1. Air Traffic Systems
‘An air-force in miniature on just one Station' (1970’s)
.AVI file with voice over
Watchman is a
Primary Airfield Surveillance radar
Range of 60 Nautical miles:
Cluttered or un-cluttered conditions.

2. Airfield Equipments Where do we start ? Who is the customer?
Thriving metropolis of Cosford ATC…. Circa 1938

3. Airfield Equipments Where do we start ? Where are our Aircraft ?
How do we know were they are ? 3

4. RADAR RAdio Direction And Ranging
Uses a directional burst of Radio Energy to locate a target in range and bearing.

5. TAC Watchman system, several subtle differences !!5

6. Purpose of the Watchman Radar
The Watchman Radar has 2 roles:
1. Airfield Surveillance Radar (ASR)
Purpose of the Watchman Radar
MOUSE CLICKS:
1. The Watchman Radar has 2 roles:
2. Airfield Surveillance Radar - Enables controllers to monitor and guide all aircraft within range, safely through their designated airspace.
3. Approach Radar - Enables controllers to guide aircraft to within visual range of the airfield or into the range of the airfields navigational landing aids, e.g: ILS or PAR.
2. Approach Radar

7. Introduction ATC Radar Head DFTI RVU DIU TX SPR Rx Tx Fibre Optic
Cable
(4km max)
Brief look at the whole Watchman system connectivity – How we get a picture to the controllers:
MOUSE CLICKS:
1. The term ‘Radar Head’ refers to the radar cabin and the aerial system.
2. Within the radar cabin is the Tx (Transmitter), and SPR (Signal Processing Rack).
3. Also on the airfield, you usually find an ATC (Air Traffic Control) tower.
4. Starting with the transmitter then, we transmit through the aerial system.
5. We get replies back and these replies are fed down the receive chain to the SPR.
6. The radar picture is fed via fibre optic to the DIU (Display Interface Unit).
7. This picture is then passed to the RVU (Radar Viewing Unit) system to give the controllers a usable radar picture in ‘Approach’ (The floor below the ‘Local’ goldfish bowl).
8. A feed of the picture is usually fed to ‘Local’ for the DFTI (Distance From Touchdown Indicator) for very short range monitoring.
RVU
DIU TX
SPR

8. Range Used by the Navy at Naval Air Stations up to 80Nm
Crown Watchman System used by RAF has a maximum range of 60Nm
Used by the Navy at Naval Air Stations up to 80Nm
Gibraltar and Cyprus have “enhanced” systems capable of 120Nm
Ranges as shown – Apparently the Gibraltar and Cyprus systems no longer use 120 nm?

9. Frequency
Operates in the S Band of frequencies 2 to 4 GHz (NATO E/F Band) This means the wavelength is approximately 10cm
Speed = Freq x Wavelength (light and radio waves travel at 300,000,000 m/s approx) Therefore 10cm is approx 3GHz

10. Frequency ‘S’ band radar Working frequency between 2.705 – 3.05 GHz
Wavelength
approx. 10 cm 10

11. Pulse Repetition Frequency
With “Uniform” triggering, the PRF is 1,100 pulses per second (pps) This means that the Pulse Repetition Interval (PRI) is 909µs

12. Transmitter Characteristics
MOPA Configuration (Master Oscillator – Power Amplifier)
- Master Oscillator = 70MHz crystal
- Power Amplifier = Travelling Wave Tube (TWT)
70MHz crystal is used for initial transmitter pulse production (multiplied/mixed to nominal 490MHz prior to mixing with our carrier frequency of approx 2.5GHz)
TWT is used as our power amplifier – wide band amplifier and very stable over the range of frequencies.

