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Radio Navigation > How it Works | Propagation > Flashcards

How it Works | Propagation Flashcards

1
Q

The ionosphere begins at about __ miles up

A

60

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2
Q

The nitrogen ionises at ___ levels

A

higher

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3
Q

The oxygen ionises at ___ levels

A

lower

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4
Q

Ionisation occurs mostly during the ___, and least just before ___

A

day, sunrise

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5
Q

Recombination is the recombining of the ___ with the ___

A

atoms electrons

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6
Q

A warmer ionosphere with ___ ionisation reflects signals ___

A

increased, better

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7
Q

The reflection is best towards the ___ in the mornings, to the South around ___, and the west in the ___ and ___.

A

East, Midday, evenings, evenings

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8
Q

_ layers of electrically charged gas atoms are produced between __ and ___km above the Earth

A

4 50 300

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9
Q

The D layer is between __ and __ km

A

50 100

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10
Q

The D layer exists during __ hours

A

daylight

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11
Q

The D layer experiences ___ ionisation as ___ UV waves penetrate so far into the atmosphere.

A

low, few

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12
Q

The D layer can refract _LF when large antenna and ___ power transmitters are used.

A

VLF high

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13
Q

The D layer is mainly responsible for absorbing and blocking _F and _F waves, whilst being transparent to _F.

A

LF MF HF

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14
Q

As it fades, _F signals can reach higher layers where they can be reflected back.

A

M

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15
Q

The E layer is between __ and ___ km

A

100 150

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16
Q

The E layer returns _F and _F bands, and waves longer than ___m

A

LF HF 100

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17
Q

The E layer is normally transparent to _HF

A

VHF

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18
Q

Sporadic E are strong patches of ionisation which can return _HF

A

VHF

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19
Q

The F layer exists in ___, and splits into __ and __

A

daylight, F1, F2

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20
Q

The F layer is responsible for most _F communications, wavelengths of less than ___m

A

HF, 10m

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21
Q

F layer atoms can stay ionised all ___ during maximum sunspot activity

A

night

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22
Q

The single hop capability in the F layer is up to ____ miles for horizontal waves.

A

3000

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23
Q

As the circumference of a wave front increases, the energy ___ per unit of length

A

reduces

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24
Q

The signal strength at any point is called the ___ strength, and is measured in ___

A

field, volts

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25
Q

Attenuation concerns the loss of ___ and ___ in various parts of the radio wave

A

energy velocity

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26
Q

Attenuation is the result of the radio wave’s energy being absorbed by the ___/___/___, on top of the normal ___ power with range.

A

Earth/atmosphere/ionosphere, decreasing

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27
Q

The only way to control attenuation is by alteration of the __

A

frequency

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28
Q

Radar attenuation ___ with frequency, and can be affected by water droplets.

A

increases

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29
Q

Radio waves can change direction as a result of ___, ___, and ___

A

refraction, reflection, diffraction

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30
Q

Refraction is the change of ___/___ as the wave travels across different media.

A

speed/bending

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31
Q

Refraction happens at the ionosphere with _F, according to the ___, ___, and ___

A

HF, temp, pressure, humidity.

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32
Q

The ___ does not change when refraction occurs

A

frequency

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33
Q

The initial and reflected waves have the ____ angle

A

same

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34
Q

A phase shift occurs, depending on the angle of ___ and the wave ___

A

incidence, polarisation

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35
Q

Diffraction of the wave is the ___ of the wave as it passes through a gap/around an edge

A

spreading

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36
Q

Radio waves bend around ___/___, and over mountains

A

dawn dusk

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37
Q

Multipath propagation is the receiving of signals from ___ sources, out of ___ with each other at the antenna

A

many, phase

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38
Q

AM will generally reflect off of different layers of the ___, arriving out of ___ at the antenna

A

ionosphere, phase

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39
Q

AM VHF will reflect off the ____, but not with SSB.

A

ionosphere

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40
Q

Reflection off of the ionosphere can severely affect ___ modulation used by GPS sats, but not in the ___ latitudes.

A

PSK, mid

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41
Q

Ground waves are associated with _LF and _F, sometimes _F

A

VLF, LF, MF

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42
Q

Ground waves don’t leave the ___ atmosphere

A

lower

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43
Q

The two factors which influence how closely ground waves follow the curve of the Earth are ___ and ___

A

scattering attenuation

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44
Q

Radio waves tend to be reflected by objects larger than about ___ their wavelength

A

half

45
Q

Lower frequency waves will curve around ___ obstacles, such as hills

A

small

46
Q

As the _ field cuts the Earth’s surface, currents are created, with the energy coming from the wave itself

A

H

47
Q

Contact with the surface will ___ the circumference of the wave

A

widen

48
Q

Widening the circumference of the wave will cause ___, curving it downward, and causing it to be ___

A

attenuation, absorbed

49
Q

The approximate length of LF/MF ground waves are ___ to ___ nm

A

1000/500

50
Q

MF ground waves must be ___ polarised to induce ground currents.

A

vertically

51
Q

Range depends on ___, type of ___, ___

A

wavelength, ground, polarisation

52
Q

A lower frequency/longer wavelength will mean a ___ reception over long distances.

A

better

53
Q

Higher frequency will mean a ___ attenuation

A

greater

54
Q

Attenuation is _ times greater over land than sea

A

3

55
Q

___ polarised have the least attenuation

A

vertically

56
Q

Ground reflected waves bounce off the ground on the way to the receiver. They travel ___ than the ground wave due to ___ attenuation, but can have their phase ___ at the point of reflection.

