Lesson 35 Flashcards#
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1. What is electromagnetic warfare (EW)?
Electromagnetic warfare (EW) is military action involving the use of electromagnetic (EM) and directed energy to control the EM spectrum or to attack the enemy.
2. What are the three major subdivisions of EW?
Electromagnetic Attack (EA)
Electromagnetic Protection (EP)
Electromagnetic Support (ES)
3. What is the signal-to-noise ratio (SNR) equation?
4. How does increasing noise power affect SNR?
As noise power increases, SNR decreases.
A lower SNR makes communication more difficult.
5. What is stand-off jamming?
Stand-off jamming is a jamming scenario where the jammer is separate from the transmitter and receiver.
6. What is the simplified SNR equation for radio jamming?
7. What three variables can a jamming platform control in the Friis equation?
Jamming power, \(P_{jam}\)
Jamming antenna gain, \(G_{jam}\)
Distance to the target receiver, \(R_{jam}\)
8. How does moving a communications jammer closer to the receiver affect jamming effectiveness?
As the jammer moves closer to the receiver, \(R_{jam}\) decreases and SNR decreases.
This makes communications jamming more effective.
9. What are three communications countermeasures against jamming discussed in this lesson?
Chirp signals
Frequency hopping
Direct-sequence spread spectrum (DSSS)
10. What is a chirp signal?
A chirp signal is a signal whose carrier frequency sweeps up or down across a range of frequencies at a set rate.
This provides some resistance to jamming.
11. What is frequency hopping?
Frequency hopping uses multiple carrier frequencies and a pseudo-random noise (PRN) code to jump between frequencies.
The transmitter and receiver must stay synchronized.
12. What is direct-sequence spread spectrum (DSSS)?
DSSS spreads a signal over a wider bandwidth by sampling at a higher rate and multiplying by a PRN code.
This makes the signal harder to detect and jam.
13. What is the SNR equation for RADAR jamming?
14. How does moving a jammer closer to a RADAR affect RADAR jamming effectiveness?
As \(R\) gets smaller, SNR gets bigger.
This means RADAR jamming becomes less effective as the jammer gets closer, which is the opposite of communications jamming.
15. What is burn through in RADAR jamming?
Burn through is the point where the RADAR can overcome the jamming and detect the target.
It occurs when the jammer becomes ineffective.