Question

The ionospheric layer acts as a reflector for the frequency range

• A. 1 kHz to 10 kHz
• B. 3 to 30 MHz
• C. 3 to 30 kHz
• D. 100 kHz to 1 MHz
• E. 3 GHz to 30 GHz

Hint:

The "Critical Frequency" of the ionosphere determines the limit. Frequencies in the 3 to 30 MHz range are ideal for "skipping" signals across the globe using ionospheric reflection.

Answer 1

The Correct Option is B

Concept: Sky wave propagation uses the ionosphere (a region of the upper atmosphere ionized by solar radiation) to reflect radio waves back to Earth, allowing for long-distance communication.
• Frequency Limits: Only specific frequency ranges are reflected. Very high frequencies (VHF/UHF and above) pass through the ionosphere into space.

Step 1: Determine the standard range for sky wave propagation. The ionosphere typically reflects radio waves in the range of 3 MHz to 30 MHz (Short Wave band). Below 3 MHz, waves are often ground waves; above 30 MHz, the refractive index of the ionosphere is not sufficient to bend the waves back to Earth.

Step 2: Verify the options. High-frequency waves like 3 GHz to 30 GHz (E) are used for satellite communication because they penetrate the ionosphere. The very low frequencies (A, C, D) do not utilize sky wave reflection as their primary mode for long-distance transmission in the same way the 3-30 MHz band does.