Introduction to Radar Warning Receiver

February 9, 2018 | Author: Pobitra Chele | Category: Electronic Engineering, Telecommunications, Wireless, Radio Technology, Radio
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2/23/2009

Introduction to Radar Warning Receivers Robins AFB February 24, 2009 Presenter: Kim Cole

Copyright by Georgia Tech Research Corporation, 2009

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What is a Radar Warning Receiver? • A Radar Warning Receiver (RWR) is a passive EW

system that does the following: • Detects RF signals transmitted by radar systems • Identifies the signal by radar type • Manages detected signals • Generates visual and audio cues to pilot • Manages interfaces to other systems

Copyright by Georgia Tech Research Corporation, 2009

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What the Pilot Sees

Copyright by Georgia Tech Research Corporation, 2009

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ALR-69 System Block Diagram CVR SUBSYSTEM

CVR 135 AM-423 45

CVR 45

J1

J1

E, G, I (135)

AM-423 135

J3

J2 J3

CVR 225

CVR 315

J1

AM-423 225

AS-3305 (45) (135) (Omni) (315) (225)

CM-479

E, G, I (45)

J2

E, G, I (225)

E, G, I (315)

ALQ-213 CMSP IP1310 F1

2X 2Y J1

J3

J1 F2

J4

J2

Diamond Audio

J2

J2

J3

J3

E, G, I Band Video (45, 135, 225, 315) C/D Band Video (45, 135, 225, 315) Omni Video

AM-423 315 AM-6971

J1 J2 J5 J4 J3

J6

J3

J1

J5

HSDB J4

J2 N1

J7

ANT7

C/D, E, G, I Band Static Video (TTL)

FSRS Subsystem AM-423 135 (FSRS)

J2

AM-423 45 (FSRS)

J1

AM-423 225 (FSRS)

AM-423 315 (FSRS)

F1 F2

J3

J1 J5

J2

J3

J3 J4

F3

R-2094 J1

J6

C-10373

Antenna Control (0-3)

SA-2263

J5

J2

J4

RI/D, Control (0-3), CW Strobe, PRF Window Rec. Int., Discrimn. Video, Bandpass Video

Copyright by Georgia Tech Research Corporation, 2009

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ALR-69 System

Copyright by Georgia Tech Research Corporation, 2009

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What the Pilot Sees

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(Very) Brief History of RWR

• RWRs have been around for about 40 years. • First-generation RWRs were used by the US Air Force

during the Vietnam War in response to Russian radarguided SAMs deployed in North Vietnam. • The Israelis suffered heavy losses to radar-directed

AAA and SAMs during the 1973 Yom Kippur War.

Copyright by Georgia Tech Research Corporation, 2009

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Example USAF RWR Installations

RWR Type

Aircraft

ALR-56C

F-15

ALR-56M

F-16, C-130, B-1

ALR-69

B-52, A-10, C-130, F-16, C-130

ALR-94

F-22

APR-39

C-130, V-22

Copyright by Georgia Tech Research Corporation, 2009

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How Does an RWR Work? • Hardware handles detection • Hardware detects radar pulses and converts pulse parameters to

digital format • Major hardware components: antennas, RF cables, receiver,

signal processor, user I/O devices

• Software handles identification and aircrew interface • Software processes digital data to determine what type of radar

system is illuminating the aircraft and then provides aircrew cues • Major software components: operational flight program and

mission data file

Copyright by Georgia Tech Research Corporation, 2009

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Why Do You Need an RWR? • The enemy is out there! • The enemy has air defense systems that are very

dependent on radar and RF-guided weapons. • They have surface-to-air-missiles (SAMs), anti-aircraft

artillery (AAA), and air-to-air missiles that are cued/targeted/guided by RF signals. • When an enemy radar points at a USAF aircraft, we

can detect that signal and warn the aircrew of the presence of that weapon system. GTRI_B-10

Copyright by Georgia Tech Research Corporation, 2009

Typical Air Defense System Encounter

MISSILE LAUNCHER

COMMAND STATION

MISSILE TRACKER COMPUTER VAN TARGET TRACKER

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SA-2 Surface to Air Missile

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RWR Operational Concept 0

7 8

7

0

8 Processor

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Copyright by Georgia Tech Research Corporation, 2009

