EW Wk1 Flashcards
(47 cards)
Explain the main military uses of the EM spectrum.
Radio communications, primary and secondary radar, IR detection and ultraviolet seekers.
Speed of light?
300 000 000m/s
162 000nm/s
186 000sm/s
Relationship between wavelength and frequency.
Inversely proportional.
Higher freq = shorter wavelength.
Polarisation of an EM wave is determined by which field?
E field.
Relationship between power density and range?
Inversely proportional.
Power density decreases as range increases.
2 forms of atmospheric attenuation?
Absorption and scattering.
Explain atmospheric absorption.
When energy dissipates as it interacts with gas molecules.
Explain atmospheric scattering.
When EM waves hit molecules and change their direction.
Explain diffraction in relation to propagation.
Bending waves, longer wavelengths diffracted more.
Different waves?
Ground wave (surface wave and space wave), sky wave.
Factors affecting a space wave?
Attenuation -(absorption,scattering).
Avge path length around 25-40km.
For longer distances relay stations are required.
Which layers of the earths atmosphere have a major effect on the performance of EM waves?
Ionosphere and troposphere.
3 types of radar transmitter?
Magnetron.
Travelling wave tube.
Field effect transistor amplifier.
What target information can we get from radar?
Range. Bearing. Height. Course. Speed. Shape/size/outline.
Different types of radar display.
PPI -Plan Position Indicator.
A-scope.
B-scope.
An ES receiver should:
Intercept.
Measure.
Identify.
Display.
Describe amplitude comparison.
Technique that involves measurement of the relative amplitudes of a signal at different angles with respect to the target.
Draw and label block schematic for an ES Rx.
Antenna. Amplifier. Receiver. Processor. DOA resolver. Output.
Describe unintentional pulse modulation and how it can be used.
Caused by system noise/ different operation/ instillation of components and helps with specific emitter identification SEI.
Explain SNR.
The ratio that describes a radar’s ability to see targets in the presence of noise.
Explain bandwidth.
The difference between the upper and lower frequencies in a continuous set of frequencies and is typically measured in Hz.
What external factors will effect signal quality (SNR)?
Distance from source.
Atmospheric conditions, sun spot activity.
No line of sight, multi path interference.
Jamming.
How can height information be obtained from a circular scanning radar?
Use 2 beams (one angled).
How does a search radar calculate height using a V-beam?
By measuring the time difference between illumination in each beam.
