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QAM (television)

From Wikipedia, the free encyclopedia

QAM is a digital television standard using quadrature amplitude modulation. It is the format by which digital cable channels are encoded and transmitted via cable television providers. 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 televisions support both of these standards. QAM uses the same 6 MHz bandwidth as ATSC, using a standard known as ITU-T Recommendation J.83 Annex B ("J.83b").[1][2]

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  • ✪ KWorld SA290-Q DVI External ATSC/QAM TVBox
  • ✪ Watch Live Over the Air HD TV with MyGica HD TV Tuner and ATV 1810


Do you have an LCD panel display that doesn't have a tuner built into it? Maybe you have a cramped space and you'd like to be able to use one display for your computer and your television but maybe you don't have a tuner built in to your computer or you don't want to buy a tuner card. This is a device that is actually going to be able to make your life a heck of a lot easier. It is the external ATSC QAM TV Box from KWorld. Now, if you don't what QAM or ATSC are, QAM and ATSC are the digital television signals that you can receive. ATSC is over the air. That's the one that you get with an antenna. And this box does come with an antenna in the box. And QAM are the unencrypted digital signals that you get from your cable provider. And those will allow you to get high definition television without paying for it. Like, you don't have to pay for the cable system's HD package or for the satellite HD package. You get free over the air, your local channels, and also over your digital cable your local channels as well. And this will make it really, really easy to use your computer in conjunction with your television. Let me show you around this thing and show you what we have going on. Take a look at this. We have two different versions of this, okay? One of them, and that's this one, is the DVI version. And the DVI version is going to be for computers that have DVI outputs and TVs that have DVI inputs. Of course, you can, with adaptors, make this work more to your liking. It also includes, right here you're going to see your audio IO, Your antenna input is right here. And your power input is right here. This is where you plug in the antenna or your cable box. On the side are your outputs. It does have component outputs on the side, in case you have component inputs on your television set. And audio outputs here to run to either your stereo system or to your TV. On the front it has a USB port, which can be hooked up to your computer so you can actually turn your TV into a digital photo frame. You'll be able to push all of your pictures to this device for display on your television, if you like. And then, on the top you're gonna find a few more controls. These are all the controls for navigating the channels. You can channel up, volume up, down and navigating the menu system in this device. So, this is going to make it easy. One touch access between your TV and your computer now. So, if you don't have a digital tuner this is perfect because it's going to make sure you can receive those QAM and those ATSC television programming signals without having to get a separate box. Without a separate converter box, and especially if you're one of those people that bought a television that didn't have a tuner built in. One of those high definition displays that didn't have a tuner. This is perfect because it's got a great digital tuner built right in. This one right here, this is the VGA version. That's the only difference between the two. One is VGA, one is HDMI so if you have a system with only VGA, this is going to be perfect. And then you have literally one touch access between it. So, if you're watching... if you're watching TV with this remote control right here you can very, very quickly switch between TV and your computer right there on your display without having to go through any fuss at all. And it's going to take care of it for you automatically. So, you can go from watching TV to using your computer, back to watching TV just by using this little box right here. And it does have a very, very high quality tuner built in. If you haven't... If you haven't sort of been turned on to the world of digital programming, like, your local channels actually have more stations now than you can get over the air, and a lot of times even through your cable system. So you can check... out those new channels, local weather channels, local news channels, they all have them. And it's gonna make it really, really easy for you to use one display for, sort of, multiple uses in your home. So, if your cramped for space or you just want to keep everything in one spot, this is perfect and it's gonna help you out. It's the KWorld ATSC QAM TV Box. A perfect edition to your home entertainment, computer, TV system. For more information on the KWorld ATSC QAM TV Box go to any of the retailers listed here: If you want the DVI version type in: O38-1468. If you want the VGA version type in: O38-1466. For ComputerTV, I'm Bauer. (C) 2008 SYX Services, Inc. All Rights Reserved Channel: TigerDirectBlog


Technical details

QAM is a modulation format and does not specify the format of the digital data being carried. However, when used in the context of US digital cable television, the format of the data transmitted using this modulation is based on ITU-T J.83 Annex B ("J.83b"). This is in contrast to DVB-C which is also based on QAM modulation, but uses a DVB-based data format which is incompatible with North American receivers.

QAM is a parallel form of modulation that transmits 2 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 1 independent signal at a symbol rate that is near, but less than, twice the bandwidth of 6 MHz. The two can be related by the fact that a VSB signal can be shown to be a form of offset QAM modulation where one of the 2 independent signals is delayed by 1/2 a symbol duration. The 8-VSB modulation in the ATSC system corresponds with the 64-QAM modulation of J.83b. In a 6 MHz channel, the data rate is at most 36 Mbit/s (for 64-QAM or 8-VSB); the 8-VSB ATSC achieves a data rate of 19.3926 Mbit/s while the 64-QAM J.83b achieves a data rate of 26.970 Mbit/s. While both systems use concatenated trellis/RS coding, the differences in symbol rate and FEC redundancy account for the differences in rate. In addition, J.83b defines a popular 256-QAM mode that achieves a data rate of 38.8 Mbit/s.

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.

QAM tuners

In North American digital video, a QAM tuner is a device present in some digital televisions and similar devices which enables direct reception of digital cable channels without the use of a set-top box.[3] 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.[4] 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.[5] However, as of 2017, there is a trend towards large screen flat panel displays that don't include any kind of tuner, often referred to as "Tuner-Free TVs" or “Tunerless Displays.”[6][7]


ClearQAM (unencrypted) lets cable subscribers avoid industry-provided set-top boxes (necessary for decoding encrypted basic cable signals).[8]

Cable operators with all-digital systems may encrypt their services.[9]


  1. ^ "ITU-T Recommendation database". ITU.
  2. ^ "HD 101: What is ATSC, PSIP, QAM, and 8-VSB?".
  3. ^ Terms & Definitions,
  4. ^ Video Noise Does Your Next Video Display Need to Have a QAM Tuner?, February 2004
  5. ^ 47 C.F.R. 76.630 and 47 C.F.R. 76.901(a)
  6. ^ Tuner Free,
  7. ^ Costco Tuner Free,
  8. ^
  9. ^ "Commission Relaxes The Cable Encryption Prohibition". 12 December 2015.
This page was last edited on 2 December 2018, at 13:12
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