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ATPL: RNAV > 01 Basic Radio Theory > Flashcards

01 Basic Radio Theory Flashcards

1
Q

Speed of Radio Waves?

A
  • Radio waves travel at the approximate speed of light in a vacuum
  • 300 000 000 m/s (3 x 10^8 m/s).
  • 300 000 km/s (3 x 10^5).
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2
Q

Cycle?

A

Cycle: A complete series of values of a periodical process.

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3
Q

Frequency?

A

Frequency: The number of complete cycles in one second, expressed in Hertz (Hz).

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4
Q

Wavelength?

A

Wavelength: The physical distance travelled by one complete wave in one cycle

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5
Q

Amplitude?

A

Amplitude: The maximum deflection in the oscillation of a (sinusoidal) wave.

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6
Q

Relationship between Wavelength and frequency?

A

Wavelength is inversely proportional to the frequency:
Wavelength (λ) = speed of light (c) ÷ frequency (f).

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7
Q

Phase Angle?

A

Phase angle: The fraction of one wavelength, expressed in degrees between 000° and 360°.

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8
Q

Phase difference (or shift)?

A

Phase difference (or shift): The angular difference in phase angle between the corresponding points of two cycles of equal frequency/wavelength, measured in degrees

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9
Q

Radio signal frequency?

A

Radio signal frequency: The frequency of the carrier wave.

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10
Q

Radio waves comprise?

A

Radio waves comprise: A carrier wave and information, modulated on upper and lower side bands.

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11
Q

Amplitude modulation?

A

Amplitude modulation: Changing amplitude of carrier wave.

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12
Q

Frequency modulation?

A

Frequency modulation: Changing frequency of carrier wave.

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13
Q

Pulse modulation?

A

Pulse modulation: Carrier wave switched off and on

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14
Q

Phase modulation?

A

Phase modulation: Intermittently reversing phase of carrier wave.

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15
Q

How is infomation extracted from modulated waves?

A

Modulated waves must be demodulated by the receiver to interpret the information.

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16
Q

SSB?

A

Single side band (SSB) is used for HF communications and HF VOLMET meteorological information.

Involves reming one of the sidebands, as sidebands are mirrored, this saves energy and improves signal efficiency, reduces bandwidth.

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17
Q

SSB SCW?

A

More energy is saves by completly removing the transmitted CW. Also means removing the point of referenece. The CW signal needs to be added back in at the recicver using a BFO.

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18
Q

NON?

A

NON: Carrier without modulation as used by NDB.

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19
Q

A1A?

A

A1A: Carrier with keyed Morse code modulation as used by NDB.

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20
Q

A2A?

A

A2A: Carrier with amplitude modulated Morse code as used by NDBs

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21
Q

A3E?

A

A3E: Carrier with amplitude modulated speech used for communication (VHF-COM).

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22
Q

Wave propagation direction?

A
  • Omnidirectional: Transmits equally in all directions.
  • Directional: Transmits main lobe and side (lateral) lobes.
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23
Q

Antenna?

A

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

24
Q

Loop Antenna?

A

Directional, used on Automatic Direction Finding (ADF) equipment.

25
Q

Dipole antenna?

A

Omnidirectional, wire equal to 1/2 of wave length.

26
Q

Parabolic dish?

A

Directional, used on modern Airborne Weather Radar equipment

27
Q

Slotted planar array? (Flat plate)

A

Slotted planar array: Directional, used in Airborne AWACS radar.

Produces Less side lobes.

28
Q

Antenna Positioning?

A

Antenna location on an aircraft is determined by the mode of use of the antenna.

29
Q

What is a Radio Wave?

A

EM Wave Featuring:
* E Field
* H Field
* E and H fields Perpendicular
* E-field aligned with antenna

30
Q

Three main types of polarization?

A

Three main types of polarization: Linear (horizontal and vertical); Circular; Elliptical.

31
Q

Antenna Polarisation?

A

Vertical antenna has a vertically polarized wave. Horizontal antenna has a horizontally polarized wave.

32
Q

Ionsosphere location?

A

Layer of atmosphere 60-400 km above the surface.

33
Q

Ionosphere layers?

