Twisted Pair wires

I. Overview
Twisted Pair wires (TP: Twisted Pairwire) are the most commonly used transmission medium in integrated cabling. Twisted Pair wires are composed of two copper wires with an insulating protective layer. The two insulated copper wires are twisted together at a certain density to reduce signal interference, the electric waves emitted by each wire during transmission are offset by the electric waves sent from the other wire. Twisted Pair wires generally consist of 22 ~ The No. 26 insulated copper wires are wound together. If one or more pairs of twisted pair wires are placed in an Insulating Sleeve tube, the twisted pair cables are formed. In a twisted pair Cable (also known as a twisted pair cable), different lines have different twist lengths. Generally, the twist length ranges from 1cm to 14cm, and is twisted in a counterclockwise direction, the twist length of the adjacent line is above 7cm. Compared with other transmission media, twisted pair wires are limited in terms of transmission distance, channel width, and data transmission speed, but the price is relatively low. Currently, Twisted Pair wires can be divided into unshielded Twisted Pair wires (UTP: Unshilded Twisted Pair) and Shielded Twisted Pair wires (STP: Shielded Twisted Pair ).
Although twisted pair wires are mainly used to transmit analog sound information, they are also suitable for digital signal transmission, especially for short-distance information transmission. During transmission, the signal attenuation is large and waveform distortion occurs. The bandwidth of a LAN Using twisted pair wires depends on the quality, length, and transmission technology of the wires used. By carefully selecting and installing twisted pair wires, you can reach a reliable transmission rate of several million bits per second within a limited distance. When the distance is short and special electronic transmission technology is used, the transmission rate can reach Mbps ~ 155 Mbps. Because the twisted pair wires are used to transmit information to the surrounding area, the information is easily eavesdropped, so it will be shielded at an additional cost. The outer layer of the shielded twisted pair cable is wrapped in aluminum pods to reduce the radiation, but the radiation cannot be completely eliminated. The price of shielded twisted pair cables is relatively high, and installation is more difficult than that of unshielded twisted pair cables. Similar to a coaxial cable, it must be equipped with a special connector that supports shielding and corresponding installation technology. However, it has a high transmission rate, which can reach 100 Mbps within 155.
In addition, unshielded twisted pair cables have the following advantages:
(1) No shield coat, small diameter, save the occupied space;
(2) light weight, easy bending, and easy installation;
(3) minimize or eliminate crosstalk;
(4) Fire-retardant;
(5) It is independent and flexible and suitable for structured integrated wiring.
Ii. Specification and Model
EIA/TIA defines five different quality models for twisted pair cables. The third, fourth, and fifth categories of integrated computer network cabling are used. The five models are as follows:
1. Category 1: Mainly used for voice transmission. The Class 1 standard is mainly used for telephone cables before the beginning of 1980s. It is not used for data transmission.
2. Category 2: The transmission frequency is 1 MHz, which is used for voice transmission and data transmission with a maximum transmission rate of 4 Mbps. It is common in the old token network that uses the 4 Mbps standard token transfer protocol.
3. Category 3: cables currently specified in ANSI and EIA/TIA568 standards. The transmission frequency of the cable is 16 MHz. It is used for voice transmission and data transmission with a maximum transmission rate of 10 Mbps. It is mainly used for 10 BASE-T.
4. Category 4: This type of cable has a transmission frequency of 20 MHz. It is used for voice transmission and data transmission with a maximum transmission rate of 16 Mbps. It is mainly used for Token-based LAN and 10base-T/100base-T.
5. Category 5: This type of cable increases the winding density. The jacket is a high-quality insulating material with a transmission frequency of 100 MHz. It is used for voice transmission and data transmission with a maximum transmission rate of Mbps, it is mainly used for 100base-T and 10base-T networks, which are the most commonly used ethernet cables.
Twisted Pair wires are divided into shielded twisted pair wires and unshielded twisted pair wires. The two categories are divided into 100 ohm cables, dual-body cables, large logarithm cables, and 150 ohm shielded cables. There are multiple models, as shown in 1. The following figure shows the u. S. Cable specification.
