What is an Analog Signal?

An analog signal is a type of signal that can take on any value from a continuous range over a given period. Its values change smoothly and are not restricted to a finite set of levels. The physical world around us is inherently analog-examples include sound waves, light intensity, and temperature changes. Human speech is a classic example of an analog signal.

The Sine Wave: The Fundamental Building Block

The simplest and most fundamental form of an analog signal is the sine wave. According to Fourier's theorem, any complex periodic signal can be broken down into a sum of simple sine waves. Understanding the sine wave is therefore crucial to understanding all analog signals.

Parameters of a Sine Wave

• Amplitude (A): This is the maximum deviation or value of the signal from its zero level (the time axis). It describes the "strength" or "intensity" of the signal. On the graph, it's the distance from the horizontal axis to the peak of the wave.
• Period (T): This is the time it takes for the wave to complete one full cycle, after which its shape begins to repeat. It is measured in seconds [s].
• Frequency (f): This is the number of full cycles the wave completes in one second. It is the inverse of the period and is measured in Hertz [Hz], where 1 Hz = 1 cycle per second.
  Formula: $f = \frac{1}{T}$

From Acoustic Wave to Transmission Signal

Physical phenomena like acoustic waves (e.g., human speech) must be converted into a transmission signal (usually electrical) to be sent over telecommunication systems. Such complex signals are also characterized by several key parameters.

• Dynamics (D): This is the ratio of the largest signal value (e.g., amplitude $A_{\text{max}}$) to its smallest value ($A_{\text{min}}$) in a given segment. It defines the range of the signal's level variations and is often expressed in decibels.
• Frequency Bandwidth ($\Delta f$): This is the range of frequencies contained within the signal, from the lowest ($f_{\text{min}}$) to the highest ($f_{\text{max}}$). For a signal to be transmitted without loss of information, the transmission channel must be able to carry this entire frequency range.