EQPS - Radar Principles (Secondary) Flashcards
What is the definition of Secondary radar? (1)
SECONDARY SURVEILLANCE RADAR
A SYSTEM OF RADAR USING GROUND INTERROGATORS AND AIRBORNE
TRANSPONDERS TO DETERMINE THE POSITION OF AIRCRAFT IN RANGE AND AZIMUTH, AND WHEN AGREED MODES AND CODES ARE USED, HEIGHT AND IDENTITY ALSO
What are the frequencies of an Interrogator & Transponder? (2)
Interrogator (on ground) - 1030Mhz
Transponder (aircraft) - 1090Mhz
What wavelength does SSR use? (1)
30cm
What is the Interrogator Process? (3)
- Communicates a request for identification information by transmitting MODE A pairs of pulses
- Vertical position information the interrogator transmits MODE C pairs of pulses
- Difference between Mode A + C is the timing between the pulses
What is the Reply Process? (3)
- The aircraft transponder recognises the interrogator Mode by the time interval
- Transponder response to an interrogation consists of a train of pulses containing binary bits of information
- Each of the binary bits in the information pulses can respond in one of two ways, either as a 0 or as a 1
Reply Process diagram
How many pulses are there in the Reply Process? (1)
12 INFORMATION PULSES
What is Mode A? (3)
- Binary bit is used to represent data in a form compatible with computer processing
- No more than 12 bits can be transmitted at a time
- Mode A = 4 numbers are needed (Squawk)
Mode A Binary process
Squawk code 4361 is:
100 011 110 001
How many possible combinations binary combinations for Mode A? (1)
4096
What is a Discrete Squawk Code? (5)
- Issued to individual aircraft
- Non Discrete
- Single codes issued to numerous aircraft
- Special codes
- Applied by aircraft on certain occasions
What is the benefit of having Mode A? (1)
Identifying aircraft
What is CCAMS? (1)
Centralised Code Assignment and Management System
(Developed by Eurocontrol and endorsed by ICAO)
What is a Participating Area (CCAMS)? (1)
A Groups of countries within a region for CCAMS
What is CCAMS designed for? (4)
- RTF
- Cockpit work-load
- Helps ATCOs in forward planning
- Assist in radar data processing & data exchange programmes
How many blocks of codes is an ACC allocated? (2)
2 blocks:
- Domestic codes
- International codes
Who will assign a discrete code within the first airspace entered? (1)
ACC with jurisdiction of the airspace
What is Conspicuity codes? (1)
Codes assigned to individual positions to identify aircraft being controlled by a particular unit to another unit
Where are Conspicuity codes found? (1)
AIP
What are the 3 special codes for emergencies? (3)
7500 - Unlawful interference
7600 - Radio failure
7700 - Aircraft emergency
How many bits is used by Mode C? (2)
11 bits
Allows digits of 8 & 9
(e.g. FL090/A028)
What is the maximum uplink capacity for Mode C? (1)
23 bits
What pressure is referred to on Mode C? (1)
1013.2 hPa
How is Altitude shown on a Situational Display? (1)
Local QNH & Transition Level is input to the computer processor
What is Garbling? (2)
Unwanted Responses
False codes may be displayed if aircraft are so close to each other that their responses to Mode A interrogation overlap
When can Garbling occur? (1)
When 2 A/C are close together to overlap their replies
(Usually happens when they pass over each other)
How is Garbling overcome? (1)
A DE-GARBLER
What is FRUIT? (2)
False Replies Un-synchronised In Time
When an interrogator receives a reply from a transponder which was triggered by another interrogator
How is FRUIT removed? (1)
Defruiter
How is Antenna shadowing mitigated? (1)
By placing more than one antenna
(Generally two: one on top of the aircraft and one at the bottom)
What is Monopulse SSR? (3)
- Single pulse
- Averaging measurements made on several or all of the pulses received in a reply from the aircraft
- FRUITING and GARBLING are minimised
Gives better accuracy
