Radio waves within the VHF range (e.g. VOR) travel as...
The Earth's surface and atmospheric environment has a significant effect on propagation of radio wave signals. These factors may reduce the effective range and quality of radio transmissions.
VHF propagates as quasi (almost)-optical, direct wave.
The VHF waves are also space waves (not sky waves). Unlike High Frequencies (HF), the ionosphere does not usually reflect VHF radio and thus transmissions are restricted to the local area.
The Space Waves are the radiowaves of very high frequency, between 30 MHz to 300 MHz (VHF) or more. The space waves can travel through atmosphere from transmitter antenna to receiver antenna either directly or after reflection from ground in the earth’s troposphere region. That is why the space wave propagation is also called as tropospherical propagation.
The Sky Waves are the radiowaves of frequency between 2 MHz to 30 MHz. These radio waves can propagate through atmosphere and are reflected back by the ionosphere of earth’s atmosphere. Since these waves go from transmitter antenna to receiver antenna while traveling through sky, hence their propagation is known as sky wave propagation.
Surface wave propagation refers to the transmission of radio waves along the Earth's surface. Surface wave propagation involves waves that follow the curvature of the Earth due to a process known as diffraction. As these waves encounter the Earth's surface, they can bend around obstacles and continue propagating beyond the line of sight covering longer distances and reach areas that are obstructed from direct line-of-sight communication. Surface wave propagation can be achieved in VLF, LF, MF and HF radio waves.
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