Question

For sky wave propagation, the radio waves must have a frequency range in between :

• A. 1 MHz to 2 MHz
• B. 5 MHz to 25 MHz
• C. 35 MHz to 40 MHz
• D. 45 MHz to 50 MHz

Answer 1

The Correct Option is B

Sky wave propagation, also known as ionospheric propagation, is the method by which radio waves travel through the ionosphere and are reflected back to Earth. The ionosphere has varying levels of ionization, which can reflect radio waves of certain frequencies.

The frequency range suitable for sky wave propagation is crucial because if the frequency is too low, the radio waves will be absorbed by the ionosphere, and if it is too high, they will pass through the ionosphere without being reflected.

The suitable frequency range for sky wave propagation is typically between 5 \text{ MHz} and 25 \text{ MHz}. This range allows the radio waves to be effectively reflected by the ionosphere and return to the Earth's surface, enabling long-distance communication.

Let's evaluate the given options to identify the correct frequency range:

1. 1 MHz to 2 MHz: This range is too low, and radio waves will likely be absorbed by the ionosphere.
2. 5 MHz to 25 MHz: This is the correct range suitable for sky wave propagation, as radio waves are efficiently reflected by the ionosphere.
3. 35 MHz to 40 MHz: This range is too high, and radio waves would tend to pass through the ionosphere rather than being reflected.
4. 45 MHz to 50 MHz: Similarly, this range is also too high for sky wave propagation.

Therefore, the correct answer is 5 MHz to 25 MHz.