Basic information
Includes: short-wave communication equipment and satellite communication equipment used for long-distance communication or short-distance tactical communication. It is the most important radio communication equipment on ships; used for line-of-sight Ultrashort wave communication equipment for tactical communication within the range; medium wave communication equipment mainly used for emergency communication; and very long wave receiving equipment mainly used for submarine underwater receiving information from shore stations. Ship radio communication equipment can transmit telegrams, telephones, data and images, and can implement confidential communications. In the early days of the ship's confidential communications, passwords and secret words were used. Because of their simplicity and convenience, they are still used. With the development of secrecy and electronic technology, modern security machines are widely used to automatically encrypt and decrypt information, which improves secrecy performance and information transmission efficiency. The ship's radio communication equipment has good electromagnetic compatibility performance, and the antenna configuration is reasonable, which reduces mutual interference and influence. In order to ensure that the submarine can conceal, safely and reliably carry out radio communication underwater, the submarine radio communication equipment is equipped with special antennas such as lifting antennas, loop antennas, towed antennas, and feeder devices, as well as fast reporting terminals and slow reporting terminals. The terminal equipment is used for concealed instantaneous shortwave transmission, satellite communication and underwater reception.
In the summer of 1897, the Russian A.S. Popov conducted a radio communication test between the "Africa" and the "Europe" in the Baltic Sea. In 1899, Italian G. Marconi installed radio communication equipment on three British navy ships to realize radio communication. In 1905, the Beiyang Navy of China in the late Qing Dynasty equipped a spark-type radio station for fleet command and communication. Naval radio communication equipment has gone through several stages of electron tubes, transistors, and integrated circuits, and has been continuously improved and updated. In the 1960s, a ship radio integrated communication system appeared. With the central control subsystem as the core, digital remote control was used to connect between equipment and equipment, and between equipment and use parts, implementing centralized management and scheduling, and automatically or semi-automatically. For processing, broadband transmitting antennas and active broadband receiving antennas are used to reduce the number of antennas and have good electromagnetic compatibility performance. The development trend of naval radio communication equipment is to continuously improve the reliability, generalization, standardization, and serialization of the equipment; improve the flexibility, electromagnetic compatibility, self-adaptation and automation level of the equipment; and continuously improve the anti-interference performance. While the naval radio communication system exists independently, it can also provide a suitable transmission channel for command automation and become an important part of the command automation system.
Lightning protection measures
Generally speaking, there are roughly four ways to avoid lightning strikes in buildings: 1) Dredging, that is, dredging the electric charge in the thundercloud to the ground to avoid direct lightning strikes Or the induced lightning current flows through the protected buildings or equipment to protect these buildings or equipment from lightning strikes. 2) Isolation, that is to isolate the lightning signal from the protected object to avoid lightning strikes. 3) Equipotentiality, that is, the ground of the tower, the work place, and the public ground of the building are at the same potential. 4) Dissipation, that is, the charge of the opposite sex is released and the charge in the thundercloud is neutralized, thereby preventing the formation of lightning. According to the above four lightning protection methods, specific to the lightning protection design of a radio communication project, the main lightning protection measures include the following methods.
1. Install lightning rods or lightning protection devices
Most of the lightning protection facilities of communication equipment, mainly install lightning rods on the communication tower. This method is economical and simple. , But must be installed in strict accordance with the following requirements.
a. The lightning rod should be installed a few meters above the tip of the antenna, and there should be a certain distance between the lightning rod and the antenna to prevent the radiation pattern of the antenna from being damaged due to the existence of the lightning rod and affecting the communication effect. The general practice is that the lightning rod becomes the main pole of the antenna tower, but the communication antenna is installed about 1.5 wavelengths away from the outer edge of the lightning rod.
b. The resistance requirement of the DC path of the lightning protection ground wire is low enough, generally 10-50Ω, because the lightning surge current is large, the frequency spectrum is wide and the duration is short, so the requirement must be as small as possible Inductance.
c. Flat wire or twisted wire cannot be used for the ground wire, because this kind of wire has a large inductance, which is not conducive to the discharge of lightning current and is easy to be corroded. Try to use a solid wire of 3 mm or more, and preferably the same metal material.
d. In order to increase the discharge area of the ground surface, multiple grounding bodies with a certain interval can be buried and welded to each other. For example, about 10 copper pipes are buried around the building at an interval of 1 to 2 meters, and they are welded together.
Although it is economical and simple to install lightning rods on communication towers, it is difficult to be foolproof. For some important communication projects, you can consider installing radioactive lightning protection devices. The radioactive lightning protection device can be said to be one of the most advanced lightning protection devices in the world.
The key part of the radioactive lightning protection device is the radioactive source, which can continuously emit particles by itself and ionize the surrounding air to generate a large number of electrons. Under the action of the lightning electric field, these electrons are continuously accelerated to produce chain multi-level ionization or avalanche ionization to the air, forming an electron current proportional to the electric field strength. At this time, the ionization and conduction generated from the radioactive source to the thundercloud will never be conducted. Intermittently neutralize and release the space charge, eliminate the existing low electric field, and reduce the high electric field that may be formed to a low electric field, thereby effectively preventing the occurrence of lightning and playing a significant lightning elimination effect. This kind of radioactive lightning protection device has a large protective area, and its radius is about 260 meters. It is safe and reliable and has no harm to humans.
2. Methods to prevent induced lightning strikes
In addition to installing lightning rods or lightning protection devices on the communication tower, attention should also be paid to eliminating induced lightning strikes. The usual practice is to install lightning arresters in the antenna feeder system.
Pay attention to the following issues when installing lightning arresters in the antenna feeder system. One is that the ground terminal of the arrester must be reliably connected to the ground, and the ground resistance must not be greater than 5Ω, otherwise it will affect the lightning protection effect. Second, due to the certain insertion loss of the arrester, it has a certain impact on the strength of the antenna radiated signal. At the same time, attention should be paid to the change of the standing wave ratio. Generally, the standing wave ratio of the antenna feed system is required to be less than or equal to 1.5. The third is when the communication antenna is installed, the antenna strut is reliably connected to the iron tower, and the connection resistance is equal to 0Ω. The feeder should hang down from the inside of the tower and be fixed with copper wires at intervals.
For important communication projects, in addition to installing lightning arresters in the antenna feeder system, attention should also be paid to the lightning protection of the power supply system. The general practice is to install lightning protection devices in transformers and power distribution rooms.