Day 1 Flashcards
1
Q
What is the doppler effect (verbatim)
A
An apparent shift in observed frequency of waveform due to difference in velocity of object relative to observer.
2
Q
Explain what happens with doppler when moving towards, away and at 90 degrees to the observer
A
Moving towards = increase in frequency
Moving away = decrease in frequency
90 degrees = no change in frequency
3
Q
What is the coherent definition?
A
Consistent or continuity in phase of signal from one pulse to the next
4
Q
What are the requirements for a doppler radar? 2
A
Coherent radar
Receiver must be linked to TX to know phase
5
Q
Explain tangential fade
A
As a target moves away from the observer, the doppler effect will decrease. Makes it hard to distinguish contact over clutter until the contact fades out as the relative direction approaches a tangent to the observer.
6
Q
Explain doppler notch
A
Any moving objects under a set velocity threshold will be classed by the radar as clutter and will not display them. Anything below the speed is considering in doppler notch.
7
Q
What is the main limitation of continuous wave on airborne platforms and what is the solution?
A
Weight & two antennas required.
Solution: interrupted continuous wave radar.
8
Q
What types of radar use pulse doppler?
A
Target tracking
Airborne intercept
9
Q
How does a pulse doppler radar work?
A
Measures targets radial velocity by measuring phase shift of return pulse, comparing the phase to originally transmitted pulse.
Separates moving targets from stationary clutter
10
Q
How does an MTI radar work?
A
Detects moving targets against stationary background clutter and and filters out those with no doppler shift.
Displays range and bearing on a PPI display often used by ATC.
11
Q
MTI vs Pulse doppler table
A
PRF Range Velocity
MTI Low Unambiguous Ambiguous (Blind speeds)
Pulse Doppler High Ambiguous (blind ranges) Unambiguous
12
Q
What are blind speeds?
A
Blind speeds occur on a coherent radar when the doppler shift of a returning pulse is equal to the PRF of its harmonics.
Can be defeated by increasing the PRF or altering the PRF on a pulse to pulse basis ie inter pulse modulation.
13
Q
What are blind ranges and how can they be defeated?
A
Occurs at ranges where a radar receives a returning transmission when the radar is set to transmit not receive. Occurs at increments of MUR and size dictated by pulse width.
Defeated by decreasing PRF or altering the PRF on a pulse to pulse basis ie interpulse modulation.
14
Q
Explain purpose and function of an amplifier
A
Converts low power radio freq to a high power signal.
—–►——
15
Q
Explain purpose and function of the Oscillator
A
Generates sinusoidal signal to enable conversion of IF to RF and RF to IF. Generally non coherent
—⍬—
16
Q
Explain the purpose and function of a mixer
A
The mixer produces the sum and difference of the modulated signal and local oscillated output
—-⦻—-
|
17
Q
Explain purpose and function of the filter
A
Removes unwanted frequencies
18
Q
List the types of filters (4)
A
High pass
Low pass
Band pass
Notch
19
Q
Explain purpose and function of the attenuator
A
Prevents high signal levels from overloading the mixer
20
Q
Explain the need for satcom
A
Long distance communications
Continuing growth in digital transmission
Usable in remote areas
HQs and commanders in different countries
21
Q
What range does SATCOM frequency use? What are the limitations?
A
240mhz - 32ghz
<1ghz cosmic noise
>15ghz atmospheric attenuation, noise & depolarisation
22
Q
What bands do NATO use for SATCOM and why (4)
A
UHF, SHF and EHF
Why: limited rain fade
High link availability
High data rate volumes
Terminal size suitable for deployed and remote locations
23
Q
What are the advantages and disadvantages of military satcom? 4 + 4
A
Jam resistant
Secure encryption
Reserved bandwidth for gov
Available in remote regions
Cost
Congestion of frequencies
Coverage is orbit dependant
Interference and propagation
24
Q
List the 6 satellite sub systems
A
Transponders Antennae Telemetry and command Attitude and orbit control Propulsion Electrical power
25
What are the two types of satellite orbit? And what 3 planes
Circular and elliptical
Equatorial, polar or inclined planes
26
Explain circular orbit
No orbit is perfectly circular but have eccentricity of 0 degrees.
