionosphere to absorb radio waves?
The ionization of the D region
The presence of ionized clouds in the E region
The splitting of the F region
The weather below the ionosphere
B-007-04-03:
Two or more parts of the radio wave follow different paths during propagation and this may result in phase differences at the receiver. This "change" at the receiver is called:
fading
baffling
absorption
skip
B-007-04-04:
A change or variation in signal strength at the antenna, caused by differences in path lengths, is called:
fading
absorption
fluctuation
path loss
B-007-04-05:
When a transmitted radio signal reaches a station by a one-hop and two-hop skip path, small changes in the ionosphere can cause:
variations in signal strength
consistent fading of received signal
consistently stronger signals
a change in the ground-wave signal
B-007-04-06:
The usual effect of ionospheric storms is to:
cause a fade-out of sky-wave signals
produce extreme weather changes
prevent communications by ground wave
increase the maximum usable frequency
B-007-04-07:
On the VHF and UHF bands, polarization of the receiving antenna is very important in relation to the transmitting antenna, yet on HF bands it is relatively unimportant. Why is that so?
The ionosphere can change the polarization of the signal from moment to moment
The ground wave and the sky wave continually shift the polarization
Anomalies in the earth's magnetic field produce a profound effect on HF polarization
Greater selectivity is possible with HF receivers making changes in polarization redundant
B-007-04-08:
What causes selective fading?
Phase differences between radio wave components of the same transmission, as experienced at the receiving station
Small changes in beam heading at the receiving station
Time differences between the receiving and transmitting stations
Large changes in the height of the ionosphere at the receiving station ordinarily occurring shortly before sunrise and sunset
B-007-04-09:
How does the bandwidth of a transmitted signal affect selective fading?
It is more pronounced at wide bandwidths
It is the same for both wide and narrow bandwidths
Only the receiver bandwidth determines the selective fading effect
It is more pronounced at narrow bandwidths
B-007-04-10:
Polarization change often takes place on radio waves that are propagated over long distances. Which of these does not cause polarization change?
Parabolic interaction
Reflections
Passage through magnetic fields (Faraday rotation)
Refractions
B-007-04-11:
Reflection of a SSB transmission from the ionosphere causes:
little or no phase-shift distortion
phase-shift distortion
signal cancellation at the receiver
a high-pitch squeal at the receiver
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