What is the primary function of an antenna tuner?

An antenna tuner primarily functions to match the impedance of the antenna system to the output impedance of the transceiver. This impedance matching is crucial for efficient power transfer and to minimize the reflection of signals. When the impedance of the antenna does not match the output impedance, which is typically around 50 ohms for most transceivers, it can lead to signal loss and increased standing wave ratio (SWR). By using an antenna tuner, operators can adjust and optimize their antenna system to ensure that they are maximizing performance, thereby facilitating better transmission and reception of signals.

The other options, while they may sound plausible, do not accurately represent the primary function of an antenna tuner. For example, the automatic tuning of receivers or selection of antennas is a separate process typically handled through different technologies or devices, rather than being the direct purpose of an antenna tuner. Additionally, while it is helpful for both transmit and receive, this feature is not the primary objective of the tuner itself, making the impedance matching function its most critical role.