On–off keying
OOK encodes data as carrier presence or absence.
On–off keying (OOK) is the most basic type of amplitude-shift keying (ASK) modulation, where digital data is encoded by either transmitting a carrier wave or not. In its simplest version, a carrier sent for a set period stands for a binary one, and no carrier for the same period stands for a binary zero. More advanced versions can change those durations to carry extra information. This method works like a unipolar line code.
OOK is mainly used to send Morse code over radio frequencies—often called continuous wave (CW) operation—but any digital encoding can be used. It has also been used in the ISM bands for computer-to-computer data transfer. Compared to frequency-shift keying, OOK uses less bandwidth, but it is more vulnerable to noise when used with a regenerative receiver or a poorly designed superheterodyne receiver.
For a given data rate, an OOK signal and a Binary Phase Shift Keying (BPSK) signal take up the same bandwidth. Besides radio waves, OOK is also used in optical communication, such as IrDA and fiber-optic systems. In aviation, some airports without staff let pilots key their VHF radio several times to request an Automatic Terminal Information Service broadcast or to turn on runway lights. OOK is also common in remote garage and gate openers, often at 433.92 MHz, and is frequently paired with rolling codes.
- Modulation type
- Amplitude-shift keying (ASK)
- Common frequency example
- 433.92 MHz
- Bandwidth equivalence
- For a given data rate, the bandwidth of a BPSK signal and the bandwidth of an OOK signal are equal.
- Spectral efficiency comparison
- More spectrally efficient than frequency-shift keying
- Noise sensitivity
- More sensitive to noise when using a regenerative receiver or a poorly implemented superheterodyne receiver
Lore & Background
On–off keying is most commonly used to transmit Morse code over radio frequencies, referred to as continuous wave (CW) operation, though any digital encoding scheme may be used. It has been employed in the ISM bands to transfer data between computers. In aviation, some possibly unmanned airports have equipment that lets pilots key their VHF radio a number of times to request an Automatic Terminal Information Service broadcast or turn on runway lights. OOK is also used in remote garage and gate keys, often operating at 433.92 MHz, in combination with rolling codes.
Reader's Guide
On–off keying holds significance as the foundational digital modulation technique, directly linking early telegraphy (Morse code) to modern data transmission. Its simplicity makes it suitable for low-cost applications such as remote garage and gate keys operating at 433.92 MHz, often with rolling codes for security. In aviation, it enables pilots to request services at some possibly unmanned airports by keying their VHF radio. OOK is also used in optical communication systems, including IrDA and fiber-optic links. While more spectrally efficient than frequency-shift keying, it is more sensitive to noise when using a regenerative receiver or a poorly implemented superheterodyne receiver. Notably, for a given data rate, the bandwidth of an OOK signal equals that of a BPSK signal, highlighting its efficiency in spectrum use despite its simplicity.
Did You Know?
- OOK is analogous to unipolar encoding line code.
- For a given data rate, the bandwidth of a BPSK signal and the bandwidth of an OOK signal are equal.
- OOK is used in optical communication systems such as IrDA and fiber-optic communication.
More in Amateur Radio, Part 2 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced