T9B04:What is the major function of an antenna tuner (antenna coupler)?
Direct answer summary (2026-2030 NCVEC pool)
The official correct answer for T9B04 is It matches the antenna system impedance to the transceiver's output impedance.
The key fact is It matches the antenna system impedance to the transceiver's output impedance. Match that fact to the exact condition in the question; the other choices describe a different rule, band, component, or operating situation.