27
Explain elliptical orbit
Maintains long dwell times
Coverage of high latitudes
4 satellites 6 hour look time to cover 24 hours continuous
PERIGEE - minimum distance to earth, maximum speed
APOGEE - maximum distance from earth, minimum speed
28
What is LEO?
Low earth orbit typically 2000km
| 1 orbit takes around 90 minutes
29
Explain geostationary orbit
Same angular velocity as the earth so remains looking at the same position of the earth. Circular equatorial orbit.
3 satellites to see 120 degrees each, 1 atlantic, 1 indian, 1 pacific, 17.5 degree beamwidth.
30
Explain geo-synchronous orbit
Elliptical inclined orbit where satellite appears at same position every 24 hours. Worldwide coverage except polar regions.
31
Explain Sub synchronous orbit
Lower than geo-synchronous, circular inclined orbit lasting upto 12 hours.
32
What are the pros and cons of the different orbit types?
```
Geo-synchronous / stationary
Infinite dwell time over region
Ground stations dont require following antennae
Expensive to put into orbit
Impossible to repair
```
Sub-synchronous
Faster coverage of large areas
Require number of satellites for full coverage
LEO
Can be fixed
Decreased lag time
Need many satellites to give full earth coverage
33
What are the pros and cons of the different orbit types?
```
Geo-synchronous / stationary
Infinite dwell time over region
Ground stations dont require following antennae
Expensive to put into orbit
Impossible to repair
```
Sub-synchronous
Faster coverage of large areas
Require number of satellites for full coverage
LEO
Can be fixed
Decreased lag time
Need many satellites to give full earth coverage
34
What the the 4 different beam types?
Global beam - 42%
Hemispheric beam - 20%
Zonal beam - 10%
Spot beam - 800km across
35
Purpose of a transponder? (Sub systems)
Receives multiple signals simultaneously and translates uplink signal frequency band to downlink frequency band.
36
Purpose of antennae (Sub systems)
Carry one or more antennae to produce a beam.
37
Purpose of telemetry and command (Sub systems)
Separate antennas :
Downlink: Engineering & equipment status info
Uplink: Commands to select equipment modes, change satellite orbit or maintain satellite orbit.
38
Purpose of attitude control (Sub systems)
Spin stabilisation - maintain antennae pointing at earth
| 3 axis stabilisation - Maintain body of satellite pointing to earth whilst solar panels at sun.
39
Purpose of orbit control (Sub systems)
Corrections to orbit N-S E-W using propulsion unit
40
Purpose of electrical power (Sub systems)
Solar panels with standby batteries 300w - 16kw
41
What is IADS? What are some examples?
Integrated air defence systems - multiple units operating cohesively to deny enemy air operations inside designated zone.
```
Missile sites
Data links
Fither aircraft
Naval vessels
Early warning radars
Tracking and Target acquisition radars
```
42
What is SEAD?
Suppression of enemy air defences
Neutralise or temporarily degrade enemy air defences
When DEAD isnt possible
Jamming or antiradiation missiles
May require multiple missions
43
What is DEAD?
Destruction of enemy air defences
Permanent suppression
Increased future safety
Frees up crew and resources
Preferred over SEAD
44
2 types of anti-radiation missile?
Hard kill (target continues to transmit until impact) & soft kill (EMCON switch off target, SEAD)
45
What is a TST?
Time sensitive targeting - targets that require immediate attention as they may or will pose a threat to friendly forces, are fleeting or highly lucrative.
46
What is joint targeting?
This is the whole process of determining the effects necessary to achieve commanders objectives with resources available. This is also the synchronisation of firing with other military authorities.
47
What is the TST process?
F F T T E A
```
Find
Fix
Track
Target
Engagement
Assesment
```
48
What is dynamic targeting?
