Ground-wave Field Strength Research Articles

LF Ground-Wave Propagation Over Irregular Terrain

Traditional methods used to predict the ground-wave field strength at low frequency are not applicable for terrains with serious irregularities because of the analytical approximations. In this paper, the two dimensional finite-difference time-domain (FDTD) algorithm is applied to calculate the field strength of the low frequency (LF) ground wave propagating over irregular terrains. The propagation characteristics are studied as functions of the mountain's gradient, height, and width, respectively. We also focus on studying the cases with multiple mountains in the path. Moreover, the error of the traditional integral equation method is analyzed by comparisons. The results show that when the mountain's gradient and height are high, additional oscillations in the field strength will appear in front of and in the mountain region due to the wave reflection and scattering. At last, measurements of the Loran-C signals are taken along a real path between Pucheng and Tongchuan in Shaanxi province, China. It is found that most of the measured and FDTD results have good agreements while some still have big errors owing to the model approximation. The FDTD method gets better precision than the integral equation method in the irregular terrain.

AM broadcast antennas with elevated radial ground systems

Results are presented of computer modeling studies indicating that an elevated vertical monopole antenna with four elevated horizontal radials produces more ground-wave field strength than does a conventional ground-mounted monopole with 120 buried radials. For the analysis, the length of the radials and the height of the monopole were set equal to 0.25 of the free-space wavelength, and the frequency of operation was fixed at 1.0 MHz. Three different sets of ground constants were used, simulating averaging, very good, and very bad soil electrical parameters in accordance with the Numerical Electrical Code (NEC-GS). >

Location Statistics of AM Broadcast Groundwave Signal Amplitudes

A location-dependent statistical distribution model for AM broadcast groundwave signal amplitudes is presented. The distribution is in the fonm of a probability density function (pdf) whose expected value is the predicted feld strength based on propagation formulas, and whose variance can be empirically derived from analysis of actual groundwave field strength measurements. The results are useful for aessing the percentage of locations at which a selected signal strength will be exceeded given the predicted signal strength and typical variance of the pdf.

A Computer Program System for Predicting AND Plotting Mediumwave Broadcast Groundwave Field Strength Contours

A computer program system and associated data bases have been developed to automate the calculation and plotting of groundwave field strength contours for mediumwave broadcast stations in the United States. The programs use the propagation curves and M3 soil-conductivity map in the FCC Rules, and produce contours suitable for engineering exhibits filled with the FCC. The programs and data bases, together with new soil conductivity data bases for Canada and Mexico, were recently implemented on the FCC computer.

Seasonal Effects on Ground-Wave propagation in Cold Regions

Abstract The ground-wave is the most important mode of propagation of radio waves in Connection with glaciology. In cold regions, special conditions are often prevalent, involving propagation over non-homogeneous earth, presence of stratified media, and low values of conductivity and dielectric constant in the upper strata. A radio wave which propagates along the Earth's surface is, however, also influenced by atmospheric refraction. As the frequency is increased, the roughness of the Earth's surface must also be taken into account. Thus seasonal variations are to be expected due to changes in the electrical and topographical properties of the ground as well as the propagation conditions in the atmosphere. It is, however, difficult to separate these various effects, a fact which reduces the possibility of using ground-wave propagation as a loot for obtaining information on the properties of the ground. Though the propagation of the ground-wave has been dealt with both theoretically and experimentally for almost a century, some of the most valuable information of major importance in cold regions has been obtained during the last ten years. New theoretical papers on propagation over stratified media offer an explanation of the amplitude and phase variations of the ground-wave field, which have been measured, as well as suggesting new methods to be tested as possible aids in solving glaciological problems. In many practical eases of ground-wave propagation in arctic regions, the formula for the ground-wave field strength can be written in a very simple way. Such a propagation model for frequencies above 30 MHz is presented in which account is taken of the Earth's curvature, the terrain irregularities, and the effect of the tropospheric refraction. This model also includes the recovery effect which occurs in propagation over mixed paths. At the higher frequencies the effect of depolarization becomes very important and sometimes overshadows field-strength variations due to the influence of the electrical properties. Finally some problems will be discussed which remain to be solved or have been given very little attention up to now.

Seasonal Effects on Ground-Wave propagation in Cold Regions

AbstractThe ground-wave is the most important mode of propagation of radio waves in Connection with glaciology. In cold regions, special conditions are often prevalent, involving propagation over non-homogeneous earth, presence of stratified media, and low values of conductivity and dielectric constant in the upper strata.A radio wave which propagates along the Earth's surface is, however, also influenced by atmospheric refraction. As the frequency is increased, the roughness of the Earth's surface must also be taken into account. Thus seasonal variations are to be expected due to changes in the electrical and topographical properties of the ground as well as the propagation conditions in the atmosphere. It is, however, difficult to separate these various effects, a fact which reduces the possibility of using ground-wave propagation as a loot for obtaining information on the properties of the ground.Though the propagation of the ground-wave has been dealt with both theoretically and experimentally for almost a century, some of the most valuable information of major importance in cold regions has been obtained during the last ten years. New theoretical papers on propagation over stratified media offer an explanation of the amplitude and phase variations of the ground-wave field, which have been measured, as well as suggesting new methods to be tested as possible aids in solving glaciological problems.In many practical eases of ground-wave propagation in arctic regions, the formula for the ground-wave field strength can be written in a very simple way. Such a propagation model for frequencies above 30 MHz is presented in which account is taken of the Earth's curvature, the terrain irregularities, and the effect of the tropospheric refraction. This model also includes the recovery effect which occurs in propagation over mixed paths. At the higher frequencies the effect of depolarization becomes very important and sometimes overshadows field-strength variations due to the influence of the electrical properties. Finally some problems will be discussed which remain to be solved or have been given very little attention up to now.

The effect of the ground constants, and of an earth system, on the performance of a vertical medium-wave aerial

The compensation theorem is used to determine the effect of finite ground conductivity, and of an earth system, on the performance of a vertical aerial, such as is used for medium-frequency broadcasting.The characteristics affected are the input impedance, the ground-wave field strength for a given aerial current and the vertical radiation pattern. The first two of these together determine the efficiency, which is the most important consideration in the design of earth systems. When the effective height of the aerial exceeds 0.1λ, little can be gained by the use of an earth system exceeding 0.2λ in radius when the ground is highly conducting and 0.3 or 0.4λ when it is poorly conducting. The effect of the earth system on the vertical radiation pattern is shown to be unimportant practically, but results are given for one case in order to compare with experimental radiation patterns. The agreement is quite good.

Calculation of Ground-Wave Field Strength over a Composite Land and Sea Path

A brief discussion of the problem is given, together with a description of the three proposed methods of solution. The results of a practical experiment are shown, and curves calculated by the three methods are compared with the observed results. It is shown that the BBC method gives field strengths much nearer to the observed values than the P. P. Eckersley method, and that the method proposed by Millington, while somewhat more laborious to use, also gives results which agree well with observed values. The difference between the three methods is small at low frequencies and when the effect of the discontinuity is not large.