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Home Theater Hacks by Brett McLaughlin

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Chapter 4. High Definition

Hacks 28–35

It’s no exaggeration to say that high-definition programming has revolutionized home theater. Just a few short years ago, the quality of a good DVD was staggering; it was far superior to anything ever before seen on a television. However, high definition (HD) is head-and-shoulders above even the best DVD-quality pictures. Broadcasters are airing more and more programming in HD, and hit TV shows such as Alias, CSI, and The Grid are now more exciting than ever, with their true-to-life imagery.

Of course, with any technological leap comes complexity, and HD is no exception. In fact, HD is a big enough topic that it warranted its own chapter in this book; there was simply too much HD-specific content to squeeze into the video components chapter (Chapter 2). In this chapter, you’ll learn about HD programming, how to get it, and how to ensure your TV will work with it. You’ll also understand how important the old antenna has become again and how you can tweak your set to get maximum performance. So, buckle up, and let’s go digital.

Ensure You Can Get HD Programming

Although high definition is certainly the future in video, it might not make sense for you to go to an HDTV unit. Learn what should push you over the edge—and what shouldn’t.

There has literally been almost a run on HD-capable television sets in recent days. However, buying an HD set doesn’t necessarily mean you’ll get an HD signal. If you don’t have HD channels available to you, the greatest set in the world is wasted on low-resolution standard-definition (SD) programming. But to determine what programming is available, you need to know a little more about HD programming.

The Telecommunications Act of 1996

The Telecommunications Act of 1996 was passed by Congress and signed by the president. One of its provisions requires all terrestrial TV stations in the country to convert to digital modulation; in other words, these stations will be required to broadcast a high-definition signal.

Tip

Contrary to a persistent rumor, the VHF channels won’t be abandoned.

The deadline for this switch is a little fuzzy, but it currently is set for around the end of 2006. To stay competitive, all cable systems are rapidly converting to digital, but there is no deadline for that.

The preexisting TV technology in the United States is called analog. It also is called NTSC (National Television System Committee), after the people who defined the standard itself. The NTSC specification was created in 1946, updated for color in 1953, and updated for stereo in 1984. Both of these updates were backward compatible, which avoided rendering anyone’s TV set obsolete. But the new digital standard is totally different; the only thing it has in common with NTSC is the 6-MHz channel width. To continue using an NTSC TV after 2006, you might have to buy a converter box, which probably will cost about $200. At the time of this writing, these boxes were not yet available. You won’t need such a box if you can rely on a cable or satellite box that has an NTSC output.

The new digital standard is called ATSC (Advanced Television Systems Committee). Soon the government will require that all new TVs be able to receive ATSC channels. The ATSC standard includes multiple formats, from 640 x 480 pixels to 1920 x 1080 pixels. All TVs must receive all of these digital formats and display them suitably. Then the broadcaster can choose from any of these formats.

To make the transition manageable (and, theoretically, gradual), the FCC is temporarily giving all terrestrial TV stations a second channel, so they can broadcast a digital channel along with their analog channel until 2006. There are 1,500 terrestrial TV stations in the United States, and 1,000 of them have their digital channel on the air. Most of these transmit some high-definition programs. More than 90% of the U.S. population can receive some high-definition programming from these stations.

Tip

These numbers are accurate as of September 2003, which is the last time reliable information was collected.

So, given all of that, here’s the bad news:

  • The cost to consumers for the new hardware is still pretty high.

  • Home TV systems can be especially complicated during the transition.

  • The picture-in-picture (PIP) feature many people enjoy doesn’t currently work with HD programming. Most TV set designers are currently concentrating on other features, but an HD version of PIP will eventually show up.

  • NTSC images sometimes look worse on a big, high-definition set than on a small, standard TV.

On the other hand, the quality of TV reception will improve dramatically. Temporary inconvenience, at least in this case, results in permanent improvement.

Should I Buy an HDTV?

When it comes to actually deciding to purchase a TV, you must consider two main questions:

  • Can I afford the step up to HDTV?

  • How much HDTV programming is available to me?

Can I afford an HDTV?

The top-of-the-line HDTVs go for $10,000 and up, but a minimal compromise in quality will put you in the $2,000 range (the first color TVs cost $500, which, adjusting for inflation, would be $3,200 today). This lower-range compromise means you lose screen size and horizontal resolution; full horizontal resolution for HDTV is 1,920 pixels. But many sets being sold today resolve to only 1,280 pixels, and it is often difficult to see the difference. As such, 1,280 is still considered high-definition.

Smaller HDTVs are now available in the $1,000 range. If this still is beyond your budget, you have two choices:

  • Postpone the purchase. Set prices will continue to come down, although much of this decline will be from the introduction of sets with lesser features.

  • Buy a cheap, standard TV and hope your finances improve with time.

How much programming is available?

Table 4-1 lists the HDTV programming available at the time of this writing, aligned with the major satellite and cable providers.

