Ham Radio General Class Practice Test

What is the approximate length for a 1/4-wave vertical antenna cut for 28.5 MHz?

1. 8 feet

2. 11 feet

3. 16 feet

4. 21 feet

The correct answer is: 8 feet

To determine the approximate length for a 1/4-wave vertical antenna cut for a frequency of 28.5 MHz, you can use the formula for the wavelength in feet, which is: Wavelength (feet) = 468 / Frequency (MHz) Using this formula, when the frequency is 28.5 MHz, the calculation would be: Wavelength = 468 / 28.5 ≈ 16.42 feet. Since you are calculating for a 1/4-wave antenna, you need to divide the full wavelength by four. Therefore: 1/4-wave length = 16.42 feet / 4 ≈ 4.1 feet. The answer of 8 feet would generally be understood as being in the right ballpark for practical dimensions, but mathematically, this suggests a misunderstanding of the wave calculation. Normally, a 1/4-wave antenna would be approximately 4.1 feet, suggesting that the length should ideally be closer to that dimension to resonate properly at 28.5 MHz. In conclusion, it is essential to always perform the calculation correctly to ensure the antenna operates as effectively as possible at its designated frequency.