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AC AC power cord and DC power cord
A power cord is a wire that carries electric current. The usual way of current transmission is point-to-point transmission. Power cord according to the use can be divided into AC power cord and DC power cord, usually AC power cord is through the higher voltage AC wire, this type of wire due to the higher voltage needs to be unified standards to obtain safety certification before official production. The DC line is basically through the lower voltage DC, so the safety requirements are not as strict as the AC line, but for safety reasons, countries still require unified safety certification.
Power cord in the twisted pair of performance indicators
For twisted-pair cable, the user is most concerned about the performance of several indicators characterizing its performance. These indicators include attenuation, near-end crosstalk, impedance characteristics, distributed capacitance, DC resistance, etc.
(1) Attenuation
Attenuation (Attenuation) is a measure of signal loss along the link. Attenuation and the length of the cable has a relationship, with the increase in length, signal attenuation also increases. Attenuation in "db" as a unit, indicating the ratio of signal strength from the source transmission end to the receiver end. Since the attenuation varies with frequency, the attenuation should be measured at the full range of frequencies within the application.
(2) Near-end crosstalk
Crosstalk is divided into near-end crosstalk and far-end crosstalk (FEXT), the tester is mainly measuring NEXT, due to the existence of line loss, so the impact of the FEXT value is smaller. Near-end crosstalk (NEXT) loss is measured in a UTP link from a pair of lines to another pair of lines of signal coupling. For UTP links, NEXT is a key performance indicator, and one of the most difficult to measure accurately. As the signal frequency increases, it becomes more difficult to measure. NEXT does not represent the crosstalk value generated at the near end point, it only represents the crosstalk value measured at the near end point. This value varies with the length of the cable, and the longer the cable, the smaller the value becomes. At the same time, the signal at the transmitter end is also attenuated, and the crosstalk to other pairs becomes relatively small. Experimentally, only the NEXT measured within 40 meters is more realistic. If the other end is farther than 40 meters from the information socket, then 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 to measure the NEXT value at both ends of the link.
(3) DC resistance
The TSB67 does not have this parameter. DC loop resistance will consume part of the signal and turn it into heat. It is the sum of the resistance of a pair of wires.
The DC resistance of the 11801 specification twisted pair must not be greater than 19.2 ohms. The difference between each pair can not be too large (less than 0.1 ohms), otherwise it indicates poor contact, you must check the connection point.
(4) characteristic impedance
Different from the loop DC resistance, characteristic impedance, including resistance and frequency of 1 to 100MHz inductive impedance and capacitive impedance, which is related to the distance between a pair of wires and the electrical properties of the insulator.
Various cables have different characteristic impedance, and twisted pair cables are 100 ohms, 120 ohms and 150 ohms several.
(5) attenuation crosstalk ratio (ACR)
In some frequency ranges, crosstalk and attenuation of the proportional relationship is another important parameter to reflect the performance of the cable ACR is sometimes expressed in terms of signal-to-noise ratio (SNR: Signal-Noice ratio).
A larger value of ACR means a stronger ability to resist interference. The general system requirements are at least greater than 10 decibels.
(6) Cable characteristics
The quality of the communication channel is described by its cable characteristics, and SNR is a measure of the strength of the data signal, taking into account the interference signal. If the SNR is too low.
If the SNR is too low, the data signal will be received in such a way that the receiver cannot distinguish between the data signal and the noise signal, which will eventually cause data errors. Therefore, in order to limit the data error within a certain range.
A minimum acceptable SNR must be defined.
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