Table 4-1. Current HDTV programming

Network

Hours/day

DirecTV

DISH network

VOOM

Cable providers

Discovery HD

24 (some repetitive content)

Yes

Yes

Yes

Time Warner Cable (TWC), Charter

HDNet

24 (some repetitive content)

Yes

Yes

No

TWC, Charter

HDNet Movies

24

Yes

Yes

No

TWC, Charter

INHD

24

No

No

No

TWC, Charter

HBO HD

18

Yes

Yes

Yes

TWC, Charter, Comcast

Cinemax HD

17

No

No

Yes

Comcast

Showtime HD

10 (plus some DVD-quality content)

Yes

Yes

Yes

TWC, Charter,

Starz HD

8 (plus some DVD-quality content)

No

No

Yes

Comcast

The Movie Channel

8 (plus some DVD-quality content)

No

No

Yes

None

Bravo

Undefined

No

No

Yes

None

Encore

Undefined

No

No

Yes

None

Playboy

Undefined

No

No

Yes

None

TNT

Undefined

No

Yes

No

TWC

CBS

4

Yes

Yes

No

Check local availability

NBC

3

No

No

No

Check local availability

ESPN

Undefined

Yes

Yes

No

Charter, Comcast

Pay-per-view

Undefined

Yes

Yes

No

None

For quality and quantity, the best networks tend to be HBO, HDNet, Discovery HD, and CBS.

Terrestrial Broadcasts

Long ago, many people switched from roof antennas to cable service because the picture quality was a little better. This argument no longer applies. ATSC channels are like satellite TV in that, if you get a channel, the picture will be perfect, snow-free, and ghost-free.

You might not want to give up cable because of the many other channels it offers. But in many locations, over-the-air (OTA) broadcasts will be the largest source of HDTV programming for the next three years. All the network stations in most large cities are broadcasting HDTV. The web site http://www.AntennaWeb.org can tell you what DTV stations are available in your area.

Tip

In smaller cities, some DTV stations might not be passing along network HD material. The easiest way to determine the HD programming available to you is to go into a store selling HDTVs and ask for the “HDTV expert.”

You need an antenna to get these ATSC signals. Information at http://www.AntennaWeb.org can tell you the compass directions to the transmitters in your area and recommend an antenna. Their recommendations are close, but not perfect, so you might want to see what others in your neighborhood have done.

If you have been told you can’t erect a small outdoor TV antenna, that is probably incorrect. The Telecommunications Act of 1996 has a provision that preempts (overrules) nearly all local restrictions such as deed restrictions, homeowners association rules, renters contracts, and so on.

Tip

For more details, see the FCC Fact Sheet at http://www.fcc.gov/mb/facts/otard.html.

If you are in an area where reception is difficult, you might see occasional distortions in the image, and dropouts lasting five seconds or so. If these occur often, a bigger antenna might help. Note that as antennas become bigger, though, they become more directional, making aiming more sensitive. Additionally, nearby trees affect UHF much more than VHF. If putting a UHF antenna on your roof doesn’t raise the antenna above the trees, you must find a place to mount it where it can see the horizon in the direction of the station. A UHF antenna should be at least 8 feet above ground, but mounting it higher doesn’t always get you a stronger signal. VHF antennas always should be mounted as high as possible. The best weak-signal UHF antennas are the multi-bowtie reflector antennas, such as the Channel Master 8-Bay.

Cable TV.

The cable TV industry was slow to take up the transition to DTV, but is now charging ahead. Digital cable is now being introduced in many areas, and some of these are carrying from 6 to 10 HD channels. About 40% of households can receive some HDTV programming via cable, although a special HD cable box is usually necessary. Ask your cable company what HDTV channels it carries. At present, HDTVs don’t have built-in digital cable receivers, but they will soon.

Some analog cable systems have added a few ATSC (8VSB) channels to their lineups as well. You can receive those channels by connecting an OTA DTV receiver to the cable system. This is temporary, as the whole cable TV industry is converting to digital cable.

DirecTV.

*To use DirecTV, you must have the oval dish that receives three satellites: 101°, 110°, and 119° west longitude. DirecTV and DISH Network are moving very slowly toward HDTV because they are spectrum-limited. None of the local channels is HD. DirecTV has stated that it is working toward HD local channels, but has not estimated when this will happen. It could take years.

DISH Network.

Presently, all the HD channels except CBS are carried on the DISH Network satellite at 110°. Thus, you need a dish with two low noise blockers (LNBs).

Tip

There was an announcement from DISH that the HD channels will be moved to a new satellite at 105° and that a new three-LNB dish will be required. This author doesn’t know the present status of that move.

None of the local channels is available in HD.

VOOM.

This is a new Direct Broadcast Satellite service, presently in start-up phase. Some Wall Street analysts have predicted this company will fail due to insufficient funding; currently the company is funded by Cablevision, a cash-rich company, and it certainly will succeed if Cablevision wants it to. VOOM service is sold through Sears, although most Sears salespeople seem surprised when asked about VOOM. Reports from the few people who have signed up for it tend to state that the service is either “fantastic” or “horrific,” but not much in between. It seems most VOOM personnel are learning as they go.

VOOM provides about 100 channels, approximately 30 of which are high-definition. About 20 of those HD channels originate at VOOM and are exclusive to VOOM.

Tip

No independent reviews of those channels were available at the time of this writing.

VOOM bills customers yearly instead of monthly; it costs $750 per year, and the receiver and dish are free. Receiver and dish installation also is free. Plus, VOOM will provide an OTA antenna for free, and install it for free (although probably not in weak-signal areas). VOOM has been giving free months to many customers to compensate for a rough start-up. I’m still neutral on whether signing up for VOOM is a good idea. The company probably will succeed, in which case VOOM would be the leader in satellite HD.

CBS national stations.

