Why modulation is necessary ?

Explanation

### Step-by-Step Solution:

**Step 1: Understanding the Need for Antenna Height**
- Modulation is necessary because the height of the transmitting antenna must be comparable to the wavelength of the signal being transmitted. For instance, if we want to transmit audio signals, the wavelength would be extremely large, leading to impractical antenna heights.

**Step 2: Power Radiation Considerations**
- The effective power radiated by an antenna is inversely proportional to the square of its height. This means that to maximize the effective power radiated, the height of the antenna should be kept small. Modulation allows us to achieve this by altering the signal's characteristics.

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