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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
Knife edge diffraction
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
26
Multi path propagation
Arrives at receiver via more than one path Change in both direction and length of signal path - navigational anomalies
27
Absorption
Radio wave energy changing to another form such as heat (Attenuated)
28
Attenuation
Weakening of radio signal Terrain/building/aircraft/dust/water droplets
29
Interference
Vary with time of day and position Noise or unusable signal Out of phase signal or anti phase cancel out
30
Superposition
2 or more signals with similar carrier waves interfere with each other
31
Fading
Two or more signals with same frequency interfering changing signal strength and polarisation
32
Layers of ionosphere
D region - weakest E region (Kennelly Heaviside layer) F1 layer (Appleton Layers) F2 layer - strongest (Appleton Layers)
33
Ionosphere day vs night + interaction with radio waves
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
D Layer
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
E Layer
90km to 150km Thinner at night time/can even disappear if weakened in day Base rises after sunset
36
F layers
150km to 500km - Appleton Barnett layer Most influence on radio wave propagation F1/F2 in the day and F2 at night Absorption layer
37
Lower frequency radio waves
VLF/LF/MF/HF - ground wave propagation
38
Higher frequency radio waves
VHF/UHF/SHF/EHF propagate as space waves via line of site
39
Max Theoretical range formula
1.23 x (Square root Transmitter height + square root receiver height)
40
Sky waves
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
Critical angle
Highest angle at which wave returns to earth
42
Skip distance
Distance between transmitter and point on surface of earth where first sky wave returns
43
Dead space/zone
Distance between the limit of surface waves and sky waves where no signal received
44
Sporadic E
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
Super refraction
Occurs in VHF+ Increases radio range Not reliable Caused by marked inversion/rapid humidity changes
46
Modulation
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
Pulse modulation
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
Amplitude Modulation
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
USB/LSB side bands
Upper side bands + lower side bands Mirror images of each other Together known as double sideband transmission
50
Single sideband modulation
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
Frequency modulation
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
Phase Modulation
Used in GPS Phase of carrier waves reversed - require complex demodulator
53
Aviation FM vs AM
AM: + More frequencies + simpler and less expensive + technology and cost problems changing to FM
54
N0N
Carrier without modulation (NDBs)
55
A1A
Carrier with keyed morse code modulation BFO required Frequency and amplitude of wave stay the same
56
A2A
Carrier with amplitude morse code
57
A3E
Carrier with amplitude modulated speech VHF
58
Phase Angle
The fraction of a wavelength expressed in degrees from 000 to 360
59
GPS Antennas are
On top of the fuselage
60
Antennas for ground based facilities are located where on aircraft
On the underside of the aircraft
61
Propagation of all wave types
VLF = Ground wave LF = Ground wave MF = Ground wave HF = Sky Wave VHF = Space wave UHF = Space Wave SHF = Space Wave
62
Systems using the Doppler principle
VOR GPS MTI AWR
63
Single sideband two way communication is used in what frequency
HF - 3-30MHZ
64
Primary Radar
Used to detect ac without secondary radar transponder One Directional antenna for transmitting and receiving - greater power and less interference
65
TNT - Classifications of radio signals
Type of modulation - AM/FM/Pulse etc Nature of signal - digital/analogue etc Type of information - morse code/voice etc
66
Dead space “skip zone” gets bigger when
Between dawn and dusk when ionosphere becomes less bouncy
67
Polarisation
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
Modulation does what to frequency
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
Pulse Length
Measure in time

Radio Navigation (13 decks)

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