What is a Signal?

Actions, expressions, gestures, sounds tell us some information, and these are the ways of communicating one side to another side. Thus the singal is a way of communicating by sending information from one system to another system. In other word signal is a function that represents information or data.

Signal is an electromagnetic wave that carries information through physical medium (wire or air). Here the data or information is converted into electromagnetic (carrier base) signal either as analog or digital and sent from transmitter to receiver.

Current and voltage are few time varying quantities that are used to represent data, by varying these quantities with respect to time data can be transmitted. Thus the signal is also represented as the function of the frequency domain rather than the time domain.

For communicating between two systems, the message signal is passed through encoder and using modulator to transmit through a medium while it is passed through decoder and using demodulator to receive the message signal at the another end.

Basically the signals are divided into two main categories based on their nature. First one is natural signal that donated by the nature and other one is human generated.

because the our universal, solar system, cosmos and world is totally base on analog system and the analog system is based on decimal number system and other is used in Digital system that is Digital Signal and the Digital signal is base on Binary number system. 

Classification of signal:

Analog  signal  which  are  continuous  as  time  varying  in  nature  are analog signals, there are some furthermore main classification analog signals which are:

1.  Analog and Digital Signal

2. Periodic and aperiodic Signal

3. Energy and Power Signal

4. Deterministic and Random Signal

Digital signal having two discrete values is known as Binary signal. However, the number of values for amplitude in a digital signal is not limited to only two.

Analog Signals:

Analog signals are the form of an electrical energy (voltage, current or electromagnetic power) for which there is a linear relationship between electrical quantity and the value that the signal represents.

The signal whose amplitude takes any value in the continuation range that is called analog signal.

Analog Signal is continuously change in nature which varies with respect to time. They can be non-periodic or periodic for example light, sound, pressure, temperature, frequency, current, voltage etc.  are the physical variables that can changes their values with respect   to time so, they can measure to get information.

When time versus voltage graph is plotted we observe the curve by changing in the continuation of upper and lower values of signal like sine waves.

These signals are more subjected to noise as they travel through the medium like air or wire, these noises result in information loss in the signals.

Analog may be convert into digital signal by using converter that converts the analog signal to digital signal by a process that is called quantization and sampling. Sound waves are convert to sequence of samples by the process Sampling.

Examples of analog signals:

simple transmitters (old) conventional, transducers convey data in analog mode.

Sine wave, other signals, included audio and video signals transmitted through wires, the video signals broadcasted using older transmitting technology, analog watches, thermometer, analog meters and radio signals.

Basic Characteristics of Signal

A signal is defined by its own basic characteristics. Its show the nature and type of the signal. These basic characteristics are given below:

Amplitude of the signal

The amplitude is the height in shape of signal and strength of the signal waveform. Visually, it is the height of the waveform from its X-axis or centerline. The Y-axis of any signal’s waveform shows the amplitude of the signal. The amplitude of the signal always varies its value with time.

For example, the amplitude of the sinewave is the maximum height portion of both positive and negative side of the waveform on Y-axis.

The signal’s strength is always measured in decibels db

Frequency

Frequency describes the number of cycle of wave form that pass a fixed point in a given amount of time. So if the time it takes for the Five cycles to pass is "1" second, so, the frequency of system is 5 Hz or cycles per second.

5 Hz Frequency Signal

Time Period

Actually the time period of any signal is the time in which it will completes its one full or complete cycle. Time period measure in Second. The time period is denoted by block letter "T" and it is the inverse of the signal frequency. i.e.

T = 1/F

For example, any signal such as sine wave having the time period is 10 second.  thus it will complete its one full cycle in 10 seconds.

Periodic Signal

A signal which repeat itself after finite time “T” then it is called periodic signal.

Aperiodic Signal

A signal that doesn’t repeat itself after a specific interval of time is called an aperiodic signal.

 

Power and Energy Signal

Energy signal is a signal whose energy is finite and power is zero whereas Power signal is a signal whose power is finite and energy is infinite.

Deterministic

A signal whose physical description is known completely either in mathematical form or graphical form known as the Deterministic signal.

Random Signal

A signal which is known only in terms of the probabilistic description like mean, mean squire value and distributions is known as the Random Signal.

Digital Signals

Digital Signals The signal, whose amplitude takes only limited or finite values is called Digital signal. Digital signal is discrete; they contain only distinct values.

Digital signals carry binary data i.e. Low "0" or High "1" in the form of bit, thus its can only contain just one value at the period of time. Digital signals are represented as clock pulse signals or square waves.

The minimum value is low (“0” volts) whereas maximum value is high (“5” volts). Digital signals are less subjected to noise as compared to analog signals. Transmission of digital data (information) in analog channel is proceed or done by process called Modulation. AM (Amplitude modulation) is a process in which digital data or information is converted digital into analog signals using single frequency carrier wave signal. thus, the FREQUENCY shift keying uses a constant amplitude carrier wave signal and two frequencies to differentiate between high "1" and low "0".

Nowadays usage of digital signals for transmitting information has increased rapidly in every field of usage as the applications and properties of digital system and signals are more productive compared to analog system and signals

Examples of some digital systems which using digital signals:

1. Smart transmitters using various protocols transmit data through analog and digital signals.

2. Digital watches.

3. Digital video signals.

4. CD’s.

5. DVD’s.

5. Computer.

Difference between Analog and Digital Signals