Analog Modulation

Analog modulation involves changing a high-frequency analog carrier wave to encode analog data, such as voice, music, or video. This process allows the signal to be transmitted over long distances, typically via radio waves, and then decoded by a receiver. Key concepts include: –

• Analog Data: A signal that varies continuously, like sound.
• Carrier Wave: A steady waveform, usually a sine wave, with a specific frequency and amplitude.
• Modulation: The act of altering a property of the carrier wave to transmit information.

Why Use a Carrier Wave

• Efficient Transmission: Carrier waves usually operate in the radio frequency range, allowing them to travel farther with less signal loss.
• Multiplexing: Multiple signals can coexist in the same medium, such as air or cable, without causing interference.
• Antenna Size: Higher frequency waves enable the use of smaller antennas.

Main Analog Modulation Techniques

There are three primary ways to modulate a sine wave to carry analog data:

1. Amplitude Modulation (AM)

• What it modifies: Amplitude of the carrier wave
• Carrier stays same: Frequency and phase remain constant
• Information carried in: Variations in amplitude
• Applications: AM radio broadcasting, aviation communications

2. Frequency Modulation (FM)

• What it modifies: Frequency of the carrier wave
• Carrier stays same: Amplitude and phase
• Information carried in: Changes in frequency
• Applications: FM radio, two-way radios

Key Advantage: Better noise immunity than AM

3. Phase Modulation (PM)

• What it modifies: Phase of the carrier wave
• Carrier stays same: Amplitude and frequency
• Information carried in: Variations in phase
• Applications: Used in some digital modulation schemes (e.g., QPSK), satellite comms

Comparison Table: