Please report any suggestions or errors of fact that you find to the author at email@example.com. Author: Ken Nist, MSEE (ret), KQ6QV
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This web site was created in 2003 to help nontechnical people cope with the digital transition. The transition is now history, and with it much of the reason for this site.
The unique parts of the web site have been left up. The site will continue to track new developments in over-the-air TV antennas.
To find information about a particular product, just Google the model number. There is a useful collection of product reviews at eCoustics.com. (Product reviews of HDTVs by amateurs are not reliable.)
If, after all the study, you still need some questions answered, then online forums are available. The Audio Visual Science Forum, AVSforum, is the oldest, largest, and most active forum devoted to TV and home theater. However this forum is not intended for amateurs, and HDTV newcomers often find its size and structure a bit imposing. The HDTV Magazine forum is simpler and friendlier. A number of experts hang out on both of these forums. Both have a huge wealth of answered questions. It is unlikely that your question has not been asked before, so you should start out with a search by keywords. Both forums require you to invent a screen name and password in order to post a question or answer, but there are no fees or other hassles.
Glossary: (optional reading)
AC-3 (see Dolby Digital 5.1)
Aspect ratio The ratio of screen width to screen height. For TVs it is either 4:3 (1.33:1) or 16:9 (1.78:1). Theater film uses many different aspect ratios, some as high as 2.5:1.
Blocking, Macro-blocking An over-compression of the image that makes the block edges slightly noticeable. This ¡°checkerboarding¡± often covers the whole screen. It is subtle and usually momentary. Some causes are:
1. Software bugs in the MPEG encoder.
2. The network allocating too little bandwidth to the broadcast.
3. The picture being portrayed is just changing too fast.
Blocks, Macro-blocks MPEG-2 divides the screen into small square regions called blocks and uses a mathematical process to compress the data for each block. Macro-blocks are a small group of blocks. See What exactly is ATSC? .
Bob and Weave Two processes for de-interlacing (converting interlaced video into progressive scan). Weave refers to combining successive fields. Also called interfield, this method preserves the original resolution. Bob refers to up-converting a field into a frame, in effect creating new lines by averaging the adjacent lines above and below. Also called intrafield, this method causes a loss of resolution but never causes motion artifacts. See also Motion Adaptive De-interlacing.
Breakup Also called dropouts, block errors, or macro-block errors, these are gross errors in the picture caused by reception errors that result from interference and signal noise. Both audio and video are affected, with video distortions about five times as prevalent as audio dropouts. This ratio never seems to change. If the ratio is anything else then the cause is a network problem, not a reception error. The shortest-lasting breakups just cause a few macro-blocks to be obviously wrong, while more severe errors cause major parts of the screen to be left un-updated for a time, and possibly the whole image to freeze. Green shows up a lot.
Cable card The Cable Card is the mechanism the industry has adopted to prevent the piracy of cable services. Nearly all cable channels are encrypted, the main exception being local stations. The cable card contains the keys to unlock encryption.
If you want the simplicity that comes with the cable receiver being integrated with the TV then you should buy a TV with a cable card slot. However if you like TiVo then you would instead get a DVR, which will have its own cable card slot. The cable card is supplied by the cable company. The card is a special purpose PCMCIA card (like used in many computers).
The present cable card system for DTV is called CableCARD 1.0. There are two types of cards: SCards (single stream) and MCards (multiple stream). MCards are used when a DVR can record multiple programs simultaneously.
CableCARD 1.0 lacks two-way features and cannot be used for ordering pay-per-view, interactive guide, and other two-way features. Millions of cable card slots in TVs already sold are going unused. Reasons include: 1. The viewer uses satellite. 2. The viewer doesn¡¯t want subscription channels. 3. The user wants two-way features and so has to use a cable box. Some TV makers are reducing the number of sets they sell having cable card slots, but they say they will increase the number when two-way is possible. Two-way is not available because the technical standard is not yet established. (The CEA and NCTA are fighting each other and the FCC has been a timid referee.) Present DTV systems with CableCARD 1.0 are labeled DCR (Digital Cable Ready). Future DTVs will likely be labeled iDCR (Interactive Digital Cable Ready).