DirecTV and DISH Network carry WCBS-HD (New York) and KCBS-HD (Los Angeles). However, they are available only to viewers in cities where the network owns the local CBS station, and even then you might have to apply for a waiver from the station. If your local CBS station is privately owned, DirecTV and DISH are not permitted to offer you these channels. You should call DirecTV or DISH to find out if you qualify for CBS-HD.

The DISH Network carries these channels on a satellite at 61.5° for East Coast viewers and on a satellite at 148° for West Coast viewers. In addition to the regular DISH Network dish, you need a second dish for the HD satellite. But the need for that second dish possibly will be short-lived.

C-band 4DTV.

C-band and Ku-band refer to the satellite systems that require an 8-foot dish. 4DTV is a digital service available on these bands. The high definition channels on C-band are HBO East and West, Showtime East and West, Starz East and West, Encore East and West, Discovery HD Theater, and Nebraska Educational TV (PBS). About 150 DVD-quality digital SD channels also are available.

—Kenneth L. Nist

Get the Right Type of HD Set

As with any other component, tons of options are available when it comes to buying HD televisions. Learn which is best for you.

Just as when it came to choosing a TV in the general sense [Hack #9] , an HD set offers an almost dizzying combination of display technologies, set types, screen sizes, and options. You’ll need to know which set fits your budget, the size of screen you want (and can afford), and how lighting affects your room to make the right choice.

Display Technologies

The first thing you need to understand is the technologies involved. Although the overall set might determine what technology you choose, understanding how each works is critical.

CRTs.

CRTs, short for cathode-ray tubes, are used in direct view, rear projection, and front projection TVs. They have several advantages over other technologies:

  • Best color fidelity.

  • Excellent blacks, and fairly bright whites.

  • Smooth blending of adjacent pixels.

  • Some draw both 1080i and 720p, avoiding errors in format conversion.

Here are the disadvantages of CRT:

  • Brightness drops as screen size increases.

  • Few sets truly achieve 1920 x 1080 resolution, although some get very close. Projection TVs employing 9-inch CRTs get the closest.

  • There is a constant need for convergence adjustments (making red, green, and blue coincide perfectly).

  • Focus and size adjustments are required every couple of years.

Many experts think CRTs produce the best pictures, but other technologies are getting better every year. Relatively few CRT sets draw both 1080i and 720p, and most draw one and require the tuner to convert the other. For example, a 720p-only CRT set doesn’t work with an external tuner that converts everything to 1080i.

Plasma.

These flat panel displays are large and very bright. Their disadvantages are many, though:

  • High price

  • Poor blacks

  • A particularly short life span (they dim with age)

Additionally, pixels can die, which often is not covered by warranty. Even worse, plasma isn’t a good choice for video games. The popularity of plasmas, despite these disadvantages, is a testament to the space they save, and the decorative enhancement they provide.

DLP.

DLP, short for digital light processor, is also called DMD for Digital Micromirror Device. This is a large chip with about one million tiny mirrors on its surface. The chip can tilt each mirror to vary the amount of light reflected off of it. DLPs are used in rear and front projection TVs. The advantages of DLP are several:

  • Very bright pictures

  • Good blacks

  • No burn-in problems

The DLP disadvantage is the “rainbow effect” (explained later in this chapter). Texas Instruments is the only maker of DLP chips. At the time of this writing, chips with two million mirrors, capable of 1080i resolution, were scheduled to be available in late 2004.

LCD.

LCD stands for liquid crystal display. Polarized light shines through a sheet of glass, onto which is deposited a liquid crystal array. Each pixel changes polarization to either pass or block the light. LCDs are used in front and rear projectors. Large LCDs are used in flat panel displays. Their most notable disadvantage is that their blacks are not as dark as on a CRT. Additionally, on cheaper models, pixel response can be a little slow, causing blurred motion.

LCOS and D-ILA.

LCOS stands for Liquid Crystal on Silicon and it’s made by Toshiba and RCA, and D-ILA stands for Direct-drive Image Light Amplifier and it’s made by JVC. Both of these are reflective chips with a polarizing LCD layer. Each pixel changes polarization to either reflect or block a light beam. Their biggest problem is that their blacks aren’t as dark as on a CRT. These chips are used in front and rear projector TVs.

Set Types

Once you understand the technologies involved, you can start to hone in on the type of set you want. Several options are available and often, size and budget will determine which are available to you.

Direct view.

This category includes flat panel and CRT TVs. A CRT produces a bright, sharp image you can view from any angle in a fully lit room. The largest of these sets are about 38 inches, measured diagonally. You might find that, due to size constraints, no more than two people can sit in front of one of these sets. Another negative is that widescreen CRTs [Hack #13] come in cases that are exceptionally deep.

Plasma and LCD flat panel TVs also are available. Plasmas are large and expensive, while LCDs are small and cheap (“cheap” means $1,000, at least right now).

Rear projection.

Rear projection sets come in sizes ranging from 40 inches to 73 inches, and are the most popular HDTV technology. Most are based on CRTs, but there are other competing technologies.

Typically, these sets have three CRTs (red, green, and blue) hidden inside a box. The CRTs point upward, into a flat mirror, and then reflect onto a diffuser screen. The CRTs have lenses that focus the image at the screen. Adequate intensity is a problem, so the diffuser screen is designed to not radiate light in directions where there are no viewers. A fully bright image is visible to about 45° to the left and right, but only to about 10° to 15° above and below any spot on the screen.

