Question T9B04
From subelement T9 - T9B
What is the major function of an antenna tuner (antenna coupler)?
Why is this correct?
An antenna tuner's primary job is impedance matching - transforming whatever impedance exists at the transmitter end of the feed line back to the standard 50 ohms that transceivers expect. When an antenna isn't resonant or has non-50-ohm impedance, this mismatch travels back through the feed line. The tuner uses adjustable inductors and capacitors to present the correct 50-ohm load to the transmitter, ensuring efficient power transfer and protecting the output stage from high SWR damage.
Memory tip
Remember the impedance matching principle: maximum power transfer occurs when source and load impedances match. Antenna tuners don't change the antenna itself - they transform the impedance the transmitter 'sees' at the tuner's input to match the transmitter's 50-ohm output requirement.
Learn more
In practical operation, antenna tuners enable multi-band operation with single antennas that may only be resonant on one frequency. While the tuner reduces reflected power at the transmitter, it doesn't eliminate losses in the feed line itself - those losses occur between the antenna and tuner. Modern automatic tuners can store impedance transformation settings for different frequencies, making band changes seamless while maintaining proper impedance matching for optimal power transfer.
Think about it
Why do you think an antenna tuner can make a poorly matched antenna system work effectively at the transmitter, yet the feed line losses between the antenna and tuner remain unchanged?