Comms and EW old Flashcards
What are the three primary qualities of wave energy?
Wavelength
Amplitude
Frequency
What is Wavelength?
The distance over which the wave’s shape repeats.
What is Amplitude?
The vertical size of the wave, measured from the mean level.
What is Frequency?
The number of occurrences of a repeating event, measured in cycles per seconds, or Hertz (Hz).
How is wavelength affected by frequency?
Increased frequency = shorter wavelength
What is the difference between Primary and Secondary radar?
Primary
Operates independently of the aircraft, it depends on receiving a radar echo reflected passively by a target.
Secondary
A transmitted radar signal is used to trigger a response from equipment in the subject.
IFF - Military
SSR (Secondary Surveillance Radar) - Civvie
What are the key principles of IFF/SSR?
IFF and SSR are normally operated in conjunction with a primary radar.
A coded interrogation signal is transmitted to the aircraft and transponders in friendly aircraft receive and decode the signal.
A coded reply signal is sent back. The reply signal is decoded and shown on the radar display along with the primary radar response.
What frequency is the interrogator frequency for IFF/SRR?
1030 MHz
What frequency is the reply frequency for IFF/SSR?
1090 MHz
What is the duration of the pulses for the Interrogator signal on IFF/SSR?
The interrogation frequency is transmitted at 1030 MHz.
It consists of a pair of pulses, each pulse lasting a duration of 0.85μs.
The separation of the pulses determines the mode.
What is Mode S?
Mode S is a discrete selective interrogation, rather than a general broadcast, that facilitates TCAS for civilian aircraft.
Mode S transponders ignore interrogations not addressed with their unique identity code, reducing channel congestion. At a typical SSR radar installation, ATCRBS, IFF, and mode S interrogations will all be transmitted in an interlaced fashion.
What is ACAS and what does it provide?
Airborne Collision Avoidance System (ACAS)
Collision avoidance protection, situational awareness and enhanced safety.
It is a ‘last resort’ collision avoidance system.
What is TCAS?
Traffic Alert and Collision Avoidance System (TCAS)
Utilizes SSR technology and utilizes the transmissions made by aircraft on IFF frequencies. Warns pilots of the presence of other transponder-equipped aircraft, which may present a threat of a mid-air collision.
What is Mode 4 operating mode?
Mode 4 is a secret, military only transponder setting valid for 24 hours. It serves as a military only identification and can be turned on/off.
What is the emergency Transponder Code?
7700
(7-7 off to heaven)
What is the transponder code for a loss of 2-way comms?
7600
(7-6 in a fix)
What is the transponder code for hijack/terrorism?
7500
(7-5 taken alive)
What types of SSR inaccuracies are there?
Fruiting
Garbling
Sidelobe signals
Transponder suppression
What is fruiting?
Fruiting
When the interrogating station receives replies from transponders replying to other ground stations. This results in false SSR responses being displayed.
What military mode of IFF cannot be set in the cockpit?
Mode 2
What is Garbling?
Garbling
If a second aircraft is sufficiently close to the first to be interrogated, garbling may occur. Its reply may overlap that of the first aircraft and the resulting pulses will mix together and be impossible to decode accurately.
What are sidelobe signals?
Sidelobe signals
Sidelobe signals may occur if the transponder is triggered by the SSR sidelobes as well as by the interrogator beam. This causes spurious replies on the display and, at short ranges can produce large sidelobes on the response, which may create a complete ring around.
What types of Electronic Warfare are there?
Electronic Support Measures
Electronic Attack
Electronic Protection
What is Electronic Attack?
Using Electronic Measures or directed energy to attack personnel, facilities or equipment with the intent of degrading or destroying combat capability.
What is a key requirement for Electronic Protection?
Frequency Agility
Crypto
Modulation changes
Complex PRF
ie. Havequick
What is the Range advantage when referring to the Radar Warning Receiver?
An aircraft that is illuminated by an enemy radar is able to intercept the threat radar transmission before the aircraft itself is detected. It receives the full pulse of the Radar via its RWR, whereas the enemy only receives the reflection.
