Customer Case

The Application of Short Wave Communication in the Field of Civil Defense

Despite the continuous emergence of new wireless communication systems, shortwave communication, as a traditional communication method, still receives attention from all parties and is the basic configuration for building communication networks.
1、 Importance of shortwave communication
Firstly, shortwave communication is the only remote communication method that is not constrained by network hubs and active relays. In the event of war or disaster, various other communication networks may be damaged, and satellites may also be attacked. Regardless of the communication method, its survivability and autonomous communication ability are unparalleled compared to shortwave communication. Secondly, in remote areas such as mountainous areas, the Gobi Desert, and the ocean, ultra short wave coverage is not available, and the cost of establishing a cluster communication network through base stations is too high, so communication mainly relies on short wave. Finally, compared to satellite communication, shortwave communication does not require payment for calls and has low operating costs.
In recent years, China's shortwave communication technology has made significant progress. These technological achievements should be used by civil air defense systems. It is undoubtedly very meaningful to transform and enrich the wireless communication networks of various civil air defense systems in China with modern shortwave equipment, making them more advanced and effective, and meeting the needs of various work in the new era.
2、 Strengthening the Construction of Short Wave Communication System Should Take the Lead
With the continuous development of shortwave communication technology in our country, military shortwave radios are gradually being replaced, and corresponding standards and documents have been introduced for civil air defense systems, keeping up with the pace of military development. Therefore, the selection of shortwave equipment for civil air defense systems should be based on the premise of domestic production and compliance with the system.
In order to achieve good communication results, special attention will be paid to the installation method of the antenna. In the process of antenna installation, the length and installation specifications of the antenna cannot be changed, but for some antennas, the installation direction and height can be controlled by oneself, and the direction and height should be strictly determined according to the communication direction and distance. At the same time, the installation position of the antenna should be on an expanded ground, and units without conditions should be placed between two buildings or on the roof. When standing on the roof, the height should be calculated based on the distance between the roof and the antenna transmitter, not the height between the roof and the ground. Another key point is the selection and layout of feeder lines. The feeder is the only channel that sends the output power of the radio station to the antenna for transmission. If the feeder is not smooth, even a good radio station and antenna will have poor communication performance. When selecting a feeder, two indicators should be noted: first, an impedance of 50 ohms; Secondly, the attenuation value for the highest usage frequency should be small. Generally speaking, the thicker the diameter of the RF cable, the smaller the attenuation and the higher the transmission power. In practical use, 100W class shortwave single sideband radio stations often use SYV-50-5 or SYV-50-7 RF cables, and if necessary, SYV-50-9 RF cables can also be selected. When installing and laying the antenna, the length of the feed line should be minimized as much as possible. The ordinary SYV-50-5 feed line causes a signal attenuation of 0.082dB every 1 meter, which means that when the 100W radio power is delivered to the antenna through the 50 meter feed line, the remaining power is less than 40W. Therefore, it is usually required to control the length of the feeder line within 30 meters. If it is necessary to extend the feeder line due to site conditions, large diameter low loss cables should be used.
To achieve good communication results, the grounding body and connecting ground wire should be buried correctly. The ground wire of shortwave communication stations is crucial, and it is actually an important component of the entire antenna feeder system. The ground wire mentioned here is not the power or security ground in the AC power supply system, but the signal ground, also known as high-frequency ground. The signal ground generally cannot be connected to the power ground or security ground, and must be buried separately. When burying the grounding body, it must be carried out in accordance with relevant standards, and the grounding resistance should not exceed 4 ohms. The grounding pole of the radio station and the grounding body must be connected with multi-stranded copper, braided copper wire, or large cross-section excellent conductors in order to have a good high-frequency grounding effect. A good high-frequency grounding is a necessary prerequisite for reducing transmission standing waves and receiving noise.
According to the characteristics of the civil air defense department, in the renovation of the civil air defense mobile rescue command system, the shortwave communication system has been upgraded and transformed, forming a hierarchical system with 125W shortwave radio as the main vehicle and 20W shortwave radio as the main mobile station. Due to the communication distance and the terrain dominated by mountains and hills in Ganzhou City, the latest half loop antenna is used in the onboard shortwave communication system. As a new type of shortwave antenna, this antenna is specifically designed to solve the communication blind spot of onboard shortwave antennas. Its semi circular structure achieves high elevation incident sky waves, utilizing the radiated high elevation electromagnetic waves that are nearly perpendicular to the ground, concentrated in the direction of 90 to 40 degrees high elevation to medium elevation, forming a "fountain like" radiation to the sky, which is reflected back to the ground through the ionosphere, forming a uniform electromagnetic wave coverage in a fixed area on the ground for communication. Its dissemination has the characteristics of uniform coverage, stable signal, and little influence due to geographical and geomorphic factors. Having the characteristic of "no blind spots", it is very suitable for the requirements of shortwave "no blind spots", "communication in motion", and "mountain communication" in a certain area.
3、 Supported by a comprehensive shortwave communication training system
The construction of the shortwave communication system has been strengthened, and shortwave communication training needs to be followed up in order to enable the shortwave communication system to play its due role. Through technical training, shortwave communication operators have reached the level of understanding, using, and repairing shortwave, establishing a scientific theoretical knowledge learning system, and forming a professional shortwave communication team. The training content will also be conducted in two aspects: basic knowledge, radio operation, and equipment maintenance.
The basic knowledge training mainly focuses on the characteristics of shortwave communication and takes into account technological development as a branch, achieving the goal of understanding shortwave communication and mastering the characteristics of shortwave communication for shortwave communication personnel. By combining "inviting in" and self-learning, we strengthen training in the history of shortwave development, communication technology, and other aspects. We focus on learning new knowledge, new technologies, and new equipment, adhere to the principle of applying what we have learned, and integrate theory with practice for training. When executing tasks, we can ensure the smooth completion of tasks with ease. Establish an assessment and reward incentive system to encourage advancement and set benchmarks. By forming study groups and conducting knowledge competitions and other activities, we can enhance our learning enthusiasm.
Radio operation training mainly focuses on the actual operation of shortwave radio stations, with an understanding of the composition and working principles of the radio station as a branch. The training effect aims to enable shortwave communication personnel to proficiently operate the radio and fully apply various functions of the shortwave radio to civil air defense shortwave communication. Equipment maintenance will establish an effective daily maintenance system, with regular personnel responsible for inspecting the radio station, mastering the general principles of equipment maintenance, and possessing the ability to preliminarily judge and solve problems in shortwave communication systems. By organizing skill operation competitions, we aim to enhance our business capabilities.
Through the construction of the shortwave communication system, training on shortwave communication knowledge, and the establishment of a shortwave communication network covering the entire city, we have trained a capable team that can be used when needed, so that shortwave communication services can be applied in civil air defense work and fully play the due role of shortwave communication.

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Zhejiang Kaichi Electronic Technology Co., Ltd.

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