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AM Broadcast Band Filters

August 25th Fact-of-the-Day

The performance of most HF communication receivers is significantly degraded by high-power AM broadcast stations located within a radius of several miles of receiving antennas. There are several forms of degradation, including harmonic signal production, signal mixing between stations resulting in the production of interfering signals at a variety of non-harmonically-related frequencies, and receiver overloading that reduces sensitivity. All these adverse effects can be eliminated or greatly reduced in nearly all cases by inserting a high-pass filter in an HF receiving antenna feed-line. Lightning static reduction is side-benefit, because lightning energy levels are much higher at lower frequencies and lightning energy at various low and medium frequencies mixes both with itself and with broadcast station signals to produce broad-spectrum HF energy. High-level low-frequency lightning energy also overloads receiver RF amplifiers, producing lightning-energy-harmonics and reducing receiver sensitivity during lightning crashes. ©2005 Martek International All rights reserved.

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