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Flashcards in Equipment Exam Deck (154)
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1

What types of waves are radio waves?

Sine Waves

2

What are the advantages of using FM radio?

• Resilience to noise: Any signal level variations will not affect the audio output

• Easy to apply modulation at a low power No boosting of the amplitude required

• Use of efficient RF amplifiers This means that for a given power output, less battery power is required and this makes the use of FM more viable for portable two-way radio applications

3

What do FM and AM stand for with regards to RT?

FM= Frequency Modulation

AM= Amplitude Modulation

4

What are the advantages of AM radio?

Stronger stations can override weaker or interfering stations, and don't suffer from a capture effect found in FM.

- If a pilot is transmitting (Tx), a control tower can "talk over" that Tx and other aircraft will hear a somewhat garbled mixture of both Tx's rather than just one or the other.

- A heterodyne (Squeal) will be heard, even if both Tx's are received with identical signal strength. No such indication of blockage would be evident in an FM system

5

What is the frequency range and Wavelength of a VHF signal?

-30-300MHz

10m-1m

6

What is the frequency range and wavelength of a UHF signal?

300MHz-3GHz

1m-10cm

7

What is the amplitude of a radio wave?

The maximum displacement or value attained by the wave from it’s mean value during a cycle.

8

What is the wavelength of a radio wave?

The distance in metres or part of a metre between corresponding points in consecutive waves

9

What is the frequency of a radio wave?

The rate of repetition of the cycle in one second (oscillation). One cycle per second would be 1 hertz. 

Ie how many oscillations/sec

10

What is velocity with regards to radio waves?

The speed in a given direction.

velocity= frequency x wavelength

11

What is a carrier wave?

A wave which carries the audio feed by modulating the audio wave and carrier wave together.

A carrier wave is produced by an oscillator

12

What type of modulation is used in Air Traffic and why?

AM

Due to the ability to overpower weaker radio signals.

Also produces a heterodyne when two or more stations are transmitting at once so that everyone knows when two or more stations are trying to transmit.

13

What is the ideal length of an aerial?

The same length as the wavelength of the wave being transmitted.

Can transmit proportions of the wave by being either half or a quarter of the wavelength instead to create more practicable lengths.

14

What is an amplifier?

It amplifies the strength of the received signal, needs a noise gate to prevent it from amplifying any static noise as well.

15

What is attenuation

The reduction in strength of a radio wave with time from the point of transmission.

As a wave attenuates the amplitude of the wave will decrease, the frequency and wavelength remain unchanged.

Longer wavelengths (lower frequencies) are less affected owing to interacting with less particles for a given distance and vice versa.

16

What are the wave-bands of the radio?

Freq Band.                                          Spectrum of frequency.                     Wavelength

Very Low (VLF)                                    3-30KHz.                                             100-10km

Low (LF).                                              30-300KHz.                                         10-1km

Medium (MF).                                      300KHz-3MHz.                                    1km-100m

High (HF).                                            3-30MHz.                                             100-10m

Very High (VHF).                                 30-300MHz.                                        10-1m

Ultra High (UHF).                                 300MHz-3GHz.                                   1m-10cm

Super High (SHF).                               3-30GHz.                                             10-1cm

Extremely High (EHF).                         30-300GHz.                                        1cm-1mm

17

What is the frequency band for VLF and what is it used for?

3KHz-30KHz

100km-10km

Long range communications

18

What is the frequency band for LF and what is it used for?

30-300KHz

10km-1km

Reliable long range communications

Requires large aerials and high transmitter power

19

What is the frequency band for MF and what is it used for?

300KHz-3MHz

1km-100m

Used for reliable long range communications.

Very congested waveband

Used for NDB’s

20

What is the frequency band and wavelength for HF and what is it used for?

3-30MHz

100m-10m

Long range communications by day and night limited by diurnal (day and night) and seasonal variation of ionosphere.

RTF communications.

21

What is the frequency band and wavelength for VHF and what is it used for?

30-300MHz

10m-1m

Line of sight communications

Small aerial and transmitter power

Used for main ATC RTF frequencies 

Free from static interference

Easy to suppress aircraft signals

Prone to ducting

VOR, VDF

Surveillance Radar

22

What is the waveband and wavelength for UHF and what is it used for?

300MHz-3GHz

1m-10cm

Line of sight comms

Used for surface communications with vehicles

Free from static interference

Prone to ducting

Used for ILS (DME element), DME’s, surveillance RADAR

23

What are the wave bands and wavelengths of SHF and EHF frequencies and what are they used for?

SHF is 3-30GHz 10cm-1cm

EHF is 30-300GHz 1cm-1mm

 

Short range communications

Precision, surveillance and airborne weather radar.

24

What is antenna shadowing?

When the transmitter aerial is shadowed from the receiver as the radio wave travels in a straight line so may be blocked by the curvature of the earth for example.

25

What happens when a wave is ducting?

It is bouncing off of a temperature inversion or under certain atmospheric conditions which may reflect VHF, UHF and SHF waves back to the ground and they will bounce around in this ‘duct’ 

26

What is propagation with reference to radio waves?

Similar to ducting but with low frequencies bending around objects that would normally shadow the signal. Can be heard a great distance from the source as the low frequencies mean lower attentuation. 

27

What do we use RADAR for in Air Traffic Control?

Area Control

Approach Control

Aerodrome Control

-Air; traffic integration, approach monitoring

-Ground; Runway protection, monitoring ground hazards

28

How does RADAR work?

By calculating the time taken for a signal of a known speed to be recevied as an echo we can calculate the distance using the following equation.

Distance= (speed x time)/2 

29

What does RADAR stand for?

Radio Detection And Ranging.

30

What are the two types of RADAR used in ATC?

Primary (PSR)

Secondary (SSR)