Secondary Radar Principles Flashcards
Define Secondary Surveillance Radar
Ground interrogators and airborne transponders determine the range and azimuth of aircraft. Height and identity will be displayed also, if equipment allows.
What frequency does the ground interrogator transmit on?
1030MHz
What frequency does an airborne transponder reply on?
1090MHz
Which wavelength is used for SSR?
30cm
Describe the interrogator process
The interrogator transmits Mode A pulses
For vertical position info, the interrogator transmits Mode C pulses
What is the difference between Mode A and C pulses?
The timing between the pulses
Mode A - 8.5uS
Mode C - 21uS
Describe the Reply process for Mode A
The airborne transponder recognises Mode A interrogation.
12 bits of binary are transmitted in reply that correspond to the allocated Squawk
How many discrete squawk codes are available?
4096
What are the three binary bit numbers used?
4, 2 and 1
Why are squawk codes issued to aircraft?
To ease the task of identification and the monitoring of an aircrafts progress.
What are the ways squawk codes can be used?
Discrete - Single codes issued to individual aircraft
Non-discrete - Single codes issued to numerous aircraft
Special Codes applied by aircraft on certain occasions
What is CCAMS?
Central Code Assignment and Management System
What is the purpose of CCAMS?
To organise squawks, by use of an algorithm, so that an aircraft can have only one squawk from takeoff to touchdown. This will reduce RTF and cockpit workload.
Describe Conspicuity Codes
Non-Discrete codes assigned to individual positions to identify aircraft being controlled by a particular unit.
What are the emergency codes?
7500 - Taken Alive
7600 - Radio Tricks
7700 - Going to Heaven
Describe the Reply Process for Mode C
Mode C interrogation is recognised, then 11 bits of data which correlate to the vertical position information are replied.
Vertical position is based on the 1013.2hPa only, from which computer processors determine and display the accurate FL or A based on inputted local QNH and Transition Level.
Describe Garbling
When responses to Mode A interrogation overlap due to aircraft proximity to each other. Usually when aircraft pass over each other.
Ground equipment can be fitted with a de-garbler.
Describe Fruit
False Replies Un-synchronised In Time
When an interrogator receives a reply from a transponder triggered by a third party rather than itself.
Removed by a de-fruiter.
What are SSRs vulnerable to?
Antenna Shadowing, mitigated by placing more than one antenna
