Modulation

Categorization for signal modulation based on data and carrier types
A low-frequency message signal (top) may be carried by an AM or FM radio wave.
Waterfall plot of a 146.52 MHz radio carrier, with amplitude modulation by a 1,000 Hz sinusoid. Two strong sidebands at + and - 1 kHz from the carrier frequency are shown.
A carrier, frequency modulated by a 1,000 Hz sinusoid. The modulation index has been adjusted to around 2.4, so the carrier frequency has small amplitude. Several strong sidebands are apparent; in principle an infinite number are produced in FM but the higher-order sidebands are of negligible magnitude.
Schematic of 4 baud, 8 bit/s data link containing arbitrarily chosen values

Process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted.

- Modulation
Categorization for signal modulation based on data and carrier types

50 related topics

Alpha

Software defined radio concept

Software-defined radio

Software defined radio concept
Microtelecom Perseus - a HF SDR for the amateur radio market
Internals of a low-cost DVB-T USB dongle that uses Realtek RTL2832U (square IC on the right) as the controller and Rafael Micro R820T (square IC on the left) as the tuner.
GNU Radio logo

Software-defined radio (SDR) is a radio communication system where components that have been traditionally implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system.

Network Packet

Channel access method

In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity.

In telecommunications and computer networks, a channel access method or multiple access method allows more than two terminals connected to the same transmission medium to transmit over it and to share its capacity.

Network Packet

Each message signal (each phone call) is modulated on a specific carrier frequency.

Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (−). Loops of electric field leave the antenna and travel away at the speed of light; these are the radio waves. In this animation the action is shown slowed down enormously.

Radio wave

Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below.

Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below.

Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (−). Loops of electric field leave the antenna and travel away at the speed of light; these are the radio waves. In this animation the action is shown slowed down enormously.
Diagram of the electric fields (E) and magnetic fields (H) of radio waves emitted by a monopole radio transmitting antenna (small dark vertical line in the center). The E and H fields are perpendicular, as implied by the phase diagram in the lower right.
Animated diagram of a half-wave dipole antenna receiving a radio wave. The antenna consists of two metal rods connected to a receiver R. The electric field ( E, green arrows ) of the incoming wave pushes the electrons in the rods back and forth, charging the ends alternately positive (+) and negative (−) . Since the length of the antenna is one half the wavelength of the wave, the oscillating field induces standing waves of voltage ( V, represented by red band ) and current in the rods. The oscillating currents (black arrows) flow down the transmission line and through the receiver (represented by the resistance R).

The information, called the modulation signal, can be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing data from a computer.

Categorization for signal modulation based on data and carrier types

8VSB

Categorization for signal modulation based on data and carrier types

8VSB is the modulation method used for broadcast in the ATSC digital television standard.

An 8-PSK. Information transmitted according to the scheme described in the above diagram is encoded as one of 8 "symbols", each representing 3 bits of data. Each symbol is encoded as a different phase shift of the carrier sine wave: 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°.

Constellation diagram

An 8-PSK. Information transmitted according to the scheme described in the above diagram is encoded as one of 8 "symbols", each representing 3 bits of data. Each symbol is encoded as a different phase shift of the carrier sine wave: 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°.
A constellation diagram for rectangular 16-QAM.
A spectrum analyzer software using different views to show a QAM 4096 constellation diagram
The constellation as received, with noise added.

A constellation diagram is a representation of a signal modulated by a digital modulation scheme such as quadrature amplitude modulation or phase-shift keying.

Digital clock. The time shown by the digits on the face at any instant is digital data. The actual precise time is analog data.

Digital data

Information represented as a string of discrete symbols each of which can take on one of only a finite number of values from some alphabet, such as letters or digits.

Information represented as a string of discrete symbols each of which can take on one of only a finite number of values from some alphabet, such as letters or digits.

Digital clock. The time shown by the digits on the face at any instant is digital data. The actual precise time is analog data.

A beacon is perhaps the simplest non-electronic digital signal, with just two states (on and off). In particular, smoke signals are one of the oldest examples of a digital signal, where an analog "carrier" (smoke) is modulated with a blanket to generate a digital signal (puffs) that conveys information.

Modern surface-mount electronic components on a printed circuit board, with a large integrated circuit at the top.

Baud

Common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel.

Common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel.

Modern surface-mount electronic components on a printed circuit board, with a large integrated circuit at the top.

It is the unit for symbol rate or modulation rate in symbols per second or pulses per second.

An arbitrary bit pattern in various binary line code formats

Line code

Pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium.

Pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium.

An arbitrary bit pattern in various binary line code formats

the line-coded signal (the baseband signal) undergoes further pulse shaping (to reduce its frequency bandwidth) and then is modulated (to shift its frequency) to create an RF signal that can be sent through free space.

Frequency mixer symbol

Frequency mixer

Electrical circuit that creates new frequencies from two signals applied to it.

Electrical circuit that creates new frequencies from two signals applied to it.

Frequency mixer symbol
Schematic diagram of a double-balanced passive diode mixer (also known as a ring modulator). There is no output unless both f1 and f2 inputs are present, though f2 (but not f1) can be DC.

Frequency mixers are also used to modulate a carrier signal in radio transmitters.

Categorization for signal modulation based on data and carrier types

Angle modulation

Categorization for signal modulation based on data and carrier types

Angle modulation is a class of carrier modulation that is used in telecommunications transmission systems.