Yude YDIT analyzes twisted pair structure and technical indicators from a professional perspective

Source:YDIT 誉德 Release time:2019/8/1 10:21:23 Views:785

 

(Paperless conference system, paperless office system, ultra-thin integrated lifter) Twisted pair (TP) is the most commonly used transmission medium for information transmission cables. The twisted pair is protected by two insulation cables. The layer consists of copper wires. The two insulated copper wires are twisted together at a certain density to reduce the degree of signal interference. The electric wave radiated by each wire during transmission is cancelled by the electric wave emitted from the other wire. The twisted pair is generally formed by winding two 22~26 insulated copper wires. Generally, four twisted pairs are included in the twisted pair, specifically white orange/orange, white blue/blue, white green/green, and white brown/brown.

Twisted pair cable is suitable for transmitting telephone voice information, computer data information, fire prevention, anti-theft security information, intelligent building information, etc. The twisted pair has 5 categories and 6 categories. At present, the twisted pair can be divided into unshielded twisted pair (Unshiielded Twisted Pair, UTP, also known as unshielded twisted pair) and shielded twisted pair (Shielded Twisted Pair, STP). The outer layer of the shielded twisted pair cable is wrapped with aluminum pouch. .
Twisted pair performance indicators
(Paperless conference system, paperless office system, ultra-thin integrated lifter) For twisted pair (whether shielded or unshielded) users are most concerned about the performance indicators that affect their transmission effect as follows.
(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 increases. The attenuation is expressed in units of dB and represents the ratio of the signal strength of the source transmitter to the signal strength of the receiver. Since the attenuation varies with frequency, the attenuation over all frequencies within the application range should be measured.
(2) Crosstalk. Crosstalk is divided into near-end crosstalk (NEXT) and far-end crosstalk (FEXT). The tester mainly measures NEXT. Due to the line loss, FEXT has less influence on signal transmission. For UTP links, NEXT is a key performance indicator and one of the most difficult to measure accurately. As the frequency of the signal increases, the measurement difficulty will increase. NEXT does not represent the crosstalk value produced at the near endpoint, it simply represents the crosstalk value measured at the near endpoint. This magnitude will vary with cable length, and the longer the cable, the smaller its value becomes. At the same time, the signal at the transmitting end is also attenuated, and the crosstalk to other pairs is relatively small. Experiments have shown that only NEXT measured within 40m is more realistic. If the other end is an information outlet that is longer than 40m, it will generate a certain degree of crosstalk, but the tester may not be able to measure this crosstalk value. Therefore, it is best to perform NEXT measurements at both endpoints. Today's testers are equipped with appropriate equipment so that the NEXT values ​​at both ends can be measured at one end of the link.
(3) DC loop resistance (TSB67 does not have this parameter). The DC loop resistor consumes a portion of the signal and converts it into heat. It refers to the sum of a pair of wire resistances. The DC resistance of a 1180 gauge twisted pair shall not be greater than 19.2 Ω. The difference between each pair should not be too large (less than 0.12 Ω), otherwise it means poor contact and the connection point must be checked.
(4) Characteristic impedance. The characteristic impedance is different from the DC resistance of the loop. The characteristic impedance includes the resistance and the impedance of the inductor and the impedance of the capacitor from 1 to 100 MHz. It is related to the distance between the wires and the electrical properties of the insulator. Various cables have different characteristic impedances, and the characteristic impedance of the twisted pair is 100, 120, and 150 Ω.
(5) Attenuation crosstalk ratio (ACR). In some frequency ranges, the proportional relationship between crosstalk and attenuation is another important parameter reflecting cable performance. ACR is sometimes expressed in terms of signal-to-noise ratio (SNR: Signal-Noiceratio), which is the worst attenuation and NEXT magnitude. The difference is calculated. The ACR value is large, indicating that the anti-interference ability is stronger, and the general system requirement is at least greater than 10 dB.
(6) Cable characteristics. The quality of the communication channel is described by the cable characteristics, which is a measure of the strength of the data signal, taking into account the interfering signal. If the SNR is too low, it will cause the receiver to be unable to resolve the data signal and the noise signal when the data signal is received, eventually causing data errors. Therefore, in order to limit data errors to a certain range, a minimum acceptable SNR must be defined. (Paperless conference system, paperless office system, ultra-thin integrated lifter)