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QAM is used in a variety of communications systems such as Dial-up modems and WiFi. In cable systems, a QAM tuner is linked to the cable in a manner that is equivalent to an ATSC tuner which is required to receive over-the-air (OTA) digital channels broadcast by local television stations when attached to an antenna. Most new HDTV digital ...
Broadcast In-band (IB) Tuner. Once the signal arrives from the physical transmission media, the IB tuner will isolate a physical from a multiplex of channels and convert to baseband. The term baseband is used to describe a single channel or digital signal, extracted from broadband signal which is a stream of multiple channels. Out Of Band (OOB ...
A RF/antenna output, if present on a converter box, is usually just a passthrough ("LOOP OUT" which does not provide the box's output signal, but only provides the raw antenna input signal to watch analog channels via a TV set's tuner if analog broadcasts have not ended yet or to connect another capable device to the same antenna feed) because ...
An ATSC (Advanced Television Systems Committee) tuner, often called an ATSC receiver or HDTV tuner, is a type of television tuner that allows reception of digital television (DTV) television channels that use ATSC standards, as transmitted by television stations in North America (including parts of Central America) and South Korea.
Within a distance of 35 to 40 miles from the broadcast stations, it is possible that a simple antenna (such as "rabbit ears") may be adequate to receive a DTV broadcast signal OTA—at least some of the time for some of the channels. Any television equipped with an ATSC tuner may display DTV broadcasts properly.
A separate tuner is required to receive HD satellite broadcasts. Cable television companies in the U.S. generally prefer to use 256-QAM to transmit HDTV. Many of the newer HDTVs with integrated digital tuners include support for decoding 256-QAM in addition to 8VSB for OTA digital. Cable television companies started carrying HDTV in 2003.
ATSC and DVB-T specify the modulation used for over-the-air digital television; by comparison, QAM is the modulation method used for cable. The specifications for a cable-ready television, then, might state that it supports 8VSB (for broadcast TV) and QAM (for cable TV). 8VSB is an 8-level vestigial sideband modulation.
QAM Mapper: the bit sequence is mapped into a base-band digital sequence of complex symbols. There are 5 allowed modulation modes: 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM. Base-band shaping: the QAM signal is filtered with a raised-cosine shaped filter, in order to remove mutual signal interference at the receiving side.