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On-off keying

 

 
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On-off keying (OOK) is a type of modulation
Modulation

In telecommunications, modulation is the process of varying a Periodic function waveform, i.e. a tone, in order to use that signal to convey a message, in a similar fashion as a musician may modulate the tone from a musical instrument by varying its volume, timing and Pitch ....
 that represents digital
Digital

A digital system uses discrete values, usually but not always symbolized numerically to represent information for input, processing, transmission, storage, etc....
 data
DATA

Debt, AIDS, Trade in Africa is a multinational Non-governmental organization founded in January 2002 in London by U2's Bono along with Robert Sargent Shriver III and activists from the Jubilee 2000 Drop the Debt campaign....
 as the presence or absence of a carrier wave
Carrier wave

In telecommunications, a carrier wave, or carrier is a waveform that is Modulation with an signal for the purpose of conveying information....
. In its simplest form, the presence of a carrier for a specific duration represents a binary
Binary numeral system

The binary numeral system, or notation with a radix of 2. Owing to its straightforward implementation in digital electronic circuitry using logic gates, the binary system is used internally by all modern computers....
 one, while its absence for the same duration represents a binary zero. Some more sophisticated schemes vary these durations to convey additional information. It is analogous to unipolar encoding
Unipolar encoding

Unipolar encoding is a line code. A positive voltage represents a Binary logic 1, and zero volts indicates a binary 0. It is the simplest line code, directly encoding the bitstream, and is analogous to on-off keying in modulation....
 line code
Line code

In telecommunication, a line code is a code chosen for use within a communications system for transmission purposes. Line coding is often used for digital data transport....
.

On-off keying is most commonly used to transmit Morse code
Morse code

Morse code is a type of character encoding that transmits telegraphic information using rhythm. Morse code uses a standardized sequence of short and long elements to represent the alphanumeric, punctuation and special characters of a given message....
 over radio frequencies
Radio frequency

Radio frequency is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves....
 (referred to as continuous wave
Continuous wave

A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration....
 operation), although in principle any digital encoding scheme may be used.






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On-off keying (OOK) is a type of modulation
Modulation

In telecommunications, modulation is the process of varying a Periodic function waveform, i.e. a tone, in order to use that signal to convey a message, in a similar fashion as a musician may modulate the tone from a musical instrument by varying its volume, timing and Pitch ....
 that represents digital
Digital

A digital system uses discrete values, usually but not always symbolized numerically to represent information for input, processing, transmission, storage, etc....
 data
DATA

Debt, AIDS, Trade in Africa is a multinational Non-governmental organization founded in January 2002 in London by U2's Bono along with Robert Sargent Shriver III and activists from the Jubilee 2000 Drop the Debt campaign....
 as the presence or absence of a carrier wave
Carrier wave

In telecommunications, a carrier wave, or carrier is a waveform that is Modulation with an signal for the purpose of conveying information....
. In its simplest form, the presence of a carrier for a specific duration represents a binary
Binary numeral system

The binary numeral system, or notation with a radix of 2. Owing to its straightforward implementation in digital electronic circuitry using logic gates, the binary system is used internally by all modern computers....
 one, while its absence for the same duration represents a binary zero. Some more sophisticated schemes vary these durations to convey additional information. It is analogous to unipolar encoding
Unipolar encoding

Unipolar encoding is a line code. A positive voltage represents a Binary logic 1, and zero volts indicates a binary 0. It is the simplest line code, directly encoding the bitstream, and is analogous to on-off keying in modulation....
 line code
Line code

In telecommunication, a line code is a code chosen for use within a communications system for transmission purposes. Line coding is often used for digital data transport....
.

On-off keying is most commonly used to transmit Morse code
Morse code

Morse code is a type of character encoding that transmits telegraphic information using rhythm. Morse code uses a standardized sequence of short and long elements to represent the alphanumeric, punctuation and special characters of a given message....
 over radio frequencies
Radio frequency

Radio frequency is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves....
 (referred to as continuous wave
Continuous wave

A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration....
 operation), although in principle any digital encoding scheme may be used. OOK has been used in the ISM band
ISM band

The industrial, scientific and medical radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial, scientific and medical purposes other than communications....
s to transfer data between computer
Computer

A computer is a machine that manipulates Data according to a list of Code .The first devices that resemble modern computers date to the mid-20th century , although the computer concept and various machines similar to computers existed earlier....
s, for example.

OOK is not very spectrally efficient
Spectral efficiency

Spectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given Bandwidth in a specific communication system....
 due to the abrupt changes in amplitude of the carrier wave. At low to medium signalling speeds
Data signaling rate

In telecommunication, data signaling rate , also known as gross bit rate, is the aggregate rate at which data pass a point in the transmission data link of a data transmission system....
, this can be mitigated by adjusting the rise and fall rates of the carrier's amplitude. At high speeds, more efficient modulation modes (such as frequency-shift keying
Frequency-shift keying

Frequency-shift keying is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave....
) are normally used instead.

In addition to RF carrier waves, OOK is also used in optical communication
Optical communication

Optical communication is any form of telecommunication that uses light as the transmission medium.An optical communication system consists of a transmitter, which encodes a message into an optical signal , a channel , which carries the signal to its destination, and a receiver, which reproduces the message from the recei...
 systems (e.g. IrDA
IRDA

IRDA may refer to:* Infrared Data Association, in information and communications technology , a standard for communication between devices over short distances using infrared signals...
).

In aviation, some possibly unmanned airports have equipment that let pilots key their VHF radio a number of times in order to request an Automatic Terminal Information Service
Automatic Terminal Information Service

Automatic Terminal Information Service, or ATIS, is a continuous broadcast of recorded noncontrol information in busier Airport terminal areas....
 broadcast, or turn on runway lights.

See also

  • Unipolar encoding
    Unipolar encoding

    Unipolar encoding is a line code. A positive voltage represents a Binary logic 1, and zero volts indicates a binary 0. It is the simplest line code, directly encoding the bitstream, and is analogous to on-off keying in modulation....