Comms & EW Flashcards
Revise for EW Exam
Name two aircraft radio frequency bands
UHF VHF
What are the properties of Radio Waves?
Oscillating electric and magnetic fields, at right angles to each other and both transverse to direction of propogation.
Describe a surface wave
Radio waves that follow the Earth’s surface
Describe a sky wave
Radio wave that is refracted by the ionosphere and returned to Earth
Describe a Space wave
Line of sight radio communication wave. (May be transmitted up to 15% further than the visual horozon)
What is attenuation?
Reduction of signal strength (due to absorption, obstructions or interference from other signals).
What is diffraction?
Waves will deflect around objects placed in their path. (Used to send signals past a mountain range when there is no line of sight). Dependant on wavelength and size of the obstacle.
What is refraction?
The bending of a wave due to the change in velocity as it passes into a new medium.
What are the components of a basic radio system?
Transducer Modulation & Power Amplification Aerial and Feeder Channel Aerial and Feeder Demodulation Transducer
What radio frequency bands do Civilian and Military Aircraft use?
Civilian - VHF Military - UHF
What is the compliance necessary when ATC give an aircraft ‘clearance’?
Clearance requires strict compliance.
What is the compliance necessary when ATC give an aircraft ‘instructions’?
To be followed and carried out where practically possible and safe to do so
What is contained in ATC ‘information’?
Info that is of benefit and usefulness to Pilot and Aircrew in the interest of safety.
What does a Primary radar do?
Passively monitors aircraft position by radar, no action required by the aircraft.
What does secondary radar do?
Sends out an ‘interrogation’ that triggers a ‘reply’ from equipment in the subject aircraft
What are the Civilian and Military versions of Secondary Radar?
Civ - SSR Mil - IFF (ID Friend or Foe)
Purposes of secondary radar
Used by ATC to identify info about an aircraft without any action from the aircrew Type Callsign Bearing Range Altitude
What are the Secondary Radar Interrogator and Reply frequencies, and the pulse pair spacing?
Interrogator 1030 MHz Reply 1090 MHz Pulse Pair Spacing 0.85microseconds (Greek letter mu)
List the Secondary Radar/ SSR / Transponder inaccuracies.
Fruiting Garbling Sidelobe Signals Transponder suppression
Describe fruiting
Interrogating Station recieves replies from transponders that are replying to other base stations. False range and baring information displayed.
Describe garbling
Two aircraft are sufficiently close to each other, the replies will interfere with each other. When flying in formation, only one aircraft leaves its transponder on.
Describe sidelobe signals
Occurs if the transponder is triggered by the main signal as well as the sidelobe signals. Causes spurious replies and a ‘ring around.
Describe transponder suppression
Transponders that have just replied to an interrogation may take up to 125microseconds to reply to another, so some interrogation signals may be ignored by the transponder.
What is ACAS?
Airborne Collision Avoidance System Principle benefit is as a last resort avoidance system













