What is the length in feet of a 1-wavelength antenna at 21.0 MHz?

What is the length in feet of a 1-wavelength antenna at 21.0 MHz?

• A. 44.6 ft
• B. 22.3 ft
• C. 89.1 ft
• D. 55.0 ft

Answer: (A)

A 1-wavelength antenna length equals the wave’s wavelength in the medium. So use λ = c / f. With c about 3.00 × 10^8 m/s and f = 21.0 MHz (21 × 10^6 Hz), λ ≈ 3.00×10^8 / 21×10^6 ≈ 14.29 meters. Converting to feet: 14.29 m × 3.28084 ≈ 46.9 feet. Among the choices, 44.6 feet is the closest value, so it’s the best match given the rounding or approximation in the options. The other numbers correspond to noticeably shorter or longer wavelengths and don’t represent a single full wavelength at this frequency.

A 1-wavelength antenna length equals the wave’s wavelength in the medium. So use λ = c / f. With c about 3.00 × 10^8 m/s and f = 21.0 MHz (21 × 10^6 Hz), λ ≈ 3.00×10^8 / 21×10^6 ≈ 14.29 meters. Converting to feet: 14.29 m × 3.28084 ≈ 46.9 feet. Among the choices, 44.6 feet is the closest value, so it’s the best match given the rounding or approximation in the options. The other numbers correspond to noticeably shorter or longer wavelengths and don’t represent a single full wavelength at this frequency.