What is the approximate length for a 1/4 wave monopole antenna cut for 28.5 MHz?
The correct answer is A: 8 feet. The approximate length for a 1/4 wave monopole antenna cut for 28.5 MHz is 8 feet. Length = 234/f (MHz) = 234/28.5 = 8.21 feet ≈ 8 feet. For amateur radio operators, this is a basic monopole length calculation. Understanding this helps when building vertical antennas.
Exam Tip
1/4 wave monopole at 28.5 MHz = 234/28.5 = 8 feet. Think 'M'onopole 'L'ength = '2'34/'F'requency (half of dipole formula). Length = 234/f (MHz) = 234/28.5 = 8 feet. Not 11 ft, not 16 ft, not 21 ft - just 8 feet.
Memory Aid
"1/4 wave monopole at 28.5 MHz = 8 feet. Think 'M'onopole 'L'ength = '2'34/'F'requency. Length = 234/f (MHz) = 8 feet. Standard monopole length formula (half of dipole formula)."
Real-World Application
A 1/4 wave monopole for 28.5 MHz: Length = 234/28.5 = 8.21 feet ≈ 8 feet. This is the approximate length for a quarter-wave monopole at this frequency (10 meters). The formula 234/f (MHz) is half of the dipole formula (468/f) because monopoles are half the length. This is a standard monopole length calculation.
Key Concepts
Why Other Options Are Wrong
Option B (11 feet): Incorrect. 11 feet is too long - that would be for about 21 MHz, not 28.5 MHz. Calculation error.
Option C (16 feet): Incorrect. 16 feet is too long - that would be for about 14.6 MHz, not 28.5 MHz. Calculation error.
Option D (21 feet): Incorrect. 21 feet is way too long - that would be for about 11 MHz, not 28.5 MHz. Calculation error.
题目解析
The correct answer is A: 8 feet. The approximate length for a 1/4 wave monopole antenna cut for 28.5 MHz is 8 feet. Length = 234/f (MHz) = 234/28.5 = 8.21 feet ≈ 8 feet. For amateur radio operators, this is a basic monopole length calculation. Understanding this helps when building vertical antennas.
考试技巧
1/4 wave monopole at 28.5 MHz = 234/28.5 = 8 feet. Think 'M'onopole 'L'ength = '2'34/'F'requency (half of dipole formula). Length = 234/f (MHz) = 234/28.5 = 8 feet. Not 11 ft, not 16 ft, not 21 ft - just 8 feet.
记忆口诀
1/4 wave monopole at 28.5 MHz = 8 feet. Think 'M'onopole 'L'ength = '2'34/'F'requency. Length = 234/f (MHz) = 8 feet. Standard monopole length formula (half of dipole formula).
实际应用示例
A 1/4 wave monopole for 28.5 MHz: Length = 234/28.5 = 8.21 feet ≈ 8 feet. This is the approximate length for a quarter-wave monopole at this frequency (10 meters). The formula 234/f (MHz) is half of the dipole formula (468/f) because monopoles are half the length. This is a standard monopole length calculation.
错误选项分析
Option B (11 feet): Incorrect. 11 feet is too long - that would be for about 21 MHz, not 28.5 MHz. Calculation error. Option C (16 feet): Incorrect. 16 feet is too long - that would be for about 14.6 MHz, not 28.5 MHz. Calculation error. Option D (21 feet): Incorrect. 21 feet is way too long - that would be for about 11 MHz, not 28.5 MHz. Calculation error.
知识点
1/4 wave monopole, 28.5 MHz, 8 feet, Monopole length calculation
Verified Content
Question from official FCC General Class question pool. Explanation reviewed by licensed amateur radio operators.