Chapter 1, Electromagnetic waves

Question 1

A transmitted radio wave will have a plane
wavefront

Answer 1

In the far field

Question 2

The lowest layer in the earth’s atmosphere is

Answer 2

The troposphere.

Question 3

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

Answer 3

A ground wave

Question 4

The height of the E-layer is approximately

Answer 4

100 km

Question 5

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

Answer 5

Tropospheric ducting

Question 6

Ionospheric sounding is used to determine

Answer 6

The critical angle and maximum usable frequency for a given path

Question 7

The critical frequency is directly proportional to

Answer 7

The square root of the electron density

Question 8

The MF range extends from

Answer 8

300 kHz to 3 MHz

Question 9

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

Answer 9

20 m

Question 10

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

Answer 10

3 × 108 m/s

Question 11

The main cause of ionisation in the upper
atmosphere is

Answer 11

Solar radiation

Question 12

The F2-layer is

Answer 12

The same height at the equator as at the
poles

Question 13

The free-space path loss experienced by a
radio wave

Answer 13

Increases with both frequency and distance

Question 14

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

Answer 14

Dawn and dusk

Question 15

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

Answer 15

HF band

Question 16

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

Answer 16

Ionospheric waves

Question 17

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

Answer 17

3500 to 5000 km

Question 18

The F1- and F2-layers combine

Answer 18

During the night

Question 19

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

Answer 19

Diffraction

Question 20

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

Answer 20

Ionospheric reflection

Question 21

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

Answer 21

Ionospheric reflection

Question 22

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

Answer 22

Atmospheric ducting

Question 23

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

Answer 23

The D-layer

Question 24

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

Answer 24

The E-layer

Question 25

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

Answer 25

Minor or moderate degradation of HF radio communication

Question 26

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

Answer 26

485 miles