The various theories on the propagation of ultra-short waves beyond the horizon

Three theories for the calculation of fields beyond the horizon have been reviewed. It has been seen that these theories rest on the instability of the propagated wave in respect various physical factors (meteorologicalor due to terrain conditions). It appears that the three methods, each having its own advantages, can be used jointly by engineers concerned with long-range communication. 1. Near the horizon, the multiple reflection theory, in good agreement with the classical method, is preferable. 2. For distances greater than 200 kmn, the pure diffraction theory, providing a simplified form of calculation of the preceding theory, is preferable, especially when using simplified formulae for the calculation of the median field and height gains. 3. Neither of these two methods supplies the law around the median value. The calculation of the turbulence field must then be made in order to obtain that law. The same applies in the case of the highly directional aerials calculation of the loss of gain obtained from the polar diagram of the turbulence sources.