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

line code In telecommunication, 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 signals ...

. In APRZ the

field intensity In physics, field strength means the ''magnitude'' of a vector-valued field (e.g., in volts per meter, V/m, for an electric field ''E''). For example, an electromagnetic field results in both electric field strength and magnetic field strength. As ...

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 each pulse. This takes place even if a number of consecutive 0s or 1s occur in the signal. The signal is s ...

can be seen as a special case of APRZ in which ''ΔΦ''=0, while

Carrier-Suppressed Return-to-Zero Carrier-Suppressed Return-to-Zero (CSRZ) is an optical line code. In CSRZ the field intensity drops to zero between consecutive bits ( RZ), and the field phase alternates by π radians between neighbouring bits, so that if the phase of the signal ...

(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 formu ...

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, th ...

, 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 w ...

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