analogue signal modulation

Analogue signal modulation is a fundamental telecommunications technique where a characteristic of a carrier wave is altered to encode information. This process is essential for several reasons: it allows signals to be transmitted over channels with specific frequency limitations by "frequency translating" them, it enables multiple users to share a channel by assigning each a unique carrier frequency (frequency-division multiplexing), and it permits the use of smaller antennas by shifting signals to higher frequencies.1

Two primary methods of analog modulation exist:
* Amplitude Modulation (AM): The amplitude of a fixed-frequency carrier wave is varied in proportion to the information signal. This is the oldest method of radio broadcasting.12
* Frequency Modulation (FM): The frequency of a fixed-amplitude carrier wave is varied in proportion to the information signal. FM is less susceptible to interference than AM and is better for transmitting stereophonic sound and television audio.12

Phase modulation (PM) is also an analog technique where the phase of the carrier wave is varied, often used in conjunction with FM. Modems are devices that perform modulation and demodulation to enable digital data transmission over analog lines.23