Chapter 1

Question 1

What type of waves are radio waves?

Answer 1

Electromagnetic (EM) waves.

Question 2

At what speed do radio waves travel?

Answer 2

At the speed of light, 3 x 10^8 m/s.

Question 3

Do radio waves require a medium to travel?

Answer 3

No, they can travel in a vacuum.

Question 4

Define a ‘cycle’ in wave terminology.

Answer 4

One complete waveform.

Question 5

Define ‘frequency’ (f).

Answer 5

The number of cycles per second, measured in Hertz (Hz).

Question 6

Define ‘wavelength’ ($\lambda$).

Answer 6

The physical length of one complete cycle.

Question 7

Define ‘amplitude’ in the context of radio waves.

Answer 7

The signal strength, which is related to power.

Question 8

What is the formula relating wavelength ($\lambda$), frequency (f), and the speed of light (c)?

Answer 8

wavelength = speed of light / frequency
wavelength = c / f

Question 9

What is the relationship between frequency and wavelength?

Answer 9

They are inversely proportional.

Question 10

What happens to wavelength when frequency is increased?

Answer 10

Wavelength decreases.

Question 11

What happens to wavelength when frequency is decreased?

Answer 11

Wavelength increases.

Question 12

What is the total length of a half-wave dipole antenna in relation to wavelength?

Answer 12

The total length is half a wavelength

Question 13

What is the length of each arm of a half-wave dipole antenna in relation to wavelength?

Answer 13

Each arm is a quarter of a wavelength.

Question 14

In which direction is the radiation from a half-wave dipole antenna at its maximum?

Answer 14

Perpendicular to the antenna.

Question 15

In which direction is the radiation from a half-wave dipole antenna at its minimum?

Answer 15

Above and below the antenna (off the ends).

Question 16

Define an ‘omnidirectional’ radiation pattern.

Answer 16

A pattern with equal radiation in all directions in the horizontal plane.

Question 17

What are the components of a ‘directional’ radiation pattern?

Answer 17

A concentrated beam, consisting of a main lobe and side lobes.

Question 18

What defines the polarisation of an electromagnetic wave?

Answer 18

The direction of its electric field.

Question 19

What type of polarisation does a vertical antenna produce?

Answer 19

A vertically polarised wave.

Question 20

What type of polarisation does a horizontal antenna produce?

Answer 20

A horizontally polarised wave.

Question 21

What is the requirement for polarisation between a transmitting and receiving antenna?

Answer 21

Their polarisation must match for optimal reception.

Question 22

What causes antenna shadowing?

Answer 22

The signal being blocked by the airframe, terrain, or structures.

Question 23

During which flight manoeuvres does antenna shadowing commonly occur?

Answer 23

During banking and turning.

Question 24

What is multipath propagation?

Answer 24

When a signal reaches the receiver via multiple different paths.

Question 25

What three phenomena cause multipath propagation?

Answer 25

Reflection, refraction, and diffraction.

Question 26

What are the three main results of multipath propagation?

Answer 26

Phase differences, variation in signal strength, and bearing errors (in ADF/VOR).

Question 27

What happens when two signals arrive in phase due to superposition?

Answer 27

A stronger signal is produced.

Question 28

What happens when two signals arrive out of phase due to superposition?

Answer 28

A weaker signal is produced.

Question 29

What is the result of two signals arriving $180^{\circ}$ out of phase?

Answer 29

Signal cancellation.

Question 30

Define 'fading' of a radio signal.

Answer 30

A random variation in signal strength.

Question 31

What are the primary causes of fading?

Answer 31

Multipath, interaction between skywave and surface wave, and weather.

Question 32

At what time of day is fading more common?

Answer 32

At night.

Question 33

Which two frequency bands are mainly affected by fading?

Answer 33

HF (High Frequency) and MF (Medium Frequency).

Question 34

What is the approximate altitude range of the ionosphere?

Answer 34

Approximately 60 to 400 km.

Question 35

What causes the ionisation of the ionosphere?

Answer 35

Solar radiation.

Question 36

Which frequency band's propagation is most significantly affected by the ionosphere?

Answer 36

HF (High Frequency).

Question 37

Which ionospheric layer exists only during the day and causes absorption?

Answer 37

The D layer.

Question 38

What happens to the D layer at night?

Answer 38

It disappears.

Question 39

Which ionospheric layer is the most important for HF propagation?

Answer 39

The F layer.

Question 40

During the day, the F layer splits into which two sub-layers?

Answer 40

The F1 and F2 layers.

Question 41

At night, what happens to the F1 and F2 layers?

Answer 41

They merge into a single F2 layer.

Question 42

What is the general rule for selecting HF frequencies based on the time of day?

Answer 42

Sun up, frequency up; sun down, frequency down.

Question 43

Which frequency bands primarily use space waves?

Answer 43

VHF, UHF, and SHF.

Question 44

What is the propagation characteristic of space waves?

Answer 44

They are line-of-sight.

Question 45

What physical feature limits the range of space waves?

Answer 45

The curvature of the Earth.

Question 46

What is the formula for calculating the maximum theoretical range of space waves?

Answer 46

$D = 1.23(\sqrt{h_{Tx}} + \sqrt{h_{Rx}})$

Question 47

Which frequency bands primarily use ground (surface) waves?

Answer 47

VLF, LF, and MF.

Question 48

How do ground waves propagate relative to the Earth's surface?

Answer 48

They follow the curvature of the Earth.

Question 49

Which polarisation is required for ground waves?

Answer 49

Vertical polarisation.

Question 50

Which common navigation aid uses ground waves?

Answer 50

The NDB (Non-Directional Beacon).

Question 51

Which propagation type is used for long-range HF communications?

Answer 51

Sky waves.

Question 52

What phenomenon allows sky waves to travel long distances?

Answer 52

Refraction by the ionosphere.

Question 53

Why are sky waves considered unreliable for radio navigation?

Answer 53

Due to the constantly changing state of the ionosphere.

Question 54

Define 'critical angle' for skywave propagation.

Answer 54

The highest angle to the vertical at which a wave of a specific frequency can be propagated and still be returned from the ionosphere.

Question 55

Define 'critical frequency'.

Answer 55

The highest frequency that will be refracted back to Earth when transmitted vertically upwards.

Question 56

Define 'MUF' (Maximum Usable Frequency).

Answer 56

The highest frequency that can be used for communication between two specific points.

Question 57

Define 'LUF' (Lowest Usable Frequency).

Answer 57

The lowest frequency usable for communication, below which the signal is completely absorbed by the D layer.

Question 58

Define 'skip zone' or 'dead space'.

Answer 58

The region between the limit of the ground wave and the point where the first sky wave returns to Earth.

Question 59

Define AM (Amplitude Modulation).

Answer 59

A type of modulation where the amplitude of the carrier wave is varied.

Question 60

Define FM (Frequency Modulation).

Answer 60

A type of modulation where the frequency of the carrier wave is varied.

Question 61

Define pulse modulation.

Answer 61

A type of modulation where information is transmitted using on/off pulses of a carrier wave.

Question 62

Define phase modulation.

Answer 62

A type of modulation where the phase of the carrier wave is varied.

Question 63

In radar pulse modulation, what does 'pulse width' refer to?

Answer 63

The duration of an individual transmitted pulse.

Question 64

In radar pulse modulation, what does 'pulse power' refer to?

Answer 64

The power level during the transmission of a pulse.

Question 65

In radar pulse modulation, what does 'continuous power' refer to?

Answer 65

The average power of the transmitter over a complete transmission cycle.