Prosecutes targets identified too late to be identified in deliberate targeting
49
What is deliberate targeting?
Prosecutes targets known to exist in operational area.
50
How can we engage TST targets?
Either method of deliberate or dynamic however due to fleeting targets, dynamic is most often used.
51
What is a multi-frequency radar?
Multi frequency radars use two or more illumination frequencies
52
What are the two types of multi frequency radars?
```
Simultaneous transmission (Freq diversity)
Differing successive pulses (Freq agility)
```
53
Explain frequency diversity
Simultaneous transmission on two frequencies via 2 antennae and transmitters.
Short pulse - high discrimination short range
Long pulse - long range, detection of small aircraft
54
Explain frequency agility
The ability of a radar to switch frequencies in a controlled manner. The receiver is synchronised to the transmitter.
Anti clutter
Elims 2nd time round returns
EPM - hard to jam
55
What is a continous wave radar? Adv Disadv & apps
Single frequency transmitted continuously
Adv
Suitable for doppler measurement
High av power
Narrow bandwidth
Disadvantages
Seperate TX & RX
Cannot calculate range
Application:
Weapon guidance
Doppler nav
56
How can a CW radar measure range?
Frequency modulated continuous wave radar
Uses different frequencies and measures the time between transmission and echo
Interrupted continuous wave (coherent)
Provides range and velocity measurements
Predominantly pulse doppler radars
57
What is meant by a coherent signal?
signals are described as coherent if their phase relationships are constant
58
What is meant by interpulse?
What happens between pulses ie PRI
59
What is interpulse modulation?
The modulation of the interval between pulses (interpulse) to overcome the issues generated by utilising a single PRI.
These are:
False targets generated by 2nd time round returns
Blind ranges
Blind speeds
60
5 different types of interpulse modulation
```
PRI steady/constant
PRI Stagger
PRI Jitter
PRI Dwell and switch
PRI Agility
```
61
Explain PRI steady / constant
Same PRI used all the time
62
Explain PRI Stagger
Small or large discrete PRI changes in recognisable pattern normally changing each pulse
Simple sequence: No. of staggers in sequence 7 or less
Complex: No. of staggers in sequence more than 7
Random sequence: Staggered PRIs in non predicatble non repetitive order
Pseudorandom: Repeats itself after a period of time
63
What is PRI Dwell and switch?
Small or large discrete PRI changes in a recognisable pattern changing after a set of pulses at each PRI
Separate dwells may be jittered
TA / TT / AI
Pulse doppler radars
64
What is PRI Jitter?
Apparently random small PRI changes
Discrete Jitter - Preset PRIs randomly between set limit
Random - No pattern between set limit
65
What is PRI agility?
Psuedorandom large PRI changes
66
What is pulse code modulation (multi-pulse)
Used for IFF, sonobouy and missile guidance.
Change of postion, order or other characterstics of pulse within frame.
67
What is firing order?
The order in which PRIs are transmitted - shortest PRI first
68
What is Element?
Describes an individual PRI
69
What are positions?
Describes total number of PRIs in cycle
70
What is cyclic length?
Time taken to complete a cycle in Ms
71
What is cyclic rate?
Inverse of cyclic length, no. of times sequence repeats in 1 second in Hz
72
What is mean PRI/PRF
Average of all the positions in the cycle
73
What is a frame?
Able to see full sequence of PRI before it repeats
74
What is Intra Pulse
# Define what is happening to the PD of a signal
Is it modulated or unmodulated?
75
What are the 2 types of modulation?
Unintentional (UMOP)
| Intentional
76
Explain UMOP
Unintentional Modulation on Pulse
Frequency, amplitude or phase variation from the intendended pulse
Specific Emitter Identification (SEI)
Fingerprint = old equipment or poor handling
77
Why modulate a pulse?
