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Purpose of the Watchman Radar
The Watchman Radar has 2 roles:
2. Approach Radar
1. Airfield Surveillance Radar (ASR)
Range
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
0 15 30 45 60
Frequency
Operates in the S Band of frequencies 2 to 4 GHz (NATO E/F Band)
This means the wavelength is approximately 10cm
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
Transmitter Characteristics
MOPA Configuration (Master Oscillator – Power Amplifier)
- Master Oscillator = 70MHz crystal
- Power Amplifier = Travelling Wave Tube (TWT)
Master Oscillator
70 MHz is multiplied & mixed with a Local Oscillator to give our operating frequency
Power Amplifier - 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).
Disadvantages of the TWT
Power Amplifier
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
Aerial
• 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
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
Signal Processing Rack
The Signal Processing Rack (SPR) has several functions:
- It houses the Tx Driver, Receiver and X-Site Link
- It carries out all the signal processing for the system
- It performs system timing and control functions
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
Radar Viewing Unit
Console itself, serving a number of sensor inputs
Accepts input from Radar
Performs some processing and Displays on PPI
Enables ATC controller functions
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)
RAF HQ Strike Command
Site 1
ARIP Telecoms Concept
SSR PSR
Main
SSR PSR
Standby
RAF Scampton
RAF Boulmer
ISDN 2 ISDN 2
Site 2
SSR PSR
Main
SSR PSR
Standby
ISDN 2 ISDN 2
Site 3
SSR PSR
Main
SSR PSR
Standby
ISDN 2 ISDN 2
Site 4
SSR PSR
Main
SSR PSR
Standby
ISDN 2 ISDN 2
Site 21
SSR PSR
Main
SSR PSR
Standby
ISDN 2 ISDN 2
Site 22
SSR PSR
Main
SSR PSR
Standby
ISDN 2 ISDN 2
Site 23
SSR PSR
Main
SSR PSR
Standby
ISDN 2 ISDN 2
Roving RX (Air Defence Battery)
Roving Tx
SSR PSR
Main
SSR PSR
Standby
ISDN 2 ISDN 2
ISDN 30ISDN 30 ISDN 30ISDN 2
Mobile phone
(?)
Roving RX (briefing and Co-ordination)
ISDN 2
Dial-up ISDN connections
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