What is modulation ? Briefly explain three reasons which make modulation an essential step in communication system.

Explanation

### Step-by-Step Solution

**Step 1: Define Modulation**
Modulation is the process of varying a carrier signal in order to transmit information. Specifically, it involves superimposing a low-frequency signal (which contains the information) onto a high-frequency signal (the carrier) to enable effective transmission over long distances.

**Step 2: Explain the First Reason - Antenna Height**
One of the primary reasons modulation is essential in communication systems is related to the height of the transmitting antenna. The height of the antenna must be comparable to the wavelength of the signal being transmitted. For example, to transmit audio signals, the antenna height would need to be around 15 kilometers, which is impractical. Modulation allows us to use shorter antennas by shifting the frequency of the signal.

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