Question

Which range of Frequencies is Suitable for sky wave Propagation ? (A) \(1 \mathrm{KHZ}\) to \(500 \mathrm{KHZ}\) (B) \(1 \mathrm{MHZ}\) to \(2 \mathrm{MHZ}\) (C) \(2 \mathrm{MHZ}\) to \(20 \mathrm{MHZ}\) (D) Above \(30 \mathrm{MHZ}\)

Short answer

The most suitable frequency range for sky wave propagation according to the provided options is (C) \(2 \mathrm{MHZ}\) to \(20 \mathrm{MHZ}\).

Step-by-step solution

Understanding radio wave behavior in the ionosphere

Radio waves propagate through the atmosphere and interact with the various layers of the ionosphere. Depending on the frequency, they will either be absorbed, reflected, or refracted by the ionosphere. Sky wave propagation describes waves that are refracted back towards the Earth's surface, allowing long-distance communication. For this to happen, the radio waves need to have a suitable frequency that can penetrate the D and E layers of the ionosphere without being absorbed and be reflected or refracted by the ionospheric F layer.

Determine the frequency range to allow for sky wave propagation

To achieve successful sky wave propagation, the radio waves should have a frequency between approximately 3 MHz and 30 MHz. Waves with lower frequencies are mostly absorbed, while waves with higher frequencies pass through the ionosphere without being refracted. Therefore, the suitable frequency range for sky wave propagation is 3 MHz to 30 MHz.

Identify the correct option

Now that we know the suitable frequency range for sky wave propagation is between 3 MHz and 30 MHz, we can look at the given options and find the one that matches this range. (A) \(1 \mathrm{KHZ}\) to \(500 \mathrm{KHZ}\): This range is much lower than the required MHz range and will be absorbed, so this option is not suitable for sky wave propagation. (B) \(1 \mathrm{MHZ}\) to \(2 \mathrm{MHZ}\): This range is lower than 3 MHz and does not cover the suitable frequency range for sky wave propagation. (C) \(2 \mathrm{MHZ}\) to \(20 \mathrm{MHZ}\): This range partially covers the suitable frequency range for sky wave propagation (it includes 3 MHz to 20 MHz, which is a significant part of the desired range). This option is the most appropriate for sky wave propagation out of the given choices. (D) Above \(30 \mathrm{MHZ}\): This range is too high for sky wave propagation and will pass through the ionosphere without refraction. So, the most suitable frequency range for sky wave propagation according to the provided options is (C) \(2 \mathrm{MHZ}\) to \(20 \mathrm{MHZ}\).