To avoid possible damage resulting from applying power into a mismatched load, ATUs are a standard part of almost all radio transmitting systems. In addition to reducing the power radiated by the antenna, an impedance mismatch can distort the signal, and in high power transmitters may overheat the amplifier. However the impedance of any antenna normally varies, depending on frequency and other factors, and consequently changes the impedance appearing at the other end of the feedline, connected to the transmitter. Transmitters are typically designed to feed power into a reactance-free, resistive load of a specific value: Essentially all radio transmitters built after the 1950s are designed for 50 Ω (Ohm) output. Īntenna tuners are particularly important for use with transmitters. English language technical jargon makes no distinction between the terms. Various alternate names are used for this device: antenna matching unit, impedance matching unit, matchbox, matching network, transmatch, antenna match, antenna tuning unit ( ATU), antenna coupler, feedline coupler. Its purpose is to optimize power transfer by matching the impedance of the radio to the impedance of the end of the feedline connecting the antenna to the transmitter. Front view of a modified π type antenna tuner, with interior partially exposed.Īn antenna tuner is an electronic device insered into the feedline between a radio transmitter and its antenna.
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