Avionics Flashcards
What is radio waves?
Electromagnetic oscillations (variants of electric and magnetic field)
Define amplitude
The magnetude of the change in the electric field intensity
Define frequency
Number of oscillations per second, measured in hertz
Define wave length
Distance between the beginning and the end of an oscillation in metres
What is the frequency spam for HF, VHF and UHF
HF = 3 MHz - 30 Mhz
VHF = 30 Mhz - 300 Mhz
UHF = 300 Mhz - 3 GHz
Different propagation
7 types
- Reflection
- Refraction
- Diffraction
- Dispersion
- Absorption
- Interference
- Polarization
Define reflection
Waves reflected by the ionosphere, mountains, buildings, ground etc.
Define refraction
Change in speed and direction due to change in air density or conductivity.
Define diffraction
Bending of waves around obstacles
Define dispersion
Seperation of waves caused by particles in the air
Define Absorption
Electromagnetic energy is transformed to other forms of energy
Define Interference
Interaction of two waves which have the same source or nearly the same frequency. Either increase or decrease amplitude.
Define polarization
Change of orientation of the oscillation
Propagation types
- Ground waves
- Sky waves
- Line of sight
Which propagation types does HF, VHF and UHF use?
HF = Generally sky waves
VHF/UHF = Line of sight
Types of modulation
- amplitude modulation
- frequency modulation
- pulse modulation
Working principle of an NDB
A signal is sent out in all directions. In a 40 degree angle directly above is the cone of silence.
Onboard equipment with and NDB
ADF
- Loop antenna (bidirectional) and sense antenna (non directional)
- Receiver
- Control panel
- Indication instrument
Errors regarding NDB
- Differences in range
- Fading
- Twilight / night effect
- Statics and thunderstorm effect
- Mountain effect
- Dip error
- Shoreline effect
- Quadrantal error
NDB ERROR:
Define difference in range
Differences in range due to the surface as an example.
Countermeasure:
- always identify tuned in NDB
NDB ERROR:
Define fading
Interference of radio waves (sky/ground)
Countermeasures:
- Use NDB within 30 nm
- Use low frequency NDBs
NDB ERROR:
Define twilight / night effect
NDB waves are reflected by the ionosphere during sunset/at night.
Countermeasures:
- NDB within 30 nm
- NDB with low frequency
NDB ERROR:
Define statics and thunderstorm effect
Electrons producing electrical fields interfering with the NDB signal.
Countermeasures:
- Turn off the instrument if possible
NDB ERROR:
Define Mountain effect
Ground waves may change direction by diffraction.
Countermeasures:
- Higher altitude
- Check course with terrestrial navigation
NDB ERROR:
Define dip error
The loop antenna is moved away from its minimum position due to banking in a turn.
NDB ERROR:
Define shoreline effect
Change of electrical conductivity over water refracts waves passing the shoreline.
Countermeasures:
- Higher altitude
- NDB close to the shoreline
Working principle of a VOR
Based on a lighthouse principle.
2 antennas:
- Reference antenna (non directional)
- Rotating antenna (directional)
Two signals are received and based on the phase shift, it calculates the radial you’re currently flying on.
What does VOR stand for?
Very High frequency omnidirectional radio range
Working principle of a DVOR?
A non directional signal is sent frem the middle of the station, surrounded by 36-50 non-directional antennas which are turned on one by one.
Advantages of DVOR
- No moving parts
- Precision
- Reduced reflection + refraction
VOR onboard equipment
- Antenna
- Receiver
- Control panel
- Indication instrument
Advantages of VOR
- No dip error
- No quadrantal error
- Less statics
- Less twilight effect
ILS working principle
3 ground components:
- Localizer
- Glideslope antenna
- Marker beacons
Localizer transmits two different signals, 90 hz on the left side of runway and 150 hz on the right side of the runway. Both AM. The receiver on board compares the signals and give an indication if you’re on the centerline, or left/right.
Glide slope antenna produce two beams, a 90 hz above the glideslope and a 150 hz below. It’s the same principle as the localizer, but your indication is if you’re above or below the GS.
Marker beacon transmits three different audio signals. One for the outer, one for the middle, and one for the inner marker.
ILS onboard equipment
- ILS antenna
- ILS receiver
- ILS control panel
- ILS indication instrument
Working principle of the DME
The aircraft DME sends out pulse pairs, which are received by the DME ground station. The ground station will reply with the same unique pulses. The time it takes between these signals to get back, can determine the slant range distance to the DME in NM.
There can be up to 100 aircrafts working with an DME at the same time.
DME onboard equipment
- Receiver
- Antenna
- DME indication instrument
What does RADAR stand for?
Radio detection and ranging
Working principle of a RADAR
It uses radio waves to determine the bearing and distance of an object. An antenna transmits radio waves which will bounce back when in contact with an object, and return with information.
Different kinds of RADAR types
Primary RADAR:
Gives direction, distance and speed. No transponder needed.
Secondary RADAR:
Gives additional altitude, identification and information. Transponder needed.
Working principle of INS
A navigational aid using accelerometers to determine position, orientation and speed, based on dead reckoning principle, without external references. You need a fixed starting point, and the longer you fly, the more inaccurate it gets, so it has to be updated once in a while.
What does INS stand for?
Inertial Navigation System
Working principle of LDNS, and what does it stand for?
Light doppler navigatjonal system.
It radiates electromagnetic waves in four directions, which are reflected by the surface.
Uses the doppler effect to determine lateral movement. It works by waves being expanded or compressed, resulting in a change of frequency. There will be a higher frequency in the front, and a lower frequency in the back.
VERY detectable!
Working principle of GPS
Working with at least 4 satellites, which transmit signals containing name, position and time. When receiving these signals, time can be computed and the position as well.
In aviation we use 8+ satellites for detecting wrongful information and redudancy.
What is D-GPS?
Differential GPS.
Working with a ground station that can help eliminate time errors and improve accuracy. A special receiver is needed.
