OPERATIONAL CHARACTERISTICS OF SMALL-SIZED ANTENNA DEVICES OF THE MEDIUM FREQUENCY RANGE IN MINES

Представлены результаты исследования трех малогабаритных антенн (электрического,магнитного и магнитоэлектрического типов)СВ-диапазона с целью определения особенностей их эксплуатации в рудниках и шахтах,т.е. в диспергирующих средах. Рассмотрены импедансные характеристики и изменение частотных зависимостей коэффициента стоячей волны в ближней зоне антенн, обусловленное непостоянством электрических характеристик горных пород при перемещении антенн вдоль горной выработки. Проведена оценка стабильности работы портативных радиостанций при подводимой к малогабаритной антенне мощности 1 Вт с учетом времени,характерного для сеансов связи. Даны рекомендации по эксплуатации антенн в условиях рудников и шахт. The article investigates three main types of small antennas (electric, magnetic and magnetoelectric) of the medium frequency range in order to determine the features of their operation in mines, i.e. in dispersing media. The impedance characteristics and the change in the frequency dependences of the standing wave ratio are considered when the situation in the near zone changes. An assessment of the stability of the operation of portable radio stations at an input power of 1 W has been carried out, taking into account the time characteristic of communication sessions. Recommendations for the operation of antennas in mines are given.

Analysis of the budget of through-the-earth communication channel

At present, radio stations of the very-long wave (VLW) range with a power of several hundred and thousands of watts with large antennas (hundreds and thousands of meters) are used for wireless through-the-earth communication in mines. Such radio stations allow providing a one-way communication channel informing miners about emergencies. In addition, in recent years, portable radio stations of the medium-frequency (MF) band have also become widespread, which use monofil or bifilar lines laid along mine tunnel for communication, and electrically small antennas. In this regard, an urgent scientific task is to estimate the budget of an underground wireless communication channel wireless through-the-earth using a portable radio station and electrically small antennas. Purpose of the article: to analyze the characteristics of through-the-earth communication channels in the range from 1 kHz to 10 MHz, to compare the budget and signal-to-noise ratio of the MF channel with the channels in the low frequency (LF) band. As a result, the losses in the through-the-earth communication channel in the range from 1 kHz to 10 MHz are estimated: at the output of the transmitting antenna, at the receiving point, at the output of the receiving antenna. A detailed calculation of the budget at a frequency of 1 MHz for a radio path with a length of 100 meters for various values of electrical conductivity characteristic of rocks is presented. Attention is focused on the antenna efficiency and its contribution to the budget of the communication channel. It is shown that two opposite factors: a drop in the antenna efficiency and a decrease in losses in a semiconducting medium with a decrease in the operating frequency, lead to the emergence of optimal radio frequencies, depending on various values of the electrical conductivity of rocks, which are semiconducting media. Practical relevance. The obtained research results justifiably confirm the effectiveness of using small-sized (including portable) radio stations of the MF band for organizing two-way through-the-earth communication between levels in mines. The obtained optimal frequencies make it possible to select the operating range in mines located in rocks with different electrophysical characteristics.

Assessment of the Electromagnetic Field Exposure during the Use of Portable Radios in the Context of Potential Health Effects

The paper presents research on the electromagnetic hazards related to the flow of electric currents throughout the bodies of employees using portable radios. The values often exceed established limits, which may lead to potential dysfunctions of the body and affect the safety of performed professional duties. The measurements of the electric field (E-field) distribution of a typical commercial portable radio, the limb contact current calculations, and the computer simulations determining a specific absorption rate (SAR) were supplemented with pilot neurophysiological tests. The assessment indicated a large spatial variability of the E-field strength around the devices. The head of the operator and the hand holding the radio were often in the electromagnetic field (EMF), which exceeded the established limits. The calculated SAR values ranged within the permitted limits. The conducted neurophysiological tests showed no effects of EMF exposure in comparison to the control group. The assessment of exposure to the EMF using a portable radio is initially performed by analyzing external measures: both computer simulations and measurements of workers’ limb currents. The SAR values exclude thermal effects; however, they do not eliminate potential neuromuscular effects. More neurophysiological tests are needed to obtain a broader picture of possible health effects.

Relative Analysis of Channel Fading Models in Wireless Networks

With a specific end goal to enhance and test the framework's viability to oppose blurring, we fundamentally need to display and simulate the correspondence situation under some blurring channel for outlining of a correspondence framework. The trademark of blurring channel is various and complex for various engendering conditions. Accordingly, suitable blurring model for a specific correspondence situation is basic in such manner. Rayleigh blurring and Ricean blurring models are the most commonly utilized little scale models in remote correspondence till date. However, after the appearance of portable radio correspondence, the plan of a situation has been changed to actualize portability of transmitter or beneficiary. Along these lines we have to change the blurring model also. This paper thinks about various blurring models-Rayleigh blurring, Rice a blurring and quick Rayleigh blurring utilizing. The re-enactment comes about demonstrate that Fast Rayleigh Fading model is most appropriate for versatile radio situations which endure thick blurring

Media and mobility: Two fields, one subject

This article advocates greater collaboration between media studies and mobility studies. After exploring the ways that media can be immobile, mobile and ambient, it examines how each field has incorporated the other. The article then presents two US case studies, the portable radio and in-car media, to demonstrate that modern electronic media have long possessed a mobile capacity. This leads to a final discussion about the role of media in fostering relations between people and built environments with their varying degrees of mobility.