How Do We Measure RWR Performance? • Typical RWR measures of performance (MOPs) are: • Detection range • Response time • Correct ID • DF accuracy • Age out

• Performance is usually measured by conducting a

flight test on an open-air range. GTRI_B-14

Copyright by Georgia Tech Research Corporation, 2009

Simplified RWR Processing Flow

Input Buffer

RF

Signal Detection Hardware

Signal Processing

Emitter Track File

Manage Interfaces

Software

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Software

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Origin of RWR Input

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RWR Frequency Coverage • A typical RWR detects pulsed radar signals in the

0.5-18 GHz frequency range. • Frequency is measured in “Hertz” • Hertz is a unit of frequency of one cycle per second. 6 Hertz 3 Hertz

One second

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Types of Radar Signals • Continuous Wave

• Pulsed

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Quick Word About Notation for Pulsed Signals

All meant to illustrate the same concept.

Time

Copyright by Georgia Tech Research Corporation, 2009

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What Measurements Does an RWR Make? • For each CW signal the RWR will measure: • Frequency, angle of arrival, and power

• For each pulse in a pulsed signal the RWR will

measure: • Frequency or frequency band, time of arrival (TOA),

angle of arrival (AOA or DF), pulse width, and power • For CW or pulsed signals outside the RF coverage

of the RWR, no measurement is made.

Copyright by Georgia Tech Research Corporation, 2009

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First Step: Detect Signal with Antenna E/J Band antenna Four per aircraft

C/D Band antenna One per aircraft

Copyright by Georgia Tech Research Corporation, 2009

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First Step: Detect Signal with Antenna

315°

45°

Four E/J band antennas are installed at quadrant locations around aircraft. 225°

Copyright by Georgia Tech Research Corporation, 2009

135°

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F-16 Forward Antenna Installation

Copyright by Georgia Tech Research Corporation, 2009

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F-16 Aft Antenna Installation

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Converting RF Pulse to Digital Data Quadrant antennas

Pulse Measurement Data

Receiver

To software For Signal processing

Copyright by Georgia Tech Research Corporation, 2009

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Basic Analog Receivers1 (1/2) Receiver

Advantage

Disadvantage

Wideband Crystal Video

Simple; Inexpensive Instantaneous High POI in frequency range

No frequency resolution Poor sensitivity Poor simultaneous signal

Tuned RF Crystal Video

Simple Frequency measurement Higher sensitivity than wideband

Slow response time Poor POI

IFM

Relatively simple Frequency resolution Instantaneous; High POI

Simultaneous signal problem Relatively poor sensitivity

Narrow Band Scanning Superhet

High sensitivity Good frequency resolution No simultaneous signals problem

Slow Response Poor POI Poor against freq agility

Wideband Superhet

Better response time Better POI

Spurious signals generated Poorer sensitivity

Copyright by Georgia Tech Research Corporation, 2009

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Basic Analog Receivers1 (2/2) Receiver

Advantage

Disadvantage

Channelized

Wide bandwidth Near instantaneous Moderate frequency resolution

High complexity, cost Lower reliability Limited sensitivity

Microscan

Near instantaneous Good frequency resolution Good dynamic range Good simultaneous signal capability

High complexity Limited bandwidth No pulse modulation information Critical alignment

Acousto-optic

Near instantaneous Good frequency resolution Good simultaneous signal capability Good POI

High complexity New technology

1 Electronic Warfare And

Radar Systems Engineering Handbook, NAWCWPNS TP 8347, April 1, 1999

Copyright by Georgia Tech Research Corporation, 2009

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Most Common RWR Receiver Architectures

Crystal Video Receiver RF Amplifier

Compressive Video Amplifier Band 1 Video

Multiplexer

Band 2 Video

Tuned Narrowband Superhet IF Amp RF Filter Tuning

Band 3 Video

IF Filter

Log Video Amp

Video

Local Oscillator

Copyright by Georgia Tech Research Corporation, 2009

Filename - 31

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Narrow-Band Superheterodyne Receiver • Narrow bandwidth • -90 dBm sensitivity • Low probability of intercept (POI) • Good signal separation • Measures frequency, PW, power, and AOA • Excellent CW Capability • Medium cost • Medium volume Copyright by Georgia Tech Research Corporation, 2009

