In-Depth Notes on Aircraft Communication Systems and Frequency Bands

Introduction to Aircraft Communication System

  • Module Overview: Discusses the fundamental aspects of aircraft communication systems and the related frequency bands.

Waves - Review

Parts of a Wave

  • Crest: The highest point of a wave.

  • Trough: The lowest point of a wave.

  • Wavelength (BB): Distance between consecutive crests or troughs, typically denoted as $BB$.

  • Amplitude: Height of the wave, indicating power.

  • Period: Time taken to complete one full oscillation.

  • Frequency (f): Number of oscillations per second, measured in Hertz (Hz).

  • Connection: The frequency can be calculated as: f=1Tf = \frac{1}{T} where T is the period.

Electromagnetic Spectrum

  • Definition: The electromagnetic spectrum encompasses all types of light, including visible light and invisible forms such as radio waves, microwaves, infrared, etc.

  • Visible Light: Only a tiny fraction of the overall electromagnetic spectrum is visible to the human eye.

Radio Frequency Spectrum

  • Definition: The segment of the electromagnetic spectrum that ranges from 1 Hz to 3000 GHz (3 THz).

  • Applications: Vital in modern technology and communications.

  • Frequency Bands: Different frequency bands are assigned for various communication applications, including aviation.

Regulatory Bodies

International Telecommunication Union (ITU)

  • Responsible for global radio spectrum allocation and technical standards that ensure connectivity.

National Telecommunications Commission (NTC) - Philippines

  • Regulates local telecommunications, allocating radio frequencies and managing efficient radio frequency usage.

Frequency Bands Overview

Very Low Frequency (VLF) - 3–30 kHz

  • Wavelength: 100 to 10 km.

  • Propagation: Primarily line-of-sight.

Applications:

  • Morse Code, Submarine communications.

Low Frequency (LF) - 30–300 kHz

  • Wavelength: 10 to 1 km.

  • Propagation: Ground-wave allows long-distance communication.

Applications:

  • Non-Directional Beacons, Differential GPS.

Medium Frequency (MF) - 300 kHz to 3 MHz

  • Wavelength: 1000 to 100 m.

Applications:

  • AM Radio, Maritime distress communications.

High Frequency (HF) - 3 to 30 MHz

  • Wavelength: 10 to 100 m.

Applications:

  • Long-distance communications, aviation.

Very High Frequency (VHF) - 30 to 300 MHz

  • Propagation: Line-of-sight; affected by terrain.

Applications:

  • FM Radio, Aviation communication (e.g., VOR, ILS).

Ultra High Frequency (UHF) - 300 MHz to 3 GHz

  • Compatibility: Susceptible to terrain interference.

Applications:

  • Wi-Fi, Satellite communications.

Super High Frequency (SHF) - 3 to 30 GHz

  • Applications: Includes satellite and microwave communications.

Extremely High Frequency (EHF) - 30 to 300 GHz

  • Applications: Used in advanced applications like automotive radars.

Aircraft Communication Systems

SELCAL (Selective Calling)

  • Definition: Alerts specific aircraft of ground station transmissions.

  • Code Structure: Pairs of letters (e.g., GQ) not using I, N, or O.

SATCOM (Satellite Communication)

  • Definition: Extends communication range between aircraft and ground stations.

  • Operational Components: Antenna, transceiver, modem, and control unit. Signal uplink and downlink with satellites.

  • Voice & Data Communication: Enables communication even in remote areas.

TCAS (Traffic Alert and Collision Avoidance System)

  • Purpose: Reduces mid-air collision risk.

How it Works:

  1. Interrogation: Sends signals to nearby aircraft.

  2. Transponder Response: Aircraft send back vital information.

  3. Threat Assessment: Analyzes traffic positions.

  4. Alerts Cockpit: Signals danger proximities and coordinations between aircraft.

ADS-B (Automatic Dependent Surveillance - Broadcast)

  • Definition: Allows automatic aircraft data broadcast (e.g., position, identification).

  • Functionality: Aircraft broadcasts location and receives data for positioning and safety updates.