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Quadrature Amplitude Modulation
built 633 days ago
Quadrature Amplitude Modulation (QAM) is the foundation for the delivery of all of cable's digital services. One of the pioneers in headend QAM technology, Vecima Networks Inc. , crossed a major milestone in the category at the end of July.
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QAM (Quadrature Amplitude Modulation) is the well-known technique used in dial-up modem standards such as v.32 and v.34. It works, but it is rather complex, and ... the AuDSL receiver currently has some trouble keeping up with an incoming QAM data stream at 48 kHz.
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Quadrature Amplitude Modulation (QAM) uses many different phases known as states: 16, 32, 64, and 256. Each state is defined by a specific amplitude and phase. This means the generation and detection of symbols is more complex than a simple phase or amplitude device. Each time the number of states per symbol is increased the total data and bandwidth increases. The modulation schemes shown occupy the same bandwidth (after filtering), but have varying efficiencies (in theory at least).
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Quadrature Amplitude Modulation refers to QPSK with Amplitude Modulation. Basically, it is a mix of phase modulation and amplitude modulation. QAM phase modulates the carrier and ... modulates the amplitude of the carrier.
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Low frequency commercial broadcast stations in the "A.M band" use amplitude modulation. Most C.B. or citizens band radios use it too. It's a simple, robust method to form a radio wave but it suffers from static and high battery power requirements, reasons enough that few personal communications devices use it.
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QAM stands for "quadrature amplitude modulation," the format by which digital cable channels are encoded and transmitted via cable. QAM tuners can be likened to the cable equivalent of an ATSC tuner which is required to receive over-the-air (OTA) digital channels broadcast by local television stations. Many new digital televisions contain both and are labeled "with ATSC/QAM Tuner". Unlike the case with ATSC tuners there is no FCC requirement that QAM tuners be included in new television sets, but the same hardware is used for both and QAM is commonly included.
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Quadrature Amplitude Modulation