Ch. 1: Basic Radio Theory

Question 1

Speed of radio waves?

Answer 1

Speed of light (in vacuum)

3x10^8 m/s

Question 2

Cycle?

Answer 2

Complete series of values of periodical process

Question 3

Frequency?

Answer 3

Number of complete cycles in one second, expressed in Hertz.

Question 4

Wavelength?

Answer 4

Physical distance travelled by one complete wave in one cycle.

Question 5

Amplitude?

Answer 5

Maximum deflection in oscillation of a sinusoidal wave.

Question 6

Wavelength relationship with frequency?

Answer 6

Inversely proportional

Speed of light = frequency x wavelength

Question 7

Phase angle?

Answer 7

Fraction of one wavelength, expressed in degrees between 000° and 360°

Question 8

Phase difference/shift?

Answer 8

Angular difference in phase angle between the corresponding points of two cycles of equal frequency/wavelength, measured in degrees.

Question 9

The 8 frequency bands?

Answer 9

“Very low minima has victor using safety equipment”

VLF (3kHz - 30kHz / 100km - 10km) - Myriametric
LF (30kHz - 300 kHz / 10km - 1km) - Kilometric
MF (300kHz - 3MHz / 1km - 100m) - Hectometric
HF (3MHz - 30MHz / 100m - 10m) - Decametric
VHF (30MHz - 300MHz / 10m - 1m) - Metric
UHF (300MHz - 3GHz / 1m - 10cm) - Decimetric
SHF (3GHz - 30GHz / 10cm - 1cm) - Centimetric
EHF (30GHz - 300GHz / 1cm - 1mm) - Millimetric

Question 10

Radio signal frequency?

Answer 10

Frequency of the carrier wave

Question 11

What do radio waves comprise?

Answer 11

Carrier wave and information, modulated on upper and lower side bands.

Question 12

4 modulation types?

Answer 12

Amplitude: changing amplitude of carrier wave
Frequency: changing frequency of carrier wave
Pulse: switching CW on and off
Phase: intermittently reversing phase of carrier wave

Question 13

What must be done upon receiving modulated waves?

Answer 13

Must be demodulated by receiver to interpret info.

Question 14

For which 2 applications is single side band (SSB) is used for?

Answer 14

HF comms

HF VOLMET met info

Question 15

4 ITU abbreviations commonly used?

Answer 15

N0N: carrier without modulation (used by NDB)
A1A: carrier with keyed morse code modulation (used by NDB)
A2A: carrier with amplitude modulated morse code (used by NDB)
A3E: carrier with amplitude modulated speech used for comms (VHF-COM)

Question 16

2 wave propagation directions?

Answer 16

Omnidirectional: equally in all directions

Directional: transmits main lobe and side (lateral) lobes

Question 17

What is an antenna (aerial)?

Answer 17

Electrical device which converts electrical power into radio waves, and vice versa.

Question 18

4 antenna types?

Answer 18

Dipole
Loop antenna
Parabolic dish
Slotted planar array

Question 19

Dipole direction and description?

Answer 19

Omnidirectional, wire equal to 1/2 wavelength

Question 20

Loop antenna direction and use?

Answer 20

Directional, used in ADF equipment

Question 21

Parabolic dish direction and use?

Answer 21

Directional, used on older airborne weather radars (AWR) equipment.

Question 22

Slotted planar array direction and use?

Answer 22

Directional, used in modern AWR (airborne weather radar) equipment.

Question 23

What determines antenna location on aircraft?

Answer 23

Mode of use

Question 24

2 fields contained in radio waves? What kind of wave is a radio wave?

Answer 24

Electric (E) field - aligned with antenna
Magnetic (H) field - perpendicular with E field

Radio wave is an EM wave

Question 25

3 main types of polarisation?

Answer 25

Linear (horizontal and vertical); circular; elliptical.

Question 26

Vertical vs. horizontal antenna - which polarisation does each have?

Answer 26

Vertical - vertically polarised wave Horizontal - horizontally polarised wave

Question 27

What is the Ionosphere? How high? Subdivided into which layers? What does it consist of? When do Ionospheric properties alter?

Answer 27

Layer of atmosphere 60-400km above surface. By day: D, E, F1, F2 By night: E, F Consists of electrons and electrically-charged atoms and molecules that have been ionised by radiation from the sun. Properties alter with changing solar activity.

Question 28

4 modes of radio wave propagation?

Answer 28

Direct (line-of-sight) Diffraction Reflection Refraction

Question 29

Multi-path propagation?

Answer 29

Signal reflected from surfaces near the receiver arrives at receiver from several directions almost simultaneously.

Question 30

When does diffraction occur?

Answer 30

Occurs when EM waves pass around an obstacle or through an aperture in an obstacle.

Question 31

When does reflection occur? What about refraction?

Answer 31

Reflection occurs at a boundary layer, where the angle of incidence is the same as the angle of reflection. Wave doesn’t pass through boundary layer. Refraction also occurs at a boundary layer, but the wave passes through the boundary layer. Refraction is caused by the difference in densities of the propagating mediums.

Question 32

Space waves mode of propagation? Ground waves? Sky waves?

Answer 32

Line-of-sight signal, directly from transmitter to receiver. Form of surface wave, diffracted along surface of Earth. Signal refracted from E and F layers in Ionosphere.

Question 33

2 factors affecting propagation? Which frequencies of wave propagate as ground and sky waves? Which as space waves?

Answer 33

Atmospheric conditions, frequency. VLF, LF, MF, HF VHF, UHF, SHF, EHF

Question 34

4 propagation errors?

Answer 34

Attenuation: weakening or cancelling out of signal. Absorption: taking up and conversion of energy. Interference: effect on each other of two signals of the same frequency. Fading: variation in degree of interference.

Question 35

Skip distance?

Answer 35

Distance from transmitter to position of first returning sky wave.

Question 36

Dead space?

Answer 36

Gap between end of ground wave and first returning sky waves. A.k.a. Skip zone.

Question 37

Doppler effect?

Answer 37

Frequency of wave changes if there’s relative motion between transmitter and receiver.

Question 38

3 ways of defining pulses?

Answer 38

Pulse length: duration in time of a pulse, measured in microseconds. Pulse power: power contained in single pulse Continuous power: average power consumed over time.