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Power line performance twisted pair

creatime:2015/10/21

For the power cable, users are most concerned about it is to characterize the performance of several indicators. These indicators include attenuation, near-end crosstalk, impedance characteristics, distributed capacitance, DC resistance and the like.
Attenuation
Attenuation (Attenuation) is a measure of signal loss along the link. The length of the cable attenuation of a relationship, as the length increases, the signal attenuation is also increased. Attenuating 'db' for the unit, indicating that the source signal is transmitted to the receiving end terminal signal strength ratio. Since the attenuation varies with frequency, therefore, should be measured attenuation of all frequencies within the range of applications.
NEXT
Crosstalk points near-end crosstalk and far-end crosstalk (FEXT), Tester is measuring NEXT, due to line losses, and therefore less affected by the magnitude FEXT. Near-end crosstalk (NEXT) loss is a measure of a UTP link signal coupling from one pair to another pair wire lines. For UTP link, NEXT is a key performance indicator, is also an indicator of the most difficult to accurately measure. With increasing signal frequency, the measurement will increase the difficulty. NEXT crosstalk value does not mean that arising in the proximal point, it just means that the proximal point of the measured crosstalk values. This value will vary with the cable length becomes, the longer the cable, and its value becomes. At the same time the sender signal is also attenuated, the crosstalk on the other line on the relatively smaller. Experiments show that only measured in the 40 meters was NEXT is more realistic. If the other side is far in the 40 meters of the information outlet, then it will produce some degree of crosstalk, but the tester may not be measured until the crosstalk value. Therefore, the best in both endpoints were measured NEXT. Now tester is equipped with the appropriate equipment, so that one end of the link can be measured NEXT value at both ends.
DC Resistance
TSB67 no such argument. DC loop resistance will consume part of the signal, and transforming it into heat. It refers to a pair of wire resistance and,
11801 standard twisted pair of not greater than 19.2 ohms DC resistance. Differences between each pair can not be too large (less than 0.1 ohm), or that poor contact, you must check the connection point.
Characteristic impedance
DC resistance of the loop is different, characteristic impedance including resistance and frequency inductive impedance and capacitive impedance 1 ~ 100MHz, which is the distance and insulators and electrical properties of a pair of wires between the relevant.
All kinds of cables have different characteristic impedance, and twisted-pair cable is 100 ohms, 120 ohms and 150 ohms several.
Attenuation to crosstalk ratio (ACR)
In certain frequency range, the ratio between the amount of crosstalk and attenuation performance is a reflection of cable
Another important parameter of the power cord. ACR sometimes signal to noise ratio (SNR: Signal-Noice ratio), said
It is calculated by the amount of attenuation and NEXT worst magnitude difference. ACR larger value indicates a stronger anti-interference ability. General system requires at least greater than 10 dB.
Cable characteristics
The quality of the communication channel is by its cable characterization. SNR is in consideration of the interference signal, the data signal is a measure of strength. If the SNR is too low,
Will result in a data signal is received, the receiver can not distinguish the data signal and the noise signal, and ultimately lead to data errors. Therefore, in order to limit data errors within a certain range,
You must define a minimum acceptable SNR.