Modulation on Pulse = Pulse Compression
Range and Detection of a long pulse
with
Accuracy and resolution of narrow pulse
78
2 Types of Intentional Modulation
FMOP = Frequency Modulation on Pulse
PMOP = Phase Modulation on Pulse
79
Explain FMOP
Also know as CHIRP
Frequency made to increase or decrease along the length of transmitted pulse
Frequency variation of the pulse is known as the sweep
Higher CHIRP = Better range resolution
Returns are passed through frequency delay lines
80
Explain PMOP
Divides the pulse into equal segments called bits, uses binary to transmit data
1 = normal, 0 = reflected
```
Bi-phase = 180 degrees = Barker Coding
Quad-phase = 90 degrees = Frank Coding = Example of Polyphase
```
Codes can be changed pulse-by-pulse making them immune to certain types of repeater jammer (which FM waveform is vulnerable to)
More likely for long pulse duration
81
What are the types of FMOP?
Linear Frequency Modulation On Pulse (LFMOP)
Non-Linear Frequency Modulation On Pulse (NLFMOP)
82
Explain LFMOP
Used to ensure a good SNR at the receiver without sacrificing range resolution
Good range resolution and target discrimination
Suffers from some range ambiguites
It is a FM waveform so simpler and cheaper
83
Explain NLFMOP
Sweeps the pulse frequency in a non-linear fashion
Aids sidelobe suppression
Poor range resoultion in comparison to LFMOP
But does not suffer as badly from range ambiguities
It is a FM waveform so simpler and cheaper
84
Explain a Surface Acoustic Wave Device
85
Explain Polyphase Coding
Basically PMOP but not limited to 0 or 180 increments
Still has to be harmonics
e.g. 0, 120, 240
0, 90, 180, 270 (Frank Coding)
86
What are the limitations of Pulse Compression?
Receiver filters complicate the receiver
Transmission of a long pulse causes higher level of reflections (problems in sidelobes)
Long pulse increase the minimum range of the radar
FM and PMOP vulnerable to deception jammers
87
What are the requirements of a Radar warning receiver? 10
```
Sensitive
100% intercept probability
Wide range of frequencies
360 degree coverage in azimuth and relevant angles
Accurate and immediate direction finding
Measure parameters
Able to deal with all types of radar
Deinterleaves signals
ID emitter and prioritise
Display results clearly and provide alarms
```
88
3 types of RWR
Crystal video receiver
Instantaneous frequency measurement receiver
Scanning superheterodyne receiver
89
What are the features of a crystal video receiver CVR
Wide bandwidth
Simple/cheap/minimal programming
Unable to measure frequency
Poor sensitivity
Cannot detect continous wave
Overcome issues by adding more
90
What are the features of a IFMR
Measures frequency
Measures quickly
Some do not provide PRF or PW
Only processes 1 signal at a time
91
How to we overcome the limitations of CVR and IFMR?
By combining the two together
92
What are the features of a Scanning superheterodyne
Very sensitive
accurate frequency measurement
Very complex compared to the others
Blind to frequencies it is not tuned to
93
What is MDD and MDS?
Mission dependent data
| Mission dependent software
94
What is dwell?
The time a RWR will spend looking and a certain emitter dependent on its:
ARP
Beamwidth
PRF
95
What is the ESM advantage (recommended to draw a picture)
RWR can detect emitter at a greater range before emitter can detect the return pulse from the RWR platform
96
What is the definition of a countermeasure?
An action taken by a platform to negate the effect of a threat
97
What are the two types of RF countermeasures
Electronic and mechanical
98
What are the two types of electronic RF CM
Jamming
Deception
99
What are the 3 types of jamming?
Spot
Sweep
Barrage
100
What are the 3 types of deception?
Electronic repeater jamming -----
Range/velocity gate pull off
Angle deception
False target generation
101
What are the two types of mechanical RF CM
Chaff
Decoys
102
What are the two types of decoys?
