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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.
Demodulation is the process of extracting the original information-bearing signal from a carrier wave. A demodulator is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content from the modulated carrier wave. [1] There are many types of modulation, and there are many types of ...
In the case of AM, φ(t) (the phase component of the signal) is constant and can be ignored. In AM, the carrier frequency is also constant. Thus, all the information in the AM signal is in R(t). R(t) is called the envelope of the signal. Hence an AM signal is given by the function
When all three terms above are multiplied by an optional amplitude function, A(t) > 0, the left-hand side of the equality is known as the amplitude/phase form, and the right-hand side is the quadrature-carrier or IQ form.
Trellis coded modulation (TCM) is a modulation scheme that transmits information with high efficiency over band-limited channels such as telephone lines. Gottfried Ungerboeck invented trellis modulation while working for IBM in the 1970s, and first described it in a conference paper in 1976.
Losev was the first to analyze this device, investigate the source of the light, propose a theory of how it worked, and envision practical applications. [63] He published his experiments in 1927 in a Russian journal, [ 65 ] and the 16 papers he published on LEDs between 1924 and 1930 constitute a comprehensive study of this device.
The demodulator's bandwidth depends on the Q factor of the resonant circuit; the phase response of the secondary (and therefore, the voltage response of the circuit) to is an S-curve. Foster–Seeley discriminators are sensitive to both frequency and amplitude variations, unlike some detectors.
The Capture effect therefore enables frequency reuse of the same frequency by imposing a sufficient distance separation, e.g. used in AM communication in the AM(R)S (Aeronautical mobile (R) service), or between FM-BC transmitter for the capture take effect.