ARRL Technician Practice Exam

What instrument other than an SWR meter could you use to determine if a feed line and antenna are properly matched?

1. Directional wattmeter

2. Oscilloscope

3. Frequency counter

4. Signal generator

The correct answer is: Directional wattmeter

A directional wattmeter is designed to measure the power flowing in a feed line and can effectively indicate whether the antenna and feed line are properly matched. When the impedance of the antenna system matches the transmission line, the majority of the power sent from the transmitter is radiated by the antenna, and the directional wattmeter will show an appropriate level of forward power while displaying minimal reflected power. If there's a mismatch, the reflected power will be significant, which the wattmeter can also detect by showing a difference between forward and reflected power readings. This makes the directional wattmeter an essential tool for assessing the performance of the antenna feed system and ensuring efficient operation. While other instruments like an oscilloscope, frequency counter, or signal generator can provide valuable information about signals and frequencies, they do not give direct measurements of the power going to or reflected from the antenna system in a way that confirms proper matching. Therefore, using a directional wattmeter is a practical and effective approach for this specific purpose.