Radar Systems & Transponders

Question 1

What phrase does the word Radar come from?

Answer 1

Radio detection and range

Question 2

What is radar?

Answer 2

An object detection system that uses radio waves to determine range and velocity.

Question 3

What are the two main elements of a radar system?

Answer 3

1. Transmitter
2. Receiving Antenna

Question 4

How does primary radar work?

Answer 4

Electromagnetic energy is transmitted as a pulse. The reflected pulse is received and displayed in range and azimuth.

Question 5

What is the limitation of Primary Radar?

Answer 5

Provides limited information.

Only tells you there is something ‘x’ distance from the radar head.

Question 6

What is radar resolution?

Answer 6

The ability to distinguish between two targets on a radar display.

Question 7

What factors determine how well a radar is able to provide separate targets?

Answer 7

• Pulse width
• Pulse length

Question 8

PRT

Answer 8

Pulse Repetition Time

Question 9

PRF

Answer 9

Pulse Repetition Frequency

Question 10

What is the Pulse Repetition Time?

Answer 10

The time between the commencement of a pulse to the beginning of the next pulse.

Question 11

What is the Pulse Repetition Frequency?

Answer 11

The number of pulses per second.

Question 12

What is the Pulse Length?

Answer 12

The total length of an electromagnetic wave emission which is equal to the product of the wavelength, frequency, and time duration of emission

Question 13

What is Range Resolution?

Answer 13

The minimum distance between targets on the same bearing, such that they are displayed as separate targets.

Question 14

What is a factor affecting range resolution?

Answer 14

Pulse Length

Question 15

What limits the range of a radar?

Answer 15

The Pulse Repetition Frequency

A low PRF gives a greater range.

Question 16

Primary Radar rotations per minute?

Answer 16

25/60 rpm

Question 17

Secondary Surveillance Radar rotations per minute?

Answer 17

15 rpm

Question 18

Primary surveillance radar give broad coverage at ______________ with minimum ‘____________’ overhead.

Answer 18

1. all altitudes
2. blind space

Question 19

Limitations of Primary Radar?

Answer 19

• Range Maximum: 30NM to 55NM
• Cost of installation
• Cost of running
• Site limitations
• Local terrain
• Weather
• Identification may be slower.

Question 20

Types of beam used by Primary radar?

Answer 20

Cosecant Squared

Question 21

Main use of Primary Radar by ATC?

Answer 21

To detect non-transponder control area penetrations.

Question 22

What is a radar responder?

Answer 22

Equipment that when “interrogated” by a radar pulse will transmit back additional information.

Question 23

How does an aircraft transponder ‘respond’ to radar pulses?

Answer 23

Sends back squawk code and pressure altitude

Question 24

SSR

Answer 24

Secondary Surveillance Radar

Question 25

Maximum range of SSR?

Answer 25

250NM

Question 26

Key elements of SSR?

Answer 26

• Developed by the military
• Uses transponders in aircraft
• May include data from the aircraft including Altitude, Range, Identification code (Squawk code & Emergency code if necessary) Bearing, Ground speed
• Requires less power

Question 27

List SSR Modes

Answer 27

►1 Military aircraft role/mission/type. IFF
►2 Military aircraft tail number. IFF
►4 Military data crypto key. IFF

►3/A Military/Civil identification. (4 x 8 bit digits = 4096 codes)

►B (Not Used).
►C Pressure altitude encoding. - minimum required to operate and receive a surveillance service.
►D (Not Used).

►S 24 bit addressable code - may include data such as Automatic Dependant Surveillance
Broadcast (ADSB) data.

Question 28

Elements of SSR Mode 3/A

Answer 28

• 4 x 8 bit digits (0-7)
• Gives 4096 possible codes
• Used for Callsign/Flight Number
• Can be a discrete code assigned by ATC
• Squawk “couples” transponder code to flight plan code when aircraft is detected.

Question 29

SSR non-discrete codes

Answer 29

• 0100 Aircraft ops at ADs (or as instructed by ATC)
• 1200 VFR in E or G airspace
• 2000 Civil IFR in G airspace
• 2100 Ground testing
• 3000 Civil flights in A, C or D airspace, IFR in E
• 4000 Civil flights (Non SAR) in G > 15NM offshore
• 5000 Military Flights in A, C, D or E airspace
• 6000 Military Flights in G airspace
• 7615 Civil surveillance

Question 30

SSR emergency codes

Answer 30

• 7400 RPAS lost link
• 7500 Unlawful interference
• 7600 Radio failure
• 7700 Emergency

Question 31

SPI

Answer 31

Special Purpose Identification

Question 32

What is Special Purpose Identification?

Answer 32

A separate pulse activated by the ‘Ident’ button

• The effect is to highlight the ATC SSR symbol
• The SPI is only activated on controller request

Question 33

WAM

Answer 33

Wide Area Multilateration

Question 34

Elements of WAM?

Answer 34

• Uses multiple SSR receivers to triangulate an aircraft’s position
• Can ‘fill-in’ areas shadowed from a main SSR antenna
• Performance equals that of conventional SSR
• Passive or active system

Question 35

How is radar data relayed?

Answer 35

• Microwave links
• UHF links
• Fibre-optic cable
• Landlines

Question 36

What kind of backup power does primary radar use and why?

Answer 36

Diesel generators.

Due to the high power requirements of Primary radar, un-interruptible power supplies are not feasible.