Typically, if you sit closer than three times the screen height, you can’t see the top and bottom of the screen at full brightness. Although three times the screen height is a correct distance, if your head moves vertically even a few inches, you might lose brightness at the top or bottom of the screen. Sitting at 3.5 times the screen height reduces this problem (see Figure 4-1). If you don’t mind the loss of brightness, you can watch standing up.

Room lighting must be controlled for RPTVs, but an absolutely black room isn’t necessary. Indirect ceiling lighting works well, but usually you can see the reflection of lamps in the large, flat screen; ditto for windows. You probably will want dark shades for windows that reflect in the screen. If the salesperson tells you the screen is nonreflective, be sure to check it out for yourself.

Front projection.

For pictures larger than 73 inches, front projection is the way to go. Usually the projector is ceiling-mounted or placed on a shelf behind the viewers. Because the screen is white, a completely blackened room is necessary; otherwise, black appears as gray.

Sitting correctly in front of an RPTV
Figure 4-1. Sitting correctly in front of an RPTV

Tip

Some systems are bright enough to project onto a gray screen, reducing this problem somewhat.

Set Configurations

Another consideration is the configuration of the set you’re looking at. There are three basic categories.

Monitor

This is a set without a tuner, and usually without any audio. This is presently the hottest-selling HDTV configuration, preferred either because external OTA receivers are thought to be better or because the owner plans to rely on cable or satellite. Many of these sets presently are being used just for viewing DVDs.

Integrated TV

This is a complete HDTV set with NTSC and ATSC tuners, and also some speakers. An external tuner always can be added.

HD-ready TV

This is a TV with an NTSC tuner. The set will draw 1080i or 720p if an external tuner is added. The FCC has mandated an end to this category [Hack #28] , and will require an ATSC tuner with any device that has an NTSC tuner. This requirement is phasing in gradually, applying to large TVs now and to the smallest TVs in 2007.

Burn-in

Another issue in today’s newest HD sets is burn-in. The phosphors used in CRTs and plasma displays become less bright with use. The phenomenon is a lot like tire wear; if you drive fast, the wear per mile increases, but there is still some wear at any speed. The speed of a car corresponds to white in a TV image.

CRT burn-in used to be rare, but the demand for brighter images has made manufacturers less conservative. Now, CRTs that have been showing a Windows desktop for a couple of years often will show a lightly burned-in task bar when the screen is painted entirely white. The CRTs in big-screen TVs are pushed even harder, especially in the largest sets.

All CRT and plasma sets dim with use. Making the screen age evenly is the user’s responsibility. The user must ensure that a fixed, unmoving shape is not displayed for many hours, or that shape will slowly become burned into the screen. LCD, LCOS, and DLP sets don’t suffer burn-in.

The Rainbow Effect

One-chip DLP sets employ a rotating color wheel. Thus, the three colors are delivered to the screen sequentially. Suppose the image comprises white text on a black background. If you shift your gaze rapidly across the image, the white lines will decompose into the primary colors (until your eyes stop moving). Most people don’t notice this, and most of the people who do see it learn to ignore it. But a few people can’t get past being distracted by this rainbow effect.

Set makers can reduce this problem by changing the colors faster (using color wheels with 6, 9, or 12 color segments). The rainbow effect is eliminated in three-chip DLP sets, which have no color wheel.

Some CRTs have a similar problem. My set employs a green phosphor that stays lit four times as long as the red and the blue. A rapid eye shift will reveal some flashes of green in an image that has only black and white.

—Kenneth L. Nist

Add a Set Top Box

Once you’ve got an HDTV set, you’ll need something to pull in HD signals and pass them onto your television. Learn what to look for, and what to buy.

Set top box, or STB, is a term that can include any type of accessory that can connect to the HDTV. Common STBs are satellite receivers, cable TV receivers, OTA receivers, DVD players, VCRs, and so on. Generally, though, an STB is a device that pulls in a high-definition signal, instead of just pushing pictures through to your TV.

Choosing a set top box is like choosing any other component; you need to find one that has the right functionality, and more important, the right connections for your gear. For an STB, that means ensuring that both the video and audio it receives can be passed on to the rest of your gear.

STB Video Output Options

Unfortunately, a single universal standard for unit-to-unit video connections doesn’t exist. Eventually, through competition, the best of the following will survive. Any STB you acquire probably will have more than one of these output connectors. When you buy an HDTV and an STB, try to select units that can connect to each other directly. Otherwise, you will have to pay for a transcoder or a video switch box. Here are your basic connection options.

CH3/CH4 output

ATSC output via a preselected channel on the TV is one of the oldest connection methods. Obviously outdated, this almost never shows up in modern components.

Composite video

This one-wire standard, in use for many years, conveys complete video images. It is designed for NTSC and can’t transport HDTV images.

S-Video

This two-wire standard is an improvement over composite video. But it was designed for NTSC and can’t carry anything else.

Component video

This three-wire standard, originally designed for DVD players, can carry HDTV via three wires with phono plugs. The three wires carry analog raster (image-scanning) signals, either red/green/blue or Y/Pr/Pb (Y=intensity, Pr=Y-red, and Pb=Y-blue). Some units can handle either color scheme. You must verify that both units can use the same scheme.

Tip

Neither the red/green/blue nor the Y/Pr/Pb scheme is better than the other.

VGA

This five-wire standard, originally devised for computer monitors, carries HDTV raster signals, usually red, green, blue, Hsync (horizontal sync), and Vsync (vertical sync). However, in some units, Y, Pr, and Pb can substitute for the color channels. Usually the five wires are bundled into a single cable.

