QAM tuner
Encyclopedia
QAM stands for quadrature amplitude modulation
, the format by which digital cable channels are encoded and transmitted via cable television
providers. 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 cable-ready digital televisions support both of these standards. Although QAM uses the same 6 MHz bandwidth as ATSC, it carries about twice the data (38.47 Mbp/s @256QAM per 6Mhz channel) due to the lack of error correction; however, this requires a significantly cleaner signal path, such as distribution through hybrid fiber-coax digital cable
.
which is also based on QAM modulation, but uses a DVB-based data format which is incompatible with North American receivers.
Many cable providers offer few or no details about unencrypted QAM channels. It is also common for cable providers to falsely insist that a set top box from the cable company is required to watch all digital cable
channels, including unencrypted channels, even though QAM channels may be distributed via their system. QAM channels may move without notification and some channels may have strange numbering schemes.
digital video
, a QAM tuner is a device present in some digital television
s and similar devices which enables direct reception of digital cable
channels without the use of a set-top box
. An integrated QAM tuner allows the free reception of unscrambled digital programming sent "in the clear" by cable providers, usually local broadcast stations, cable radio
channels, or in the case of providers which have transitioned to do so, Public-access television
cable TV channels. Which channels are scrambled varies greatly from location to location and can change over time; the majority of digital channels are scrambled because the providers consider them to be extra-cost options and not part of the "basic cable" package.
Most US TVs sold after 2006 include a QAM tuner, though some low end and less expensive models still do not include the functionality to tune QAM channels as of 2009. Even though the hardware used to tune ATSC
(over the air digital) and QAM (digital cable) channels is similar, there are still plenty of devices on the market as of 2009 which can tune ATSC
signals but not QAM signals. Some do have the QAM feature but do not describe it in the operator's manual or on-screen menu options, choosing instead to place it under the category of a channel scan and forcing viewers to delete many scrambled channels after a scan. The FCC mandates that all new TVs sold in the US must include an ATSC tuner
, but there are no requirements for QAM tuning functionality. FCC Sec. 76.630 and CFR Title 47, §76.901(a).
Unencrypted QAM tuners are available for computers and many software DVR options exist to work in conjunction with QAM, namely Elgato's EyeTV, SageTV
(native support of high definition QAM), MythTV
(also native support for HD QAM), and Snapstream's Beyond TV, Microsoft's Windows Media Center
software supports QAM on supported tuners (on Vista with the TV Pack update or with Windows 7).
Quadrature amplitude modulation
Quadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
, the format by which digital cable channels are encoded and transmitted via cable television
Cable television
Cable television is a system of providing television programs to consumers via radio frequency signals transmitted to televisions through coaxial cables or digital light pulses through fixed optical fibers located on the subscriber's property, much like the over-the-air method used in traditional...
providers. QAM tuners can be likened to the cable equivalent of an ATSC tuner
ATSC tuner
An ATSC tuner, often called an ATSC receiver or HDTV tuner is a type of television tuner that allows reception of digital television television channels transmitted by television stations in North America, parts of Central America and South Korea that use ATSC standards...
which is required to receive over-the-air
Terrestrial television
Terrestrial television is a mode of television broadcasting which does not involve satellite transmission or cables — typically using radio waves through transmitting and receiving antennas or television antenna aerials...
(OTA) digital channels broadcast by local television stations; many new cable-ready digital televisions support both of these standards. Although QAM uses the same 6 MHz bandwidth as ATSC, it carries about twice the data (38.47 Mbp/s @256QAM per 6Mhz channel) due to the lack of error correction; however, this requires a significantly cleaner signal path, such as distribution through hybrid fiber-coax digital cable
Digital cable
Digital cable is a generic term for any type of cable television distribution using digital video compression or distribution. The technology was originally developed by Motorola.-Background:...
.
Technical details
QAM is only a modulation format and does not specify the format of the digital data being carried. However, when used in the context of digital cable television, the format of the data transmitted using this modulation is based on ATSC. This is in contrast to DVB-CDVB-C
DVB-C stands for Digital Video Broadcasting - Cable and it is the DVB European consortium standard for the broadcast transmission of digital television over cable...
which is also based on QAM modulation, but uses a DVB-based data format which is incompatible with North American receivers.
