Systec Exam Study Flashcards
Define EM spectrum
the range of wavelengths or frequencies over which electromagnetic radiation extends
What are the seven different behaviours of EM waves
- Absorption
- Reflection
- Refraction
- Diffraction
- Polarisation
- Spreading
- Power loss
Name five benefits of Radar
- Day or night
- Continuous monitoring
- Range
- Autonomous (no human required)
- All weather
- Ability to measure range, speed etc
List four benefits of IR or optical systems
- Passive
- Day or night
- Can penetrate weather
- High resolution
List four drawbacks of IR or optical systems
- Short range compared to radar / ES
- May require illumination
- Can be attenuated strongly
- Background heat may mask target
In terms of radio comms, explain signal fading
- The attenuation of a signal due to atmospheric or other causes
- Signal fades in quality and intensity
Define Radio frequency spectrum
High wavelength, low frequency part of the EM spectrum typically used for communications or long range radar
List conditions that affect the propagation of EM radiation
6 marks
- Changes in pressure,
- Changes in temperature
- humidity
- particulates
- ionosphere
- ducts
What Comms would I use for space comms
Use a higher band, could use SHF, EHF
What comms for Long range, over the horizon surface to surface comms
HF using ionospheric propogation
What comms for Short range, surface to surface comms with low probability of intercept
UHF
What comms for Medium range, beyond horizon
UHF (if within range), VHF
What frequency does Link 22 use?
UHF
What would I use to penetrate water
VLF
Name five reasons for propagation loss for sound waves in water
- Spreading
- Absoprtipon
- scattering
- bottom
- surface
Describe the movements of sound through water
A longitudinal pressure wave of compressions and rarefractions
List two ways a propeller can cause noise through the water
Cavitation
Vibration
What affects the speed of sound through the water
Pressure
Temperature
Salinity
What are tonals
Specific frequency that is being listened to
Name the three Radio Wave propogation
Sky wave
direct wave
ground wave
What is the relationship between wavelength and return of fidelity?
Wavelength needs to be equal to or smaller than the target to increase the fidelity
Relationship between the wavelength and the power from the source
I = 1/r2
How does air density affect EM waves?
Higher temperatures = lower density, therefore lower pressure and faster EMR
Higher humidity = higher density, therefore high pressure and slower EMR
Define scattering
When particles alter the path of EM waves. The waves bounce of dust, rain, air molecules etc to change the direction of the EM wave
What is the doppler effect
When the source is moving towards (increase frequency, decrease wavelength) (TIF) or away (decrease frequency, increase wavelength) (ADF) from a stationary observer.
What sort of wave does sonar utilise
sound wave, a mechanical pressure wave which is longitudinal in nature
The peaks and troughs in soundwaves is formed by what?
pressure
What is the range of Low frequency sonar band
long range
What equipment would use Medium frequency sonar band
hull mounted sonar
What is High frequency sonar band used for?
short range imagery
What causes cavitation
the moving blade creates a low pressure zone, causing the water to boil
What is the noise the submarine from cavitation can hear
bursting of the cavitation bubbles
When considering the seabed what factors will contribute to how that seabed transfers the energy
the topography,
bottom type (clay, mud, sand, silt)
obstructions (rough surfaces, objects, coral)
What is ambient underwater noise
background noise from marine life, sea and swell, shipping, weather, seismic events
Common types of torpedo guidance
wake homing,
active and passive acoustic,
wire guided,
magnetic fuse
What are the benefits of a normal light system
efficient and directional for same amount of power
low probability of intercept
Link 16 beyond line of sight
SHF space comms
What is the standard mission set of AI?
dirty, dull and dangerous
List three benefits of Analog Signal
- Easy Processing
- More Accurate
- true representation of original source
List four disadvantages of Analog Signal
- Not encrypted
- low bandwidth
- higher power consumption
- slow transmission rate
List five benefits of Digital Signal
- High bandwidth
- Encrypted
- almost zero interference
- low data density
- fast transmission rate
List disadvantages of Digital signal
- less accurate