Active
Passive
103
Explain spot jamming
Spot jamming: covers 1 frequency with all of its power
Must know frequency
Must cover tx bandwidth
104
Explain sweep jamming
Shifts frequency from 1 to another (spot jammer that moves)
Suffers from AGC and fade out
105
Explain barrage jamming
Wide bandwidth covering multiple frequencies at once
Suffers from wasted energy and low power
106
Explain radar burn through
When target radar power is more powerful than the jamming power. Usually occurs at closer range.
107
EXplain false target generation
To produce on the victims radar display a set of returns which look like targets to confuse the operator. Does this by re transmitting the pulse earlier, later or into side lobes.
108
What are the 3 types of deception?
False target generation
Angle lock breaking
Gate stealing
109
What is range gate pull off?
Taking target lock on and re producing similar signal to your echo and relaying back to target with a time delay or time advance to make yourself appear closer or futher away
110
What is velocity range gate pull off?
Walks off signal similar to range gate pull off but targets doppler radars which are measuring your speed
111
What are the two types of active radar decoys?
Towed radar decoy
| Expendable active decoy
112
What are the 2 types of passive decoys
Chaff
| Naval decoys
113
What do decoys need to have to be effective?
Speed/velocity
Radar x section
Height
114
What is chaff?
Elemental passive reflectors, absorbers or refractors of EM radiation.
Float and suspend in atmosphere
Replicate wavelength
115
What does radar detection depend on?
```
Low observability
Size
Shape
Material
Detection frequency
```
116
Explain the engagement process
SATLI
```
Search
Acquire
Track
Launch
Intercept
```
117
Explain search (Engagement process)
EW
CI
Height finding
Air traffic
118
Explain acquire (Engagement process)
Acquire a target during search
Establish position
Target Acquisition Radar
119
Explain track (Engagement process)
Accurate tgt position
Compute firing solution
Target Tracking Radar
120
Explain launch (Engagement process)
Illuminate target
Establish seeker track
Maintain target
Target Illuminate Radar
Missile Guidance Radar
Fire Control Radar
121
Explain intercept (Engagement process)
Maintain target illumination
Maintain seeker track
Fuse
122
What are the 4 fire control radars?
Target acquisition
Target illumination
Target tracking
Missile guidance
123
Explain target acquisition radar
Longest range
Lower frequency
Locates target and tracks if threat
124
Explain Target tracking
TT is then pointed at target by TA
Looks further than weapons range
Higher frequency transmissions
125
What are the features of a multi function array?
Electronically scanned phased array
Rapid and unpredictable scan in azimuth and elevation of sectors to around 90 degrees
G band
Utilises: freq agility, pulse compression, multiple PRF, pulse doppler.
126
2 Types of missile guidance
```
Command guidance
Homing guidance (semi active)
```
127
What are the 3 types of homing guidance?
Passive
Active
Semi active
128
Explain passive homing?
RF - Detects targets radar transmission using homing signal
IR - Detects target IR signature
UV - Detects target UV signature
Little or no warning
Doesnt now being tracked
No guarantee of hit
129
Explain semi -active homing
Still homes passively
Ground platform transmits a powerful illumination signal at the target
Missile home in to reflected energy
130
Explain active homing
Carries own radar and receiver
Homes onto own reflected energy of own transmissions
Downlink for initial guidance
131
Explain active vs semi active seekers
Active = autonomous, expensive, complex, less room for explosives but passive until latter stages.
Semi active = requires launch platform to illuminate, vulnerable launch platform, can use AESA radar to engage multiple targets, cheaper, more explosive, target is aware.
132
What can an AESA do?
Engage multiple targets at once?
133
Explain command to line of site CLOS and COLOS
CLOS: Launch point follows target, missile is guided and commanded to stay LOS.
COLOS: Predicts point of interception
134
What are the types of CLOS?
