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Shielding and Grounding
Published in Christos Christopoulos, Principles and Techniques of Electromagnetic Compatibility, 2022
Three aspects of cable screening are considered in this section, namely the transfer impedance, connectors, and earthing. These are all important in establishing EMC in a cable system. There are cases where cable screening is not required, either because emission is negligible or when the equipment has a high immunity threshold. Twisted pair and ribbon cable are widely used in many applications without screening. A twisted pair cable is quite effective in minimizing interference at low frequencies and may also be shielded to provide additional isolation. Ribbon cable is used extensively in information technology equipment. Screening may be used, if required, but in most cases some effort on improving ground returns is worthwhile. Placing the ribbon cable near a ground plane, providing an integral ground plane, or providing several ground returns in the ribbon cable to minimize ground loops are all matters to be considered in design.18 In the most demanding applications, however, fully screened cables are used.
Distribution of audio signals
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2012
A `twisted pair', as the name implies, consists of two individually insulated wires twisted together to prevent cross-talk between pairs in the cable. Copper wire (normally 0.5 mm diameter) is normally preferred for the conducting core, but aluminium is sometimes used for lower cost. Each of the two wires is surrounded by its own colour-coded polyethylene, polyvinal chloride (PVC) or, in early days of multicore cable, paper insulation. Anything from 6 to 4000 twisted pairs can be layed up together to form a multicore cable. Distribution of twisted-pair cables To enable customers to be given service without delay, every distribution network must contain spare pairs in the cable. For economy the telephone operators require to balance the number of spare pairs in the cable for future usage against the cost of pulling in additional cables. This has resulted in the need for a flexible distribution system from the customer's premises to the local exchange. A typical telephone operator's distribution network is shown in Figure 6.25. Groups of customers are connected to a distribution point which is a multiple termination block either in a building or on a telegraph pole. The wiring from the telegraph pole to the customer's premises is strengthened to withstand the strain of its own weight and snow, and is normally called the `drop wire'.
Crosstalk and Electromagnetic Coupling Between PCB Tracks, Wires, and Cables
Published in David A. Weston, Electromagnetic Compatibility, 2017
The very high levels of crosstalk measured in cables manufactured from untwisted conductors and used in either balanced or unbalanced circuits may be greatly reduced by replacement with twisted-pair or shielded twisted-pair cables. To reduce problems due to reflections, such as pulse degradation, long cables used for communications or cables used for transmission of data with short rise and fall times are usually terminated in the characteristic impedance of the lines. These terminated cables are the focus of attention here. In a properly designed, appropriately terminated communication signal interface, the characteristic impedance of the cable will be extended to the back plane inside the equipment and even to the tracks of the PCB on which the interface circuits are mounted. The characteristic impedance of a number of different cables and PCB track configurations may be computed from the equations contained in Appendix 1. A statistical model has been developed for predicting the near-end and far-end crosstalk in cross-stranded multiple twisted-pair cable versus measured crosstalk (Ref. 5). A cross-stranded multiple twisted-pair cable comprises a number of twisted pairs randomly positioned within the cable during manufacture. The advantage of the cross-stranded over the more typical construction, in which the pairs rotate around a fixed point, is that the same pairs are not always in close proximity down the length of the cross-stranded cable. Assuming that the group twist frequency is the same (that is, the twist period is the same for all twisted pairs in the cable), the near-end crosstalk isolation varies between 60 and 70 dB and the far-end crosstalk isolation between 45 and 57 dB for a 10-pair cross-stranded cable.
A Novel Method for Predicting Crosstalk in Lossy Twisted Pair Cable Based on Beetle Antennae Search and Implicit Wendroff FDTD Algorithm
Published in Electromagnetics, 2021
Jianming Zhou, Shijin Li, Wei Yan, Yanxing Ji, Zhaojuan Meng, Yang Zhao, Xingfa Liu
As people’s requirements for electronic equipment increase, the circuit system gradually becomes smaller and more accurate. Bell invented twisted pair cable (TPC) in 1877 to solve the problem of crosstalk between telephone lines (Bell 1877). The increase of operating frequency has caused various electromagnetic interference (EMI) and crosstalk problems (Chabane, Besnier, and Klingler 2017), the impact of crosstalk becomes more and more serious and frequent, and then influences the signal integrity (SI). Unintentional coupling of energy between electromagnetic fields will cause crosstalk in the cable, that is, the energy in the signal cable is coupled to other cables. This part of the energy coupled into other devices or systems is useless (Paul 1994; Rotgerink, Schippers, and Leferink 2019).