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Presents the results of propagation studies carried out on a smooth-Earth diffraction path for assessing the enhanced ratio fields for certain though small, percentages of time. Characteristics of duct propagation; Propagation losses in duct; Empirical estimation of electromagnetic interference level.

Many experiments have been carried out to study the absorption and scattering properties of forest vegetation on radiowaves but very little has been reported on the measurements of relative permittivity (ε[sub r]) and conductivity (σ) of forest slab. Due to various constraints, the in-situ measurements of ∈[sub r] and σ were limited to 75 MHz. Inverse methods have reportedly been employed to evaluate ∈[sub r] and σ for forest slab from the experimental data on the measurements of antenna pattern, reflection coefficient, wave impedance, and path loss, etc. These studies were restricted to 400 MHz. In this paper the values of ε[sub r] and σ for the forest slab have been estimated by fitting the theoretical model to the measured data on lateral wave attenuation constant derived from the height-gain measurements conducted in forest, in the frequency range of 50-800 MHz. [ABSTRACT FROM AUTHOR]

It is found from experimental investigations that the normal mode helical antenna used with a ground plane may be used in the medium and short wave region. In this paper, analytical expressions for the radiation field (EΦ and Eθ) of this antenna are found from the appropriate vector potential for the helix. The analytical expressions are derived on the assumption of a sinusoidal current distribution. The helix is considered to be cylindrical. The theoretical results are in good agreement with experimental observations. [ABSTRACT FROM AUTHOR]

Axial mode helical antennae are well known for many applications. Compared with them, little attention has been paid to normal mode helical antennae. However, it has been found recently that normal mode helices have wide applications in different fields--some of which have been investigated by the author and his co-workers and may be summarized as follows.
(a) A log periodic antenna has been designed using normal mode helices as elements and its impedance and radiation characteristics have been measured. This study reveals that a helical log periodic antenna is electrically equivalent to a log periodic dipole antenna with the advantage that the former has a much reduced height (reduction factor being 022 in our case).
(b) Investigations have been made to study the feasibility of using normal mode helical antennae in the medium and short wave regions. Experimental results indicate that it is quite possible to reduce the height of the mast antenna by a factor of 5 to 10 and the bandwidth is enough for the purpose of broadcasting.
(c) The method of slewing the radiation angle is also studied. In the broadcast frequency range the usual height of the mast is 05-064 to have the desirable angle of maximum radiation. It has been shown that the same thing can be achieved in a normal mode helical antenna by introducing a phase shift at an appropriate point in the helix.
The normal mode helical antennae have been seen to be greatly advantageous in certain fields of applications. In the near future they may be useful in other fields also. So it is wise enough to think about the mechanical aspects of constructing these antennae, e.g. the material of the antenna should be such that the antenna becomes light as well as strong and it withstands specified wind velocity and radial ice load. The factors, namely, the material cost, the mounting device, the ease of winding, withstand of specified temperature and humidity should also be... [ABSTRACT FROM AUTHOR]

Investigates the possibility of carrier bunching by velocity modulation inside a block of semiconductor material. Application of a constant magnetic and electric field; Illustration of a coordinate system showing the distribution of the electric and magnetic fields; Derivation of equations for the complex motion of velocity.