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 determine 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. **Understand the Frequency Range**:
- The question specifies a frequency range from 3 MHz to 30 MHz. This range is categorized as shortwave frequencies in the radio spectrum.

2. **Identify Propagation Modes**:
- There are several modes of radio wave propagation, including ground waves, direct waves, and sky waves. Each mode has its own characteristics and is suitable for different frequency ranges.

3. **Analyze Shortwave Propagation**:
- Shortwave radio waves can travel long distances by reflecting off the ionosphere, which is a layer of the Earth's atmosphere that is ionized by solar radiation. This reflection allows the waves to be received far beyond the horizon.

4. **Determine the Correct Mode**:
- Given that the frequency range of 3 MHz to 30 MHz is typically associated with shortwave broadcasting, the primary mode of propagation used in this range is sky wave propagation. Sky waves are reflected back to Earth by the ionosphere, allowing for long-distance communication.

5. **Conclusion**:
- Therefore, the mode of propagation used by short wave broadcast services in the specified frequency range is **sky waves**.

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

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