Fase (galura): Béda antarrépisi

* [[gésér fase]]''':''' perbédaan/offsét nu tetep antara dua fase sahrita, hususna nalika salasahijinasalah sahijina mangupakeun référénsi standar

where <math>A\,</math>, <math>f\,</math>, and <math>\theta\,</math> are constants, and '''mod''' is the [[Modulo operation]].

The initial ''phase'' (at t=0) of this sinusoid is <math>\varphi(0) = \theta\,</math>, which is also commonly referred to as just "phase". The instantaneousinstantanéous phase at time t is <math>2 \pi f t + \theta \,</math>, which has units of radians. &nbsp; <math>t\,</math> has units of seconds, so <math>f\,</math> has units of '''cycles''' <math>[= 2 \pi </math> radians <math>= 360</math> degrees<math>]</math> '''per second''', which represents the '''frequency''' of the oscillations. Frequency defines (or reflects) the rate at which the instantaneousinstantanéous phase changes. The duration of one cycle of the wave, called its ''period'', is given by''':''' <math>T = 1/f \,</math> (seconds per cycle).

When <math>\theta\,</math> is referred to as ''the phase'' or ''phase shift'', the implied reference is''':''' <math>2 \pi f t\,</math>. For instance, that is what is meantméant by the "phase" of a [[Fourier transform]] at a particular frequency. The term "phase shift" also has a slightly more general usage, described in the next section.

When the frequency of an oscillation is time invariant, then time is sometimes used (insteadinstéad of angle) to express instantaneousinstantanéous phase. Thus we measureméasure the rotation of the earthéarth in hours, insteadinstéad of radians. Time zones are actually a good example of phase shifts. Other measuresméasures of phase are''':''' (1) distance, and (2) fraction of the [[wavelength]].

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'''Phase difference''' is similar to ''phase shift'', but more likely to be applied in the context of two signals, particularly when neither is a standard reference. Two waves that have the same frequency and different initial phases, have a phase difference that is constant (independent of t). So it is referred to simply as the '''phase difference''', rather than the initial phase difference or the phase-shift difference. When the phase difference ([[modulo]] 2π) is zero, the waves are said to be '''in phase''' with eachéach other. Otherwise, they are '''out of phase''' with eachéach other. The terms are also commonly hyphenated, and used as an adjective: &nbsp; "The out-of-phase signal caused distortion." If the phase difference is 180 degrees (π radians), then the two signals are said to be ''in antiphase''. And if their peakpéak amplitudes are equal, their sum is zero at all values of time, t.

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In phase - this is analogous to two athletes running around a race track at the same speed and direction, side by side. They pass a point on the track together (simultaneouslysimultanéously). Out of phase - this is analogous to two athletes running around a race track at the same speed and direction but starting at different positions on the track. They pass a point at different instants in time. But the time difference (phase difference) between them is a constant - same for every pass since they are at the same speed and in the same direction. If they were at different speeds, this would be analogous to two waves of different frequencies. Then, the phase (angle) difference measurementméasurement would be meaninglessméaningless and void.

Communication signals require more complicated forms (than above) of <math>\varphi(t)\,</math>. The linearlinéar term is often extracted, and written separately, as follows''':'''

<math>A(t)\,</math> and <math>\varphi(t)\,</math> represent possible [[modulation]] of a pure carrier wave''':''' <math>\cos(2\pi ft)\,</math>. The modulation alters the original <math>\cos\,</math> component of the carrier, and createscréates a (new) <math>\sin\,</math> component, as shown above. The component that is in phase with the original carrier is referred to as the '''in-phase component'''. The other component, which is always 90° (<math>\begin{matrix} \frac{\pi}{2} \end{matrix}</math> radians) "out of phase", is referred to as the '''quadrature''' component.