Which of the following frequencies will be suitable for beyond-the-Zorizon communication using sky waves ?

Options

A. 10 kHz
B. 10 MHz
C. 1 GHz
D. 1000 GHz

Answer

To determine which frequency is suitable for beyond-the-horizon communication using sky waves, we can follow these steps:

### Step 1: Understand the Concept of Sky Waves
Sky waves are radio waves that are reflected back to Earth by the ionosphere. For effective communication using sky waves, the frequency of the radio waves must be appropriate to ensure they can be reflected by the ionosphere.

**Hint:** Remember that different frequencies interact differently with the ionosphere.

### Step 2: Identify the Frequency Range for Sky Wave Communication
Generally, frequencies in the range of 3 MHz to 30 MHz are considered suitable for sky wave propagation. Frequencies below this range may not be efficiently radiated due to the size of the antennas required.

**Hint:** Frequencies below 3 MHz may not be effective for sky wave communication.

### Step 3: Evaluate the Given Options
- **Option A: 10 kHz** - This frequency is too low for efficient sky wave communication and requires very large antennas, making it impractical.
- **Option B: 10 MHz** - This frequency falls within the suitable range for sky wave propagation and can be reflected by the ionosphere effectively.
- **Option C: 1 GHz** - Frequencies in this range typically penetrate the ionosphere rather than being reflected, making them unsuitable for sky wave communication.
- **Option D: 2 GHz** - Similar to 1 GHz, this frequency is too high and will not be reflected by the ionosphere.

**Hint:** Focus on frequencies that are typically used for long-distance communication via sky waves.

### Step 4: Conclusion
Based on the evaluation of the options, the frequency that is suitable for beyond-the-horizon communication using sky waves is **10 MHz**.

**Final Answer:** 10 MHz