Tip

Five separate cables are advisable for runs longer than 12 feet.

The connector can be a 15-pin VGA connector or five BNC connectors.

Warning

Some HDTVs have VGA inputs that accept only computer formats, such as 600 x 800 and 720 x 1024. Many makers use the term RGB in place of VGA despite the confusion that causes.

DVI (Digital Visual Interface)

This connector conveys HDTV raster-like signals in binary data form. The data rate is very high (1.65 Gb/s). Monitors other than CRTs, such as plasma, LCD, DLP, LCOS, and others, prefer binary data. DVI comes with a decryption option called HDCP (High-bandwidth Digital Content Protection), which will decode encrypted programs such as first-run movies. However, there is a serious problem here: the motion picture industry might try to require distributors (HBO, Cinemax, etc.) to use HDCP encryption on all high-definition movies. HDCP decryption hardware is proprietary, and any hardware manufacturer must sign a contract to include it in his product. That contract forbids high-definition analog output (VGA or component video) when encryption is enabled, and allows HDCP decryption to take place only in the monitor. This is an attempt by Hollywood to prevent unauthorized copying and distribution of high-definition material. However, it means that millions of HDTVs already sold that have only analog inputs could become useless, except for viewing whatever sitcoms or dramas the networks allow. The FCC hasn’t yet ruled on this, and doesn’t seem to be in any hurry to step into the issue.

HDMI

This new 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 control line that allows the STB to sense the monitor’s state and native formats.

IEEE 1394

Also called FireWire or i.link, this is a high-speed bus common in computers. IEEE 1394 is fast enough to carry compressed MPEG-2 video data plus audio and controls. There is an encryption standard for IEEE 1394, called DTCP (Digital Transmission Content Protection, and sometimes called 5C copy protection). But because IEEE 1394 is an open standard, Hollywood has less control over it. Because it is a two-way bus, it could allow units to control each other. This holds out the promise of eliminating the need for 5 or 10 handheld remotes to control the home theater. IEEE 1394 is just a connector definition plus a software shell. Additional software is required for the units to talk to each other.

Tip

Home Audio Video Interoperability (HAVi) is such software. HAVi allows plug and play recognition of devices, interoperability, and brand independence.

If the STB has a CH3/CH4, composite, or S-Video connector, it is for standard-definition images only. When a high-definition program is being received, these connectors are either disabled or carry an image that has been down-converted to NTSC.

Neither VGA nor component video is superior to the other. For a cable length of six feet, VGA is more convenient. For longer runs, component video is usually more convenient.

When using DVI, VGA, and component video, very few sets will draw both 1080i and 720p. If you feed the set a mode that it can’t draw, you will get either a blank screen or garbage.

Tip

The law requires a set to receive all 18 modes. However, the law only regulates tuners, not these intermediate inputs.

An exception to this is fixed-pixel displays that will redigitize component video.

DVI and 1394 are presently competing for the hearts and minds of the manufacturers, but which will win is unclear. A third possibility is that both will be adopted, DVI for video and 1394 for audio and control. All record devices likely will use 1394.

More on DVI.

DVI was originally developed for computer monitors, but has been adopted by HDTV. DVI comes in different versions. All versions use the same 29-pin connector. Sometimes you can tell which version you have by seeing how many of the 29 pins are missing.

DVI-D

This is the version most commonly used for HDTV. The five large pins usually are missing. There is a single-link version of this that uses only 12 of the 24 small pins. Single link will work properly with all HDTVs.

DVI-I

This version uses all 29 pins. The 5 large pins pass analog VGA signals. Presently, the computer industry primarily uses DVI-I, but front projector HDTVs, from a number of makers, support DVI-I. DVI-to-VGA adapters and adapter cables are available for these units. Front projectors from a couple of makers accept component video signals through their DVI connectors. These companies provide DVI-to-component adapter cables. However, this is nonstandard.

These adapter cables work only with DVI-I. In most cases, if you want to connect a DVI unit to a VGA or component unit, these adapters won’t work. That would require a transcoder circuit that can convert between analog and digital signals.

HDMI

HDMI is a single-link DVI plus digital audio and a control line in a miniature connector. It carries no analog signals.

Avoiding (most) risk.

Unfortunately, you can’t avoid risk completely. When you select an STB, you must decide among DVI, 1394, or analog (VGA and component video are considered analog). There is no way to tell which will become the long-term winner. Presently, Hollywood doesn’t want any DBS or cable set top box to have a 1394 connector passing MPEG-2 data. They even consider analog to be a piracy threat. If the DVI interface catches on big, Hollywood could order all DBS and cable companies to disable all STB analog or 1394 video outputs whenever a high-definition movie is showing. Some people think the FCC would delay that order by 10 years to allow depreciation of the millions of HDTV sets that would become OTA- or SD-only as a result.

I believe Hollywood will not carry out its threat anytime soon. What Hollywood is most concerned about is movie piracy via the Internet. Currently that is not practical at high definition because it takes too long to download huge movies in this resolution. However, if it should become practical and piracy proliferates, Hollywood will try to shut down those STBs that contribute to it. The FCC certainly will side with Hollywood if movie piracy makes movie-making unprofitable. This is not all bad, though, because it guarantees home access to first-rate films.

