Signal velocity

The signal velocity is the speed at which a wave carries information. It describes how quickly a message can be communicated (using any particular method) between two separated parties. Every signal velocity is always slower than (or equal to) the speed of a light pulse in a vacuum (by Special Relativity).

In the vast majority of cases, signal velocity is equal to group velocity (the speed of a short "pulse" or of a wave-packet's middle or "envelope"). However, in a few special cases (e.g., media designed to amplify the front-most parts of a pulse and then attenuate the back section of the pulse), group velocity can exceed even the vacuum speed of light.

Signal velocity is alwaysFact|date=June 2008 the same as front velocity.

For light (electromagnetic waves) in vacuum, the signal velocity is the same as the group velocity and the phase velocity (the speed of any individual crest of the wave).

In electronic circuits, signal velocity is one member of a group of five closely related parameters. In these circuits, signals are usually treated as operating in TEM mode. That is, the fields are perpendicular to the direction of transmission and perpendicular to each other. Given this presumption, the quantities: signal velocity, the product of dielectric constant and magnetic permeability, characteristic impedance, inductance of a structure, and capacitance of that structure, are all related such that if you know any two, you can calculate the rest. In a uniform medium if the permeability is constant, then variation of the signal velocity will be dependent only on variation of the dielectric constant.

In a transmission line, signal velocity is the reciprocal of the square root of the capacitance-inductance product, where inductance and capacitance are typically expressed as per-unit length. In circuit boards made of FR4 material, the signal velocity is typically about six inches per nanosecond. In these boards, permeability is usually constant and dielectric constant often varies from location to location, causing variations in signal velocity. As data rates increase, these variations become a major concern for computer manufacturers.

See also

* Dispersion (optics)
* Front velocity
* Phase velocity


* Brillouin, Léon. "Wave propagation and group velocity". Academic Press Inc., New York (1960).
* Clayton R. Paul, "Analysis of Multiconductor Transmission Lines". Johm Wiley & Sons., New York (1994)

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Velocity of propagation — (VoP) or velocity factor (VF) is a parameter that characterizes the speed at which an electrical signal (e.g. radio) passes through a medium. Expressed as a number between 0 and 1 (or a percentage), it is the ratio of a signal s transmission… …   Wikipedia

  • Signal-flow graph — A signal flow graph (SFG) is a special type of block diagram[1] and directed graph consisting of nodes and branches. Its nodes are the variables of a set of linear algebraic relations. An SFG can only represent multiplications and additions.… …   Wikipedia

  • Velocity Gate Pull-Off — Bei einem Velocity Gate Pull Off (VGPO) handelt es sich um eine EloGM Technik zum Stören von Radargeräten. Beschreibung Die VGPO Technik kommt dann zum Einsatz, wenn ein Radarsystem bereits ein Ziel erfasst hat. Um Störungen zu vermeiden und um… …   Deutsch Wikipedia

  • Velocity of money — Chart showing the log of US M2[1][2] money velocity (green), calculated by dividing nominal GDP by M2 stock, M1 plus time deposits. M2 velocity is not stable and correlates with the Employment Population ratio (blue), an indicator of economic… …   Wikipedia

  • VELOCITY Broadcasting — Infobox Company name = VELOCITY Broadcasting type = Private company foundation = Pittsburgh, Pennsylvania, U.S. (2005) founder = Philip Elias location city = Pittsburgh, Pennsylvania location country = U.S. key people = Philip Elias… …   Wikipedia

  • signal propagation velocity — signalo sklidimo greitis statusas T sritis automatika atitikmenys: angl. signal propagation velocity vok. Signalausbreitungsgeschwindigkeit, f rus. скорость распространения сигнала, f pranc. vitesse de propagation de signal, f …   Automatikos terminų žodynas

  • Velocity air meter — A Velocity air meter measures the force of air rushing into an engine against a spring loaded door in an air tunnel. A linear potentiometer rotated along with the hinge of the air door measures the angle of the opening and sends an electrical… …   Wikipedia

  • velocity modulation — /vəˌlɒsəti mɒdʒəˈleɪʃən/ (say vuh.losuhtee mojuh layshuhn) noun the process of altering the velocity of a beam of electrons in proportion to the strength of a control signal …   Australian English dictionary

  • Group velocity — [ Frequency dispersion in bichromatic groups of gravity waves on the surface of deep water. The red dot moves with the phase velocity, and the green dots propagate with the group velocity. In this deep water case, the phase velocity is twice the… …   Wikipedia

  • Phase velocity — periodic gravity waves on the surface of deep water. The red dot moves with the phase velocity, and is located at a fixed wave phase: the crest for the case shown.The phase velocity (or phase speed) of a wave is the rate at which the phase of the …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.