(1) Coaxial cable
The coaxial cable takes hard copper wire as the core and is covered with a layer of insulating material. This layer of insulating material is surrounded by a densely woven mesh conductor, and a layer of protective material is covered outside the mesh. There are many different specifications of coaxial cable, the most commonly used are thin coaxial cable and thick coaxial cable. Thin coaxial cables are mainly used for network connections in buildings, while thick coaxial cables are often used for connection between buildings. The difference is that the thick coaxial cable has better shielding and can transmit longer distances.
The coaxial cable is composed of a center conductor, a layer of insulating material, a shielding layer composed of a mesh fabric, and an external insulating material layer. Its structure is shown in Figure 1:
Figure 1-3-1 Schematic diagram of the coaxial cable structure
(2) Twisted pair
Twisted pair is the most commonly used transmission medium in integrated wiring projects. The twisted pair consists of two copper wires with an insulating protective layer. Twisting two insulated copper wires with each other at a certain density can reduce the degree of signal interference. The radio waves radiated by each wire during transmission will be canceled by the radio waves emitted by the other wire, compared with other transmission media The twisted pair is subject to certain restrictions in terms of transmission distance, channel width, and data transmission speed, but the price is relatively low. Currently, twisted-pair cables can be divided into unshielded twisted-pair cables and shielded twisted-pair cables.
The structure of the twisted pair is shown in Figure 2:
Figure 1-3-25 Category 4 pairs of unshielded twisted pair
(3) Optical fiber
Optical fiber is a kind of soft medium that can directly transmit light waves with a diameter of 50 ~ 100um, generally made of glass. The optical fiber is divided into: the transmission point modulus class is divided into single mode fiber (SingleModeFiber) and multimode fiber (MulTIModeFiber). The core diameter of a single-mode fiber is very small, and it can only be transmitted in a single mode at a given operating wavelength, with a transmission frequency bandwidth and a large transmission capacity. Multimode fiber is an optical fiber that can be simultaneously transmitted in multiple modes at a given operating wavelength. Compared with single mode fiber, multimode fiber has poor transmission performance. The basic structure of the optical fiber communication system is shown in Figure 3.
Figure 1-3-3 Basic composition of optical fiber communication system
The AGM is a newer type sealed lead-acid that uses absorbed glass mats between the plates. It is sealed, maintenance-free and the plates are rigidly mounted to withstand extensive shock and vibration. Nearly all AGM batteries are recombinant, meaning they can recombine 99% of the oxygen and hydrogen. There is almost no water is loss.
The charging voltages are the same as for other lead-acid batteries. Even under severe overcharge conditions, hydrogen emission is below the 4% specified for aircraft and enclosed spaces. The low self-discharge of 1-3% per month allows long storage before recharging. The AGM costs twice that of the flooded version of the same capacity. Because of durability, German high performance cars use AGM batteries in favor of the flooded type.
Advantages
· Inexpensive and simple to manufacture.
· Mature, reliable and well-understood technology - when used correctly, lead-acid is durable and provides dependable service.
· The self-discharge is among the lowest of rechargeable battery systems.
· Capable of high discharge rates.
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