15 AMT 311 - Radio Communication

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• Radio communication: first use of radio frequency transmissions in aviation

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• Radio waves: electromagnetic in nature, part of the electronic spectrum

• Electromagnetic spectrum: range of wave activity

  • Shorter wavelength (centimeters) to longer wavelength

  • Gamma ray, X-ray, Ultraviolet, Infrared, Radio

  • Higher frequency (number of waves per second) to lower frequency

  • Visible, UHF, VHF, HF, MF, LF, VLF

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• Types of radio waves: Very Low Frequency (VLF), Low Frequency (LF), and Medium Frequency (MF)

  • Long wavelengths, long antennas

  • Range from 3kHz to 3MHz

  • Use ground waves or surface waves

  • Used by ADF and LORAN navigational aids

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• High Frequency (HF)

  • Travels in straight line/line-of-sight transmission

  • Used by transoceanic aircraft for voice communication

  • Frequency range between 2 to 25 MHz

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• Very High Frequency (VHF)

  • Primary used by communication radios in aviation

  • Frequency range from 118.0 MHz to 136.975 MHz

  • Used for aircraft and air traffic control communication, as well as air-to-air communication between aircraft

  • Transmit and receive function

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Loading information onto a radio wave

• Carrier wave: continuous electromagnetic radiation of constant amplitude and frequency

• Modulation of carrier wave by an information signal

• Transmission of information from transmitting radio to receiving radio via antennas

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• Amplitude Modulation

  • Varies in relation to the fluctuating current input

  • Carrier wave altered by information signal

  • Demodulated signal carries audio information

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• Frequency Modulation

  • Carrier wave retains constant amplitude

  • Signal represented as variations to the normally consistent timing of the oscillations of the carrier wave