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Wideband Crystal Video Receiver • Wide instantaneous bandwidth • - 45 dBm sensitivity • High probability of intercept • Poor signal separation • Measures frequency band, PW, power, and AOA • Poor CW Capability • Low cost • Small volume Copyright by Georgia Tech Research Corporation, 2009

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Input Scheduling • Another important RWR term is input scheduling. • Both superhet and CVR architectures require

sophisticated input schedulers. • The input schedule is usually defined in the mission

data file. • We have said that a typical RWR covers the 0.5-18

GHz frequency range, but they typically do not collect inputs from the entire range at one time. GTRI_B-34

Copyright by Georgia Tech Research Corporation, 2009

CVR Input Scheduling • A typical CVR RF signal is fed to an

amplifier/detector that splits the covered RF range into multiple frequency bands. • A typical CVR looks (collects input) from a single RF

band at a time. • Example band breaks are shown below. Band 0

Band 1 2 GHz

0.5 GHz

Band 2 8 GHz

Band 3 12 GHz

18 GHz

Copyright by Georgia Tech Research Corporation, 2009

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Example CVR Input Schedules More realistic schedule Really simple schedule Band Look Time

Band

Look Time

0

10 ms

0

25 ms

1

12 ms

1

25 ms

2

15 ms

2

25 ms

3

15 ms

3

25 ms

0

50 ms (conditional)

2

1 ms

3

1 ms

1

20 ms

3

25 ms

Copyright by Georgia Tech Research Corporation, 2009

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Simple Probability of Intercept Example Scanning threat radar

RWR input scheduler Band 0

Band 1

Band 2

Band 3

Band 0

Filename - 37

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Copyright by Georgia Tech Research Corporation, 2009

Emitter Transmitted Frequency Range Threat ID A B C D E F G H I J K L M N O P Q R 2

4

6

8

10 RF (GHz)

12

14

16

18

GTRI_B-38

Copyright by Georgia Tech Research Corporation, 2009

Superhet Input Scheduler • The input schedule for a superhet receiver is much

more complex than the input schedule for a CVR. • This is because the superhet is a narrow-band

receiver, i.e. the total frequency range is broken into many smaller segments that must be covered. • Superhet input schedulers contain more numerous,

shorter looks.

0.5 GHz

2 GHz

8 GHz

12 GHz

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18 GHz

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Pulse Measurements

• If the RWR detects a pulse, it collects a set of data

for that pulse. • The formats differ among various RWRs, but this

pulse data is generally called a pulse descriptor word (PDW). • The PDW contains all data collected for a single RF

pulse.

GTRI_B-40

Copyright by Georgia Tech Research Corporation, 2009

Pulse Descriptor Word • A typical PDW contains time of arrival (TOA), angle,

pulse width, power, and frequency (superhet) or frequency band (CVR). • The ALR-69 PDW format is shown below: 0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

TIME OF ARRIVAL (16 LSBs) PULSE WIDTH

TIME OF ARRIVAL (8 MSBs)

POWER IP

PP FO1 FO2 PRI

ANGLE DT RB1 RB2 DCB COR CDM B0

B1

B2

B3

B4

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Copyright by Georgia Tech Research Corporation, 2009

Key Pulse Parameters Frequency

Pulsewidth

Power

PRI “PRI” is Pulse Repetition Interval. Time

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Input Buffer

• The final output of the Signal Detection component

of the RWR is an Input Buffer. • An Input Buffer is a series of PDWs that were

collected during a single look. • The Input Buffer is processed by the RWR software

to determine what type radar (or radars) transmitted the pulses.

GTRI_B-43

Copyright by Georgia Tech Research Corporation, 2009

Simplified RWR Processing Flow

Input Buffer

RF

Signal Detection

Signal Processing

Hardware

Emitter Track File

Manage Interfaces

Software

Software

GTRI_B-44

Copyright by Georgia Tech Research Corporation, 2009

OFP and MDF Operational Flight Program (OFP)

• Executable code • Input scheduler • PRI deinterleaver • Track file management • Missile guidance

Mission Data File (MDF)

• Data (no executable

code) • Input schedule • Threat identification • Threat information • Ambiguity resolve tables

algorithms • Interface management

• Missile guidance data

Copyright by Georgia Tech Research Corporation, 2009

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Major Signal Processing Components

Emitter Track File

Input Buffer PRI Deinterleave

Ambiguity Resolve

Threat ID

Track File Management

Filename - 46

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Copyright by Georgia Tech Research Corporation, 2009

