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BAK > Communications > Flashcards

Communications Flashcards

1
Q

What does the International Telecommunications Union do?

A

Coordinates the shared global use of the radio spectrum.

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2
Q

What is the Australian Communications and Media Authority responsible for?

A

The regulation of:
- broadcasting
- the internet
- radio communications
- telecommunications
- implementation of ICU policy and procedures

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3
Q

What kind of wave does sound travel by?

A

Pressure waves

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4
Q

What is the speed of sound?

A

Approx 340m/s or 1224 km/hr or 60 knots.

This speed will vary depending on air temperature.

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5
Q

What are radio waves?

A

Electromagnetic waves.

They can be transmitted through any medium.

Can be used for communication.

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6
Q

What is the speed of light?

A

300 million m/second

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7
Q

What are examples of electromagnetic waves?

A
  • Radio and television signals
  • Microwaves
  • Radar signals
  • Lamp light
  • Fire heat
  • Radiation from the sun and radioactive materials
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8
Q

What are the three main elements of wave motions?

A
  • Amplitude
  • Frequency
  • Wavelength
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9
Q

What is the amplitude of a wave?

A

The distance from one extremity of the oscillation (or vibration) to the middle point or neutral value.

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10
Q

What is the frequency of a wave?

A

The number of complete waves (or cycles) passing a point per second.

Measured in Hertz (Hz).

One complete wave cycle past a given point = 1 Hz.

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11
Q

What is wavelength?

A

The length of one single wave.

Can also be expressed as the distance travelled by the wave during the transmission of one cycle.

Wavelength = Velocity/Frequency

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12
Q

What frequency and wavelength is HF?

A

3 - 30MHz
100m - 10m

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13
Q

What frequency and wavelength is VHF?

A

30 - 300MHz
10m - 1m

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14
Q

What frequency and wavelength is UHF?

A

300 - 3000MHz
1m - 100mm

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15
Q

At what rate does increasing transmitter power increase range?

A

The square root factor.

e.g. doubling power will increase range by 1.414

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16
Q

What is interference?

A

The reinforcement or cancellation that occurs when two waves overlap.

17
Q

What are the advantages of the HF communications?

A

Allows communication with aircraft in:
- remote areas
- over the horizon
- out to sea beyond line-of-sight

18
Q

What are the limitations of HF communications?

A
  • Very susceptible to interference
  • Fading due to interaction of ground and sky waves, particularly at night
  • Coverage unreliable - affected by the Ionosphere
  • Difficult to silence receivers during ‘no signal’ periods (annoying ‘hash’ when strong interference is present)
  • HF antenna arrays are very large
19
Q

What are the advantages of VHF communication?

A
  • Principal VHF advantage is the signal quality. Static and other interference are almost non-existent.
  • Waves are ‘direct’, and not refracted or reflected, so fading and garbling are also minimal.
  • Requires small antenna systems, saving in space and weight in airborne equipment.
  • Low transmitter power suits aircraft systems.
20
Q

True or False. UHF has the same advantages and limitations as VHF.

A

True

21
Q

What is UHF used for?

A

Military applications

22
Q

What are VHF frequencies used for?

A
  • Air Traffic Control
  • General aviation
  • Radio navigation aids
23
Q

What is refraction?

A

The bending of radio waves across the boundary between media of differing density.

The velocity varies with density of the medium and layers can bend certain radio waves so they are effectively reflected back to Earth.

24
Q

What are three types of refraction that radio waves may be affected by?

A

Ionospheric: The Ionosphere is a high altitude layers of ionised gases (approx 30 to 300 nm). HF band waves are susceptible but this depends on the frequency and the variable state of the Ionosphere. Reflected strength can vary from hour to hour, and minute to minute.

Atmospheric: Signal paths may be bent as a result of slight variations in atmospheric density, which arise from differing temperatures, pressures, and humidity, especially in the lower levels of the atmosphere.

Coastal: Radio wave path changes as it crosses a coastline. The degree to which a signal is affected is primarily dependent upon its frequency.

25
Q

What is reflection?

A

Occurs when radio waves ‘bounce off’ a reflecting surface.

This is utilised in radar systems.

26
Q

What is attenuation?

A

When radio signals are progressively weakened as they radiate further from the transmitter.

The rate at which a signal is reduced is determined by the Inverse square law (twice the distance, the signal would be reduced by a factor of four).

Can be offset by increasing transmitter power.

27
Q

What is absorption?

A

When a radio signal is weakened or eliminated as a result of passing through, or failing to pass through, a medium such as a building.

28
Q

What is diffraction?

A

When radio waves pass close to the edge of a large solid object through which they cannot pass and their travel is bent.

29
Q

True or False. VHF signals travel in straight lines and must be able to pass directly from the transmitting antenna to the receiving antenna with no significant obstructions.

A

True

30
Q

List and define various communications systems used in aviation

A

Morse code: a simple and internationally recognisable code. Identifies radio navigation aids.

Radios: HF, VHF & UHF used for communication with aircraft.

Controller Pilot Data Link Communication (CPDLC): allows a sophisticated text based exchange between Air Traffic Control and pilots which mirrors voice communications.

Selective calling system (SELCAL): replaces voice with coded tones. Silences HF communications receiver until a relevant tone code is received.

31
Q

What are the levels of the readability scale?

A
  1. Unreadable
  2. Readable now and then
  3. Readable but with difficulty
  4. Readable
  5. Perfectly readable
32
Q

Define the phonetic alphabet

A

A set of internationally accepted words that are used to clearly represent each letter of the alphabet.

32
Q

True or False. The individual digits of altitudes, cloud height, visibility and runway visual range are always transmitted.

A

False.

Numbers in these categories which contain whole hundreds and or whole thousands must be transmitted by pronouncing each digit in the number of hundreds or thousands followed by the word HUNDRED or THOUSAND as appropriate.

e.g. 1800 - wun ait hundred

33
Q

How should altitudes above the transition layer of standard pressure 1013.25HpA be expressed?

A

Flight Level ‘Altitude’

e.g. FL 185 (Flight Level wun ait fife)

34
Q

How are altimeter settings defined?

A

By either “QNH” (observational/actual) or “AREA QNH” (forecast area)

35
Q

What must headings always be prefixed by?

A

‘Heading’ and the direction of turn.

36
Q

What is group form?

A

The grouping of numbers into pairs, or where a number ending in “00” is spoken in hundreds. For three digit numbers, the second and third numbers are grouped.

EASTERN 1220 - EASTERN TWELVE TWENTY
CLASSIC 12 - CLASSIC TWELVE
VIRGIN 702 - VIRGIN SEVEN ZERO TWO
BIRDOG 021 - BIRDOG ZERO TWENTY ONE

37
Q

What is the term used when ATC procedures require a reference to UTC?

A

Zulu

e.g. 0920 UTC “ZERO NINE TWO ZERO ZULU”

38
Q

What is UTC?

A

Universal Coordinated Time.

It is the successor to Greenwich Mean Time (GMT)

BAK (6 decks)

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