The ఏకాక్షక కేబుల్ uses hard copper wire as the core and a layer of insulating material. This layer of insulating material is surrounded by a densely woven mesh conductor, and the net is covered with a layer of protective material. There are two widely used ఏకాక్షక కేబుల్s. One is a 50-ohm cసామర్థ్యం, which is used for digital transmission, and is also called baseband ఏకాక్షక కేబుల్ because it is mostly used for baseband transmission; the other is a 75-ohm cసామర్థ్యం, which is used for analog transmission, which is the broadband ఏకాక్షక కేబుల్ to be discussed in the next section. This difference is caused by historical reasons, not technical reasons or manufacturers.
This structure of ఏకాక్షక కేబుల్ makes it have high bandwidth and excellent noise suppression characteristics. The bandwidth of a ఏకాక్షక కేబుల్ depends on the cసామర్థ్యం length. A 1km cసామర్థ్యం can reach a data transmission rate of 1Gb/s~2Gb/s. Longer cసామర్థ్యంs can also be used, but the transmission rate should be reduced or intermediate amplifiers should be used. Currently, ఏకాక్షక కేబుల్s are largely replaced by optical fibers, but they are still widely used in cసామర్థ్యం television and some local area networks.
A ఏకాక్షక కేబుల్ system that uses a limited TV cసామర్థ్యం for analog signal transmission is called a broadband ఏకాక్షక కేబుల్. The term "broadband" comes from the telephone industry and refers to a frequency band wider than 4kHz. However, in computer networks, "broadband cసామర్థ్యం" refers to any cసామర్థ్యం network that uses analog signals for transmission.
Because the broadband network uses standard cసామర్థ్యం television technology, the usసామర్థ్యం frequency band is up to 300MHz (often to 450MHz); due to the use of analog signals, an electronic device needs to be placed at the interface to convert the bit stream entering the network into an analog signal, and Convert the signal output from the network into a bit stream.
Broadband systems are divided into multiple channels, and TV broadcasting usually occupies 6MHz channels. Each channel can be used for analog TV, CD quality sound (1.4Mb/s) or 3Mb/s digital bit stream. TV and data can be mixed on a single cసామర్థ్యం.
A major difference between a broadband system and a baseband system is that because the broadband system covers a wide area, it requires an analog amplifier to periodically strengthen the signal. These amplifiers can only transmit signals in one direction. Therefore, if there are amplifiers between computers, packet packets cannot be transmitted backwards between computers. To solve this problem, two types of broadband systems have been developed: dual-cసామర్థ్యం systems and single-cసామర్థ్యం systems.
A dual cసామర్థ్యం system has two identical cసామర్థ్యంs laid side by side. In order to transmit data, the computer transmits the data through the cసామర్థ్యం 1 to a device at several roots of the cసామర్థ్యం, that is, the head-end, and then the head-end transmits the signal down the cసామర్థ్యం through the cసామర్థ్యం 2. All computers send via cసామర్థ్యం 1 and receive via cసామర్థ్యం 2.
Another solution is to allocate different frequency bands for internal and external communications on each cసామర్థ్యం. The low frequency band is used for communication from the computer to the top device, and the signal received by the top device is moved to the high frequency band and broadcast to the computer. In the subsplit system, the 5MHz~30MHz frequency band is used for inward communication, and the 40MHz~300MHz frequency band is used for outward communication. In the midsplit system, the inward frequency band is 5MHz~116MHz, and the outward frequency band is 168MHz~300MHz. This choice is caused by historical reasons.
A dedicated permanent channel can be allocated between a pair of computers; other computers can apply to establish a temporary channel through the control channel, and then switch to the applied channel frequency; and all computers can share one or a group of channels. Technically speaking, broadband cసామర్థ్యంs are worse than baseband (single channel) cసామర్థ్యంs in sending digital data, but its advantage is that it has been widely installed.