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Microlight » Flight Radio » Basic Radio Wave Propagation

  • Flight Radio Telephony is the study of how to operate the aircraft's radio.
  • In aviation Very High Frequency (VHF) is used.

Radio Waves

  • Radio waves do not require a medium to work in.
  • This means that they can travel not only through air and solid materials, but also through the vacuum of space, and travel at the speed of light (300,000 Km/sec)
  • Electromagnetic (radio) waves propagate outward from a source by causing alternate increases and decreases in the electrical field and the magnetic field at the same time.
  • We use changes in the electrical fields to send out and receive radio waves.
  • Dropping a stone in a pond and watching a cork in the water move up and down on the resulting waves moving outwards is a good analogy for this.

Frequency

  • The number of complete waves that will travel past a point in one second. 
  • It is measured in Hertz.

Amplitude

  • The distance from the base line to the highest point of a peak (or lowest point of a trough).
  • Generally measured in volts (being the maximum change in the electrical field).

Wavelength

  • The length of a single wave.
  • The distance travelled by the wave during transmission of one cycle.
  • Because the speed of light is constant, if you increase the wavelength then less of the waves will pass a point each second, so the frequency must be lower.
  • Radio sets take the sound waves from our voice (through the microphone) and convert them into an electrical signal.
  • This radio then produces a carrier wave, which is modulated by the signal from the microphone.
  • This modulated signal is sent in all directions (like the waves from our stone in the pond).
  • Radio carrier waves can be modulated by adjusting the amplitude of the waves (AM) or by adjusting the frequency of the waves (FM).
  • Generally aviation radio is on the FM band.
  • Radio waves may be reflected, refracted (bent), attenuated (weakened), absorbed or diffracted (scattered).
  • Thus they are subject to terrain and atmospheric interference.
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