What Are Signals?
Before we can understand analog and digital systems, we need to understand what a signal is.
A signal is a way of carrying information from one place to another, using a varying quantity such as voltage, light intensity, or sound pressure.
Think about how you communicate every day. When you speak, your vocal cords create pressure waves in the air — that's a signal. When you text a friend, your phone converts your message into electrical and electromagnetic signals. In both cases, information travels from a sender to a receiver.
Signals can be grouped into two fundamental types: analog and digital. Understanding the difference between these two types is one of the most important ideas in modern communication technology.
Analog Signals
An analog signal is a continuously varying signal that can take any value within a range. It changes smoothly over time, like a wave.
Analog signals mirror the real world. Think about temperature throughout the day — it doesn't jump from 15°C to 20°C instantly. It rises and falls smoothly through every value in between. An analog signal works the same way.
Examples of analog signals:
- Sound waves from a musical instrument
- The voltage from a traditional microphone
- The signal in an old-fashioned vinyl record
- The signal transmitted by old AM/FM radio stations
- A mercury thermometer reading
Think of an analog signal like a ramp or a hill. You can stand at any height on the ramp — there are infinite possible positions. The signal flows smoothly from one value to the next, just like walking up a gentle slope.
An analog signal, when graphed, appears as a smooth, continuous wave. The wave's amplitude (height) and frequency (how often it repeats) can both vary to carry different information.
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