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
What is TCAS?
Traffic Alert and Collision Avoidance System Warns pilots of the presence of other transponder-equipped aircraft.
Why do we use transponders?
Removes need for constant verbal communication with ATC. Can be used to signal danger, in an emergency.
What are the 3 emergency transponder codes and in what situations are they each used in?
7700 - emergency (going to heaven) 7600- loss of radio (in a fix) 7500- hijack (taken alive)
What are the 3 primary qualities of the Electomagnetic Spectrum and how do they form into the Wave Equation?
Wavelength (distance over which a waves shape repeats) Amplitude (size of the wave measured from the mean level) Frequency (number of pccurances of a repeating event) Speed=frequency x wavelength
List the names of the EM Spectrum, in order of ascending frequency and descending wavelength.
Radio waves Microwaves Infra-Red Visible Light Ultraviolet X-Rays Gamma Ray Cosmic Rays
Describe the Doppler Effect
The observed wavelength and frequency of a wave shifts due to relative motion.
What atmospheric variables affect Radar propagation?
Increase in moisture increases refraction Increase in temperature decreases refraction
What are the 3 classes of refraction and what effects do they have on a transmitted EM wave?
Sub-refraction causes wave to refract upwards towards the atmosphere Normal is a typical wave path Super-refraction causes the waves to be refracted downwards towards the earth. This can also cause ducting.
Describe the use of scatter in communication
A radio wave sent into the atmosphere causes minor local variations and a small proportion of the energy to be deflected away from the main wave path. A reciever monitors the atmosphere so that their beams intersect over an optimum scattering region.
Define EW
Electronic Warfare is any military action that involves the use, or control, of the EMS to reduce or prevent hostile use by, or to attack, an enemy.
What are the 3 types of EW
Electronic Support Electronic Attack Electronic Defence
What is ES and what is it used for?
Electronic Support Intercept, identify and locate sources of (un)intentional EM energy Threat recognition Info for immediate actions involving ECM or tactical actions (threat Avoidance, targeting, homing)
What is EA and what is it used for?
Electronic Attack Uses EM or DE to attack resources with intent of degrading, neutralising or destroying combat capability Prevention of an enemy’s effective use of EM (jamming and deception) Weapons that use EM or DE as their primary destructive mechanism (eg lasers, particle beams and radio frequency weapons)
What is ED and what is it used for?
Electronic Defence Actions taken to protect resources from effects of friendly or enemy EW that degrade, neutralise or destroy friendly combat capability.
What is a RWR and what does it do?
Radar Warning Reciever Decent, localise and identify threats to allow appropriate ECM to be used.
What is Range Advantage?
An aircraft will detect the radar before the radar can detect the aircraft. Can be 10-50%
Name the radar countermeasures
Electronic Jamming Electronic Deception
What is electronic jamming
The deliberate radiation, re-radiation or reflection of EME with the objective of imparing the effectiveness of electronic devices, equipment and systems.
What is electronic deception and what is it used for?
The deliberate radiation, re-radiation, alteration, absorption or reflection of EME in a manner intended to confuse, distract or seduce an enemy or their electronic systems. DECM equipment is used in self-protection against fire control radars.
What is a decoy?
An expendable, or semi expendable device that is launched from the target aircraft or the ground with the objective of simulating a genuine target.
What is chaff?
Passive reflectors, absorbers, or refractory of radar , communication and other weapon system radiation.
Describe flying tactics used in lieu of ECM
Low level (difficult to see due to limited radar horizon) Evasive manoeuvre whilst enemy system is temporarily degraded by ECM
What makes an aircraft stealth?
Low radar cross section, achieved by: Shape Radar absorbant material Reflect radiation away from cavities (eg cockpit, engine intakes)
What parts of an aircraft are IR targets?
Jet pipe hot metal Exhaust plume Kinetically heated leading edges
Describe uses of a surface wave, and the frequency bands used.
The extreme stability of low frequency surface waves makes them useful for: High grade comms Nav aids Submarines VLF - MF
Describe the uses and frequency bands of a skywave.
Medium and long range point to point comms with low power. However, signal stability is not achieved due to changes in the ionosphere on a daily basis. HF
Describe the uses and frequency bands of a spacewave
Short range comms TV and radio broadcasts Radar Nav/approach aids VHF
How far beyond the visual horizon does the radio horizon extend to?
15%