Yoshiharu Akiyama

Jamming technique to prevent information leakage caused by unintentional emissions of PC video signals

A working personal computer (PC) and/or a PC display monitor usually produce unintentional electromagnetic fields. Information from a video display unit could be reconstructed by intercepting such emissions at a distance. Proper measures are needed to prevent information leakage through such eavesdropping. We have investigated countermeasures for such a problem and proposed jamming schemes for industrial and home use. We also developed a prototype for protecting devices and evaluated its performance in preventing such emanation eavesdropping.

Calculation of radiating magnetic field from indoor AC mains cable using four-port network

Recent progress in home networks is increasing the interest in high-speed power line communication (PLC). This has the advantage of not needing the installation of new communication cable. However, the electromagnetic field radiating from the cable could disturb other radio communication systems. Thus, the field radiated from the cable should be evaluated In this paper, a pair of conductors of an indoor AC mains cable and its ground plane were represented by four-port networks and the common-mode current was calculated. In the calculation, the capacitance between conductors and between one conductor and the ground plane were obtained from numerical calculations to consider the effect of the cable insulator. The radiated magnetic field was calculated from the common-mode current distribution along the cable. The magnetic field radiated from a 4-m-long indoor AC mains cable was measured in an anechoic chamber to evaluate the validity of the calculation model. The results indicate that the deviation between the calculated and measured values was within 4 dB, and the radiated magnetic field strength was almost in proportion to the longitudinal conversion loss of an AC mains line. The calculation method was applied to an AC mains line with branches and the results almost agreed with the measured ones.

Influence of appliance state on transmission characteristics of indoor AC mains lines in frequency range used power line communication

High-speed power line communication (PLC) systems have been developed for home networks. However, the transmission characteristics of an indoor AC mains line have not been clarified. We studied the influence of the appliance operation state on the transmission characteristics of the indoor AC mains line. The AC mains line and appliances were represented by four-port networks and two-port networks. The transmission characteristics were calculated by a model constructed with these networks. The two-port network parameters of the appliances were measured in both operating and stop states. The equivalent circuits were determined for both states based on the condition that the frequency characteristics of the circuits agreed with the measured value. A simple AC mains system was constructed and the transmission characteristics were measured to compare with the calculated value in various states. The results indicate that the calculated value agreed well with the measured one, and the transmission loss deviation resulting from the appliance state was within 10 dB. A common mode choke coil was inserted between the AC mains line and the appliances to reduce the transmission loss deviation resulting from different states. The measured and calculated values indicate that the deviation was reduced from 10 dB to 0.5 dB by inserting the filter.

A Design Method for the Asymmetric Artificial Network With an Asymmetrical Transformer

Conducted asymmetric disturbances are measured at telecommunication ports of equipment under test using an asymmetric artificial network (AAN). Therefore, theoretical investigations are carried out to characterize an AAN with a mode-impedance matrix, introducing the common-mode and differential-mode impedances. By referring to this matrix, a theoretical design method is developed for the AAN with an asymmetrical transformer to satisfy the requirements for the mode impedances and the longitudinal conversion loss. By using this design method, two different prototype AANs are assembled: one meets the CISPR 22 specifications, and the other is used in power line telecommunication modem tests. A detailed experimental examination of the assembled AANs validates the proposed theoretical design method.

Influence of a PLC signal induced into the modem on the communication performance of VDSL

We investigate the influence of a high-speed power line communication (PLC) signal induced into the very high-bit-rate digital subscriber line (VDSL) modem from the power line on the communication performance of VDSL. Differential-mode signal transmission loss between input signal at the modems mains terminal and output signal at the modems telecommunication terminal was estimated by using a 4-terminal-pair-network-model of the VDSL modem. We estimated modems supplied by two manufactures. The transmission losses were more than 45 and 70 dB and the throughputs were degraded when the signal power of the VDSL were attenuated by more than 38 and 45 dB, respectively

Calculation of Longitudinal Conversion Loss and Input Impedance for Indoor AC Mains Line Considering High-Speed PLC

The power line communication (PLC) system should be investigated with respect to the influence on electromagnetic environments. Longitudinal conversion loss (LCL) and input impedance are important parameters for evaluating the influence because they are closely related to the radiated, conducted, and inducted emission. An indoor AC mains system consisting of electrical equipment and an AC mains line was modeled by four-port networks, and the LCL and the input impedance were calculated. The parameters of the four-port networks were determined from theory and measurement. The analytical model was examined using a simple network and the results show that the calculated values agreed with the measured ones. The LCL and the input impedance were investigated at the AC mains port in some existing buildings, and the measured results almost agreed with the calculated results derived from the indoor AC mains system model.

Investigation of electromagnetic noise transmission characteristics from AC mains port to telecommunication port

A method of evaluating the isolation factor from an AC mains port to a telecommunication port was investigated. Telecommunication equipment was represented by a 4-port network consisting of a pair of wire and ground. The relationship between input and output signals of the network was represented by an F-matrix and the isolation factor (ratio of input to output signals) was derived from the matrix. We developed a method of measuring the parameters and the measured values for a resistance-network agree well with calculated ones. The evaluation results of the isolation factor for three types of telecommunication equipment show that isolation for differential-mode noise from AC mains to telecommunication ports is larger than that for common-mode noise.

Technical Problems of the Shunt-Type Asymmetric Artificial Network

Theoretical and experimental investigations were carried out on the characteristics of the shunt-type asymmetric artificial network (AAN). The findings are as follows: 1) The theoretical formulas for the differential- and common-mode impedances as well as the longitudinal conversion loss (LCL) were derived for the shunt-type AAN in terms of the AAN circuit parameters. 2) The common-mode disturbance voltage estimated from the measured voltage is not proportional to the actual common-mode current flowing in the network cable of the equipment under test (EUT). 3) For the common-mode EUT, the shunt-type AAN with a low LCL of less than about 42 dB yields incorrect measurement results with an error greater than 0.5 dB. 4). A more crucial problem is that, for the differential-mode EUT, the measured disturbance voltage decreases as the EUT common-mode impedance decreases.

Electric field strength specification method under 80 cm for RF immunity testing

Electric field distribution below 80 cm should be specified to test the RF immunity of the floor-standing equipment. To determine this specification, a model in which the equipment is set on an infinite ground plane was used. Calculations using the moment method show that the height pattern of the field below 80 cm is independent of frequency. The height pattern measured in a room is close to the calculated pattern in this model. Experiments show that a suitable electric field can be almost generated by arranging RF absorbers on the floor of a semianechoic chamber.<<ETX>>

Comparison of conducted disturbance voltages at telecommunication ports measured using different reference ground planes in accordance with CISPR 32

To prevent radio interference due to the electromagnetic field generated by conducted disturbances at the telecommunication ports of information technology equipment, the disturbances are measured using test arrangements in accordance with standards published by the International Special Committee on Radio Interference (CISPR). We compared the conducted disturbance voltages at the telecommunication ports of two laptop PCs and one desktop PC measured using three test arrangements specified in CISPR 32. Whether the reference ground plane is vertical or horizontal is a major difference in the three test arrangements. As a result, the differences between the voltages of the laptop PCs measured using the three test arrangements were smaller than 2 dB. The differences between the voltages of the desktop PC measured using these test arrangements were about 3 dB at a few frequencies. The standard measurement instrumentation uncertainty for conducted disturbance measurement determined in the CISPR standard is 4.59 dB. Hence, the differences in voltages measured using the three test arrangements were not significant.