Warning: The term CableCARD 2.0 has two conflicting definitions. 1. CableCARD 2.0 was first used to refer to the next generation of cable services that included two-way features. 2. SCards were introduced first. Later, when MCards were introduced they were commonly referred to as CableCARD 2.0.
C-band / Ku-band 1. a range of RF spectrum. C-band is approximately 4 GHz. Ku-band is app. 12 GHz. 2. Geo-stationary satellites the networks use to acquire and distribute programming to affiliates and cable TV companies. These satellites use C-band and Ku-band frequencies. 3. a consumer service that uses the satellites the networks originally set up for themselves. An 8-foot steerable dish is required. Some channels are free. Others are available by subscription. The digital channel subscription service is called 4DTV.
CEC (Consumer Electronics Control) This feature allows units to control each other. The commands tend to be the same as the buttons of an infrared remote control, so fewer remotes are necessary. The implementation is a single-wire bus that is a ¡°party line¡± connecting to all units. The HDMI cable carries this line.
COFDM modulation technique. This technical standard has been used in Europe and other places for digital TV. 8VSB is used in the U.S.
Color temperature This describes how white is displayed. Low temperature means slightly reddish, while high temperature means slightly bluish. Standard NTSC white corresponds to the color a glowing hot object would be at 6500¡ã K
Component video This 3-wire convention was originally created for connecting DVD players to TVs or monitors. It avoids downgrading the signal to NTSC. The signals may be RGB or YPrPb. Some HD STBs have only component video output.
Composite video This 1-wire standard contains all video information: intensity, color, and sync. The encoding is the same as NTSC, and thus has the ¡°overlapping sideband¡± problem which sometimes causes wrong colors to appear.
DBS (direct broadcast satellites) These satellites are powerful enough to be received by an 18 inch dish. They use Ku-band and Ka-band frequencies. Companies that provide DBS services to consumers in the U.S. are DirecTV and Dish Network. Canadian DBS providers are Star Choice and Bell ExpressVu. Also called DSS.
DirecTV (see DBS)
Dish Network (see DBS)
DLP (digital light processor). A technology for video projection, also call DMD (Digital Micro-mirror Device). It is a large chip with about a million tiny mirrors on its surface. The chip can tilt each mirror to vary the amount of light reflected off of it.
Dolby Digital 5.1 Also known as AC-3, it provides 6 channels of sound: left, center, right, left rear, right rear, and sub-woofer. It is also called ¡°5.1 channels¡± since the 6th channel has reduced bandwidth. Dolby Digital 5.1 is the audio standard for all U.S. digital TV stations, most DVDs, some DBS programs, and many theaters.
Dolby Pro Logic Surround This is a 4-channel analog system. During recording, the 4 channels are ¡°folded¡± into 2 stereo channels. If played back without a Pro Logic decoder, it sounds like normal stereo. This format is becoming obsolete.
DTCP (Digital Transmission Content Protection) This is an encryption standard for IEEE 1394 that prevents the copying of first-run movies and pay-per-view events. DTCP is also called 5C Copy protection (in reference to the ¡®five companies¡¯ that license it).
¡¤ DVB-T is for terrestrial (OTA) broadcasts.
¡¤ DVB-S is for satellite broadcasts.
¡¤ DVB-C is for cable broadcasts.
DVI (Digital Visual Interface) This connector conveys HDTV image scanning signals in binary data form. The data rate is very high (1.65 Gb/s). Binary data is preferred by monitors that are not CRTs. DVI comes with a decryption option called HDCP which will decode encrypted programs such as first-run movies.
FCC (Federal Communications Commission) This is a Federal agency responsible for regulating radio wave usage and some other media. The FCC answers to Congress and also implements international radio standards.
