Question

A receiving station on the ground is receiving a signal of frequency \(10 \mathrm{MHz}\), then the mode of transmission is (A) ground wave propagation (B) sky wave propagation (C) both ground wave and sky wave propagation (D) neither ground wave nor sky wave propagation

Short answer

The correct answer is (B) sky wave propagation, as the frequency of the received signal, 10 MHz, lies within the effective frequency range of sky wave propagation (3 MHz to 30 MHz) but not within the effective range for ground wave propagation (typically below 3 MHz).

Step-by-step solution

Conclusion for ground wave propagation

Since the frequency is higher than the effective range for ground wave propagation, it is unlikely that the mode of transmission is ground wave propagation. #Step 2: Compare frequency with sky wave propagation# The frequency of the received signal is 10 MHz, which is within the effective frequency range of sky wave propagation (3 MHz to 30 MHz).

Conclusion for sky wave propagation

Since the frequency is within the effective range for sky wave propagation, it is likely that the mode of transmission is sky wave propagation. #Step 3: Select the correct answer# Comparing the given frequency with the properties of ground wave and sky wave propagation, we can rule out ground wave propagation and conclude that the 10 MHz signal is being transmitted via sky wave propagation.

Correct Answer

The correct answer is (B) sky wave propagation.

Key concepts

ground wave propagation

Ground wave propagation is a type of radio wave transmission that travels close to the earth's surface. This method is effective for sending signals over short to medium distances, especially in areas with good ground conductivity, such as over water or moist ground. However, its effectiveness is largely dependent on the frequency of the signal.
In general, ground wave propagation is most effective at lower frequencies, usually below 2 MHz. At these frequencies, the radio waves can follow the curvature of the earth due to diffraction. If the frequency of your signal is above this range, the efficiency of ground wave propagation decreases. Higher frequencies suffer from more significant attenuation when traveling over the ground, which makes them unsuitable for long-distance ground wave transmission.
Key characteristics of ground wave propagation include:

• Effective for lower frequency bands (below 2 MHz).
• Suitable for local and regional broadcasting.
• Better performance over conductive surfaces like water.

For signals like the 10 MHz frequency from the exercise, ground wave propagation would not be effective, which is why it was ruled out as the mode of transmission.

sky wave propagation

Sky wave propagation is a fascinating method of radio wave travel that relies on the ionosphere, a layer of the atmosphere that contains a high concentration of ions and free electrons, to reflect signals back down to the Earth's surface. This technique plays a crucial role in long-distance radio communications.
The ionosphere reflects radio waves with frequencies typically ranging from about 3 MHz to 30 MHz, making it possible to receive signals well beyond the horizon or even across the globe. Given the 10 MHz frequency of the signal in the original exercise, it comfortably falls within this range, explaining why sky wave propagation is the likely mode of transmission.
Important points about sky wave propagation include:

• Effective frequency range from 3 MHz to 30 MHz.
• Enables communication over large distances, beyond the line of sight.
• Depends on the ionosphere’s characteristics, which can vary with time of day and solar activity.

Overall, sky wave propagation allows radio transmissions to reach far-flung destinations, making it an essential tool for global communication.

frequency range

The frequency range of a radio signal is an important factor that determines the suitability of various propagation methods. Different propagation methods work effectively over different frequency bands.
For ground wave propagation, the suitable frequency range is predominantly below 2 MHz. As you move to higher frequencies, ground wave propagation becomes less effective and more limited in range, mainly due to increased signal loss.
In contrast, sky wave propagation is exceptionally suited for frequencies between 3 MHz and 30 MHz. Within this spread, signals can be bounced off the ionosphere, greatly extending their travel distances. This is why many long-distance communication networks use frequencies within this range.
Understanding the effective frequency ranges of these propagation methods is crucial for selecting the right mode for your specific communication needs.

• Ground wave: Best below 2 MHz.
• Sky wave: Best from 3 MHz to 30 MHz.

These frequency guidelines help ensure optimal signal strength and clarity based on the chosen transmission technique.