2 Electronic Support Flashcards
ESM receivers are used for _____ reaction.
Real-time
ES Receivers may be devided into two categories:
Threat Warning Receiver (TWR) and;
Reconaissance/Surveillance Receivers
What is a Threat Warning Receiver (TWR)?
Provides threat warning over a preset frequency range in real time. It gives you advanced warning that a threat is present.
TWR is _____ sensitivity.
Low
What is a Reconnaissance/Surveillance Receiver?
Have higher sensitivity and direction finding accuracy to measure more radar parameters. Can be real time or long analysis.
Reconnaissance/Surveillance Receivers are _______ sensitivty.
High
What are the four functions of an Electronic Support system?
Reception - radar pusle is intercepted and detected
Measurement - signal parameters are measured
Recognition - compare against library
Display / Report - to operator and CCS
What are three domains which ES systems must operate?
Signal Domain
Temporal Domain
Spatial Domain
Signal Domain
Receiver polarization and frequency must match
Temporal Domain
Receiver must be operating at the same time as the radar system transmits energy.
Spatial Domain
Antennas must be able to receive energy from the direction of the transmission
What are the performance requirements of ES systems?
Frequency coverage
Sensitivity and selectivity
Dynamic range
Bearing and elevation coverage
Quick Analysis Time
For a receiver to intercept a signal it must _____ and then ______
Cover the frequency band
Be tuned to the correct frequency of the transmitter
Sensitivity refers to the ability to ______
detect signals in noise (SNR)
A wide bandwidth _____ sensitivity.
Reduces
What is selectivity?
The ability to select a certain range of frequencies and reject all others.
Selectivity is _______ proportional to bandwidth.
A selective receiver is ______ sensitive.
Inversely
More
Remember sensitivity is inversely proportional to bandwidth.
If a receiver is very selective, it has ________ probablity of intercept.
Reduced.
Selectivity is the ability to select a certain range of frequencies and reject all others. It will not be able to cover a wide range all at once but it can cover one narrow range very well.
What is Dynamic Range?
Ability to process very weak and very strong signals equally well.
What is Analysis Time?
The period of time required for reliable target identification.
What are two factors which limit sensitivyt of the receiver?
Noise Figure
Noise Bandwidth
What is dwell time?
After a receiver detects a signal, such as a radar pulse, there is a short period of time during which other pulses will be missed.
What is Range Advantage?
Ratio of the distance where an ESM receiver can detect a radar to the distance a radar can detect the ESM receiver’s platform.
What is Probability of Intercept
A qualitative measurement of probability of intercept based on time, frequency, direction
How do you calculate the number of sweeps required for a certain POI?
What are the 4 types of ES Receivers?
Direct Detection or Crystal Video
Superheterodyne
Instantaneous Frequency Measurement
Compressive
Direct Detection: Crystal Video Receiver
Extracts the signal from the carrier wave but removes frequency and phase information. It simply tells you there is a threat.
It has a very wide BW though, giving it a high POI.
Direct Detection: Scanning Crystal Video Receiver
Adds an electronically scanning narrowband microwave filter before the detector.
This provides some frequency measurement by increasing selectivity but it decreases the probability of intercept and it is still low sensitivity.
Direct Detection: Multi-Channel Crystal Video Receiver
A combination of basic crystal detectors, each tuned to a different band of frequencies.
This allows frequency measurement,
Improved sensitivity because each detector is over a narrower BW.
Imrpoved POI
Faster than the scanning crystal receiver.
Superheterodyne Receiver
High sensitivity and selectivity
Low POI
Superhet: Automatic Tuning Superhet Receiver
automatically variable local oscillator frequency. So the LO will automatically sweep over a range of IFs. The conventional will require an operator to change the IF.
Results in very high sensitivity.
Higher POI over conventional superhet.
Superhet: Channelized Superhet Receiver
One LO and a number of IF amplifiers that together covera wide bandwidth.
Improved sensitivity, POI,
Instantaneous Frequency Measurement (IFM) Receiver
A bank of frequency discriminators. Each discriminator in series makes progressively more precise measurements.
You can create a parallel array of these discriminators and sum them together progressively more precise to create a digital IFM system.
What are the limitations of IFM?
Processing time
Low sensitivity
High POI
Compressive Receiver
Uses an automatic tuning superheterodyne receiver to sweep frequencies with the LO. The signals are multiplied with a delay filter which delays the signal proportional to its frequency. This time delay then corresponds to a frequency. Its another way of differentiating multiple frequency signals without a FFT.
High POI
High sensitivity
Multiple simultaneous signal handling
Good frequency resolution
Phase Comparison Array
Measures the phase difference to determine direction
Simultaneous Amplitude Comparison
Compares relative amplitude from different directions to determine strongest direction. This is used because at radar frequencies, you cannot use Adcock array.
Steerable Direction Antenna
Rotating antenna which indicates its bearing info when the return is strongest. Low POI
Four basic actions of recognition
Pulse Sorting
PRI Analysis
Scan Analysis
Emitter Comparison
What is Pulse Sorting?
Determining which incoming pulse is which.
How do we describe a signal when Pulse Sorting?
AOA
Frequency
Duration
TOA
Amplitude
Each pulse is represetned as 80 to 100 bit description
What are 3 methods of direction finding?
Time Difference of Arrival
Angle of Arrival
Frequency DIfference of Arrival (doppler)
Define Quick Analysis Time
The ability of an ESM system to process and analyze EM signals to extract useful information about targets.
What is a threat library? What is it used for? How is it generated?
Threat library is a collection of information used to identify and classify targets based on their EM emissions.
Information is gathered and analyzed and added to the threat libary for future deployements.
What factors affect receiver sensitivity
Draw a superheterodyne receiver
