What frequency yields a 1-wavelength length of approximately 74.4 ft?

What frequency yields a 1-wavelength length of approximately 74.4 ft?

• A. 12.6 MHz
• B. 7.4 MHz
• C. 25.0 MHz
• D. 9.0 MHz

Answer: (A)

Understanding how wavelength and frequency relate in free space is key: wavelength is inversely proportional to frequency. In practice, you can estimate wavelength in feet from frequency in MHz with the rough rule λ(ft) ≈ 984 / f(MHz). To hit about 74.4 ft for 1 wavelength, the needed frequency is f ≈ 984 / 74.4 ≈ 13.2 MHz. Among the given choices, the frequency closest to 13.2 MHz is 12.6 MHz. It gives a wavelength of about 984 / 12.6 ≈ 78.1 ft, which is reasonably close to 74.4 ft for quick, approximate calculations used in antenna work. The other options produce much larger discrepancies (for example, 25.0 MHz yields ~39 ft, and 9.0 MHz yields ~109 ft).

Understanding how wavelength and frequency relate in free space is key: wavelength is inversely proportional to frequency. In practice, you can estimate wavelength in feet from frequency in MHz with the rough rule λ(ft) ≈ 984 / f(MHz).

To hit about 74.4 ft for 1 wavelength, the needed frequency is f ≈ 984 / 74.4 ≈ 13.2 MHz.

Among the given choices, the frequency closest to 13.2 MHz is 12.6 MHz. It gives a wavelength of about 984 / 12.6 ≈ 78.1 ft, which is reasonably close to 74.4 ft for quick, approximate calculations used in antenna work. The other options produce much larger discrepancies (for example, 25.0 MHz yields ~39 ft, and 9.0 MHz yields ~109 ft).