Radio Principles Flashcards
Sound waves travel at what speed?
The Speed of Sound
Radio waves travel at what speed?
The speed of light
What allows radio waves to travel so far without attenuating?
They are part of the electromagnetic spectrum and therefore do not require a medium to travel through.
What does attenuation mean?
Weakening of waves
What is a wavelength?
Measurement of a wave from crest to crest
What is frequency?
Number of times a wave oscillates per second
If frequency and wavelength are inversely proportional, then a high frequency will mean?
Short Wavelength
What travels further, high frequency or low frequency?
Low frequency. The wavelengths are longer and therefore less susceptible to attenuation.
Outline the process of a basic radio transmission?
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.
What are the 4 methods of moodulation?
Pulse Modulation, Frequency Modulation, Amplitude Modulation, Keying.
In general civil ATC, HF, VHF and UHF are used for what purposes?
HF - Oceanic R/T
VHF - R/T between ATC and a/c
UHF - use on ground between ATC and vehicles
What are the emergency frequencies that are constantly monitored?
121.5 and 243.0 VHF.
Name 4 NAVAIDS that use radio waves in aviation?
VOR, DME, ILS, NDB
What is propagation?
The behaviour of radio waves when they are transmitted from one point to another or into the atmosphere
Name some methods of propagation experienced by radio waves
Reflection, refraction, diffraction, attenuation, absorption
State the difference between skywaves and groundwaves
Skywaves are refracted by ionosphere and redirected back to the Earth’s surface, groundwaves follows paths parallel to the Earths surface
What is the purpose of a repeater station?
As ground waves travel in a ‘line of sight’ path, repeater stations can help to increase range
Ionosphere’s effect on sky waves
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
HF & NDB signals suffer from some forms of interference. Name them.
Static interference, station interference, night effect
Explain antenna shadowing
As the aircraft turns, some parts of the airframe block the antenna. Less apparent in modern planes that have multiple antenna.
Whats is a VDF?
VHF Direction finder. Uses the radio transmissions of an aircraft to determine the aircraft’s bearing from the station.
Whats is VCCS?
Voice Communications Control Centre. It connects various systems for ATC communications and merges them on the same software/interface.
What is Selcal?
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.
What is ACARS?
Aircraft Communications Addressing and Reporting System. Airline to aircraft communications. Broadly 3 types: ATC messages, Aeronautical operational control, airline administrative control.
What frequencies does civil aviation use?
118-137 Mhz VHF frequencies.
What is AMS?
Aeronautical Mobile Service. Dedicated frequencies communications system for emergencies and instances related to the safety and regularity of flight.
