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.