Browse Definitions :
Definition

phase modulation (PM)

Also see modulation and phase-shift keying.

Phase modulation (PM) is a method of impressing data onto an alternating-current (AC) waveform by varying the instantaneous phase of the wave. Thisscheme can be used with analog or digital data.

In analog PM, the phase of the AC signalwave, also called the carrier, varies in a continuous manner. Thus, thereare infinitely many possible carrier phase states. When the instantaneous data inputwaveform has positive polarity, the carrier phase shifts in one direction; when theinstantaneous data input waveform has negative polarity, the carrier phase shifts in theopposite direction. At every instant in time, the extent of carrier-phase shift(the phase angle) is directly proportional to the extent to which the signalamplitude is positive or negative.

In digital PM, the carrier phase shifts abruptly, rather than continuouslyback and forth. The number of possible carrier phase states is usually a power of2. If there are only two possible phase states, the mode is called biphasemodulation. In more complex modes, there can be four, eight, or more differentphase states. Each phase angle (that is, each shift from one phase state to another)represents a specific digital input data state.

Phase modulation is similar in practice to frequency modulation (FM). When theinstantaneous phase of a carrier is varied, the instantaneous frequency changes as well. The converse also holds: When the instantaneous frequency is varied, theinstantaneous phase changes. But PM and FM are not exactly equivalent, especially inanalog applications. When an FM receiver is used to demodulate a PM signal, or whenan FM signal is intercepted by a receiver designed for PM, the audio is distorted. This is because the relationship between phase and frequency variations is not linear;that is, phase and frequency do not vary in direct proportion.

This was last updated in September 2005

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.

-ADS BY GOOGLE

File Extensions and File Formats

SearchCompliance

  • Whistleblower Protection Act

    The Whistleblower Protection Act of 1989 is a law that protects federal government employees in the United States from ...

  • smart contract

    A smart contract, also known as a cryptocontract, is a computer program that directly controls the transfer of digital currencies...

  • risk map (risk heat map)

    A risk map, also known as a risk heat map, is a data visualization tool for communicating specific risks an organization faces. A...

SearchSecurity

  • challenge-response authentication

    In information security, challenge-response authentication is a type of authentication protocol where one entity presents a ...

  • Secure Shell (SSH)

    SSH, also known as Secure Shell or Secure Socket Shell, is a network protocol that gives users, particularly system ...

  • honeypot (computing)

    A honeypot is a network-attached system set up as a decoy to lure cyberattackers and to detect, deflect or study hacking attempts...

SearchHealthIT

SearchDisasterRecovery

  • virtual disaster recovery

    Virtual disaster recovery is a type of DR that typically involves replication and allows a user to fail over to virtualized ...

  • tabletop exercise (TTX)

    A tabletop exercise (TTX) is a disaster preparedness activity that takes participants through the process of dealing with a ...

  • risk mitigation

    Risk mitigation is a strategy to prepare for and lessen the effects of threats faced by a data center.

SearchStorage

  • exbibyte (EiB)

    An exbibyte (EiB) is a unit used to measure data capacity.

  • zebibyte (ZiB)

    A zebibyte (ZiB) is a unit used to measure computing and storage capacity.

  • tiered storage

    Tiered storage is a way to assign different categories of data to various types of storage media with the objective of reducing ...

Close