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Antenna Tuner Circuits

August 5th Fact-of-the-Day

A variety of antenna tuner circuits can be used in both feed-line-to-antenna and feed-line-to-radio applications. Common designs consist of series- or parallel-tuned resonant circuits with link coupling, inductor taps, or capacitor dividers; or of L, T, or Pi reactance networks. L, T and Pi networks can have series inductors and shunt capacitors or the opposite. The best circuit for a particular application depends in part on whether a tuner is used in a transmitting or receiving application. Antenna tuners can transform the resistive component of a complex-impedance to a different value. They also can 'cancel out' the reactive component and make a load appear perfectly-resistive. Those are the two most common reasons for using an antenna tuner. However, tuners also function as frequency filters that pass some frequencies and discriminate against others. Low-pass tuners are useful in transmitting applications to filter harmonics, but high-pass tuners tend to be better in receiving applications to filter powerful AM broadcast stations and strong low-frequency lightning crashes and other noise. ©2005 Martek International All rights reserved.


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