　
Iii. Performance indicators
For twisted pair wires, users are most concerned with several indicators that characterize their performance. These indicators include attenuation, near-end crosstalk, impedance characteristics, distributed capacitance, DC resistance, etc.
(1) Attenuation
Attenuation is a measure of signal loss along the link. Attenuation is related to the length of the cable. As the length increases, the signal attenuation also increases. The attenuation unit is db, indicating the signal strength ratio from the source transmitter to the receiver. Because the attenuation changes with the frequency, the attenuation of all frequencies within the application range should be measured.
(2) near-end Crosstalk
Crosstalk is divided into near-end crosstalk and remote crosstalk (FEXT). The tester is mainly used to measure NEXT. Due to line loss, the value of FEXT has little impact. The NEXT loss measures signal coupling from one line to the other in an UTP link. For UTP links, NEXT is a key performance indicator and the most difficult to accurately measure. As the signal frequency increases, the measurement difficulty will increase. NEXT does not indicate the crosstalk value generated at the near-endpoint. It only indicates the crosstalk value measured at the near-endpoint. The value varies with the length of the cable. The longer the cable, the smaller the value. At the same time, the signal at the sending end also degrades, And the crosstalk on other line pairs also decreases. Experiments show that only the NEXT measured within 40 meters is more realistic. If the other end is a 40 m information outlet, it will produce a certain degree of crosstalk, but the tester may not be able to measure this crosstalk value. Therefore, it is best to perform NEXT measurement on both endpoints. The current testers are equipped with corresponding devices, so that the NEXT value at both ends of the link can be measured. For the results of the NEXT test, see table 1 and table 2.
　
　
The above two indicators are the main content of the TSB67 test, but some models of the tester can also provide DC resistance, characteristic impedance, attenuation crosstalk ratio and other indicators.
(3) DC Resistance
TSB67 does not have this parameter. DC loop resistance consumes part of the signal and converts it into heat. It refers to the sum of a pair of wire resistors,
The DC resistance of the 11801 twisted pair cannot exceed 19.2 ohm. The difference between each pair cannot be too large (less than 0.1 ohm). Otherwise, it indicates poor contact and the connection point must be checked.
(4) Characteristic Impedance
Different from loop DC resistance, Characteristic Impedance includes resistance and frequency of 1 ~ MHz inductance impedance and capacitance impedance, which are related to the distance between a pair of wires and the electrical performance of the insulator.
Various cables have different characteristic impedance, while twisted pair cables have 100 ohm, 120 Ohm, and 150 ohm.
(5) attenuation crosstalk ratio (ACR)
In some frequency ranges, the proportional relationship between crosstalk and attenuation is another important parameter that reflects the cable performance. ACR is also sometimes expressed in Signal-to-noise ratio (SNR: Signal-Noice ratio,
It is calculated by the difference between the worst attenuation and the NEXT value. A large value of ACR indicates stronger anti-interference capability. Generally, the system requires at least 10 decibels.
(6) cable Characteristics
The quality of a communication channel is described by its cable characteristics. SNR is a measure of the data signal strength when the interference signal is taken into account. If the SNR is too low,
When a data signal is received, the receiver cannot distinguish the data signal from the noise signal, which leads to a data error. Therefore, to limit data errors to a certain range,
A minimum acceptable SNR must be defined.
Iv. Test Data
100 ohm 4 pairs of unshielded twisted pair wires can be divided into three types of cables, four types of cables, five types of wires, and over five types of wires. The main performance indicators are attenuation, distributed capacitance, DC resistance, DC resistance deviation,
Impedance Characteristics, return loss, and near-end crosstalk. Standard test data is shown in table 1.
　
5. Common twisted pair cables
The most commonly used twisted pair cables in Integrated Wiring are:
1. Category 5, 4 pairs of unshielded twisted pair wires
It is a 24-core bare Copper Conductor of U. S. cables. It is made of vinyl fluoride as insulating material and has a transmission frequency of 100 MHz. The composition of wires is shown in table 4 and physical structure 2.
