Radar Principles - Secondary

Question 1

What is SSR?

Answer 1

Secondary Surveillance Radar

Question 2

Define SSR?

Answer 2

A system of Radar using Ground Interrogators and Airborne Transponders to determine the position of Aircraft in Range and Azimuth.
When agreed Modes are used, Altitude and Identity also.

Question 3

What signal does the ground transponder use to request information?

Answer 3

1030MHz

Question 4

What signal is used by the airborne transponder to reply to an interrogation?

Answer 4

1090MHz

Question 5

What types of codes are issued?

Answer 5

Discrete squawk codes
- Issued to individual aircraft
Non-Discrete codes
- Single codes issued to numerous aircraft (Cicuit)
- Special codes (Emergency Codes)
Applied by aircraft on certain occasions

Question 6

What are the emergency codes and their meanings?

Answer 6

Code 7700 - Aircraft emergency;
Code 7600 - Radio failure;
Code 7500– Unlawful interference.

Question 7

What is CCAMS?

Answer 7

Centralised Code Assignment and Management System,

(Before Mode S)

• Developed by Eurocontrol and endorsed by ICAO

Question 8

What does CCAMS do?

Answer 8

A world-wide system, where Squawk codes are given to different regions, usually with another region in between.
it has been necessary to group certain countries together into PARTICIPATING AREAS (PA)
The ICAO EUR region is divided into Seven PA

Question 9

Benefits of CCAMS?

Answer 9

• reduce RTF and cockpit workload by allocating an SSR code which will be retained by the aircraft from take-off to touchdown

Question 10

What is Mode C?

Answer 10

The transmission of vertical position information is the response to an interrogation in Mode C

Question 11

What pressure setting is used for Mode C?

Answer 11

1013.25hPA
To avoid operational errors

Question 12

What are the disadvantages of SSR? (3)

Answer 12

Garbling
Fruiting
Antenna Shadowing

Question 13

What is Garbling?

Answer 13

False codes may be displayed if aircraft are so close to each other (passing over eachother) that their responses to Mode A interrogation overlap.

Removed by a De-Garbler

Question 14

What is FRUIT?

Answer 14

False Replies Un-synchronised In Time.

Occurs when an interrogator receives a reply from
a transponder which was triggered by another interrogator.
These are removed by using a defruiter

Question 15

What is Antenna Shadowing?

Answer 15

When the onboard antenna is shadowed by the aircraft fuselage. (e.g. due to the bank angle).
This is mitigated by placing more than one antenna.

1 on top of the aircraft and 1 at the bottom.

Question 16

What is Monopulse SSR?

Answer 16

A single pulse used, and accuracy is improved by
averaging measurements made on several or all of
the pulses received in a reply from the aircraft.
FRUITING and GARBLING are minimised.

Monopulse SSR Range Accuracy
13 m