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Wireless Transmission Mediums
Published in Mário Marques da Silva, Cable and Wireless Networks, 2018
Figure 5.17 shows the field strength curves as a function of the distance for several different frequencies, for seawater with σ = 5 S/m and ε = 70. Similar curves for different terrains can be obtained from ITU-R P.368-7. As can be seen from Figure 5.17, the groundwave propagation is normally achieved with frequencies that span from few kilohertz up to around 3 MHz. Frequencies higher than this upper limit are subject to high attenuations, and therefore, their range becomes limited.
Introduction
Published in Mike Tooley, David Wyatt, Aircraft Communications and Navigation Systems, 2017
As their name suggests, ground waves (or surface waves) travel close to the surface of the earth and propagate for relatively short distances at HF and VHF but for much greater distances at MF and LF. For example, at 100 kHz the range of a ground wave might be in excess of 500 km whilst at 1 MHz (using the same radiated power) the range might be no more than 150 km and at 10 MHz no more than about 15 km. Ground waves have two basic components; a direct wave and a ground reflected wave (as shown in Figure 1.6). The direct path is that which exists on a line-of-sight (LOS) basis between the transmitter and receiver. An example of the use of a direct path is that which is used by terrestrial microwave repeater stations which are typically spaced 20 to 30 km apart on a LOS basis. Another example of the direct path is that used for satellite TV reception. In order to receive signals from the satellite the receiving antenna must be able to ‘see’ the satellite. In this case, and since the wave travels largely undeviated through the atmosphere, the direct wave is often referred to as a space wave. Such waves travel over LOS paths at VHF, UHF and beyond.
Waves propagation for magneto-thermoelastic medium during the two-temperature theory with the gravitational field
Published in Waves in Random and Complex Media, 2022
A surface wave is one of two types of waves that travel across the surface of a medium as opposed to through it. Surface waves usually have larger amplitudes and longer wavelengths than body waves, and they travel more slowly than body waves. Love waves and Rayleigh waves are two types of surface waves. In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A surface wave can also be an electromagnetic wave guided by a refractive index gradient. In radio transmission, a ground wave is a surface wave that propagates close to the surface of the earth [19–26].