This material was developed with funding from the
National Science Foundation under Grant # DUE 1601612
Modulation is a process of mixing a signal with a sinusoid to produce a new signal. This new signal, conceivably, will have certain benefits over an un-modulated signal. Mixing of low frequency signal with high frequency carrier signal is called modulation.
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Frequency Modulation (FM)
Amplitude Modulation (AM)
Digital signal modulation is the process of mixing a digital (discrete) signal with an analog carrier signal. The analog signal can then carry the digital information to analog receivers. Digital signal modulation is produced by a discrete signal being used to modify the amplitude, frequesncy or phase of the original analog signal.
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The amplitude of a signal is the strength of the signal. There are various definitions of amplitude.
Root Mean Square Amplitude (RMS)
The RMS amplitude is used especially in electrical engineering: the RMS is defined as the square root of the mean over time of the square of the vertical distance of the graph from the rest state.
Peak-to-Peak Amplitude is the change between peaks (highest amplitude value) and trough (lowest amplitude value, which can be negative).
Peak amplitude is used to measure the signal rise above and below a reference value.
Frequency is the number of occurrences of a repeating signal pattern per unit of time. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a persons heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second (60 seconds divided by 120 beats).
In electronic signaling, phase is a definition of the position of a point in time (instant) on a waveform cycle. A complete cycle is defined as 360 degrees of phase as shown in Illustration A below. Phase can also be an expression of relative displacement between or among waves having the same frequency . Phase difference, also called phase angle , in degrees is conventionally defined as a number greater than -180, and less than or equal to +180. Leading phase refers to a wave that occurs "ahead" of another wave of the same frequency. Lagging phase refers to a wave that occurs "behind" another wave of the same frequency. When two signals differ in phase by -90 or +90 degrees, they are said to be in phase quadrature . When two waves differ in phase by 180 degrees (-180 is technically the same as +180), the waves are said to be in phase opposition . Illustration B shows two waves that are in phase quadrature. The wave depicted by the dashed line leads the wave represented by the solid line by 90 degrees.