DTV Roy Walker WA5YZD
History • In the United States, the National Television System Committee (for which the NTSC standard is named) standardized on 525 lines at 30 fps in 1940, with regular broadcasts starting on July 1, 1941. • NTSC standard was updated to include first a non-compatible 441-line color standard in 1950, which was replaced by a compatible 525-line, 29.97fps color standard approved in 1953 and used to this day. • Current high definition video standards were developed during the course of the advanced television process initiated by the Federal Communications Commission in 1987 at the request of American broadcasters • FCC process, led by the Advanced Television Systems Committee (ATSC) adopted a range of standards from interlaced 1080 line video with a maximum frame rate of 30 fps, and 720 line video, progressively scanned, with a maximum frame rate of 60 fps. The FCC officially adopted the ATSC transmission standard (which included both HD and SD video standards) in 1996, with the first broadcasts on October 28, 1998.
Who is Affected by Change to DTV? • Consumers who receive over-the-air television signals through antennas on television sets that are equipped with analog tuners – and who do not subscribe to cable, satellite or a telephone company television service provider – will be affected by the transition. • At least 19.6 million households receive over-the-air signals exclusively in their homes, and 14.9 million households have secondary over-the-air television sets in their bedrooms or kitchens. Overall, nearly 70 million television sets are at risk of losing their signals on February 17, 2009, if consumers do not make the transition to DTV.
Analog vs. Digital Television • Analog TV – AM vestigial sideband • 6 MHz of bandwidth per channel plus the audio • High power transmitters for coverage – 45 to 75KW Avg. Out • ~300KW to 5MW ERP • Noise and multi-path interference common • Digital TV – 8VSB MPEG-2 Stream • 6 Mhz Channel can produce multiple programs viewable with ATSC tuner (multicasting) • 5 to 7.5 KW Average Transmitter Output Power • Austin Broadcasters - 98 KW to 1.5 MW ERP • Received picture is either perfect or not at all • 5.1 Surround Sound • UHF Channel Spectrum
Why the Change to Digital TV ? • Increase number of programs local broadcasters can provide • Improve the Quality of Picture and Sound • Converting to DTV will also free up parts of the scarce and valuable broadcast airwaves. Those portions of the airwaves can then be used for other important services, such as advanced wireless and public safety services (for example, police, fire departments, and rescue squads, commercial wireless).
Transition to Digital Television • TV stations serving all markets in the United States are airing digital television programming today, most will continue to provide analog programming through February 17, 2009. • Full-power TV stations will cease broadcasting on their current analog channels, and the spectrum they use for analog broadcasting will be reclaimed and put to other uses. • The Commission's digital tuner rule specifies that as of March 1, 2007, all new TVs must include digital tuners.
Converter Box Coupon Program • Between Jan. 1, 2008, and March 31, 2009, all U.S. households will be eligible to request up to two coupons, worth $40 each, to be used toward the purchase of up to two, digital-to-analog converter boxes. • The National Telecommunications and Information Administration (NTIA) has responsibility for administering the coupon program. More information can be found at www.ntia.doc.gov/otiahome/dtv/dtvcoupon.html.
Digital Television Quality Levels • Standard Definition TV (SDTV) - SDTV is the basic level of quality display and resolution for both analog and digital. Transmission of SDTV may be in either the traditional (4:3) or wide screen (16:9) format. • Enhanced Definition TV (EDTV) - EDTV is a step up from Analog Television. EDTV comes in 480p wide screen (16:9) or traditional (4:3) format and provides better picture quality than SDTV, but not as high as HDTV. • High Definition TV (HDTV) - HDTV in wide screen format (16:9) provides the highest resolution and picture quality of all digital broadcast formats. Combined with digitally enhanced sound technology, HDTV sets new standards for sound and picture quality in television. (Note: HDTV and digital TV are not the same thing -- HDTV is one format of digital TV.)
What You Should Know Before You Buy • Compare DTV picture quality. Go to the showroom and look at what you are paying for. Contrast and compare the cost with the picture quality and features within a brand you are considering. Look at the next brand and repeat the comparison. • Image Processor Engines make the difference in picture quality. • Bravia • DLP • Make sure you have all the DTV equipment you need. DTV equipment can be purchased as an integrated set or as separate components. “Integrated” digital televisions have built-in tuners and a monitor to display the programming. If you buy a DTV monitor (without an integrated tuner), you will need a stand-alone tuner, cable set-top box, or satellite set-top box to watch DTV. • HDTV is the Top End Quality of DTV. HDTV requires special equipment, so make sure to ask about HDTV-capable equipment and talk to your cable or satellite provider to verify you have the proper set-top box to view HDTV.
Can You See the Difference? • Is 720p vs. 1080i worth being concerned about? Yes and no. If you're a consumer looking for a new TV, you can happily ignore the 720p vs. 1080i debate because every TV which is described as HDTV or HDTV Ready is required to support both formats. • You should be aware that lots of TVs which support 1080i have fewer than 1080 lines on their display and so scale the 1080 signal down. That's not a huge issue as even scaled down 1080i is far ahead of a regular NTSC picture. It is worth bearing in mind that more expensive HDTVs tend to have better scalers than cheaper ones, and this may be an issue
720p vs. 1080i • 720p signal is made up of 720 horizontal lines. Each frame is displayed in its entirety on-screen for 1/30th of a second. This is know as progressive scan (hence the 'p'). The quality is like watching 30 photographic images a second on TV. • A 1080i signal comprises 1080 horizontal lines but all the lines are not displayed on-screen simultaneously. Instead, they are interlaced (hence the 'i'), i.e. every other lines is displayed for 1/60th of a second and then the alternate lines are displayed for 1/60th of a second. So the frame rate is still 30 frames per second, but each frame is split into two fields, which your brain then puts together subconsciously.
Interlacing • Most of the time interlacing works fine, but for fast moving images such as sports like baseball and hockey it can cause problems which manifest themselves as a 'stepping' effect on-screen. Progressive scan signals don't have this problem and so are better suited to sports. • ESPN puts it like this: 'Progressive scan technology produces better images for the fast moving orientation of sports television. Simply put, with 104 mph fastballs in baseball and 120 mph shots on goal in hockey, the line-by-line basis of progressive scan technology better captures the inherent fast action of sports. For ESPN, progressive scan technology makes perfect sense.'
Screen Technologies • Cathode ray tube (CRT) screens – traditional color television screens updated for digital • Rear Projection TVs – rear projection TVs can create brilliant, wide angle pictures on ever-larger screens (It’s the Mirrors – DLP) • LCD screens - are very thin and produce extremely clear pictures, but are currently expensive and limited in size • Plasma screens - create a bright, clear picture up to enormous sizes while remaining very thin. Cause high rf noise that interfere with HF communications.
Aspect Ratio • 4 X 3: Traditional TV “aspect ratio,” that is, the screen’s width as compared to its height. For example, a “32 inch TV screen” would be 25 ½ inches wide and 19 inches tall. • 16 X 9: “Wide screen” TV ”aspect ratio” that is more like a movie screen than a traditional TV. For example, a “32 inch TV screen” would be 28 inches wide and 16 inches tall. • Most new sets allow you to stretch or zoom the picture to fill the screen. Some do a ‘smart zoom’ that maintains linearity of the picture. Cheaper set let you watch a distorted picture and most people never notice how bad it looks.