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Analog QAM: PAL color bar signal on a vectorscope. In a QAM signal, one carrier lags the other by 90°, and its amplitude modulation is customarily referred to as the in-phase component, denoted by I(t). The other modulating function is the quadrature component, Q(t). So the composite waveform is mathematically modeled as:
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The phase modulation (φ(t), not shown) is a non-linearly increasing function from 0 to π /2 over the interval 0 < t < 16. The two amplitude-modulated components are known as the in-phase component (I, thin blue, decreasing) and the quadrature component (Q, thin red, increasing).
Carrierless amplitude phase modulation (CAP) is a variant of quadrature amplitude modulation (QAM). Instead of modulating the amplitude of two carrier waves, CAP generates a QAM signal by combining two PAM signals filtered through two filters designed so that their impulse responses form a Hilbert pair .
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave.In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to that of the message signal, such as an audio signal.
QAM is a parallel form of modulation that transmits two independent signals at a symbol rate that is near, but less than, the bandwidth of 6 MHz. VSB modulation, on the other hand, is a serial form of modulation that transmits one independent signal at a symbol rate that is near, but less than, twice the bandwidth of 6 MHz.
This is the standard positive logic signal format used in digital circuits. forces a high level forces a low level NRZ–M: Non-return-to-zero mark forces a transition does nothing (keeps sending the previous level) NRZ–S: Non-return-to-zero space does nothing (keeps sending the previous level) forces a transition RZ: Return to zero
Single-sideband modulation with full carrier (e.g. as used by CHU) J: Single-sideband with suppressed carrier (e.g. Shortwave utility and amateur stations) K: Pulse-amplitude modulation: L: Pulse-width modulation (e.g. as used by WWVB) M: Pulse-position modulation: N: Unmodulated carrier (steady, single-frequency signal) P: Sequence of pulses ...