Glossary

Short definitions of terms used across QAM.net.

8VSB
Eight-level vestigial sideband modulation, used by ATSC 1.0 over-the-air digital TV in the United States.
ATSC 1.0
The digital broadcast TV standard used by US stations since the end of analog broadcasting. About 19.39 Mbit/s per 6 MHz channel.
ATSC 3.0
A newer, IP-based broadcast standard using OFDM, sometimes marketed as NextGen TV. Not receivable on ATSC 1.0 or QAM tuners, and some channels use DRM.
Basic service tier
The lowest level of cable service, which includes local broadcast stations. It once had to be sent unencrypted; all-digital systems may now encrypt it.
CableCARD
A removable security card from the cable operator that lets a compatible retail device decrypt channels you subscribe to. One-way devices with a CableCARD do not get on-demand or interactive features.
CableLabs
The cable industry's research and development organization, which developed CableCARD and certifies devices that use it.
Clear QAM
Digital cable channels sent without encryption, receivable by any QAM tuner.
Coaxial cable (coax)
Shielded cable used for TV and cable signals. Home systems use 75-ohm cable, usually RG-6, with F-connectors.
Constellation
The pattern of points representing every allowed symbol in a QAM signal. 256-QAM has 256 points.
CTA-542
The industry plan that numbers cable channels by frequency, with Standard, HRC and IRC variations.
dBmV
Decibels relative to one millivolt, the usual unit for cable signal power.
DLNA
Digital Living Network Alliance guidelines for sharing media between devices on a home network.
DOCSIS
Data Over Cable Service Interface Specification, the standard for cable modems.
DRM
Digital rights management. Technology that controls how protected content can be played, copied or recorded.
DTA
Digital transport adapter. A small box from a cable operator that tunes its digital channels, including encrypted ones, for a single TV.
Forward error correction (FEC)
Extra data added to a digital signal so the receiver can repair errors without asking for a resend.
HDCP
High-bandwidth Digital Content Protection. Copy protection used on HDMI and other digital video connections.
HDHomeRun
A line of network TV tuners from SiliconDust that receive antenna broadcasts and, on many models, clear QAM cable, and stream them to apps on a home network.
HDMI
High-Definition Multimedia Interface, the common digital audio and video connection. HDMI 2.0 supports up to 18 Gbit/s and HDMI 2.1 up to 48 Gbit/s.
HTPC
Home theater PC. A computer set up for media playback, often with a TV tuner for watching and recording TV.
M-Card
A multi-stream CableCARD that can decrypt several channels at once.
MER
Modulation error ratio. A measure of how closely received symbols match their ideal positions, similar to SNR.
MPEG-2 transport stream
The container that carries digital TV programs, audio and data on cable QAM and ATSC 1.0 channels.
NTSC
The former US analog TV standard, replaced by ATSC for full-power broadcasting.
OFDM
Orthogonal frequency-division multiplexing. Spreads data across many closely spaced carriers. Used by ATSC 3.0.
OTA
Over the air. TV received with an antenna.
Physical channel
The actual 6 MHz frequency slot a signal occupies.
PSIP
Program and System Information Protocol. ATSC data that gives broadcast channels their virtual numbers, names and guide information.
QAM
Quadrature amplitude modulation. Combines two carriers a quarter cycle apart, varying their amplitudes, to send several bits per symbol. Used for US digital cable.
Roku
A brand of streaming players and TVs for internet video services.
SDV
Switched digital video. Sends a channel to a neighborhood only when someone tunes to it. One-way CableCARD devices need a tuning adapter to use it.
SNR
Signal-to-noise ratio. How much stronger the wanted signal is than the noise, in dB. Higher is better.
Splitter
A device that divides a coax signal among several outputs, with loss on each output.
Symbol rate
How many QAM symbols are sent per second. About 5.36 million per second for 256-QAM cable.
Tuning adapter
An operator-supplied device that lets a one-way CableCARD tuner request switched digital video channels.
Virtual channel
The channel number viewers see, such as 7.1, which may differ from the physical channel.
WD TV Live
A Western Digital network media player for streaming internet video and playing local media files on a TV.
Windows Media Center
Microsoft's TV and media software, included in certain editions of Windows Vista and Windows 7 and offered as an add-on for Windows 8. It was not carried forward to Windows 10.
Windows Media Center Extender
A device that showed Windows Media Center on another TV in the home. The Xbox 360 was the best-known example.

Sources

Good to know. Cable lineups, encryption policies, equipment fees and device support are set by each provider and manufacturer and can change. Check with your provider and the sources listed before you buy equipment.
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