atc

1. Air Traffic Systems

2. SECONDARY
SURVEILLANCE RADAR
INTRODUCTION
AND
BASIC PRINCIPLES
Air Traffic Systems

3. Radar Picture
Timing
&
Control
Transmitter Pulses
TX
RX
& PROCESSING
Received Signal
Basic Primary Radar

4. DISADVANTAGES OF
PRIMARY RADAR
 High Power
 Clutter
Permanent Echo's
Weather i.e. Rain etc.
 Identification

5. Radar Picture
Timing
&
Control
TX
RX
& PROCESSING
Basic Secondary Radar
SSR
Tx 1030 MHz
Rx 1090 MHz
123
ABC
Decoder Secondary returns

6. Military A/C Ident - Mode 1 3µs
Military Mission Ident - Mode 2
5 µs
Joint Military & Civil A/C Ident - Mode 3/A 8 µs
Civil A/C Ident - Mode B 17 µs
Altitude Data - Mode C
21 µs
Modes and Pulse Spacing

7. SSR Questions (Modes)
 Who are you ? (Mode 1 and 3/A)
 What is your altitude ? (Mode C)
 What is your mission number ? (Mode 2)
 Are you FRIEND or FOE ? (Mode 4)

8. Mode Interlacing
 The ability of the system to automatically
change modes.
 This enables more diverse information to
be gathered.

9. Military transponder
set to :-
Mode 1, code = 1100
Mode 3/A, code = 4170
Mode C, code = h1
Civil transponder
set to :-
Mode 3/A, code = 2210
Mode C, code = h2
Military
Civil No 2210 h2 No 2210 h2 No 2210 h2
1100 4170 h1 1100 4170 h1 1100 4170 h1
Coded
Replies
1 3/A C 1 3/A C 1 3/A C
Mode interlace pattern 1, 3A, C
MODE INTERLACING
h1 h2

10. EMERGENCY REPLIES
CIVILIAN EMERGENCY
GENERAL EMERGENCY - 7700
RADIO FAILURE - 7600
HI-JACK - 7500

11. ADVANTAGES OF SSR
OVER PRIMARY RADAR
 POSITIVE IDENTIFICATION
 CLUTTER ELIMINATION
 LOWER POWER FOR EQUIVALENT RANGE
 ACCURATE HEIGHT INFORMATION
 EMERGENCY INFORMATION

12. DISADVANTAGES OF SSR
INTERROGATIONS VIA SIDE LOBES
FALSE REPLIES UNCORRELATED IN TIME
(FRUIT)
GARBLING
TRACK WANDER

13. 200 Miles
80 miles
Aircraft
A
Aircraft
C
Aircraft
B

14. 200 Miles
80 miles
Aircraft
A
Aircraft
B
P1 P2 P3
2 s

INTERROGATION SIDE LOBE SUPPRESSION
Aircraft
C

15. Site A
PRF 250Hz
Site B
PRF 260Hz
F.R.U.I.T.

16. FRUIT
Correct reply
De-fruited
video O/P
DEFRUITER PRINCIPLE
1 PRF DELAY
Coincidence
Gate
(Frame pulses + 2 information..)
First PRP
Replies
Second PRP
Replies

17. GARBLE
A4 B2 D2 D4 F2
A2
C2 C4
F1
End of
pulse
train from
aircraft A
Beginning of
pulse train
from
aircraft B
Overlapping
replies
OVERLAPPING

18. TRACK WANDER
1st
sweep
2nd
sweep
3rd
sweep
4th
sweep

19. TRACK WANDER
1st
sweep
2nd
sweep
sweep
sweep
track

20. THE MONOPULSE SYSTEM
ELIMINATES TRACK WANDER
BECAUSE ONLY ONE PULSE
FROM A REPLY TRAIN IS NEEDED
TO OBTAIN AN ACCURATE
BEARING.

21. BORE
SIGHT
COMBINED SUM & DIFFERENCE PATTERNS

22. Mono-pulse
Secondary
Surveillance
Radar
MSSR

23. Cardion Secondary Surveillance
Radar
Antenna mounted
on Tactical
Watchman
Mounted on T101
Air Defence Radar

24. AIR
TRAFFIC
CONTROL
CIVILAIRCRAFT
MILITARY AIRCRAFT
MARITIME AIRCRAFT
NAVAL SYSTEMS
MISSILE
SSR SYSTEM APPLICATIONS

26. This is my discrete address
MODE S
Bit 1 Bit 2 Bit 3 Bit 4
1 0 1 1 1 1
0 0 0 0
Bit N
Preamble 8.0 s
I am able to reply to
your “ALL CALL”
because I have Mode S
Data block 56 s or 112 s
0.5 s
0.5 s

27. The future of SSR
Mode S – becoming
compulsory under EASA rules
CSSR and MSSR don’t
support Mode S

28. Airfield layout

29. Any Questions