This chapter is from the book
This chapter is from the book
This chapter is from the book
Broadcast Technology Development
All of the traditional television and radio services that we have grown up with use analog transmission to provide a signal that can be converted to audio or video. We've already covered the problems inherent with analog signal transmission, so it is just a matter of time before broadcast audio and video signals become digitally transmitted.
There have been some recent attempts to broadcast digital audio via satellite, providing a CD-quality sound to your home or car. High definition television (HDTV) is also making inroads with limited availability. HDTV provides movie-quality video and CD-quality audio right in your living room.
It will be some time before these new broadcast technologies mature enough to replace traditional analog television and radio. Recent attempts by the Federal Communications Commission (FCC) to make HDTV a standard system by the year 2008 are met by much skepticism.
Digital Radio
Satellite radio has been talked about since 1992 when the Federal Communications Commission (FCC) allocated 2.3 GHz for Digital Audio Radio Service (DARS), also known as satellite radio. Very soon, three companies will begin broadcasting music from space via satellites. The three companies are:
Sirius Satellite Radio—Digital radio broadcast within the United States.
XM Satellite Radio—Digital radio broadcast within the United States.
Worldspace—Digital radio broadcast within South America, Asia, and Africa.
The concepts for digital satellite radio include an automotive receiver as well as a table receiver. An uplink earth station facility will transmit digital CD-quality music, talk, and news to the satellite 22,300 miles above the earth for reception across the entire United States. Because of the wide footprint of satellite reception, you will be able to drive across the entire country without having to change your radio dial. There will be no static because of the digital signals transmitted. The three companies developing this technology are promising over 100 channels (each) of uninterrupted CD-quality stereo sound with few or no commercials.
Agreements with traditional broadcasters are also being formed to provide services. BBC, CNN, and the Weather Channel are some examples of traditional radio network broadcasting services that will also broadcast via the satellite (Figure 10.3).
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Figure 10.3 Satellite radio.
For approximately $10 a month, subscribers will decode an encrypted signal that will allow them to receive digital satellite radio. Many car manufacturers have formed agreements with satellite radio providers for installation in their future models. Radio manufacturers including Sony, Sharp, and Pioneer have also begun development on receivers for both auto and home use.
Digital satellite radio has a bright future indeed.
Timetable of Historic High Definition Television Events
| 1987 |
The FCC indicates that HDTV standards should be compatible with SDTV service. |
| 1988 | The FCC receives 23 different proposals for potential HDTV service. |
| 1990 | The FCC requests simultaneous broadcasting of HDTV and SDTV services. |
| 1993 | The FCC narrows down the ensuing technology to four contenders and creates a "grand alliance" among all four of them. |
| 1995 | The HDTV standard is tested and adopted. |
High Definition Television
High definition television (HDTV) has approximately twice the horizontal and vertical resolution of current 525-line analog television broadcast systems. The problem with HDTV isn't the technology itself but its compatibility with existing standards. In 1957, compatibility was a major issue when color television was first introduced. The standard definition television (SDTV) signal needed to be compatible with both black and white and color receivers.
Compatibility between SDTV and HDTV is much more complex than the black and white versus color television issue. First of all, there is the bandwidth; HDTV requires 20 MHz, whereas SDTV requires 6 MHz. Second, SDTV has a 4/3 aspect ratio (almost square), whereas HDTV has a 16/9 wide (letterbox) format. Third, SDTV uses analog signal transmission, and HDTV uses digital signal transmission. Fourth, HDTV lines are scanned sequentially and not interlaced as in SDTV. Because of these issues, HDTV is simultaneously broadcast along with an SDTV signal (on a different set of frequencies).
The design goal of HDTV is to provide more compatibility with computers rather than with the existing SDTV format. HDTV offers 60 frames a second, which is twice the resolution of SDTV. This feature adds to the smooth motion and signal clarity with a movielike quality. Let's also not forget the 5.1 channel AC3 digital sound broadcast included with the video signal.
HDTV is available through digital broadcast satellite (DBS) and from cable TV providers. You must check with either your satellite company or cable provider to determine HDTV compatibility.
Remember our earlier discussions regarding analog and digital transmission? Analog signal transmission is subject to noise and distortion whereas digital signal transmission is relatively noise free and distortion free. For example, an HDTV broadcast originating from Manhattan will look as clear in Jersey City, New Jersey (eastern New Jersey) as in Phillipsburg, New Jersey (western New Jersey). An SDTV broadcast cannot be received well (if at all) in Phillipsburg, New Jersey. Digital signals are either on or off, so unguided transmission noise will not affect the HDTV signal. An extremely weak HDTV digital signal will not work at all.
Original plans, mandated by the FCC, would require SDTV shutdown by the year 2008. Whether this will happen is based largely upon how rapidly HDTV becomes entrenched in our households. HDTV broadcasts are available from cable and satellite companies. As of this writing, HDTV receivers still remain fairly expensive and, when available, are almost always sold with rear projection television systems.
Check out HDTV at your local audio or video electronics store. You don't need any knowledge in telecommunications transmission systems to see the visible difference between SDTV and HDTV.