Off-air, Cable, Satellite,
Digital TV decodes five
voltages from digitally encoded component
video* to create a television
*refer to previous page
4. Horizontal Sync
5. Vertical Sync
(Horizontal and vertical sync
are the start and finish points of each video frame.)
A digital TV decoder processor converts component video to
red, green, blue sub-pixels while progressively building each
picture frame line by line. OLED, IOLED, Micro LED, LCD,
and plasma processors hold the progressive-lines of data until
they have a complete frame. They then flash the entire
video frame to the television screen. DLP projectors
build each frame progressively line by line on the
Digital TV Broadcast
Digital broadcasted - local off-air & satellite -
component video does not fit within allocated data bandwidth
and storage as is. Broadcasters reduce the data with
MPEG video compression. Off-air ATSC TV also employs
ATSC 8VSB codec, and cable TV providers use QAM codec to
accommodate MPEG audio and video compression.
Notes: codec is an acronym for
MPEG Video Compression
MPEG video compression is a
cycle of incomplete video frames inserted between complete
uncompressed frames. MPEG compression eliminates
redundant video data. It is somewhat similar to
animation. Unchanging elements of moving scenes, such
as the static background of a blue sky, are held and
repeated frame after frame. Changing data of motion
passes without interruption.
The data reduction, plus the number of incomplete frames
placed between complete frames, is determined by the version
of MPEG employed: MPEG2, MPEG4, MPEG HEVC, MPEG VCC,
MPEG-DASH. Each succeeding version increases the
amount of data reduction.
- ATSC HDTV off-air broadcast employs MPEG2.
- Satellite broadcast uses MPEG4.
- ATSC 3.0 Next GenTV/UltraHD uses MPEG HEVC.
- MPEG VCC will replace HEVC in the near future.
- Internet HTTP live streaming
(HLS) engages MPEG-DASH
The final stage of an off-air digital ATSC broadcast also
employs ATSC 8VSB RF modulation. 8VSB divides MPEG
video and audio into interleaving packets of data called
PIDS. It is a continuing cycle of a video PID followed
by an audio PID. An ATSC 8VSB television tuner decoder
The digital cable TV provider's final stage utilizes QAM
modulation. QAM is similar to 8VSB interweaving of the
video and audio data. As an 8VSB, a QAM cable
television tuner decodes and restores order.
Satellite TV Distribution
An umbrella of communication
satellites distributes TV programming to local broadcasters,
cable companies, and 'small dish' satellite providers.
Several dozen communication satellites hover in
geosynchronous orbit more than 22,000 miles above the
equator of the earth. They receive and redirect
programming to your TV provider's 'tree farm' of large dish
- Local broadcasters
re-transmit programming via a broadcast tower to indoor and
- Cable TV providers redistribute programming via cable
wired directly to residences.
- Small dish satellite providers up-link their programming
to proprietary satellites that bounce the programming back
to small rooftop dish antennas.
Dish antenna, why?
A local TV broadcaster may engage thousands of watts of
broadcast power. As a result, the local TV receiving
antenna can be as little as a "rabbit ear" antenna sitting
on the TV. In contrast, satellites are limited to only
five to fifteen watts of down-link broadcast power.
Also, they broadcast at radio frequencies that are
impractical for a satellite receiving tuner to manage.
Consequently, the satellite receiving system needs a
Assistance comes in the form of a satellite dish with a
low-noise-block-feed-horn (LNBF) mounted in front of the
satellite dish. The satellite dish magnifies incoming
signal hundreds of fold by reflecting and focusing the
energy at a mounting arm that holds the antenna element
located in the LNBF. The LNBF amplifies the signal
still further and shifts the incoming-signal from the 12GHz
region to the more manageable neighborhood of 950 MHz to
1450 MHz. Small dish operators also employ MPPEG4
digital compression to squeeze hundreds of channels within
their bandwidth. The combination of the dish antenna,
the LNBF, and MPEG4 produces a signal that a satellite
receiver can handle and display on a TV.
Expanding Internet bandwidth has allowed IPTV (Internet
protocol television) to become a significant means of TV
program distribution. IPTV is accessed via an ISP
(Internet service provider) --- cable company, telephone DSL
or cellular provider, satellite, or soon NextGenTV
The program content is delivered over a managed or unmanaged
Internet network. A managed network delivers content
via an MVDP (multi-channel program distributor) program
package. An unmanaged network ... Netflix, Amazon,
Hulu, etc. ... distributes programming direct to
This is known as OTT (over the top).
Digital TV Result
horizontal sync, and vertical sync data, derived from
television camera CCD sensors, are converted to component
video. A digital broadcast compresses the component video
within allocated data storage. A digital TV restores
the component video data to RGBHV to recreate the original
sequence of pixel framed images on the TV screen