Which of the following statement is wrong?

Options

A. Ground wave propagation can be sustained at frequencies 500kHz to 1500 kHz
B. Satellite communication is useful for the frequencies above 30 MHz
C. Sky wave propagation is useful in the range of 30 to 40 MHz
D. Sky wave propagation takes place through tropospheric space

Answer

To determine which statement is wrong, we will analyze each statement one by one based on the principles of communication systems.

### Step 1: Analyze the First Statement
**Statement:** Ground wave propagation can be sustained at a frequency that is 500 kHz to 1500 kHz.

**Analysis:**
Ground wave propagation occurs when radio waves travel along the surface of the Earth. This type of propagation is effective at low frequencies, typically in the range of 500 kHz to 1500 kHz. Therefore, this statement is **correct**.

### Step 2: Analyze the Second Statement
**Statement:** Satellite communication is useful for frequencies above 30 megahertz.

**Analysis:**
Satellite communication typically operates at much higher frequencies, often in the range of 1 GHz to 50 GHz (which is equivalent to 1000 MHz to 50000 MHz). Since 30 MHz (30 megahertz) is much lower than 1 GHz, this statement is also **correct**.

### Step 3: Analyze the Third Statement
**Statement:** Skywave propagation is useful in the range of 30 to 40 megahertz.

**Analysis:**
Skywave propagation involves the reflection of radio waves off the ionosphere. The effective frequency range for skywave propagation is typically between 5 MHz to 25 MHz. Since the statement claims a range of 30 to 40 MHz, which is outside the effective range, this statement is **wrong**.

### Step 4: Analyze the Fourth Statement
**Statement:** Skywave propagation takes place through the tropospheric space.

**Analysis:**
Skywave propagation does indeed involve radio waves that are reflected from the ionosphere back towards the Earth. While the waves may pass through the tropospheric layer, the primary propagation mechanism is through the ionosphere. However, the statement is still **correct** as it does mention that the waves travel through the tropospheric space after being reflected.

### Conclusion
The only incorrect statement is the third one, which claims that skywave propagation is useful in the range of 30 to 40 megahertz.

### Final Answer
The wrong statement is: **Skywave propagation is useful in the range of 30 to 40 megahertz.**

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