NAVCOM

• James Clerk Maxwell (physicist, mathematician) - predicted the Electromagnetic waves in 1873. proposed that a coupled oscillating electric field and magnetic field could travel through space as a wave, and proposed that light consisted of electromagnetic waves of short wavelength
• 1873 - the year Electromagnetic waves was predicted
• Heinrich Rudolf Hertz - a German physicist who first conclusively proved the existence of the waves which are electromagnetic
• November 11, 1886 - the date when hertz attempted to confirm Maxwell's theory, first observed radio waves Hertz generated using a primitive spark gap transmitter
• Radio - the technology of signaling and communicating using radio waves
• Radio - generated by an electronic device called a transmitter connected to an antenna which radiates the waves, and received by another antenna connected to a radio receiver
• Radio waves - radiated by electric charges undergoing acceleration
• 299,775 km/s - the speed of light in vacuum
• Electromagnetic waves - transverse waves, meaning that their oscillations occur perpendicular to the direction of prop
• Modulation - generate a modulated signal suited to the characteristics of a transmission channel
• The 3 types of Modulation:

  • Amplitude Modulation
  • Phase modulation
  • Frequency Modulation
• Amplitude Modulation - a kind of modulation where the amplitude of the carrier signal is changed in proportion to the message signal
• 540 to 1600 Hertz - amplitude modulation frequency
• Phase modulation - phase of the carrier signal is altered according to the low frequency of the message signal
• 88.1 to 107.9 MHz - Phase Modulation frequency
• Frequency Modulation - the frequency of the carrier signal is altered in proportion to the message signa
• 88.1 to 107.9 MHz - Frequency modulation frequency
• Modulation Mechanisms

  1. Analogue
  2. Digital
• Demodulation - defined as extracting the original information-carrying signal from a modulated carrier wave
• Demodulator - an electronic circuit that is mainly used to recover the information content from the modulated carrier wave
• Frequency band - refers to a specific range of frequencies in the electromagnetic frequency spectrum assigned to certain applications
• Polarization - describes the direction in which the electric field oscillates as the wave propagates through space
• Horizontal polarization - If the electric field lines are parallel with the earth surface.
• Vertical polarization - when those electrical field lines are perpendicular to the earth surface (Low FQ, 10 MHz or lower)
• Antennas and filters - can be designed to transmit, receive, or filter specific polarizations to optimize performance in different scenarios
• Types of Polarization:

  • Linear Polarization - Elliptical Polarization
  • Circular Polarization
• Linear polarization - electric field oscillates in a single plane. This plane is perpendicular to the direction of wave propagation
• Circular polarization - electric field vector rotates in a circular manner as the wave propagates.
• two types of circular polarization:

  • right-handed
  • left-handed
• Elliptical polarization - combination of linear and circular polarization. The electric field vector traces an elliptical path as the wave propagates
• Frequency - number of waves passing through a fixed point per time interval.
• Amplitude - maximum displacement of a point in the wave from the equilibrium position.
• Wavelength - distance between successive crests or troughs in a wave
• trough - the lowest point on a wave .
• Crest - the highest point in the wave is the
• Radio wave propagation three types attributes:

  • Free space propagation
  • Ground wave propagation
  • Ionospheric propagation
• Radio wave propagation consists of three main attributes:

  -        Reflection

  -        Diffraction

  -        Scattering
• Ionosphere - contains a high proportion of free electrons which influence radio propagation
• Ionization - different at different heights above the earth and is affected by the time of day and solar activity
• Three main regions within the ionosphere:

  • D Region
  • E Region
  • F Region