NEXT Between Screened Twisted Pairs



VENUE: Presented at the 65th IWCS Conference/International Cable Connectivity Symposium, October 2-5, 2016, Providence, RI, USA

ABSTRACT - A mechanism of coupling between different lay lengths individually screened in Aluminum foil pairs (FTP) is discussed in the paper. Following a series of simulations and measurements the author found that there are distinct frequency points with high near end crosstalk (NEXT). It is established that the high coupling is caused by harmonic repetition patterns in mutual inductance of the pairs. It is shown that the optimal screen thickness is not only dependent on the transmission spectrum but also on the design parameters like pair lay lengths, wire dimensions and overall cable length. The paper suggests an analytical formula for the coupling parameters which helps investigate the impact of lay length, attenuation and cable length on the peak crosstalk levels between the pairs and also helps in optimizing screen thickness.

Simulated and measured NEXT attenuation between two adjacent FTP cables with clearly visible peak crosstalk at about 70 MHz.

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