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