The mode of propagation used by short wave broadcast services having a frequency range from a few 3`MH_z "up to 30" MH_z` is

Options

A. ground wave
B. space wave
C. sky wave
D. all of these

Answer

To solve the question regarding the mode of propagation used by short wave broadcast services with a frequency range from 3 MHz to 30 MHz, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Frequency Range**: The question specifies a frequency range from 3 MHz to 30 MHz. This range is crucial for determining the type of wave propagation used.

2. **Understand Wave Propagation Types**: There are different types of wave propagation methods used in radio communication, including:
- Ground wave propagation
- Sky wave propagation
- Line of sight propagation

3. **Determine the Relevant Propagation Method**: For frequencies in the range of 3 MHz to 30 MHz, the most suitable method of propagation is sky wave propagation. This is because:
- Sky wave propagation is effective for shortwave radio frequencies, allowing signals to be transmitted over long distances by reflecting off the ionosphere.

4. **Explain Sky Wave Propagation**: Sky wave propagation involves:
- The transmission of radio waves that are reflected or refracted back to Earth by the ionosphere, which is a layer of the atmosphere that contains charged particles.
- This allows for communication over distances that exceed the horizon, making it ideal for shortwave broadcasting.

5. **Conclude the Answer**: Based on the analysis, the mode of propagation used by short wave broadcast services in the specified frequency range is **sky wave propagation**.

### Final Answer:
The mode of propagation used by short wave broadcast services having a frequency range from 3 MHz to 30 MHz is **sky wave propagation**.