Aircraft Communication Systems Chapter 2

This chapter covers aircraft communication systems
Topics include principles of radio communication, VHF communication systems, HF communication systems, satellite communication systems, intercommunication and passenger address systems, and inflight entertainment systems

Electromagnetic waves (EM): Information is converted to an electrical signal, which is then converted to an electromagnetic wave.
EM waves consist of electric (E) and magnetic (M) fields that are transverse to the direction of propagation.
Radio frequency (RF) waves: A type of EM wave, used in radio communication.
Modes of radio wave propagation: Reflection, refraction, diffraction, and scattering are discussed in the context of how radio waves travel. These impact signal strength and range.
VHF/UHF radio communication: Details on these communication frequencies are covered.
Path loss models: Mathematical models used to predict signal strength based on distance and atmospheric conditions. Common models are Free Space Loss and Plane Earth model.
Terminology and regulatory agencies: Details regarding technical terms and regulatory bodies involved in aircraft communication. Includes the International Telecommunications Union (ITU).

EM waves travel long distances via guided or unguided mediums
The radiated magnetic field of a remote antenna generates the signal
Polarization: The orientation of the electric field (E-field) of an EM wave.
- Vertical Polarization: The E-field is in the vertical direction
- Horizontal Polarization: The E-field is in the horizontal direction
Wavelength and frequency: Wavelength (λ) is the distance between two corresponding points on a wave, and frequency (f) is the number of waves that pass a given point per second. Related by the equation: λ = v / f, where v is the velocity of the wave.
- The velocity of propagation for EM waves in free space is approximately 3 x 10⁸ m/s (often represented as 'c').
Electromagnetic spectrum: Various frequency bands (ELF, VF, VLF, MF, HF, VHF, UHF, SHF, EHF) with their associated wavelengths and uses for specific radio applications
Examples and Calculations: Provided examples demonstrate calculations related to wavelength and frequency.

Reflection: Reflection occurs when an EM signal encounters an object significantly larger than its wavelength.
Refraction: Bending of EM waves as they pass from one medium to another with different densities. This is impacted by the electrical characteristics of the medium. Refraction is also affected by the atmosphere.
Diffraction: Bending of EM waves around sharp objects.
Scattering: Scattering occurs when EM waves encounter small objects or rough surfaces, causing the wave to spread in multiple directions.

Space wave: direct and ground reflected wave
Ground wave: propagates along the surface of the Earth, generally used for shorter distances at lower frequencies.
Sky wave: propagates through the ionosphere and back to Earth—used for long distances, typically for high frequencies.
Ionosphere: layers in the atmosphere where radio waves are refracted
Critical angle and skip distance: factors affecting the range of skywave propagation

Primarily use space wave propagation, meaning signals travel in a straight line.
Radio Horizon: The farthest distance one can see on a clear day—important in calculating the range of a communication link between two sites with known heights
- Empirical formula for determining the radio horizon distance based on the heights of the transmitter and receiver antennas is provided.
Path Loss and Fade Margin: Path loss is the decrease in signal strength over distance. A fade margin is often added to communications to compensate for fluctuating or unreliable signal strength
Space wave types: Direct wave and Ground reflected waves

Factors influencing communication links: Radio Line of Sight (LOS), transmitter output power, receiver sensitivity, antenna gain, and path loss are considered when designing systems.
Path loss models: Free Space Loss and Plane Earth models (Egli) are examined.
Fade margin: Techniques are shown to determine reliability in communication.

HF communications: use the skywave propagation mode for long-distance communication
Advantages and disadvantages: Discusses the advantages and disadvantages of skywave propagation for HF use. (e.g., the need for very large antennas).
MUF, LUF, OWF: Parameters that are used to determine suitable operating frequencies (e.g., Maximum Usable Frequency, Lowest Usable Frequency, and Optimum Working Frequency).
Relationships Between variables are provided (e.g., MUF, critical frequency, angle of incidence to calculate required frequencies.)

Provides details about organizations such as the ICAO (International Civil Aviation Organization), FAA (Federal Aviation Administration), and CAAS which regulate international communication standards, safety, and aviation matters.
Importance of standards for aircraft equipment and for pilots.