Why is modulation necessary at all ?

Options

A. To select suitable size of antenna
B. To increase effective power radiated by antenna
C. To avoid mixing up of signals from different transmitters
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Modulation**: Modulation is the process of varying one or more properties of a carrier signal (like its amplitude, frequency, or phase) in accordance with the information signal that is to be transmitted.

2. **Reason for Modulation**:
- **Antenna Size**: The size of the antenna is related to the wavelength of the signal. For low-frequency signals (like those below 20 Hz), the wavelength is very long, making it impractical to build antennas of such size. Modulation allows us to shift the frequency of the signal to a higher range where the antenna can be more reasonably sized.

3. **Effective Power Radiation**:
- Modulated signals can be transmitted over longer distances. By increasing the frequency of the signal through modulation, we can increase the effective power radiated by the antenna. Higher frequency signals can travel further and penetrate obstacles better than lower frequency signals.

4. **Avoiding Signal Mixing**:
- In communication systems, multiple transmitters may operate in close frequency ranges. Modulation helps in distinguishing between these signals, preventing them from mixing. This ensures that the receiver can accurately decode the intended signal without interference from others.

5. **Conclusion**:
- Therefore, modulation is necessary for selecting suitable antenna sizes, increasing effective power radiation, and avoiding mixing of signals from different transmitters. All these factors contribute to the efficiency and clarity of communication systems.