STB Audio Output Options

An STB is likely to provide one or more of the following audio outputs:

  • Six-channel audio (six wires with phono plugs)

  • Coaxial digital audio (one wire with phono plug)

  • Optical digital audio (one TOSlink fiber optic line)

  • IEEE 1394 audio and video

  • DVI audio and video

Again, it is wise to plan for audio connectivity before buying. You could be in a real bind if the TV and STB don’t have compatible connectors for video, or if your receiver/processor and STB can’t speak audio to each other.

—Kenneth L. Nist

Properly Size Your HD Image

Once you’ve got your HD signal coming in, you’ll need to ensure that it appears properly on your television set. Otherwise, you’ll miss important detail and lessen the HD experience.

Many are the stories of a consumer buying an expensive HD-ready wide-screen TV [Hack #29] , spending hundreds on killer programming [Hack #28] , and still seeing only 70% or 80% of the overall image. The choice seems to be between black bars on the side [Hack #13] or an image that clearly extends below the bottom of the screen and above the top. Some careful tweaking can take care of this once and for all.

HD programming needs to form an exact 16 x 9 image, form-fitted to your TV’s 16 x 9 screen. Unfortunately, this almost never is set up for you out of the box. RPTVs are overscanned quite heavily from the factory, meaning you are missing substantial parts of your picture. This process of reducing the overscan is not for the faint of heart, however, because doing so hoses your geometry and convergence, all of which have to be totally recalibrated [Hack #62] afterward.

You’ll need to enter your television’s service menu, and then manually set both the vertical and horizontal size.

Tip

As always, when dealing with service menus, write down everything before changing anything.

When you’ve found the menu options you want, load up a true HD image. You can usually get one of these by setting your set top box [Hack #30] to PBS or HDNet; both channels have true HD broadcasts most of the day. Then, as the broadcast is showing, squeeze in the edges of the screen vertically until you can just see the edges of the picture on the top and bottom of your TV. Then you can just nudge the size back up, and you’re all set. Repeat the same process horizontally: squeeze in, and then set the overscan.

As you’re setting the size, you might find that the picture is also off-center. You can see this is happening when one side of the picture is flush with the edge of the display on your set, but the other side is not. You’ll have to move the image toward the side that shows the extra edge and then resize again. This is a trial-and-error process, and can take some time.

Tip

For those of you used to working with computer monitors, this is the same way you ensure your monitor is displaying all of the video image and not cutting some off (or leaving wasted display space along an edge).

If you’re having trouble getting the edges aligned, focus on the center of the edge you’re working on; in other words, don’t worry about the corners. When you rework the convergence and geometry of your screen via calibration, these corners will take care of themselves.

Finally, with the picture just where you want it, you’ll have to go back to calibration, working on the color levels, convergence, and the like. This can be a lengthy process; the more the screen is off when you get it, the larger the error your adjustments can cause. Still, it’s well worth it to see all of the image you’re working with rather than just part of it.

—Robert Jones, Image Perfection

Get the Right Antenna

An over-the-air antenna can provide you crystal-clear HD broadcasts. Learn how antennas work, where to mount them, and what commercial offerings are good buys.

Even if your cable or satellite provider offers great HD programming [Hack #28] , you’ll still probably want an OTA antenna. In some cases, the antenna can provide local channels your provider might not yet offer; more important, though, an OTA antenna is the key to HD broadcasts of local networks. Until cable and satellite providers offer you local channels in HD, an OTA antenna is an essential part of a high-end home theater.

Antenna Basics

If you’re going to get into antennas, you’re going to need some basic background. This section gives you that background, while still keeping things at a fairly mild technical level.

The TV channels.

Hertz (Hz) means cycles per second.

Tip

Heinrich Hertz was the first to build a radio transmitter and receiver, at least while understanding what he was doing.

The radio frequency spectrum is divided into major bands, as shown in Table 4-2.

Table 4-2. Major radio frequency bands

Abbreviation

Meaning

Frequency

Wave length (in meters)

VLF

Very low frequency

3 kHz–30 kHz

100 Km–10 Km

LF

Low frequency

30 kHz–300 kHz

10 Km–1 Km

MF

Medium frequency

300 kHz–3 MHz

1 Km–100 m

HF

High frequency

3 MHz–30 MHz

100 m–10 m

VHF

Very high frequency

30 MHz–300 MHz

10 m–1 m

UHF

Ultra high frequency

300 MHz–3 GHz

1 m–100 mm

SHF

Super high frequency

3 GHz–30 GHz

100 mm–10 mm

EHF

Extremely high frequency

30 GHz–300 GHz

10 mm–1 mm

Tip

The terms kiloherz (kHz) means 1,000 hertz, megahertz (MHz) means 1 million hertz, and gigahertz (GHz) means 1 billion hertz.

A TV channel in the United States will always occupy 6 MHz of this spectrum (see Table 4-3).

Table 4-3. Spectrum occupied by channel groups

Channels

Spectrum occupied

2–6

54 MHz to 88 MHz (with one small gap)

7–13

174 MHz to 216 MHz

14–69

470 MHz to 806 MHz

Channels 2–13 are the VHF channels. These are split into two groups so that antennas will work better: in general, an antenna designed for frequency N also works well at 3N, but very poorly at 2N.

The wave length of a radio wave is defined as:

                  λ = 300/F

Here, F is the frequency in MHz, and λ is the wave length in meters. Antenna elements are usually about half a wave length long.

Decibels.

