Question
What is the approximate length for a 1/4 wave monopole antenna cut for 28.5 MHz?
Answer Options
- A) 8 feet
- B) 11 feet
- C) 16 feet
- D) 21 feet
Correct Answer: A
Explanation
The length of a quarter-wave monopole antenna (vertical element) is half the length of a half-wave dipole. Therefore, the simple approximation formula is L_{\text{feet}} = 234 / F_{\text{MHz}}, where F_{\text{MHz}} is the design frequency. This antenna is for the 10\text{-meter} band.
Using the given frequency F = 28.5 \text{ MHz}: L_{\text{feet}} = \frac{234}{28.5} \approx 8.21 \text{ feet.} The approximate length for the vertical element (and the radials, if \frac{1}{4} wave) is 8 feet. This compact size makes \frac{1}{4} wave verticals popular for VHF/UHF and mobile HF operation.
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