A

Further subdivided into layers, the D, E, F1, and F2 layers by day and E and F layers by night.

34
Q

Ionosphere composition?

A

Consists of electrons and electrically charged atoms and molecules that have been ionized by radiation from the sun.

Consists of electrons and electrically charged atoms and molecules that have been ionized by radiation from the sun.

35
Q

Modes of radio wave propagation?

A
  • Direct (line-of-sight).
  • Diffraction.
  • Reflection from surfaces near the receiver arrives at multiple paths.
  • Refraction: Signal reflected from surfaces near the receiver arrives at multiple paths.
36
Q

Ground waves:

A

A form of surface wave, directly along the surface of the Earth.

Formed of a surface wave, direct space wave, and indirect (reflected space wave).

Currents induced by the radio wave contacting the surface of the earth slows down the wave front at the surface, causing the leading front of the wave to tilt downwards towards the earth.

37
Q

Space waves:

A

Line-of-sight signal, diffracted from transmitter to receiver.

38
Q

Sky waves:

A

Deflected by atmospheric conditions; ionosphere.

Refraction in the E and F layer can cause lower frequencies, (VLF, LF, MF and HF) to return to earth.

Critical angle, The highest angle at which emission returns to earth.

39
Q

Skywaves: Increasing and decreasing frequency?

A

As frequency increases, the signal penetrates further into the E and F layers before being refracted back to earth. This results in increased skywave range.

Thue should not be used for nav, due to there random nature.

40
Q

Sporadic E?

A

When present in the E layer, HF and certain lower VHF signals can refract in the E layer. The returning signals can then sometimes reflect off the earths surface and back up to the ionosphere, resulting in multihop propagation, which can transmit over very logn distances.

Most prevelant in the summer months.

41
Q

Propergation of different frequencies?

A

All frequency bands propagate signals by space wave

  • VLF, LF, MF, and HF propagate as ground (surface) wave (sometimes skywaves).
  • VHF, UHF, SHF, and EHF propagate as direct line-of-sight space wave only.
42
Q

Causes of propagation error?

A
  • Attenuation: Weakening or cancelling out of signal.
  • Absorption: Taking up other conversion of energy.
  • Interference: Effect on each other of two signals of the same frequency.
  • Fading: Variation in degree of interference to the position, effects the lowest frequencies the most during the day.
43
Q

Skip distance:

A

Skip distance: The distance from the transmitter to the position; the first returning sky wave. Also known as skipped zone.

44
Q

Dead space:

A

Dead space: The gap between the end of the ground wave and the first returning sky wave. Also known as the skip zone.

45
Q

Doppler Effect?

A

Doppler Effect: The frequency of a wave increases or decreases if there is relative motion between the transmitter and the receiver.

46
Q

How are pulses defined?

A
  • Pulse length: Duration in time of a pulse, measured in microseconds.
  • Pulse power: The power contained in a single pulse.
  • Continuous power: Average power consumed over time.
47
Q

HF Comms frequencies in the day and night?

A

Sun up frequency up, sun down frequency down.

48
Q

How does the skip distance normally increase at night?

A

E layer weakens, and the base of it rises, meaning reflection occurs at a higher altitude increasing the range.

49
Q

D layer

A

50-90km, present during the day. MF and HF siginifcantly attentuated.

Daytime absorption of HF radio waves, peaking around noon, particualry at 10Mhz and below.

50
Q

E layer

A

90-150km,

Thinner in the lower layer at night, causing ski diatances to increase.

51
Q

F layer

A

150 to 500km

Most significant influence on radio propegation, particularly HF comms.

F1 and F2 in the day, F2only at night.

52
Q

Skip Zone?

A
53
Q

GPS Antenna type?

A

Helical antennas - due to circular polarisation.

Circular polarization is used in radar systems because when the energy is reflected from water droplets the circularity is reversed and therefore the so called ‘clutter’ of precipitation can be eliminated.

54
Q

Antenna shadowing?

A

Shadowing by parts of an aircraft (such as a wing) may prevent signals from being received if the antenna is not sited properly.

55
Q

Airband?

A

108 - 137 MHz

ATPL: RNAV (14 decks)

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