Fire-wire (see IEEE 1394)
FTA ¡°Free To Air¡± or ¡°Free To All¡±. This is a digital satellite technology employing MPEG-2, but it is not compatible with DBS systems (Dish or DirecTV) or with Motorola Digicipher II (C-band 4DTV) and it doesn¡¯t have a provision for encryption. At the present time the only high definition stations on FTA are PBS, NBC, Voom, The History Channel, and 4 Denver stations. Lyngsat.com lists all the stations. Skyvision.com, FTAsatellite.com, and others sell receivers. The frequencies used are Ku-band and C-band. FTA¡¯s forte is that it is cheap and very international. FTA is heavily used outside the U.S. FTA started becoming popular in the U.S. about 2002 among experimenters and immigrants. In the opinion of some people the rise of FTA is a mistake and HDTV might eventually kill it. It might survive in the U.S. market because of a need for an unregulated domain for international stations.
HAVi (Home Audio Video Interoperability) This is a standard for 1394 bus audio and video devices. It is software that is required for the units to talk to each other. HAVi allows plug-and-play recognition of devices, interoperability, and brand independence.
HDCP (High-bandwidth Digital Content Protection) This is a DVI decryption option. It will decode encrypted programs such as first-run movies. (It¡¯s real function is to prevent unauthorized copying of programs.)
HDMI (High-Definition Multimedia Interface) This miniature connector is intended to replace DVI. It is backward compatible with DVI, and an adapter will connect it to a DVI unit. It has 19 pins and carries DVI plus digital audio. It also has a reverse data line (DDC) that allows the STB to sense the monitor¡¯s state and native formats, and a control line (CEC) for system level control.
IEEE 1394 Also called Firewire or iLink. Originally a serial bus for PCs, 1394 may or may not become the interconnection standard for DTV products. It is competing with HDMI. IEEE 1394 is a spec for a hardware interconnect plus a software shell. But additional software, such as HAVi, is required for connected units to actually talk to each other.
i.link (see IEEE 1394)
Interlaced scan Historically, TV CRTs are interlaced, while computer CRTs are not. Interlaced means that the electron beam skips every other horizontal line, filling in the missing lines on the next pass. A frame is composed of 2 fields. One field is all of the odd numbered lines, and the other field is all of the even numbered lines.
Ka band A range of RF spectrum centered around 30 Gigahertz. Historically never used, DirecTV and Dish Network are starting to launch satellites that use these frequencies. (The name comes from ¡°above K band¡±. K band is a long established military band.)
LNB (Low Noise Block converter) An LNB can be found at the focus point of a dish antenna. It is a low noise amplifier that also converts the signal to a lower frequency. (The original higher frequency would not travel very far in ordinary coaxial cable.)
Mosquitoes Fuzzy dots that can appear near sharp edges in MPEG and JPEG images, possibly looking like a swarm of mosquitoes. These artifacts are caused by over-compression or over-enhancement of edges.
Motion Adaptive De-interlacing The image is divided into regions where there is motion and where there is none. Areas of the image without motion are de-interlaced using ¡°weave¡±, and areas with motion are de-interlaced using ¡°bob¡±. See Bob and Weave.
MPEG-2 (Motion Picture Experts Group technical standard 2) This is a widely used standard for digital encoding of motion pictures. It typically achieves a 50 to 1 compression of data. It achieves this mainly by not retransmitting areas of the screen that have not changed since the previous frame.
Multipoint convergence Projection TVs with 3 CRTs require periodic adjustment to keep the 3 images perfectly aligned. Typically this is a simple 5 minute procedure the consumer must do every month or so.
Multi-path interference Some neighborhoods are plagued with this problem: The signal finds more than one path to the antenna. Multi-path results from diffraction around the sides of hills and buildings. For NTSC sets this will result in ghosts: multiple images shifted laterally. For DTVs the result can be an unusable signal, even though it may be strong. The solutions are moving the antenna or selecting a very directional antenna. Newer generations of DTV receivers are better able to cope with multi-path.
