Yoshifumi Shimoshio

Influence of balance-unbalance conversion factor on radiated emission characteristics of balanced cables

We investigated LCTL (longitudinal conversion transfer loss) and radiated emission characteristics of a twisted pair wire in UTP (unshielded twisted pair)-category 5 for a few hundred MHz, with unbalance elements inserted to imitate an actual terminal equipment. As the result, it can be seen that after inserting unbalance element, radiated emission increased due to deterioration in LCTL. The LCTL results calculated using 4-terminal-pair-network chain matrix agreed well with the measured results. The calculated results of the radiated emissions were also obtained using by our proposed analysis method.

Common-mode and differential-mode analysis of common-mode chokes

In this paper, three methods for the measuring common-mode and differential-mode S-parameters of common mode chokes are presented. The three methods involved: (1) ABCD chain matrix; (2) using hybrid couplers; and (3) modal decomposition. Each measurement method provides a specific level of accuracy. The modal decomposition method can work up to 10 GHz. Given a full characterization of a common mode choke, a passive equivalent circuit model can be synthesized that provides a fundamental understanding of the physical performance. SPICE equivalent circuit model of common mode chokes and the extraction of model parameters are provided.

Suppression effect of radiated emission from twisted pair wires with ferrite core

Telecommunications signal emissions from unshielded twisted pair (UTP) cable should be suppressed to maintain EMC of telecommunication systems. This paper describes the suppression effects of the ferrite cores which are installed on the UTP cable. Twisted pair wire with ferrite core was modeled by 4-port network to evaluate suppression effect. Parameters of the networks which are constructed with UTP cable or ferrite core with wires were determined from calculation and measurement. Using the networks, the common-mode current distribution on the cable was obtained, and emitted electric field strength was calculated from the distribution. The emission suppression effect was obtained from the result, and the results were almost agreed with measured value. The calculation results suggest that 1) the ferrite cores should be arranged side by side, 2) these should be placed near the signal supply end of the cable.

Immunity of communications systems using a balanced cable

In communications systems using balanced cables, there is a possibility of the common mode voltage induced on the cable causing damage to the LSI of a communication system. The authors measured the voltage induced by a strong electric field on a balanced cable, and confirmed the presence of a large induced common mode voltage. As effective approaches in the reduction of this common mode voltage, the use of a twisted pair with shielding and the use of a common mode choke coil are examined. As a result, it was shown clearly that these were able to decrease the common mode voltage by 20 dB, and that the protection of an LSI by using a common mode choke coil on the receiving end is possible.

Electromagnetic noise induced on unshielded part in shielded pair cable

This paper describes an inducing mechanism of the electromagnetic noise in shielded pair cables with an unshielded part. The paper also examines the electromagnetic noise characteristics for an unshielded part considering the height above the ground, pair cable unbalance and pair cable terminal impedance, theoretically and experimentally.