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Bandwidth and Impulse Noise

February 4th Fact-of-the-Day

There many types of radio noise that can be classified various ways. Two common types are white noise, which has a hissing sound, and impulse noise, of which ignition noise and lightning crashes are two examples. Most types of noise have wide bandwidths, so one way to reduce received noise energy is to reduce receive bandwidth to the minimum necessary to accommodate a desired signal. Unfortunately, high Q resonant circuits are required components of narrow bandpass filters and high Q resonant circuits ring. The ringing widens noise pulses, so they last longer. As a result, the use of narrow bandpass filters to reduce ignition noise or lightning crashes tends to be counter productive. In fact, if the passband is reduced sufficiently, pulses will widen to where they overlap continuously and there will be continuous interference instead of pulses. Try using a wide bandwidth to receive signals covered by impulse noise and you may find that reception improves. ©2005 Martek International All rights reserved.


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