ARRL Technician Practice Exam 2025 – Complete Prep Guide

To determine the length of a quarter-wavelength vertical antenna for a frequency of 146 MHz, you can use the formula for calculating the wavelength (λ) in meters, which is:

\[ \lambda (m) = \frac{300}{f (MHz)} \]

Substituting 146 MHz into the formula gives:

\[ \lambda = \frac{300}{146} \approx 2.05 \text{ meters} \]

Since a quarter-wavelength antenna is one-fourth of the full wavelength, you would divide this result by 4:

\[ \text{Quarter-wavelength} = \frac{2.05 \text{ m}}{4} \approx 0.5125 \text{ m} \]

To convert meters to inches, you multiply by 39.37 (since there are approximately 39.37 inches in a meter):

\[ 0.5125 \text{ m} \times 39.37 \approx 20.2 \text{ inches} \]

The closest length to this measurement in the provided choices is 19 inches. This is why the choice of 19 is approximately the correct answer — it represents the closest rounded figure to the calculated length based on the