BelFone Provides Tunnel Radio Communication Solutions for State Grid Jilinsheng Electronic Power Supply Company

July 17,2019.

The Challenge

As the city undergoes rapid development, the construction of power grid in Changchun is making steady progress. Telegraph poles multiply wherever the city extends. However, these standing telegraph poles are inconvenient, inadequate and unaesthetic. For this reason, State Grid Jilinsheng Electronic Power Supply Company is taking the cables underground, at an annual speed of 100 km. In tunnel areas, communications get challenging as, due to the geographic features of tunnels, signals get weak and unstable. Cellphones are helpless and ordinary two-way radios are hardly any better. Communications become a great challenge for the construction and maintenance of power grids in tunnel areas.

Radio System Overview

Information technology is playing an increasingly significant role in our life and work. As an important way of information exchange, radio communication gains worldwide importance with its extensive application. Users want instant communications with one another at any place, which generates a new need---radio signal coverage system. As a radio communication platform for the daily operating and dispatching between functional departments, the system needs to solve the signal blindness problem caused by geographic difficulties, ensuring efficient signal coverage in the relevant area, extending communication range, conquering geographic challenges, to optimize the work coordination and dispatching within the area.

Radio Signals in Tunnels

On Leaky Cables

Leaky cables integrate the transmitting and receiving of signals, and can function both as coaxial cables and antennas. They are widely used in areas where the transmission of radio signals is restricted, such as roads, rails, tunnels, metros, and mines. The structure of a leaky cable is similar to that of a coaxial cable, which consists of an inner conductor, an insulating medium, and an outer conductor with periodic grooves. Electromagnetic waves, during their vertical transmission in a leaky cable, radiate outward through the periodic grooves. The electromagnetic field outside senses the radiation (through the periodic grooves) and transmits to the receiver. In tunnel areas radio waves, especially HF and VHF waves, are usually blocked. Test results show that a radio device, whose communication range is otherwise above 5000m, when operating in a tunnel or under a well, can only transmit as far as dozens or hundreds of meters at most. We can always try to extend the range by increasing the transmitting power, but the effect is far from satisfactory. According to relevant expert experiments, in a tunnel environment, when you increase the transmitting power of a radio device by a hundred times, you can only extend its communication range by 1/5, just as the illumination of a high power torchlight cannot penetrate very far ahead (in a tunnel). Besides, it is not allowed to increase transmitting powers at will in a tunnel environment, for it may compromise the health of work staff or result in other serious accidents. Leakage cable communication is to use leaky cables as radio antennas to achieve an even and steady signal field, which is stable with great anti-interference ability. With leaky cables there is no blind zone.

Project Introduction

According to the requests of and materials provided by the user, and based on more than 30 years of experience and expertise in the PMR industry, BelFone decides to cover the tunnel with leaky cables to ensure the even distribution of repeating signals. Meanwhile, we install FRP antennas (high gain & omnidirectional) in the tunnel, so that  radio communications within the tunnel become smooth and clear, making it a lot easier for workers to carry out their power grid construction. In addition, multi-site IP connections can be achieved to make communications between the different tunnels and the power company possible, further facilitating the command and dispatch work of the company(extra devices are needed for this feature).

Radio Signals in Tunnels

The project designs vary for different tunnels, each according to the specific geographic features of the tunnel. Project 1 covers 2.05kms, from Hunan Mid Street to Yiyi Road. Using Hunan Mid Street as a starting point, BelFone installs an IP connection repeating system at 0.7km and 1.4km respectively, which consists of a BF-TR8050 repeater and a BF-TR908 link module. The repeating systems are connected using fiber transceiver and optical cables. The signals from 0.7km repeater, processed by a divider, travel in two different ways, one via FRP antennas, the other via leaky cables which covers the distance from 0.7km to 2.1km (at the end of the cables are installed ceiling antennas or dummy loads ). The system is composed of BF-TR8050 repeaters, BF-TR908 IP link modules, dividers , leaky cables, ceiling antennas (dummy loads), fiber transceivers, and optical cables.

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