PRI Deinterleaving Algorithm • Many years of research have been done regarding

PRI deinterleaving algorithms. • The PRI deinterleaving algorithm is the most

complex algorithm, and uses the most processor time, of any function in an RWR OFP. Input Buffer

Pulse train statistics: Frequency/band PRI Power Angle Pulse width PRI agility info Quality statistics

PRI Deinterleave

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Copyright by Georgia Tech Research Corporation, 2009

PRI Agility Stable • For a “stable PRI” emitter the interpulse period is

the same for every pulse. 175

175

175

175

175

175

175

175

175

175

175

175

175

175

175

175

175

Copyright by Georgia Tech Research Corporation, 2009

175

175

175

175

175

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PRI Agility Stagger • For a “staggered PRI” emitter, a set of interpulse

periods are repeated continuously. • 2-level stagger 150

175

150

175

150

175

150

175

150

175

150

175

150

175

150

175

150

175

150

175

150

175

175

225

150

175

225

150

175

225

150

175

225

150

175

225

150

200

150

175

125

200

150

175

125

200

150

175

125

200

150

175

• 3-level stagger 150

175

225

150

175

225

150

• 4-level stagger 150

175

125

200

150

175

125

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Copyright by Georgia Tech Research Corporation, 2009

PRI Agility Cycler • For a “cyclic PRI” emitter a stable PRI is generated

for N pulses followed by another stable PRI for N pulses, etc. • For example, this cycler generates a PRI of 175 for

seven pulses and then a PRI of 150 for four pulses. 175

175

175

175

175

175

175

150

150

150

150

175

175

175

175

175

175

175

150

150

150

150

GTRI_B-50

Copyright by Georgia Tech Research Corporation, 2009

PRI Agility Jitter • For a “jitter PRI” emitter, the interpulse period

varies between every pulse usually within a known percentage range. • For example, the pulse train below is a 200 +/- 10%

jitter pulse train, i.e. the interpulse periods vary randomly between 180 and 220.

200

183

182

201

199

185

217

216

209

188

181

199

207

207

187

183

184

Copyright by Georgia Tech Research Corporation, 2009

218

203

204

200

181

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PRI Deinterleaving Radar Signal A

Radar Signal B

Radar Signal C

Interleaved Signal

Copyright by Georgia Tech Research Corporation, 2009

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PRI Deinterleaving - Sorting

Hardware Measurement

Useful for Sorting?

Frequency or Frequency Band

Yes

Time of Arrival

Yes

Angle of Arrival

Yes

Power

No

Pulse Width

Not so much

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Copyright by Georgia Tech Research Corporation, 2009

Major Signal Processing Components

Emitter Track File

Input Buffer PRI Deinterleave

Threat ID

Ambiguity Resolve

Track File Management

Copyright by Georgia Tech Research Corporation, 2009

Filename - 54

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Threat Identification • Initial threat identification is usually a very simple

process. • The MDF assigns an initial threat ID based on

frequency/band and PRI. • So, “threat ID” is simply finding the corresponding

entry in a table in the Mission Data File. • Most initial threat IDs are ambiguous and require

ambiguity resolution. GTRI_B-55

Copyright by Georgia Tech Research Corporation, 2009

Emitter PRI Range Threat ID A B C D E F G H I J K L M N O P Q R 0

500

1000

1500 2000 2500 PRI (microseconds)

3000

3500

4000

GTRI_B-56

Copyright by Georgia Tech Research Corporation, 2009

Major Signal Processing Components

Emitter Track File

Input Buffer PRI Deinterleave

Threat ID

Ambiguity Resolve

Track File Management

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Filename - 57

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Ambiguity Resolution • Initial threat ID is done based on frequency/band and

PRI. • This usually results in an ID that says “this could be either Threat

A, Threat C, Threat D, or Threat H”.

• Additional measurements are used/required to resolve

ambiguities and determine which a unique ID. • PRI agility (jitter, stagger, cycler) • Multiband • Scan type/rate • Missile guidance GTRI_B-58

Copyright by Georgia Tech Research Corporation, 2009

Major Signal Processing Components

Emitter Track File

Input Buffer PRI Deinterleave

Threat ID

Ambiguity Resolve

Track File Management

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Filename - 59

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Track File Management

• All RWRs have some concept of a Track File. It may

be called different names in different RWRs, but the concept is the same. • The Track File is where the OFP stores all threat

information that is has measured/computed.