Many cable providers offer few or no details about unencrypted QAM channels. It is also common for cable providers to falsely insist that a set top box from the cable company is required to watch all digital cable
Digital cable
Digital cable is a generic term for any type of cable television distribution using digital video compression or distribution. The technology was originally developed by Motorola.-Background:...
channels, including unencrypted channels, even though QAM channels may be distributed via their system. QAM channels may move without notification and some channels may have strange numbering schemes.
QAM tuners
In North AmericanNorth American
North American generally refers to an entity, people, group, or attribute of North America, especially of the United States and Canada together.-Culture:*North American English, a collective term used to describe American English and Canadian English...
digital video
Digital video
Digital video is a type of digital recording system that works by using a digital rather than an analog video signal.The terms camera, video camera, and camcorder are used interchangeably in this article.- History :...
, a QAM tuner is a device present in some digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
s and similar devices which enables direct reception of digital cable
Digital cable
Digital cable is a generic term for any type of cable television distribution using digital video compression or distribution. The technology was originally developed by Motorola.-Background:...
channels without the use of a set-top box
Set-top box
A set-top box or set-top unit is an information appliance device that generally contains a tuner and connects to a television set and an external source of signal, turning the signal into content which is then displayed on the television screen or other display device.-History:Before the...
. An integrated QAM tuner allows the free reception of unscrambled digital programming sent "in the clear" by cable providers, usually local broadcast stations, cable radio
Cable radio
Cable radio or cable FM is a concept similar to that of cable television, bringing radio signals into homes and businesses via coaxial cable. It is generally used as cable TV was in its early days when it was "community antenna television", to enhance the quality of terrestrial radio signals that...
channels, or in the case of providers which have transitioned to do so, Public-access television
Public-access television
Public-access television is a form of non-commercial mass media where ordinary people can create content television programming which is cablecast through cable TV specialty channels...
cable TV channels. Which channels are scrambled varies greatly from location to location and can change over time; the majority of digital channels are scrambled because the providers consider them to be extra-cost options and not part of the "basic cable" package.
Most US TVs sold after 2006 include a QAM tuner, though some low end and less expensive models still do not include the functionality to tune QAM channels as of 2009. Even though the hardware used to tune ATSC
ATSC
ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....
(over the air digital) and QAM (digital cable) channels is similar, there are still plenty of devices on the market as of 2009 which can tune ATSC
ATSC
ATSC standards are a set of standards developed by the Advanced Television Systems Committee for digital television transmission over terrestrial, cable, and satellite networks....
signals but not QAM signals. Some do have the QAM feature but do not describe it in the operator's manual or on-screen menu options, choosing instead to place it under the category of a channel scan and forcing viewers to delete many scrambled channels after a scan. The FCC mandates that all new TVs sold in the US must include an ATSC tuner
ATSC tuner
An ATSC tuner, often called an ATSC receiver or HDTV tuner is a type of television tuner that allows reception of digital television television channels transmitted by television stations in North America, parts of Central America and South Korea that use ATSC standards...
, but there are no requirements for QAM tuning functionality. FCC Sec. 76.630 and CFR Title 47, §76.901(a).
Unencrypted QAM tuners are available for computers and many software DVR options exist to work in conjunction with QAM, namely Elgato's EyeTV, SageTV
SageTV
SageTV Media Center was a proprietary, commercial DVR and HTPC software for Mac OS X, Windows and Linux. It requires that the host computer have a hardware based TV tuner card. The SageTV software has an integrated Electronic Programming Guide that is updated via the Internet...
(native support of high definition QAM), MythTV
MythTV
MythTV is a free and open source home entertainment application with a simplified "10-foot user interface" design for the living-room TV, and turns a computer with the necessary hardware into a network streaming digital video recorder, a digital multimedia home entertainment system, or home theater...
(also native support for HD QAM), and Snapstream's Beyond TV, Microsoft's Windows Media Center
Windows Media Center
Windows Media Center is a digital video recorder and media player developed by Microsoft. It is an application that allows users to view and record live television, as well as organize and play music and videos...
software supports QAM on supported tuners (on Vista with the TV Pack update or with Windows 7).