Decibels (dB) are commonly used to describe gain or loss in circuits. The number of decibels is found from this formula:

Gain in dB = 10*log(gain factor)

Alternatively, you can just use the diagram in Figure 4-2.

Determining decibels (dB) from gain factor
Figure 4-2. Determining decibels (dB) from gain factor

For example, suppose 10 feet of cable loses 1dB of signal. To figure the loss in a longer cable, just add 1dB for every 10 feet. In general, decibels let you add or subtract instead of multiply or divide. There are also some specific decibel markers, and the effect they have on gain, that you might want to memorize:

  • 20dB = gain factor of 100

  • 10dB = gain factor of 10

  • 3dB = gain factor of 2 (actually 1.995)

  • 0dB = no gain or loss

  • –1dB = a 20% loss of signal

  • –3dB = a 50% loss of signal

  • 10dB = a 90% loss of signal

Noise.

Whether a signal is receivable is determined by the signal-to-noiseratio. For TVs there are two main sources of noise.

Atmospheric noise

This noise can come from many different types of sources. For example, a light switch creates a radio wave every time it’s turned on or off. As another example, motors in some appliances produce nasty RF (radio frequency) noise.

Receiver noise

Most of this noise comes from the first transistor the antenna is attached to. Some receivers are quieter than others.

Receiver noise dominates on the VHF and UHF bands, and atmospheric noise is usually insignificant. On an analog channel, noise looks like snow. If there is only a barely perceptible amount of snow, it corresponds to how noise-free a DTV signal must be for a DTV receiver to lock on to it.

Signal amplifiers and preamplifiers.

Many people think that connecting an external amplifier to the antenna can improve the performance of the antenna. Unfortunately, this is usually wrong.

The signal-to-noise ratio is generally set by the receiver’s first transistor. But if an external amplifier is added, the first transistor in the (added) amplifier determines the signal-to-noise ratio.

Tip

Because the signal and the external amp’s noise are magnified greatly, the receiver’s noise becomes insignificant.

Because there is no reason to think the external amp’s first transistor is quieter than the receiver’s first transistor, there is generally no benefit to the signal-to-noise ratio from an external amplifier.

However—and here’s the good news—an external amplifier can compensate for signal loss in the cable if the amplifier is mounted at the antenna. Without this amplifier, a weak signal, just higher than the noise level at the antenna, could sink lower than the noise level due to loss in the cable, and be useless at the receiver.

RG-6 cable loses 1dB of the signal every 18 feet at channel 52. For a DTV channel, 1dB can be the difference between dropouts every 15 minutes (probably acceptable) and every 30 seconds (unwatchable). I recommend a mast-mounted amplifier whenever the cable length exceeds 20 feet.

Tip

If you are in a good-signal area or you have no high-numbered UHF channels, you can, to an extent, ignore this advice.

The amplifier should have a gain equal to the loss in the cable (for your highest channel) plus another 10dB (to keep the receiver’s first transistor out of the picture). You generally can overshoot this target by 10dB without causing any trouble.

When figuring the cable loss, be sure to include the loss in any splitters and baluns. If a 2-to-1 splitter were 100% efficient, you would figure a 3dB loss because each TV gets half of the power. More realistically, splitters are usually 80% to 90% efficient.

The antenna and the amplifier both have gains measured in dB, and many people add these two numbers (and then maybe subtract the losses) to find the strength of the signal at the receiver. However, this calculation has little real value; you always should keep the net gain in front of the amplifier separate from the net gain that follows.

Receiver noise.

Actually there is a reason to think the external amplifier is quieter than the receiver is. Long ago, designers made an effort to make the TV’s first amplifier stage very quiet. But now 90% of homes use cable or satellite boxes (strong sources) and most of the rest are rural homes using antennas that have mast-mounted amplifiers. So, the TV’s noise is rarely a factor. Many TV makers no longer put any effort into making their sets quiet.

Suppose you live in an apartment 15 miles from the transmitter of the signal you’re trying to capture. Your indoor antenna mostly works, but you are troubled by dropouts. Will adding an amplifier right at the TV improve things? Yes, if it is quieter than the TV. Unfortunately, TV makers see no reason to publish the noise figures for their receivers. So, buying an amplifier for an indoor antenna is a total crapshoot. I recommend that you try a Channel Master Titan or Spartan amplifier, but make sure you can return it if it is of no help.

Transmission cable.

Twinlead (ribbon cable) used to be common for connecting TVs to antennas, and it does have its advantages. However due to its unpredictability when positioned near metal or dielectric objects, it has fallen out of favor.

Tip

Such objects, even if not touching the cable, cause a portion of the signal to bounce, return to the antenna, and get retransmitted.

Coaxial cable is recommended instead. It’s fully shielded and not affected by nearby objects. Coaxial cable has a feature called characteristic impedance, which for TVs always should be 75 ohms.

Warning

Fifty-ohm coaxial cable is also common. Avoid that cable!

Although rated in ohms, this measurement has nothing to do with resistance. A resistor converts electric energy into heat. The “75 ohms” of a coaxial cable don’t cause heat. Where it comes from is mathematically complicated, and beyond our scope here.

But coax also has ordinary resistance (mostly in the center conductor: see Table 4-4) and thus loses some of the signal, converting it into heat. The amount of this dissipation (loss) depends on the frequency as well as the cable length.