Copyright by Georgia Tech Research Corporation, 2009

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Track File Management (cont.)

• The Track File management software is almost as

complex as the PRI Deinterleaving software. • The OFP updates the track file as new information

becomes available. • There are many sources of new information:

correlation, missile guidance, angle, power, PRI agility, etc.

GTRI_B-61

Copyright by Georgia Tech Research Corporation, 2009

Track File Management (cont.) • The Emitter Track File is the most important data

maintained by the RWR OFP. • The ETF content affects operation of almost all

other OFP functions • Pilot cues (audio and display) • Initiates additional measurements for ambiguity

resolution • Alters input scheduling

• The ETF is output to other systems in an integrated

EW suite and may drive their operation as well. GTRI_B-62

Copyright by Georgia Tech Research Corporation, 2009

Simplified RWR Processing Flow

Input Buffer

RF

Signal Detection Hardware

Signal Processing

Emitter Track File

Manage Interfaces

Software

Copyright by Georgia Tech Research Corporation, 2009

Software

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User Interface • Buttons/Lamps • CRT Display • Audio • Missile launch • New guy • Diamond

Copyright by Georgia Tech Research Corporation, 2009

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Interface Management

• Besides the user interface the OFP also manages

other intrasystem and intersystem input/output. • Intrasystem: Setting up pulse collection hardware,

messaging on intrasystem hardware interfaces, messaging between OFPs within the RWR, etc. • Intersystem: MIL-STD-1553B data bus (EW Bus and

Avionics Bus), blanking interface, etc.

Copyright by Georgia Tech Research Corporation, 2009

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RWR “Challenges” • There are many challenges to accurately and

effectively operating an RWR in a real-world environment: • High pulse densities • Interference from other onboard systems • Aircraft maneuvers • Urban noise • Antenna patterns Copyright by Georgia Tech Research Corporation, 2009

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ALR-69 System Block Diagram CVR SUBSYSTEM

CVR 135 AM-423 45

CVR 45

J1

J1

E, G, I (135)

AM-423 135

J3

J2 J3

CVR 225

CVR 315

J1

AM-423 225

AS-3305 (45) (135) (Omni) (315) (225)

CM-479

E, G, I (45)

J2

E, G, I (225)

E, G, I (315)

ALQ-213 CMSP IP1310 F1

2X 2Y J1

J3

J1 F2

J4

J2

Diamond Audio

J2

J2

J3

J3

E, G, I Band Video (45, 135, 225, 315) C/D Band Video (45, 135, 225, 315) Omni Video

AM-423 315 AM-6971

J1 J2 J5 J4 J3

J6

J3

J1

J5

HSDB J4

J2 N1

J7

ANT7

C/D, E, G, I Band Static Video (TTL)

FSRS Subsystem AM-423 135 (FSRS)

J2

AM-423 45 (FSRS)

J1

F1 F2

J3

J3 J4

J1 J5

J2

J3

AM-423 315 (FSRS)

F3

R-2094 J1

J6

AM-423 225 (FSRS)

C-10373

Antenna Control (0-3)

SA-2263

J5

J2

J4

RI/D, Control (0-3), CW Strobe, PRF Window Rec. Int., Discrimn. Video, Bandpass Video GTRI_B-67

Copyright by Georgia Tech Research Corporation, 2009

The Travels of “Joe Pulse” RF

RF cable

Input Buffer

Process Buffer Pre-Process (PRE_PROC)

A6 RAM

ETF Record ETF

A6 RAM

A6 OFP Display Update

Display File A4 RAM

Pre-amp

Antenna Air

Pulse packet

Video pulse

RF

Input Buffer

AM-6639

J1

J2

PRI Deinterleave (PRIDE)

A4 OFP Display Update

Quadrant video signals

PRIDE Outputs A6OFP variables

Refresh Buffer A4 RAM

Video Processor (A5 CCA)

Emitter ID (EIDR)

Display Refresh

DMA FIFO

Threat ID A6OFP variables CRT Drive H/W

A6 RAM

ETF Mgt (ETE)

ETF Record ETF

IP-1310

I/O

Copyright by Georgia Tech Research Corporation, 2009

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