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Toroid Filter Effectiveness

May 19th Fact-of-the-Day

Toroid AC power-line filters reduce line-noise many decibels in some cases and provide little benefit in others. There are a variety of reasons. An important issue that often is overlooked is the RF impedance of the AC power circuit. Properly designed toroid filters insert some amount of RF resistive loss and some amount of RF inductive reactance in series with a line. The attenuation that results depends not only on those values, but also on the RF impedance of the line. How much would received signals be attenuated if you put a resistor and an inductor in series with a receiving antenna? The inductor might actually increase signal strengths if the receiving antenna was too short to be resonant. A high-value resistor would decrease signal strengths if it was inserted in series with a low-impedance antenna, but would have little effect if the antenna impedance was high. The same considerations apply to AC power-lines. ©2005 Martek International All rights reserved.

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