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Radio Navigation > Basic Radio Wave Theory > Flashcards

Basic Radio Wave Theory Flashcards

1
Q

Amplitude

A

Measure of max deflection in oscillation or wave

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2
Q

Frequency

A

Number of cycles in one second in hertz

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3
Q

Kilohertz

A

Khz

1 x 103
(1000)

VLF
LF
MF

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4
Q

Megahertz

A

MHz
1 x 106
1,000,000

HF
VHF
UHF

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5
Q

Gigahertz

A

GHz
1 x 109
1,000,000,000

SHF
EHF

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6
Q

Formula for wavelength/speed of light/frequency

A

Speed of light
——————-
Wavelength x frequency

Wave length = speed of light / frequency

Speed of light = wave length x frequency

Frequency = speed of light / wavelength

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7
Q

Relationship between wavelength and frequency

A

Wave length up frequency down
Wave length down frequency up

Inversely proportional

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8
Q

Very little mice have very usual sandwiches everyday

A

Very Low frequency
Low Frequency. KHz
Medium Frequency

High frequency
Very high frequency MHz
Ultra high frequency

Super high frequency. GHz
Extremely high frequency

3 - 30
30 - 300
300 - 3000

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9
Q

Doppler Effect

A

Frequency increases or decreases due to relative motion between transmitter and receiver

Moving away - frequency decreases
Moving towards - frequency increases

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10
Q

How does a antenna work

A

Convert electrical power into radio waves and vice versa

Voltage applied to make current
Em field created around the antenna
Current switched off
Em collapses
Current switched on again

Em field bounces off the expanding em fiel into space rapidly

Enduces voltage on receiver

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11
Q

Antenna must be

A

Half the wavelength

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12
Q

Polarisation

A

Orientation of electromagnetic wave with direction of propagation

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13
Q

Linear vs circular vs elliptical types of polarisation

A

Plane of oscillation rotates:
Circular
Elliptical

Plane of oscillation fixed:
Linear

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14
Q

Loop Antenna

A

Used in ADF
Detect direction a signal is coming from (null seeking)

In line with electromagnetic wave = different phase angle = current
(Sideways)
- No signal/no phase difference either side of loop

Not in line = same phase angle = no potential difference = no current flowing
(Front on)
- Strong signal/Significant phase different

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15
Q

Parabolic Antenna

A

Common in old AC/weather radars

Collects EM waves and reflects them back to a single focal point
Used in UHF and SHF
Directional
Can amplify weak signals

Beam width = size of dish/frequency/wavelength

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16
Q

Slotted Planar Array Antenna

A

Flat antenna matrix
Slots that behave like dipoles
Electronically scanned rather than mechanically

Simpler/lighter more suitable for aircraft
Used in modern aircraft weather radars

+ Narrower beams than parabolic - more efficient
+ less side lobes - requires less power

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17
Q

Helical Antenna

A

Wire coiled into helix
Diameter and distance of coils determine wavelength sensitivity
Used for GPS

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18
Q

Antenna shadowing

A

Roll/pitch shadow signal via body
Terrain/buildings/other AC also block line of sight between transmitter and receiver

Most likely at low elevation/built up areas

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19
Q

Wave Propagation

A

Means by which signal is sent from transmitter to receiver

Bending etc

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20
Q

Categories of radio waves

A

Space waves - line of sight waves (straight)

Surface waves - move along differing media with different electrical properties
Ground waves - follow curvature of earth between surface and ionosphere

(SW + GW used interchangeably)

Sky waves - transmitted skywards and refracted by ionosphere back to surface

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21
Q

Factors effecting propagation

A

Weather
Solar activity
Ionosphere
Frequency
Antenna used

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22
Q

Reflection

A

Angle of incidence is equal to reflection
Can degrade quality of signal if reflected
Terrain/buildings/vehicles/ac/water droplets

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23
Q

Refraction

A

One medium to another and speed up or slow down (density etc)

Higher frequency = less refraction (move higher into ionosphere)

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24
Q

Diffraction

A

Signal bending to match curvature of earth (ground waves)

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25
Q

Knife edge diffraction

A

EM waveform contacts sharp edge of terrain (mountains)
Results in propagating of new diffracted wavefront into free space

Secondary transmitting source in forward direction only

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26
Q

Multi path propagation

A

Arrives at receiver via more than one path
Change in both direction and length of signal path

  • navigational anomalies
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27
Q

Absorption

A

Radio wave energy changing to another form such as heat

(Attenuated)

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28
Q

Attenuation

A

Weakening of radio signal

Terrain/building/aircraft/dust/water droplets

29
Q

Interference

A

Vary with time of day and position
Noise or unusable signal

Out of phase signal or anti phase cancel out

30
Q

Superposition

A

2 or more signals with similar carrier waves interfere with each other

31
Q

Fading

A

Two or more signals with same frequency interfering changing signal strength and polarisation

32
Q

Layers of ionosphere

A

D region - weakest
E region (Kennelly Heaviside layer)
F1 layer (Appleton Layers)
F2 layer - strongest (Appleton Layers)

33
Q

Ionosphere day vs night + interaction with radio waves

A

Strongest in day via solar activity
Weaker at night

radio waves move electrons in ionsphere which cause collisions so loss of energy (attenuates)