13. Master Oscillator
70 MHz is multiplied & mixed with a Local Oscillator to give our operating frequency

14. The TWT is only 20% efficient, the other 80% dissipated as heat
Power Amplifier - TWT
Disadvantages of the TWT
Efficiency
The TWT is only 20% efficient, the other 80% dissipated as heat
Cost
A new TWT cost around £100,000 (can be refurbished – identified by being blue in colour and may have a suffix ‘R’ after the serial number). 14

15. Power Amplifier Travelling Wave Tube (TWT) RF In Helix RF Out Heater
Simplified picture of the TWT. Elements are:
Heater – This is used to excite electrons so they are just “hovering” above the Cathode plate – If a heater wasn’t used, the Catchode would be stripped of its’ coating when transmission starts
Cathode – Set at a high negative potential; This is the source of the electron beam during transmission
Grid – Set more negative than the Cathode during non-transmission periods to “Gate off” the TWT
Helix – A Coil running through the tube which employs “Velocity Modulation” (simply put, it slows some electrons down and speeds some up causing electron bunching!) It is this that performs the amplification we require.
Collector – Set at a more positive potential than the Cathode to attract the electrons (when the grid says so of course!) and produce the TWT beam.
RF In – For the watchman this is fed in on co-axial cable at the required power level for the TWT.
RF Out – To minimise losses, this is fed out on waveguide.
MOUSE CLICKS:
Shows Beam Current when Grid gated on
Showing small RF In arriving
Showing Amplified RF Out
Heater
Cathode
Grid
Collector

16. Power Amplifier - Stability - Very stable across the frequency range
So why use a Travelling Wave Tube (TWT)?
- Bandwidth – Wide band so we can transmit at different frequencies
- Stability - Very stable across the frequency range
Advantages of using TWTs

17. Travelling Wave Tube
Emulator graphics of the Watchman TWT.

18. Mean Output Power = Approx 1 kW
TWT Output Power
Peak Output Power = kW
Mean Output Power = Approx 1 kW
Watchman TWT Output powers – 1.5 kW

19. The Aerial consists of a parabolic reflector and 2 horns
The Main Beam horn
which is used for Tx
and Rx
The Aux Beam horn
for Rx only
Nice picture of Watchman Aerial.

20. Aerial Properties The Aerial rotates at 15rpm (4 Seconds)
It can survive wind speeds of up to 70 knots while operating
If switched off and left to weathercock, it can survive up to 120 knot winds
The slide says it all!

21. Signal Processing Rack
The Signal Processing Rack (SPR) has several functions:
- It houses the Tx Driver, Receiver and X-Site Link
Signal Processing Rack Functions
MOUSE CLICKS
It houses the Tx Driver and Receiver
2. It carries out all the signal processing for the system
3. It performs system timing and control functions
- It carries out all the signal processing for the system
- It performs system timing and control functions

22. Signal Processing 4 video channels in the watchman system
3 processed video channels
Normal Radar Video (NR)
Ground Clutter Filter (GCF)
Moving Clutter Filter (MCF)
1 unprocessed channel
Background Video 22

23. Radar Viewing Unit Accepts input from Radar
Console itself, serving a number of sensor inputs
Accepts input from Radar
Signal Processing Rack Functions
MOUSE CLICKS
It houses the Tx Driver and Receiver
2. It carries out all the signal processing for the system
3. It performs system timing and control functions
Performs some processing and Displays on PPI
Enables ATC controller functions

24. Display Monitor Processor Unit
Nice photo of the Display Console showing the Display Monitor and Processor Unit locations. The processor Unit is just a standard desktop PC unit.

25. Severe sea clutter appears in Main beam; sea conditions where not excessive, but probably due to anaprop beam bending.