Manual
Semi automatic
Automatic
135
Explain manual CLOS
Target and missile tracked manually (old technology)
Training intensive
Poor against fast moving targets
136
Explain Semi auto CLOS
Target tracked manually
| Missile tracked automatically
137
Explain automatic CLOS
Target and missile tracked automatically
| Can be EO or Radar
138
What are the features of CLOS
```
Cost
Poor trajectory efficiency
Launch pad vulnerability
Single fire channel
Alerts enemy ESM
```
139
What are the 3 types of command links
Wire
Fibre optic
RF
140
Explain track via missile
Uses semi active but calculations and commands are made on the ground not in the missile head
141
Advantages of track via missile
More flexible
More accurate
EA resistant
Radar can track and illuminate multiple targets simultaneously
142
What is SAGG seeker aided ground guidance
Similar to TVM
Ground station conducts early engagement
Missile tacks over during the latter stages
More jam resistant
143
What are the requirements for a MWS?
SHLLATS
```
Spherical coverage
Long rage early warning
Speed
High probability of detection
Low FA rate
Aspect information
Threat lethality assessment
```
144
Typical missile flight diagram
Eject - Boost - Sustain - Coast - Fuse
UV - eject boost sustain
IR - All apart from fuse
RF - Close range
145
What does a MWS detect?
```
An objects Radar cross section and relative velocity
Muzzle flash
Motor ignition
Motor plume
Leading edge heating
Residual heat on motor
```
146
MWS process
Detect - Track - Declare
147
What are the issues with a MWS? 4
Launch may be outside of max detection range
Motor burn out too early
Emissions may be supressed
Clutter
148
Factors affecting detection performance? 6
```
Sensor location and FOV
Sensor sensitivity
Sensor resolution
Sensor angular discrimination
Reliability
Software
```
149
What are the 4 types of MWS?
Radar
IR
UV
Laser
150
Explain radar MWS
Incoming object should create doppler shift, affected by size, speed and approach angle
Advantages
All weather & accurate range and velocity
Disadvantages
Limited detection range
Overt
151
Explain a UV MWS
Detects UV signature from rocket motors and muzzle flashes within solar blind range.
Advantages
Covert
Can detect ignition and in flight
Disadvantages
Can't detect after MBO
Suffers atmospheric attenuation
152
Explain IR MWS
Detects IR emissions from muzzle flush and rocket motors
Advantages
Long range
Detects all flight
Disadvantages
High FA rate
Serviceability and cost
153
Explain Laser MWS
Must be able to dectect scattered laser energy or the laser itself. Looks for coherent pulsed fast rise time radiation with very narrow bandwidths.
```
Limited CM:
Absorption
Jamming
Ablation
Reflection
```
154
What parts of the spectrum to IR missiles operate?
1,2 & 4
155
What are the IR sources on an AC
```
Exhuast plume
Engine inlets
Leading edges
Nose
Engine Nozzles
```
156
What is the purpose of an IRCM? (FLARES)
To create a larger IR signature than the AC.
157
What is peak intensity?
Must radiate with sufficient intensity to be both credible and more attractive than the air platform
158
What is fast rise time?
Must reach effective intensity prior to leaving missile FOV
159
What is burn time?
Must maintain credible signature until target no longer in missile FOV
160
What are the two types of IRCCMs and what are there IRCCCMs?
Dual Band Detector = Spectral Flares
Kinematic Flare Rejection = Aerodynamic Flares (Forward Firing)
161
Explain Dual Band Detector
Looks at Band 1 and 4 to compare signatures
162
Explain Kinematic Flare Rejection
Detects flares by the sudden change in the angle of the sensor head and ignores
163
Explain Spectral Flares
Higher intensity then aircraft in all bands
164
Explain Aerodynamic Flares (Forward Firing)
Fire forward to reduce angle change in the sensor head
165
Explain BOL-IR Flares
AMD = Active Metal Decoy
Black Flares
Not visible and help against dual colour
166
Explain MTV Flares
Effective against earlier missles but show at night and give off UV
167
What are the three types of IR Jammers
```
DIRCM = Directional
LIRCM = Large Aircraft
CLIRCM = Closed Loop Laser
```
168
Explain a IRCM (Lamp System)
Emits modulated pulses similar to the ones used by missles for direction
Lamp System = Omnidirectional Emission = Wasted Energy = Less Effective range
169
Explain DIRCM
MWS detects IR threat
Handed over to DIRCM
Focuses energy, better range for same power
Needs MDD to fire a pred-determined laser jamming sequence
170
What are the advantages of a Laser IR Jammer?
