CHAPTER 24Antenna Tuners (ATUs)

The primary task of an impedance-matching or antenna tuning unit (ATU) located at the transmitter end of the transmission line is to present the transmitter output stage with an apparent antenna feedpoint impedance (after transformation through an arbitrary-length transmission line) equal to the output impedance of the transmitter. This results in maximum power transfer from the power amplifier stage of the transmitter to the feedline and antenna. So located, a properly designed ATU provides the station owner with multiple benefits:

• It minimizes the standing wave ratio (SWR) that the transmitter or power amplifier—whether vacuum tube or solid-state—sees. RF power amplifiers are not tolerant of high SWR; when ...

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