Modulation is not used to :-

Options

A. Reduce the bandwidth used
B. Separate the transmissions of different users
C. Ensure that intelligence may be transmitted to long distances
D. Allow the use of practical antennas

Answer

To solve the question regarding the use of modulation, we need to analyze the provided options and understand the purpose of modulation in communication systems.

### Step-by-Step Solution:

1. **Understanding Modulation**: Modulation is a technique used in communication systems to encode information onto a carrier wave. This allows for the transmission of signals over long distances and through various mediums.

2. **Analyzing the Options**:
- **Option A**: Reduce bandwidth used.
- **Option B**: Separate the transmissions of different users.
- **Option C**: Ensure that the intelligence may be transmitted to long distances.
- **Option D**: Allow the use of practical antennas.

3. **Evaluating Each Option**:
- **Option A (Reduce bandwidth used)**: This statement is incorrect. Modulation does not reduce the bandwidth; instead, it can increase the effective bandwidth required for transmission. Therefore, modulation is not used for reducing bandwidth.
- **Option B (Separate the transmissions of different users)**: This is a correct use of modulation. By using different carrier frequencies, different users can transmit their signals without interference.
- **Option C (Ensure that the intelligence may be transmitted to long distances)**: This is also a correct use of modulation. Modulation allows low-frequency signals to be transmitted over long distances by converting them to higher frequencies.
- **Option D (Allow the use of practical antennas)**: This is correct as well. Modulation enables the use of smaller antennas by allowing the transmission of higher frequency signals.

4. **Conclusion**: The option that is incorrect regarding the use of modulation is **Option A**, as modulation does not reduce bandwidth but can actually require a larger bandwidth for transmission.

### Final Answer:
Modulation is not used to reduce bandwidth used. Therefore, the correct option is **Option A**.

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