Good jamming to signal ratio
| Small aperture requirement = small device
171
What are the challenges of a Laser IR Jammer?
Very narrow beam-width so requires stable and precise tracking controls
172
Explain a CLIRCM
Closed Loop Laser IRCM
Reflected energy used to identify missle to determine best jamming signal
173
What is a LPI RADAR and why do we use it?
A radar employing measures to avoid detection by passive radar detection equipment (RWR/ESM)
To overcome ESM advantage
174
What are the three LPI Radar Levels?
LPID = Low Probability of Identification
Easily detectable but not easily identifiable
LPI = Low Probability of Interception
Can detect a target but not detected itself by ESM receiver at same range outside main beam
Quiet Radar
Can detect a target and not be detected by an ESM receiver located on the target
175
What are the three types of LPI Radar Implementation?
Power Optimisation
Beam Control
Waveform Management
176
Explain Power Optimisation (LPI Radar)
Ensures minimum necessary power radiated
Power level consistent with target RCS
Only transmit when operationally essential
Power reduced as range to target decreases
Use of atmospheric absorption
177
Explain Beam Control (LPI Radar)
Narrow Mainlobe = less chance of being detected
| Extremely Low Sidelobe Levels through Tapered Ilumination
178
Explain Waveform Management (LPI Radar)
Signal energy spread in frequency reducing the signal strength and therefore the SNR in any receiver attempting to intercept
Tactics:
Frequency Hopping (Agility)
Chirping
Direct Sequency Spread Spectrum (DSSS)
179
Explain Primary Radar
Sends out a pulse of RF, small proportion is reflected back to antenna
180
Explain Secondary Radar
Ground station transmit a code signal at the target
| Transponder responds to interrogation which replies with a coded signal
181
Advantages of SSR?
Reply signal is much stronger when received at the ground station = greater range
Reduced transmitting power required by ground station for a given range = less cost
Signals in each direction are electronically coded = transmit additional information
182
Disadvantages of SSR
Aurcraft has to carry an operating transponder --> primary used in foreseeable future
Ground antenna are highly directional but cannot be designed without sidelobes
183
Applications of SSR?
Safety of flight through ATC ID/position
Safety of flight through TCAS
Communication of emergencies
IFF = stops blue on blue and ID hostiles
184
Explain Fruiting
FRUIT = False Replies Unsynchronised with time
SSR interogates on 1030MHZ, aircraft transponder replies on 1090MHz
Ground station receives replies from aircrafts responding to other ground station
Can lead to indication of aircraft which does not exist
185
Explain Garbling
Replies from two aircraft overlap if their range seperation is less than 20.3 microseconds in reply length (3.2 Nm)
186
What are the Military IFF Modes and Civilian SSR Modes?
```
Mil Mode 1
Mil Mode 2
Mil Mode 3 / Civ Mode A
Mil Mode 5
Civ Mode B
Civ Mode C
Civ Mode S
```
187
Explain Mode 1
Cockpit selectable
2-digit misson code
designates aircraft type and mission
188
Explain Mode 2
Assigned by command
4-digit octal unit code
unique identifier for a particular aircraft
189
Explain Mode 3/Civilian A
Assigned by ATC
4-digit octal unit code
Who is controlling it
190
Explain Mode C
Alitude information in increments of 100ft
| Often combined with Mode 3/A
191
What are the Emergency Mode 3/A Codes?
7500 Hijacking
7600 Lost Comms
7700 Emergency
192
Explain Military Mode 5
Encrypted message of Mode 1,2,3/A,C
| Enhanced secure data response
193
Explain Civ Mode S
Automatic collision avoidance = Traffic Collision Avoidance System (TCAS)
Functions of Mode A/C
Reduces over interrogation of transponder
