Multi-Channel Digital Television

See on Scoop.itKH6JRM’s Amateur Radio Blog



HDTV signals at 60 Hz require around 19 megabits per second to carry all the necessary information to recreate the video. This 19 Mbits is achieved by compressing the pure signal through a special high definition subset of the MPEG-2 video compression scheme and Dolby‘s AC-3 audio compression scheme. In fact, the uncompressed HDTV data is about sixty times larger than the compressed 19 Mbit signal!


A 19 Mbit HDTV signal fits into a standard 6 MHz frequency band used for uncompressed, analog NTSC television signals. Each HDTV broadcaster has been allotted a frequency band for their HDTV broadcasts. However, using digital compression technology, that same bandwidth can carry a single high definition signal or multiple standard resolution signals. Since a 640 by 480 resolution standard definition digital television signal is not as large as a 1,920 by 1,080 resolution signal, several of the smaller signals can supplant the single high definition one.


Imagine a one-lane road through a small neighborhood. The street can only fit one large, wide-load truck. However, it can fit two small family sedans, and it can accommodate six motorcycles. The road remains the same size so it can be used for a variety of purposes from single extra-large trucks to multiple motorcycles. The same is true of a digital television channel. It can accommodate one “extra-large” HDTV signal (1,920 x 1,080 at 60 Hz interlaced or 1,280 x 720 at 60 Hz progressive) or up to five or six standard definition 640 by 480 signals. Thus, digital television allows broadcasters to provide multiple channels of standard quality programming (similar to the quality of a DVD) or a single channel of ultra-pure, ultra-high quality high definition programming.


Presently, the major networks have voiced their support of high definition programming for prime time shows. However, any television station broadcasting in high definition may also break down their high definition channel to present multiple standard channels. In theory, a television station could broadcast five different news shows in standard resolution during the evening news hour tailoring one to each area of a city or to each county in the broadcast area for instance. True HDTV is where digital television really shines, but DTV also lends flexibility to broadcasters that has never been available before.

Russ Roberts‘s insight:

Thanks to reporter David Hall for this excellent description of multi-channel digital television.  Unlike uncompressed analog NTSC television signals, digital television can accommodate up to five different shows in standard resolution or one true HDTV signal.  Digital Television “lends flexibility to broadcasters that has never been available before.”  Impressive.  Now, if only we can get quality programming to fill in those available spaces.  Aloha de Russ (KH6JRM).

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