Chapter 1, Electromagnetic waves Flashcards

1
Q

A transmitted radio wave will have a plane
wavefront

A

In the far field

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2
Q

The lowest layer in the earth’s atmosphere is

A

The troposphere.

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3
Q

A radio wave at 115 kHz is most likely to
propagate as

A

A ground wave

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4
Q

The height of the E-layer is approximately

A

100 km

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5
Q

When a large mass of cold air is overrun by warm air the temperature inversion produced will often result in

A

Tropospheric ducting

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6
Q

Ionospheric sounding is used to determine

A

The critical angle and maximum usable frequency for a given path

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7
Q

The critical frequency is directly proportional to

A

The square root of the electron density

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8
Q

The MF range extends from

A

300 kHz to 3 MHz

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9
Q

A radio wave has a frequency of 15 MHz.
What is the wavelength of the wave?

A

20 m

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10
Q

Which one of the following gives the velocity at which a radio wave propagates?

A

3 × 108 m/s

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11
Q

The main cause of ionisation in the upper
atmosphere is

A

Solar radiation

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12
Q

The F2-layer is

A

The same height at the equator as at the
poles

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13
Q

The free-space path loss experienced by a
radio wave

A

Increases with both frequency and distance

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14
Q

For a given HF radio path, the MUF changes most rapidly at

A

Dawn and dusk

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15
Q

Radio waves tend to propagate mainly as line-of-sight signals in the

A

HF band

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16
Q

In the HF band, radio waves tend to propagate over long distances as

A

Ionospheric waves

17
Q

The maximum distance that can be achieved from a single-hop reflection from the F-layer

A

3500 to 5000 km

18
Q

The F1- and F2-layers combine

A

During the night

19
Q

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

A

Diffraction

20
Q

Radio waves at HF can be subject to reflections in ionized regions of the upper atmosphere. This phenomenon is known as

A

Ionospheric reflection

21
Q

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

A

Ionospheric reflection

22
Q

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

A

Atmospheric ducting

23
Q

The layer in the atmosphere that is mainly
responsible for the absorption of MF radio waves during the day is

A

The D-layer

24
Q

The layer in the atmosphere that is mainly
responsible for the reflection of HF radio
waves during the day are

A

The E-layer

25
Q

On the sunlit side of the Earth, an M-class
solar flare is likely to cause

A

Minor or moderate degradation of HF radio communication

26
Q

Low Earth orbiting (LEO) satellites operate at an altitude of approximately

A

485 miles