Ham Radio General Class Practice Test

Which of the following can be determined with a directional wattmeter?

1. Standing wave ratio

2. Antenna front-to-back ratio

3. RF interference

4. Radio wave propagation

The correct answer is: Standing wave ratio

A directional wattmeter is specifically designed to measure the power of RF signals in a circuit, particularly distinguishing between forward and reflected power. This capability makes it invaluable for assessing the standing wave ratio (SWR), which is a measure of how much of the power being transmitted is actually being radiated by the antenna versus how much is being reflected back due to impedance mismatches. The SWR is calculated using the forward and reflected power readings obtained from the directional wattmeter, allowing operators to evaluate the efficiency of their antenna system. The other options do not directly stem from the functions of a directional wattmeter. For instance, while a directional wattmeter can give some insight into antenna performance, it does not provide a direct measurement of the antenna front-to-back ratio, which is the comparison of the antenna's gain in the desired direction to its gain in the opposite direction. Additionally, RF interference and radio wave propagation involve more complex phenomena that are not quantifiable using a wattmeter alone. RF interference often requires signal strength measurements and analysis of the frequency spectrum, whereas radio wave propagation entails studying environmental factors, frequencies, and wave behavior over distances, which are not measured directly by a wattmeter.