How can a Radar Warning Receiver identify direction of a radar threat?
An RWR can utilize amplitude or phase comparison techniques.
Why do chaff packages consist of varying length filaments?
Chaff is cut to match the half-wavelength of the victim’s radar frequency. The varying lengths allow response to varying frequencies.
What is the fundamental parameter behind radar stealth techniques?
Radar Cross Section (RCS)
What types of electronic defence measures are there?
ECM - Electronic Counter-Measures
ESM - Electronic Support Measures
EPM - Electronic Protection Measures
What must an IR jammer do to be effective?
An IR jammer must disrupt the modulation pattern produced by the missile seeker head.
What are the principle paths in which a radio wave can travel?
Surface Wave
Sky Wave
Space Wave
What are the three main pieces of equipment for an Electronic Support Measure Kit?
RWR - Radar Warning Receiver
MWS - Missile Warning System
LWR - Laser Warning Receiver
What methods of Electronic Attack/Countermeasures are there?
Chaff
Flares
Decoys
Stealth Measures
How does an RWR identify threats?
Receivers and Antennas
Programme Library cross referenced
Threat identified
What is the time unit reference used for flying?
UTC
What is Distress?
Serious, imminent danger requiring immediate interference.
MAYDAY MAYDAY MAYDAY
What is Urgency?
There is a safety concern for aircraft, other vehicle or person on board but does not require immediate assistance.
PAN PAN PAN
What information is required for a MAYDAY call?
Type + PoB
Nature
Intentions
Position
Level
Heading
TNIPLE
Surface wave propagation is suitable for what uses?
Submarine Communication
Systems requiring consistency of signal over long distances
What frequency bands are suitable for surface wave propagation?
VLF
LF
MF (to some extent)
Describe the principles behind skywave propagation?
Sky waves ascend into the upper atmosphere and encounter the ionosphere.
The electrically charged particles in the ionosphere allow refraction back towards earth
What is the skip distance in sky wave propagation?
The skip distance is the distance between the transmitter and the point of reception of the first sky wave.
What is the maximum usable frequency for sky wave propagation?
MUF is the highest frequency at which reflection can take place for a given angle of incidence.
If the frequency is increased, a sky wave penetrates more deeply into the ionosphere before return.
What are the applications of space wave?
Short-range comms
TV and FM sound broadcasting
Radar
Nav and Approach aids
Satellite Communication
What is attenuation?
Attenuation is the reduction of signal strength, also known as fading. It can be caused by obstructions, absorption, interfering waves and the configuration of the transmitter and receiving antenna.
How can diffraction be utilized to aid signal transmission?
Diffraction can occur as waves deflect around obstacles placed in their path.
The wave spread into the shadow zone behind the obstacle. This can be used to send radio signals over a mountain range where there is no LoS path available.
What is the role of a transducer in a basic radio system?
The transducer creates a baseband signal from an analogue input (comprising a wide spectrum of frequencies)
What is the role of modulation and power amplification in a basic radio system?
It is the role of the transmitting equipment to convert the baseband signal into a suitable part of the frequency spectrum for transmission.
What frequency range is utilized for VHF transmissions?
30-300 MHz
For comms:
118 - 136.975 MHz
8.33 KHz spacing
1300 VHF frequencies
What is the spacing of VHF frequencies?
8.33 kHz
What is the spacing of UHF frequencies?
25 kHz
What is the usable frequency range for UHF transmissions?
25.0 - 399.95 MHz
with 25 kHz
What is a CCS and what services will it typically provide?
Communications Control System (CCS)
These are used in multi-crew aircraft and offer crew members the option to communicate with each other through an intercom.
Intercom and radio facilities for the crew
‘Listen only’ positions
External inputs: ground crew
What is an auxiliary jack box?
Cabin/ground crew can use the normal intercom by plugging a headset into a convenient ‘jack box’.
This action closes a switch, which provides a path from the 28V DC supply to the relays in the crew amplifier.