Native format Most DTVs will convert the 18 ATSC formats into 1 or 2 formats and will draw only those. For these sets, the ¡®native¡¯ format is 1. a format the set will draw or 2. the original format. (These are contradictory definitions, but they reflect current practice. 1 is probably the preferred meaning.)
NTSC (National Television System Committee technical standard) This is analog TV invented in 1946. NTSC has 525 lines (483 visible) interlaced, 60 fields per second. This standard is in use in North America, Japan, South Korea, Burma, Taiwan, the Philippines, and half of South America.
Over-scan/Under-scan Computer CRT monitors under-scan, which means they leave a thin black border around the image. TVs over-scan, which means a small part of the image perimeter is lost. (Digital displays don¡¯t necessarily do either.)
PAL (Phase Altering Line standard) This alternative to NTSC has 625 lines, interlaced, 50 fields per second. It is used in most of Europe, Asia (except USSR), Africa, and Australia, and half of South America.
PSIP data (Program and System Information Protocol) This data is arranged as a table with multiple sub-tables. The data identifies the station name, what the sub-channels are, the program name, the following programs, content advisories, language options, and caption options. Some of this data is transmitted as often as 7 times per second.
PVP-UAB Protected Video Path User-Accessible Bus. Encrypts video content as it passes over the PCI Express bus from the high-def disc to prevent other PCI Express devices from intercepting the video stream.
Rainbow effect A side effect of delivering the image colors sequentially instead of simultaneously. DLP displays have this effect if they use a spinning color wheel or sequentially-firing LEDs. Most viewers are not bothered by the rainbow effect.
Raster A group of closely-spaced lines whose brightness changes so as to appear to be an image.
RGBHV See VGA.
SECAM (Sequential Color And Memory standard) This alternative to NTSC has 625 lines interlaced, 50 fields per second. It is used in the former USSR, France, and parts of Eastern Europe, the Middle East, and Africa.
SVGA See VGA.
S-video Also called Y/C, this two-wire standard keeps the color separate from the intensity signal, and thus avoids the overlapping sideband problem of composite signals. (Converting an NTSC signal to S-video gains you nothing since what was lost cannot be recreated.) Although the quality of S-video is close to component video, S-video cannot transport anything better than 480i.
Transponder A satellite channel. There is often one program per transponder. Some transponders are wider than 6 MHz and can carry more than one NTSC program. Several digital channels can fit on one transponder.
VGA a 5-wire standard interface, originally for computer monitors, now common for HDTV monitors. Usually the 5 wires are in one cable. The connector can be either a 15-pin connector or five BNC connectors. The signals are usually red, green, blue, horizontal sync, and vertical sync. But Y, Pr, and Pb can replace the colors.
YPrPb Color representation requires three independent variables. CRTs prefer red, green, and blue. Ink jet printers prefer yellow, magenta, and cyan. NTSC encodes color as luminance (brightness), hue (color), and saturation (absence of white in colors). Storage media such as DVDs prefer Y, Pr, and Pb, where Y is luminance, Pr is red-Y, and Pb is blue-Y. This is because Pr and Pb can be at lower resolution and not degrade the image noticeably, thus saving storage space.
YPrPbHV See VGA.
3:2 pull-down This is the process of converting a 24 frames/sec image into a 30 frames/sec image. Some line-doublers will reverse this process to acquire the original, and then re-perform it.
8VSB modulation technique (8-level vestigial sideband) DTV stations in the U.S. use 8VSB modulation. This is an AM mode wherein the carrier is multiplied by an 8-level digital signal, and then a filter is used to remove all but the carrier and 6 MHz of the upper sideband. (¡°8VSB¡± is often used as a synonym for OTA.)
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The author has B.S. and M.S. degrees in Electrical Engineering from Carnegie-Mellon University. KQ6QV home page.
This document is Copyright 2002-2009 by Ken Nist. The ¡°document¡± includes all web pages at www.hdtvprimer.com. The author places no restrictions on the use of this document. It may be used by anyone in any manner for any purpose.