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%
How is refraction affected by an increase in moisture in the atmosphere?
Increase in moisture increases refraction
How is refraction affected by a decrease in temperature in the atmosphere?
A decrease in temperature increases refraction
Does pressure affect refraction?
Pressure has no significant impact on refraction
As EM energy propagates through the atmosphere, why does the signal strength reduce?
Attenuation (Absorbtion and scattering by particles)
Describe Infrared Decoys
Aim to present a target which is more compelling than the aircraft Flares which emit energy at all appropriate IR frequencies and the missile guidance transfers guidance lock to the flare Must burn sufficiently brightly whilst the aircraft is still in the missiles field of view and for long enough for the aircraft to escape the missiles range
Describe infrared jamming
The tracking system of an IR missile employs a device which modulates the incoming infrared energy, either in amplitude or frequency, in response to the direction of the infrared source with respect to the missile boresight The IR jammer disrupts this modulated signal so as to cause errors in the missile guidance, and lead to the missile moving away from the aircraft instead of towards it.
What is the spacing between UHF channels?
25 kHz
What is the spacing between VHF channels?
8.33 kHz
What can the propagation of electromagnetic waves be affected by?
Reflection Refraction Diffraction Attenuation
What effect reduces signal strength and limits range of radio signals due to obstructions, absorption and dust particles?
Attenuation
What phenomenon causes wave to appear to bend around objects?
Diffraction
What effect, caused by a change of velocity as a result of a change of medium?
Refraction
What takes place when the angle of incidence is equal to the angle of reflection?
Reflection
Which of the atmospheric variables that can affect the refraction of EM waves cannot have significant impact without changes in the other variables?
Pressure
What are the 3 classifications for refraction?
Sub-refraction Normal-refraction Super-refraction
What are the 3 principle paths that radio waves may follow above the Earth, between a transmitter and a reciever?
Surface wave Sky wave Space wave
What effect occurs in abnormal climatic condition, when some radio waves are refracted back to the surface, then reflected, therefore trapping the wave energy and leading to performance abnormalities?
Ducting
What frequency band is VHF?
30 MHz - 300 MHz
What is the HF frequency band?
3 MHz - 30 MHz
What is the UHF frequency band?
300 MHz - 3 GHz (300 MHz - 3,000 MHz)
What do radio waves consist of?
Electric and magnetic fields that oscillate at right angles to each other, both transverse to the direction of propagation
Will radio waves pass through many opaque bodies?
Yes
Fill in the missing labels for the Sky Wave diagram
Which path of radio propagation relies on the earth to bend the wave to follow the earth?
Surface wave
Which path of radio propagation is referred to as line of sight?
Space wave
Which frequency bands benefit the most from surface wave propagation?
VLF and LF
Label this basic radio system
Roughly how many VHF frequencies are available and what is the spacing?
1300 channels 8.33 kHz spacing
Roughly how many UHF frequencies are available and what is the spacing?
7000 channels 25 kHz spacing
What function on the intercom station box can be set to bypass the PTT switch?
NORM/HOT MIC switch
What part of the CCS is provided at each of the principle crew positions and permits individual selection of transmitters and recievers as required?
Intercom Station box
What is the difference between primary and secondary radar?
Primary radar depends on recieving a radar echo reflected passively by a target Secondary Radar system uses a transmitted radar signal to trigger a response from a target
What frequencies does IFF/SSR use?
Interrogator - 1030 MHz Transponder- 1090 MHz
Why was transponder mode S introduced?
To support the automation of some ATC functions and is a required component of TCAS
Which military IFF and Civilian SSR mode are the same?
IFF 3 and SSR A (3/A)
Which military IFF Mode is pre-set and cannot be changed in-flight?
Mode 2
Which mode may you be asked to squawk to assist ATC in locating you on their display?
IDENT
What are the 3 IFF/SSR emergency frequencies?
7700 7600 7500
What IFF phenomenon occurs when the interrogating station receives replies from transponders replying to other ground stations?
Fruiting
What IFF phenomenon occurs when two aircraft are sufficiently close enough to each other that their resulting reply pulses mix together and cannot be decoded correctly?
Garbling
What term describes equipment used to pass tactical information between units I a manner that can be readily understood and absorbed into the units’ system?
Data Link
What prefix proceed a distress call?
MAYDAY MAYDAY MAYDAY
What prefix precedes an urgency call?
Pan Pan, Pan Pan, Pan Pan
What aviation word means ‘I have recieved all of your last transmission’?
Roger
What are the emergency frequencies?
VHF 121.500 MHz UHF 243.000 MHz
What is the universal format for Transmitting time?
UTC (Co-ordinated universal time)
What is the purpose of the prefix “SECURITÉ SECURITÉ SECURITÉ”?
To inform all air traffic that a message contains information affecting safety
What techniques enable the operator to transmit clearly and satisfactorily on the radio?
Use normal conversation tone Listen out to avoid interfering with another station Use standard RT words and phrases where possible
What conditions are classified as urgent?
When there is a safety concern for the aircraft, other vehicle or person on board or within sight, but immediate assistance is not required
Although not mandated by ICAO, what other useful information could be included in the emergency message passed to the controller?
Pilot qualifications held
1what should you do if you loose sight of the ground marshaller?
Bring the aircraft to a stop and seek further assistance
What is the purpose of a ground marshaller?
Ensure the aircraft is manoeuvred safely on the ground
Who is ultimately responsible for the safety of the aircraft whilst manoeuvring on the ground?
Aircraft commander
What is the recognised marshaling signal for an engine fire?
Point to source of fire and draw a horizontal figure of 8 with the other arm
What is the marshaling signal for cutting an engine?
Swipe a flat hand across the front of your neck
What is the marshaling signal for affirmative?
Thumbs up
What is the marshaling signal for stop?
Crossed arms above your head
What is EW defined as?
Any military action that involves the use, or control, of the EMspectrum 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 the name for actions taken to Intercept, identify and locate intentional and unintentional radiated EM Energy?
Electronic support
What is the name for actions taken to prevent or reduce an enemy’s effective use of the EM Spectrum, such as jamming and EM deception?
Electronic attack
What is the name for actions taken to protect personnel, facilities and equipment from any effects of friendly, or enemy, employment of EW?
Electronic defence
What equipment is designed to detect, localise and identify threat radars so that appropriate countermeasures can be taken?
Radar warning reciever (RWR)
A RWR should be able to detect a radar before the radar can detect the aircraft. This margin of benefit is known as what?
Range advantage
To reduce the effectiveness of radar, the ECM waveforms used must be a type which will be accepted by what?
The radar reciever
Why would a pilot consider canceling the afterburner and reducing engine power to ‘military range’ during takeoff in hostile conditions?
To take IR countermeasures
What name is given to the deliberate radiation, re radiation or reflection of EM energy to impair the effectiveness of electronic devices, equipment and system?
Electronic jamming (noise jamming)
Which EW systems are classified as Electronic Support measures (ESM)?
RWR, MWS LWS
What is designed and programmed to identify threats, give warning to the crew and, where available, generate countermeasures?
DAS
What does an aircrafts IR jammer try to disrupt?
The modulated signal so as to cause errors in the missile guidance
Give examples of possible measures that provide Electronic Defence.
Frequency agility & diversity Equipment design SOPS Voice authentication Parallel operations
Label the Space Wave diagram
Chocks away
Cut engine
Proceed straight ahead
Slow down
Start engine
Turn left
Turn right
Stop
