Radio Navigation Flashcards
What two characteristics define electromagnetic waves?
- Amplitude (is the magnitude of change in the electric field intensity)
- Frequency (f) (is the number of oscillations per second, measured in Hertz (Hz).
What is wavelength?
The distance between beginning and the end of one oscillation. Given en metres.
Wavelength = speed of light/frequency
Name all 3 propagation types
- Ground wave
- Sky wave
- Line of sight
Phenomena of propagation
- Reflection
electromagnetic waves may be reflected by ionized air layers of the ionosphere, mountains, buildings metal surfaces or the ground.
Phenomena of propagation
- Refraction
is an alteration in speed and direction of propagation which is caused by a change of the air density or conductivity e.g. changes of humidity (coastline) or ionization (ionosphere).
Phenomena of propagation
- Diffraction
bending of waves around obstacles e.g. at the edges of mountains, buildings or layers of the ionosphere.
Phenomena of propagation
- Dispersion
separation of waves caused by particles in the air e.g. rain, fog or dust.
Phenomena of propagation
- Absorption
electromagnetic energy is transformed to other forms of energy, for example to heat, especially near the ground (rain, fog, haze, dust) and the lower layers of the ionosphere.
Phenomena of propagation
- Interference
interaction of two waves which have the same source or nearly the same frequency, it results in increased or decreased amplitude.
Phenomena of propagation
- Polarization
is the change of the orientation (e.g. vertical / horizontal) of the oscillation.
What propagations characteristics has these frequency bands?
- VLF/LF
- MF
- HF
- VHF/UHF
- VLF/LF = only ground wave
- MF = generally ground wave (up to 50km).
Additionally sky wave component at night (from 50 km). - HF = Generally sky wave
- VHF/UHF = propagate direct and straight (Line of Sight)
What are the 3 basic types of modulation called?
- Frequency modulation (FM)
- Amplitude modulation (AM)
- Pulse modulation (PM)
NDB abbreviation:
Non Directional Beacon
To a NDB facility belongs:
- a radio antenna
- a transmitting unit
- monitoring unit
NDB monitoring unit monitors what?
- transmitting power
- deviation of frequency
- identifier transmission
Two types of antenna are in use for the NDB:
- high (35 m), vertical pole (radio tower)
- T-type antenna between to vertical poles (T-antenna)
What is an NDB station?
- principle
- what equipment
- what propagation
- what errors
Principle: it transmits a continuous low/medium frequency signal (200 – 1750 kHz).
Aircraft use an Automatic Direction Finder (ADF) to detect the direction of the signal.
Equipment: NDB transmitter antenna
Propagation: Works in low and medium frequency (LF/MF) bands. usually ground wave.
Errors: Night effect, Dip error, mountain effect.
ADF abbreviation
Automatic Direction Finder
On board ADF equipment contains:
- antenna unit (loop and sense antenna)
- reciever
- control panel
- indication instrument
Explain the error (Differences in Range)
Differences in Range: Signal takes multiple paths of different lengths, causing bearing errors.
The Book:
“NDB signals propagate mostly as ground waves which have smaller ranges over dry surfaces and longer ranges over wet surfaces and water.”
Countermeasures: Identify tuned in NDB.
Explain the error (Fading)
Interference between ground waves and sky waves, or multiple sky waves, may lead to errors up to total annihilation of the signal.
Countermeasures: Use low frequency NDB
Example:
🎯 Imagine you’re standing in a field with your friend shouting directions to you:
- Your friend represents the NDB station.
- You are the aircraft with the ADF.
- Their voice is the radio signal.
Now, suppose:
- Your friend shouts directly at you (this is the direct signal).
- At the same time, their voice also bounces off a nearby wall or hill (this is the reflected signal).
- The reflected voice reaches you a tiny bit later than the direct one.
🌀 Sometimes, the two voices add up (get louder) → stronger signal.
💤 Other times, they cancel each other out (go quiet) → weaker signal or fading.
That up-and-down in loudness is what your ADF experiences as fading.
And because the ADF relies on a stable signal to point accurately, fading makes the needle wander or swing, causing errors in direction.
Explain the error (Night effect/twilight)
Night effect: Skywave reflection at night interferes with ground wave, causing bearing errors on the ADF.
The Book:
“NDB radio waves are reflected at the layers of the ionosphere especially during sunset and night. This process causes a change in polarization of the sky wave.”
Countermeasures: Use low frequency NDB
Explain the error (statics and thunderstorm effect)
Lightning and static electricity produce noise on NDB frequencies, causing ADF needle deflections and unreliable bearings.
Countermeasures: Turn off instrument if possible
Example:
⚡ Statics and Thunderstorm (Electrical) Effect
When you’re flying near a thunderstorm or around heavy electrical activity in the atmosphere, the air gets full of electrical noise — kind of like static on a radio.
This static is caused by:
- Lightning, which gives off strong bursts of radio waves.
- Other electrical disturbances in the atmosphere.
Now, your ADF is trying to lock onto a steady signal from an NDB station. But all this static can:
- Overwhelm or interfere with that signal.
- Make the ADF needle jump, wander, or even point in the wrong direction.
Imagine trying to listen to a friend in a quiet room (easy), versus trying to hear them during a loud thunderstorm with static crackling all around (hard!).
Explain the error (Mountain effect / Terrain effect)
NDB signals reflect off mountains, causing signal distortion and incorrect ADF indications.
Countermeasures: Climb to higher altitude.
Example:
⛰️ Mountain Effect — Simple Explanation
Radio signals from NDBs usually travel in straight lines close to the ground. But when they hit mountains or hilly terrain, they can bounce or get distorted.
The ADF doesn’t know the signal is reflected — it just follows whatever signal it picks up. So if it locks onto a bounced signal instead of the direct one, the needle can point in the wrong direction.
