Chapter 1, Electromagnetic waves Flashcards
A transmitted radio wave will have a plane
wavefront
In the far field
The lowest layer in the earth’s atmosphere is
The troposphere.
A radio wave at 115 kHz is most likely to
propagate as
A ground wave
The height of the E-layer is approximately
100 km
When a large mass of cold air is overrun by warm air the temperature inversion produced will often result in
Tropospheric ducting
Ionospheric sounding is used to determine
The critical angle and maximum usable frequency for a given path
The critical frequency is directly proportional to
The square root of the electron density
The MF range extends from
300 kHz to 3 MHz
A radio wave has a frequency of 15 MHz.
What is the wavelength of the wave?
20 m
Which one of the following gives the velocity at which a radio wave propagates?
3 × 108 m/s
The main cause of ionisation in the upper
atmosphere is
Solar radiation
The F2-layer is
The same height at the equator as at the
poles
The free-space path loss experienced by a
radio wave
Increases with both frequency and distance
For a given HF radio path, the MUF changes most rapidly at
Dawn and dusk
Radio waves tend to propagate mainly as line-of-sight signals in the
HF band
In the HF band, radio waves tend to propagate over long distances as
Ionospheric waves
The maximum distance that can be achieved from a single-hop reflection from the F-layer
3500 to 5000 km
The F1- and F2-layers combine
During the night
The path of a VHF or UHF radio wave can be bent by a sharply defined obstruction such as a building or a mountaintop. This phenomenon is known as
Diffraction
Radio waves at HF can be subject to reflections in ionized regions of the upper atmosphere. This phenomenon is known as
Ionospheric reflection
Radio waves at UHF can sometimes be
subject to dispersion over a wide angle in
regions of humid air in the atmosphere. This phenomenon is known as
Ionospheric reflection
Radio waves at VHF and UHF can sometimes
propagate for long distances in the lower
atmosphere due to the presence of a temperature inversion. This phenomenon is known as
Atmospheric ducting
The layer in the atmosphere that is mainly
responsible for the absorption of MF radio waves during the day is
The D-layer
The layer in the atmosphere that is mainly
responsible for the reflection of HF radio
waves during the day are
The E-layer
On the sunlit side of the Earth, an M-class
solar flare is likely to cause
Minor or moderate degradation of HF radio communication
Low Earth orbiting (LEO) satellites operate at an altitude of approximately
485 miles
