Which of the following modes is used for line of sight

Options

A. Ground wave
B. Sky wave propagation is useful in the range of 30 to 40 MHz.
C. Space wave
D. All of these

Explanation

To solve the question "Which of the following modes is used for line of sight?", we will analyze the different modes of communication and their characteristics.

### Step-by-Step Solution:

1. **Understanding Line of Sight Communication**:
- Line of sight communication refers to a transmission method where the transmitter and receiver are aligned in a straight line, allowing the signal to travel directly without any obstruction.

2. **Identifying Different Modes of Propagation**:
- There are several modes of propagation, including:
- Ground Wave Propagation
- Sky Wave Propagation
- Space Wave Propagation

3. **Analyzing Ground Wave Propagation**:
- Ground wave propagation operates at lower frequencies, typically in the range of 530 kHz to 1710 kHz.
- This mode is not suitable for line of sight communication due to its reliance on the ground for signal transmission.

4. **Analyzing Sky Wave Propagation**:
- Sky wave propagation is effective in the frequency range of 2 MHz to 40 MHz.
- This mode involves reflection of signals off the ionosphere and is not a line of sight method.

5. **Analyzing Space Wave Propagation**:
- Space wave propagation operates at higher frequencies, typically above 54 MHz, and is suitable for line of sight communication.
- This mode includes microwave links, which are commonly used for point-to-point communication over long distances.

6. **Conclusion**:
- Based on the analysis, the mode used for line of sight communication is **Space Wave Propagation**.

### Final Answer:
The correct answer is **Space Wave Propagation**.

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