ARRL Technician Practice Exam

What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?

1. 16

2. 19

3. 24

4. 30

The correct answer is: 19

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