What is the major function of an antenna tuner (antenna coupler)?

The major function of an antenna tuner, also known as an antenna coupler, is to match the impedance of the antenna system to the output impedance of the transceiver. This impedance matching is crucial for efficient power transfer between the transceiver and the antenna. When the impedances are matched, it minimizes reflections of the RF energy back to the transmitter, which can result in better performance and reduced risk of damage to the equipment due to high SWR (Standing Wave Ratio).

Impedance mismatch can lead to significant losses in signal strength and can also affect the quality of the transmitted signal. The tuner allows for adjustments in real-time, enabling operators to optimize their system for different frequencies and conditions.

While the other options highlight important aspects of a radio system, they do not correctly describe the primary purpose of an antenna tuner. For example, the tuner does not automatically select antennas or help in tuning receivers for weak signals. Its core function centers around impedance matching to ensure efficient transmission and reception of radio signals.