A

further, lower, reversed

57
Q

Space waves are contained within the ___

A

troposphere

58
Q

Space waves are ___ and do not bounce like HF waves

A

direct

59
Q

VHF/SHF/UHF are line of sight and (won’t) curve to follow the Earth’s surface.

A

won’t

60
Q

A/G transmissions are limited to __nm in the UK

A

25

61
Q

Tower transmissions are limited to ___ft

A

4,000

62
Q

Approach frequencies are limited to ___ft

A

10,000

63
Q

Theoretical direct wave range is given by the formula:

A

( 1.23 x Sqrt( H ) ) + ( 1.23 x Sqrt( h ) )

With H and h being the height of the aircraft/height of the ground antenna.

64
Q

Sky waves reflect off of the ___ when the angle is correct, reaching a further distance.

A

ionosphere.

65
Q

The HF frequencies allocated to commercial aviation range from _ to __ _Hz

A

2 22 MHz

66
Q

HF waves hitting the ionosphere can be ___ if the angle is correct

A

bent

67
Q

The side of the HF wave hitting the ionosphere will speed up, due to the ___ delectric constant from ionisation

A

reduced

68
Q

The speed of radio waves in the atmosphere is determined by the ___ ___

A

dielectric property

69
Q

The dielectric property depends upon ___, ___, and ___

A

temp, pressure, and relative humidity

70
Q

Dielectric constant is ___ proportional to pressure and relative humidity, and ___ proportional to temperature.

A

directly, inversely.

71
Q

Deceasing dielectric constant is why radio waves ___ their speed with height

A

increase

72
Q

As a radio wave moves away from the surface, the decreasing dielectric constant will cause the top to move ___, bending it back towards the Earth

A

faster

73
Q

The dielectric constant is the ratio of the ___ of the condenser in a given medium, to its capacity in a vacuum, or a measure of the ___ of the air to wave propagation.

A

capacity, resistance

74
Q

The dielectric constant causes the radio wave to follow a curved path with a radius . times the visual horiozon.

A

1.3

75
Q

The angle at which the bending of a wave first happens is the ___ angle

A

critical

76
Q

Any rays which are more vertical than the critical angle are called ___ rays, typically used for ___.

A

escape, satellites

77
Q

The critical frequency is the frequency at which ___ occurs. It depends upon the ___ of the layer concerned.

A

bending, density

78
Q

The first wave to reach the ground after being refracted/reflected is called the ___ ___ ___

A

first returning sky wave

79
Q

Between the point at which the ground wave fades, and the first returning sky wave comes back from the ionosphere is the ___ zone

A

skip

80
Q

The ___ ___ is the Earth distance taken by a signal after each reflection

A

skip distance

81
Q

30 MHz do (not) return as they are too high frequency, __-__ _Hz is the most typical for bouncing.

A

not, 15-25

82
Q

With increasing ionization, the skip zone gets ___

A

narrower

83
Q

With lower frequency , and longer wavelength, the ___ the skip distance

A

smaller

84
Q

The skip zone of HF transmissions will ___ with higher frequencies and higher reflecting ionospheric layers.

A

increase

85
Q

At night time, the skip distance will ___ for the same frequency.

A

increase

86
Q

A lower frequency will ___ the critical angle and the skip distance will ___

A

reduce decrease

87
Q

Skip is best when the sun is ___ between you and the area from which you are receiving.

A

halfway

88
Q

Long path skip takes the ___ way around the Earth, usually because ionospheric conditions are better that way

A

long

89
Q

Beyond the ground wave zone, we depend upon the ionosphere for all __ contacts

A

HF

90
Q

ADF suffers from night effect around ___/___, when the needle swings erratically as the plane of polarisation changes after reflections.

A

sunrise sunset

91
Q

During the night is when you will receive ___ ADF stations best

A

distant

92
Q

HF comms are always possible when the frequency is ___ enough to be reflected, and ___ enough to not be attenuated.

A

low, high

93
Q

HF Datalink uses the ___ sideband of a selected frequency to send ___ modulated digital information

A

upper., phase

94
Q

Normal refractivity is existent for about __% of the time

A

50

95
Q

Normal refractivity will cause the wave to be bent ___ from its usual straight line.

A

downward

96
Q

Normal reactivity exists when moisture, pressure, and temp, ___ with altitude

A

decrease

97
Q

When lapse rates differ significantly from normal, _HF, _HF, and _HF can follow different curved paths.

A

V U S

98
Q

An inversion and steep lapse rates can bend the wave ___ toward the surface of the Earth, and ___ propagation distances; known as ___ refraction.

A

more, increase, super

99
Q

Super refraction can cause the waves to become trapped between the ___ and the ___ ___ causing the refraction.

A

Earth, negative gradient

100
Q

Super refraction ducts are associated with regions of ___ pressure, over __ terrain, and the sea.

A

high, flat

101
Q

For radar, ducting will ___ the ground clutter

A

reduce

102
Q

_LF signals can travel long distances through a process similar to super refraction, involving ionospheric layers and a ___ wave, which is ___ rather than refracted.

A

VLF, conduit, reflected

103
Q

HF frequencies must be higher during the ___, or when you’re ___ ___ the station

A

day, .further from

104
Q

As the ionosphere is higher at night, you can use ___ frequencies.

A

lower

105
Q

The maximum usable frequency is the point at which refraction is ____

A

no longer possible

106
Q

The level of ionisation is less by night than by day, meaning that a ___ frequency can be used to get the same type of refraction

A

lower

107
Q

Attenuation is ____ by night

A

reduced

108
Q

HF transmitter use frequencies between _-__ _Hz

A

2 20 MHz

109
Q

The lowest usable frequency is the point below which refraction ____ ____

A

cannot start

Radio Navigation (59 decks)

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