Lower frequency has greater attenuation due to greater displacement of electrons = more collisions

34
Q

D Layer

A

50-90km above surface
Greatest in day/disappears at night
MF/HF attenuated here

Sun up - frequency up (high frequency used in day)
Sun down - frequency down (lower frequency used at night)

35
Q

E Layer

A

90km to 150km
Thinner at night time/can even disappear if weakened in day
Base rises after sunset

36
Q

F layers

A

150km to 500km - Appleton Barnett layer

Most influence on radio wave propagation
F1/F2 in the day and F2 at night

Absorption layer

37
Q

Lower frequency radio waves

A

VLF/LF/MF/HF - ground wave propagation

38
Q

Higher frequency radio waves

A

VHF/UHF/SHF/EHF propagate as space waves via line of site

39
Q

Max Theoretical range formula

A

1.23 x (Square root Transmitter height + square root receiver height)

40
Q

Sky waves

A

Refracted from E/F layers
VLF/LF/MF/HF
Higher frequency increases length of surface wave less diffraction

Higher frequency greater sky wave range less accuracy

2MHz to 30 MHz

41
Q

Critical angle

A

Highest angle at which wave returns to earth

42
Q

Skip distance

A

Distance between transmitter and point on surface of earth where first sky wave returns

43
Q

Dead space/zone

A

Distance between the limit of surface waves and sky waves where no signal received

44
Q

Sporadic E

A

VHF usually limited to line of sight but can be refracted in E layer
Abnormal event where transmitted over long range
Can happen in summer

45
Q

Super refraction

A

Occurs in VHF+
Increases radio range
Not reliable
Caused by marked inversion/rapid humidity changes

46
Q

Modulation

A

Process of altering signal to carry info
Impressing and transporting info via radio waves

Modulator to be transmitted and demodulator to return to raw form via receiver

Carrier wave modulated to higher frequency with audio at lower frequency

47
Q

Pulse modulation

A

On/off to produce pulse radio waves (pulse strings) - used in radar

Pulse width - length of pulse in unit of time

Pulse power - power contained in single pulse

Continuous - power consumed over time including periods of no transmission

Keying - pulses for morse code

48
Q

Amplitude Modulation

A

Altering amplitude of the carrier
Modulating audio applied to CW
Audio wave mixed in modulator with CW of constant frequency and power

  • noisy/static
    + simple design
49
Q

USB/LSB side bands

A

Upper side bands + lower side bands
Mirror images of each other
Together known as double sideband transmission

50
Q

Single sideband modulation

A

Removing one of the side bands to improve single efficiency
Used in HF transmissions
+ power saving
+ energy saving
+ maintain range
+ less bandwidth occupation
+ less risk of interference

51
Q

Frequency modulation

A

Altering frequency of the carrier
Adjusted in line with amplitude of audio signal

+ more efficient
+ less power wastage
+ better signal quality
+ less effected by noise than AM (clips excess)

Used on frequencies above 30MHz (VHF FM)

  • Less frequency bandwidth as use more than AM
52
Q

Phase Modulation

A

Used in GPS
Phase of carrier waves reversed

  • require complex demodulator
53
Q

Aviation FM vs AM

A

AM:
+ More frequencies
+ simpler and less expensive
+ technology and cost problems changing to FM

54
Q

N0N

A

Carrier without modulation (NDBs)

55
Q

A1A

A

Carrier with keyed morse code modulation
BFO required

Frequency and amplitude of wave stay the same

56
Q

A2A

A

Carrier with amplitude morse code

57
Q

A3E

A

Carrier with amplitude modulated speech VHF

58
Q

Phase Angle

A

The fraction of a wavelength expressed in degrees from 000 to 360

59
Q

GPS Antennas are

A

On top of the fuselage

60
Q

Antennas for ground based facilities are located where on aircraft

A

On the underside of the aircraft

61
Q

Propagation of all wave types

A

VLF = Ground wave
LF = Ground wave
MF = Ground wave
HF = Sky Wave
VHF = Space wave
UHF = Space Wave
SHF = Space Wave

62
Q

Systems using the Doppler principle

A

VOR
GPS
MTI
AWR

63
Q

Single sideband two way communication is used in what frequency

A

HF - 3-30MHZ

64
Q

Primary Radar

A

Used to detect ac without secondary radar transponder

One Directional antenna for transmitting and receiving - greater power and less interference

65
Q

TNT - Classifications of radio signals

A

Type of modulation - AM/FM/Pulse etc
Nature of signal - digital/analogue etc
Type of information - morse code/voice etc

66
Q

Dead space “skip zone” gets bigger when

A

Between dawn and dusk when ionosphere becomes less bouncy

67
Q

Polarisation

A

Orientation of the plane of oscillation of the electrical component of the electromagnetic wave

Light direction well defined = polarised (laser for example)

Linear - confined to single plane
Circular - rotates in circle
Elliptical - differing amplitudes/phase

68
Q

Modulation does what to frequency

A

Addition of a low frequency signal (tone/voice) onto a high frequency carrier wave

Input signal onto carrier wave

Reason: adding low frequency human voice onto a high frequency carrier wave

69
Q

Pulse Length

A

Measure in time

Radio Navigation (13 decks)

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