　
Category 5, 4 pairs of unshielded twisted pair wires
　
The electrical properties are shown in table 5. Among them, "9.38 ohm MAX. Per100m @ 20 ℃" refers to the resistance of 100 ohm twisted pair wires per 9.38 meters at a constant temperature of 20 ℃ (similar to the following table ).
　
Class 2, Category 5, 4 pairs of 24AWG100 ohm shielded cable
It is a 24-wire bare Copper Conductor using vinyl fluoride as insulation material, with a 24-wire TPG leakage line. The transmission frequency is up to 100 MHz, as shown in table 6,
Physical Structure 3 and electrical properties are shown in table 7. In table 6, the shielding item "0.002 [0.051] minimum overlap of aluminum/Polyester tape @ 20℃ and a 24AWG TPC leakage line" has the following meanings:
The screen thickness is 0.002 cm or 0.051 inch.
@ 20 ℃ represents a constant temperature at 20 ℃.
　
Class 5, 4-to-24 awg100 ohm shielded cable
　
　
Category 3, Category 5, 4 pairs of 26AWG shielded soft Cables
It consists of 4 pairs of cables and a 26AWG TPC leakage line with a transmission frequency of 100 MHz. The composition of wires is shown in table 8, physical structure 4, and electrical properties as shown in table 9.
　
　
4. Category 5 4 to 24AWG unshielded soft Cables
It consists of 4 pairs of cables for high-speed data transmission, suitable for extending the transmission distance, used for interconnection or jumper wiring. The transmission rate is 100 MHz. The wire composition is shown in table 9, its physical structure is shown in table 5, and its electrical properties are shown in table 10.
　
　

6. cat5e Cabling System
The cat5e cabling system is an unshielded twisted pair wire (UTP) cabling system. It is indicated by testing its "Link" and "channel" performance, it exceeds the requirements of Class 5 of TIA/EIA568.
Compared with common five types of UTP, it has lower attenuation and less crosstalk, and has a higher ratio of attenuation to crosstalk (ACR) and signal-to-noise ratio (SRL ),
With lower latency error, the performance is improved. It has four advantages:
(1) provides a solid network foundation to facilitate the transfer and update of network technologies.
(2) meet the requirements of most applications and meet the requirements of low deviation and low crosstalk sum.
(3) it is considered as a solution for future network applications.
(4) Sufficient performance margin to facilitate installation and testing.
Compared with Category 5 cables, Category 5 cables are greatly improved in terms of near-end crosstalk, total crosstalk, attenuation, and signal-to-noise ratio.
Near-end crosstalk (NEXT) is the most important criterion for evaluating performance. A high-speed LAN synchronizes data transmission and receiving. NEXT is the interference signal generated when both transmission and reception are performed. The unit of NEXT is db, which indicates the ratio between the transmitted signal and the crosstalk signal.
In common applications, the standard method to measure NEXT is to transmit with one line, and the other line is used for receiving, such as 10BASET and TokenRing, or even 100 BASET and 155 Mbps ATM. However, sometimes you can use the other two lines and connect them to another workstation to speed up the LAN, such as 622 Mbps ATM and 1000BASE-T, it uses not only one pair (maybe all four pairs) for transmission and receiving. Transmitting multiple pairs in a cable increases the crosstalk of the cable. This situation is not taken into account in the current four-to five-category twisted pair.
The total Power Sum NEXT (crosstalk) is the Sum that generates NEXT from multiple transmission ends. If a wiring system can meet the NEXT requirements of five types of cables under Power Sum, it can handle any problems from application sharing to high-speed LAN applications. The NEXT of the 5-class cabling systems is only 1/8 of the requirements of the 5-class cabling systems.
Structural Return Loss (SNR) is the benchmark for measuring the impedance consistency of cables. Changes in Impedance cause reflection. The energy of some signals is reflected to the sending end to form noise. SRL is the standard for measuring energy changes. The impedance changes due to the change of the cable structure, which changes the energy of the signal. The less reflected energy, the more complete the transmission signal, the less noise the cable has.
Compared with common category 5 twisted pair wires, over 5 types of systems provide users with a balance of 8 dB near-end crosstalk when running at a MHz frequency, the user's device is only affected by 1/4 of the ordinary 5-class cable system, making the system more independent and reliable.