Radio Principles

Question 1

Sound waves travel at what speed?

Answer 1

The Speed of Sound

Question 2

Radio waves travel at what speed?

Answer 2

The speed of light

Question 3

What allows radio waves to travel so far without attenuating?

Answer 3

They are part of the electromagnetic spectrum and therefore do not require a medium to travel through.

Question 4

What does attenuation mean?

Answer 4

Weakening of waves

Question 5

What is a wavelength?

Answer 5

Measurement of a wave from crest to crest

Question 6

What is frequency?

Answer 6

Number of times a wave oscillates per second

Question 7

If frequency and wavelength are inversely proportional, then a high frequency will mean?

Answer 7

Short Wavelength

Question 8

What travels further, high frequency or low frequency?

Answer 8

Low frequency. The wavelengths are longer and therefore less susceptible to attenuation.

Question 9

Outline the process of a basic radio transmission?

Answer 9

MICROPHONE detects small audio waves, an OSCILLATOR creates a basic carrier wave. A MODULATOR superimposes the audio wave onto the carrier wave by one of 4 methods of modulation. TRANSMITTER sends the radio signal. It is received by the receiving antenna, dmeodulated and amplified via the speaker.

Question 10

What are the 4 methods of moodulation?

Answer 10

Pulse Modulation, Frequency Modulation, Amplitude Modulation, Keying.

Question 11

In general civil ATC, HF, VHF and UHF are used for what purposes?

Answer 11

HF - Oceanic R/T
VHF - R/T between ATC and a/c
UHF - use on ground between ATC and vehicles

Question 12

What are the emergency frequencies that are constantly monitored?

Answer 12

121.5 and 243.0 VHF.

Question 13

Name 4 NAVAIDS that use radio waves in aviation?

Answer 13

VOR, DME, ILS, NDB

Question 14

What is propagation?

Answer 14

The behaviour of radio waves when they are transmitted from one point to another or into the atmosphere

Question 15

Name some methods of propagation experienced by radio waves

Answer 15

Reflection, refraction, diffraction, attenuation, absorption

Question 16

State the difference between skywaves and groundwaves

Answer 16

Skywaves are refracted by ionosphere and redirected back to the Earth’s surface, groundwaves follows paths parallel to the Earths surface

Question 17

What is the purpose of a repeater station?

Answer 17

As ground waves travel in a ‘line of sight’ path, repeater stations can help to increase range

Question 18

Ionosphere’s effect on sky waves

Answer 18

During the day, the ionosphere is excited by the suns radiation, leading to increased absorption of sky waves. At night the ionosphere contracts leading to increased reflection

Question 19

HF & NDB signals suffer from some forms of interference. Name them.

Answer 19

Static interference, station interference, night effect

Question 20

Explain antenna shadowing

Answer 20

As the aircraft turns, some parts of the airframe block the antenna. Less apparent in modern planes that have multiple antenna.

Question 21

Whats is a VDF?

Answer 21

VHF Direction finder. Uses the radio transmissions of an aircraft to determine the aircraft’s bearing from the station.

Question 22

Whats is VCCS?

Answer 22

Voice Communications Control Centre. It connects various systems for ATC communications and merges them on the same software/interface.

Question 23

What is Selcal?

Answer 23

Sends two 2-tone consecutive signals on a list of frequencies that chimes in the cockpit. This saves the pilot from continuously listening to noisy frequencies.

Question 24

What is ACARS?

Answer 24

Aircraft Communications Addressing and Reporting System. Airline to aircraft communications. Broadly 3 types: ATC messages, Aeronautical operational control, airline administrative control.

Question 25

What frequencies does civil aviation use?

Answer 25

118-137 Mhz VHF frequencies.

Question 26

What is AMS?

Answer 26

Aeronautical Mobile Service. Dedicated frequencies communications system for emergencies and instances related to the safety and regularity of flight.