Cable Shielding Effectiveness Measurement

A plot of the chamber s dynamic range is shown in figure 2.

Cable shielding effectiveness measurement.

When a cable specification calls for 90 db of rf shielding the 100 db dynamic range allows a 10 db margin in the measurement range. Making accurate measurements is a challenge because shields have many different shapes and purposes. For these products we primarily use two techniques the triaxial fixture method and the mode stirred method. The test method permits measurement of long specimens using high currents with a uniform current distribution along the cable shield.

Measurement method for determining shielding effectiveness of cable feedthroughs. This is a typical margin recommended by various industry specifications. The measurement method is validated by comparing measurements on an isolated conductor penetrating the shield with a simple theory based on basic circuit theory in combination with antenna theory. Cable interconnects which allow cables inside the cage to connect to cables outside may undergo modification for additional connectors that damage the shielding integrity.

Ventilation is another example and one that is usually problematic with regards to shielding effectiveness. An efficient and repeatable measurement method for determining shielding effectiveness of cable feedthroughs based on the use of nested reverberation chambers is presented. There could also be changes in compliance standards. The shielding effectiveness is measured by comparing the reading of reference and the load devices.

This method is effective for frequencies less than 500 megahertz. The method is offered as a standard technique for measuring the shielding effectiveness of shielded cables. To verify the periodic calibration two gold standards are employed. For example housings connectors or cables all use shields and each application requires a unique test fixture to ensure accurate and repeatable se measurements.

It involves the use of a sealed box with an opening.