Alternate-Phase Return-to-Zero (APRZ) is an optical

line code In telecommunications, a line code is a pattern of voltage, current, or photons used to represent digital data transmission (telecommunications), transmitted down a communication channel or written to a storage medium. This repertoire of signal ...

. In APRZ the field intensity drops to zero between consecutive bits, and the

field Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an airport * Battlefield * Lawn, an area of mowed grass * Meadow, a grass ...

phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform *Phase space, a mathematica ...

alternates between neighbouring bits, so that if the phase of the signal is, for example, 0 in even bits (bit number 2''n''), the phase in odd bit slots (bit number 2''n''+1) will be ''ΔΦ'', the phase alternation amplitude.

Special cases

Return-to-zero Return-to-zero (RZ or RTZ) describes a line code used in telecommunications signals in which the signal drops (returns) to zero between pulses. This takes place even if a number of consecutive 0s or 1s occur in the signal. The signal is se ...

can be seen as a special case of APRZ in which ''ΔΦ''=0, while Carrier-Suppressed Return-to-Zero (CSRZ) can be viewed as a special case of APRZ in which ''ΔΦ''=π (and the

duty cycle A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle. As a for ...

is 67%, at least in the standard form of CSRZ). APRZ can be used to generate specific optical modulation formats, for example, APRZ-

OOK Ook, OoK or OOK may refer to: * Ook Chung (born 1963), Korean-Canadian writer from Quebec * On-off keying, in radio technology * Toksook Bay Airport (IATA code OOK), in Alaska * Ook!, an esoteric programming language based on Brainfuck * Ook, the ...

, in which data is coded on the intensity of the signal using a binary scheme (light on=1, light off=0). APRZ is often used to designate APRZ-OOK.

Characteristics

The characteristic properties of an APRZ signal are those to have a spectrum similar to that of an RZ signal, except that frequency peaks at a spacing of ''B_R''/2 as opposed to ''B_R'' are observed (where ''B_R'' is the

bit rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction ...

). Line codes Fiber-optic communications {{Telecom-stub