26. MOUSE CLICKS:
QWERTY Control Panel
Trackball / Hotkey Array

27. WATCHMAN RDS 1600 DISPLAY

28. WATCHMAN RDS 1600 DIST UNIT

29. WATCHMAN RDS 1600 KEYBOARDAND TRACKERBALL ASSY

30. AIRFIELD RADAR INTEGRATION PROJECT
(ARIP)
The system must, therefore, be poised to counter threats that develop with warning and, more importantly, those that arise with little or no warning. To counter the threat the ASACS must be capable of detecting the presence of such rogue aircraft and, then directing the effective employment of AD assets, in accordance with political guidance, to thwart the terrorists aims and protect the general public.
Given the potentially short warning times associated with rogue aircraft incidents and the unpredictability of likely terrorist targets the ASACS is to be provided, under the ARIP programme, with the maximum degree of low level primary radar coverage. Under this programme, existing ASACS radar coverage is to be enhanced with data from a large number of military and civil-owned airfield radars which provide coverage of likely target areas. During Phase 1 of ARIP, this airfield radar data will be provided via separate stand-alone displays. Following introduction of a major ASACS equipment upgrade known as the UKADGE Capability Maintenance Programme (UCMP) in 2004, Phase 2 of the ARIP will allow airfield radar data to be integrated more fully into the ASACS system such that the data will be presented to operators on a common UCMP display.

31. Why ARIP?
After the September 11th attacks in the USA, it was decided to augment the UK’s Air Defence network by feeding in Airfield Radar pictures to the Control & Reporting Centres (CRCs)
Reason why ARIP came along was directly due to the September 11th attacks in 2001.
It was decided that the UK Air Defence network (UK ASACS = Air Surveillance And Control System) would benefit from additional coverage that could be provided from Airfield Radars.

32. Roving RX (Air Defence Battery) RAF Scampton RAF Boulmer
Site 1
Site 2
Site 3
Site 4
Site 21
Site 22
Site 23
Main
Standby
Main
Standby
Main
Standby
Main
Standby
Main
Standby
Main
Standby
Main
Standby
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
SSR
PSR
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
ISDN 2
Roving Tx
Dial-up ISDN connections
Main
Standby
SSR
PSR
SSR
PSR
Roving RX (briefing and Co-ordination)
ISDN 2
ISDN 2
ISDN 2
Mobile phone (?)
Roving RX (Air Defence Battery)
ISDN 2
RAF Scampton
ISDN 30
RAF HQ Strike Command
ISDN 30
RAF Boulmer
ISDN 30
ARIP Telecoms Concept

33. ARIP WATCHMAN DISPLAY REPRESENTATION

34. Airfield layout

35. Any Questions?
1. What is the range of the standard Crown Watchman Radar? (A: 60Nm)
2. What Frequency Band does the Radar Operate on? (A: S Band or NATO E/F – 2 to 4GHz)
3. What is the “Uniform” PRI in µs? (A: 909 µs)
4. Why do we normally use “Staggered PRFs”? (A: To overcome the effects of Blind Speeds)
5. Our transmitter configuration is described as MOPA – What is MOPA and Describe it? (A: MOPA= Master Oscillator Power Amplifier, We use a 70MHz Oscillator and a TWT Power Amplifier).
6. What are the 2 advantageous characteristics of the TWT that causes us to use it? (A: It is a “Wideband” amplifier, that operates with a high degree of “Stability” across the frequency range)
7. What is the approximate PEAK output power of the Watchman? (A: 50 to 55kW)
8. What are the 2 pulse lengths of the Short Pulse and Long Pulse? (A: 0.4 µs and 20 µs)
9. How often are the 2 frequencies (F1 and F2) swapped in “Diversity“ mode? (A: Every 9 PRIs)
10. Why do we use 2 horns on the Watchman System? (A: We use 2 Rx beams, Main and Aux – The Aux beam just looks at the first 17Nm and is pointed slightly upwards to eliminated close-in ground clutter; The Main beam is selected for the remainder of the 60Nm range)
11. What is the approximate Azimuth Beamwidth at the 3dB points? (A: 1.5°)
12. What is the rotational Speed of the Aerial? (A: 15 rpm)
13. Give me 2 functions of the Signal Processing Rack (SPR) (A: 1. Houses Tx Driver and Receiver; 2. Carries out Signal Processing for the System; 3. Performs system timing and control functions)