Table 4-4. Cable diameter and center conductivity

Type of cable

Center conductor

Cable diameter

RG-59

20–23 gauge

0.242 inches

RG-6

18 gauge

0.265 inches

RG-11

14 gauge

0.405 inches

The cable loss is shown pictographically in Figure 4-3.

The table in Figure 4-3 is only approximate. There are many cable manufacturers for each type, and there is no enforcement of standards. If the mast-mounted amplifier gain exceeds the cable loss, it shouldn’t matter what cable type you use. But there are two problems with this.

  • Some cable has incomplete shielding. This is most common for RG-59 and is another reason to avoid it.

  • When the cable run is longer than 200 feet, the low-numbered channels can become too strong relative to the high-numbered channels. In this case, RG-11 or an ultra-low-loss RG-6 is recommended (these alternatives are expensive). Alternatively, frequency-compensated amplifiers will work.

Cable loss per 100 feet
Figure 4-3. Cable loss per 100 feet

I usually recommend RG-6 for all TV antennas. It can be stapled in place using a staple gun with common 9/16-inch T25 staples. How long the cable lasts depends solely on how long you can keep water out of it. 3M Vinyl Electrical Tape is a good waterproofer. Even better is an asphalt putty called “Coax Seal” (RadioShack 278-1645), but it is so tenacious it should not be used for temporary connections. Cover the connectors completely.

Receiver overload.

Signal amplifiers are supposed to be linear. That is, the output is a magnified but otherwise unaltered version of the input. But too much signal can make an amplifier nonlinear, usually clipping off the tops and bottoms of the sine waves. When this happens, all channels are affected, not just the one that is too strong. In fact, the too-strong signal usually is not a TV station. A close FM station or police station is more likely.

If you add a good amplifier to your antenna system and your results get worse instead of better, you have overload, and you need to reconsider more carefully what you are doing.

An attenuator is a resistor network that can reduce the gain of an amplifier; 6dB attenuators are available at RadioShack. Insert the attenuator between the TV and the power injector. If you are close to an FM station, there might be a narrow range between too much and too little gain. You can make that range larger by using an amplifier with an FM trap or by using a more directional antenna.

Types of Antennas

First, you’ll need to have some more basic terms under your belt.

Gain

A measure of how much signal the antenna will collect.

Beamwidth

A measure of how directional the antenna is.

Bandwidth

A measure of how the gain varies with frequency. A narrow-band antenna will receive some channels well, but others poorly.

The dipole antenna.

This is the simplest TV antenna. Variations on the dipole are the bowtie (which has wider bandwidth), the folded dipole (which can solve an efficiency problem), and the loop (a variation on the folded dipole). All four have the same gain and the same radiation field: a toroid (doughnut shape: see Figure 4-4). The gain is generally 2.15dBi, which means “dB of improvement over an isotropic radiator.” That’s a lot of verbiage that simply means an antenna that radiates equally in all directions.

Dipole antenna radiation field and variations
Figure 4-4. Dipole antenna radiation field and variations

The dipole has positive gain because it doesn’t radiate equally in all directions. This is a universal truth. To get more gain, an antenna must radiate in fewer directions. Imagine a spherical balloon. Now press on it from opposite sides with a finger of each hand. Push in until your fingers meet. The result looks like the toroid, as in Figure 4-4. But more important, the balloon expanded in the other directions. Aha! Gain! That’s the way antennas work.

Keep this balloon analogy in mind. More complicated antennas work by reducing radiation in most directions. They distort the balloon considerably, but the volume of the balloon remains constant.

Another rating system for antennas uses dBd, which means “dB of improvement over a dipole antenna.” To convert dBd to dBi, just add 2.15. Antenna makers specify their gains in dB. They actually mean dBd, but given the way they exaggerate their claims, dBi is usually closer to the truth.

In the United States, TV antennas are always horizontal. If you rotate an antenna about the forward axis (a line from the transmitting antenna) the signal strength will vary as the cosine of the angle. In other words, when the antenna elements are vertical, no signal is received because TV signals have horizontal polarization.

Stacked dipoles.

Two heads are better than one, and so it is with dipoles. N dipoles will take in N times as much RF power as one dipole, provided they are not too close to each other. Thus, a four-dipole antenna would have a gain of 8.15dBi. (That is 2.15dBi doubled once [plus 3dB] and doubled again [plus another 3dB].) This assumes their positions and cable lengths are adjusted so that their signals add in-phase. This explanation of gain might seem at odds with the balloon explanation, but ultimately they are equivalent.

Tip

Adding dipoles doesn’t increase the volume of the balloon because phase cancellation occurs in some directions.

Dipoles are commonly stacked horizontally (collinearly), vertically (broadside), and in echelon (end-fire). Figure 4-5 shows examples of all three configurations.

When dipoles are stacked horizontally, the horizontal beamwidth becomes very narrow. This is because they don’t add in-phase for directions that are not straight ahead. Similarly, when stacked vertically, the vertical beam-width becomes narrower.

Let’s say you are 20 miles from a city, and TV transmitters are scattered all over the city. A medium-gain antenna might be too weak, but a high-gain antenna would be so directional you’d need a rotor. Solution: a bunch of dipoles stacked vertically can give you the gain you need (as illustrated in Figure 4-6). The vertical narrowness of the resulting beam is of little importance, but the horizontal broadness of the beam means no rotor is needed.

Various stacked dipoles
Figure 4-5. Various stacked dipoles
Stacked dipoles
Figure 4-6. Stacked dipoles

Reflector antennas.

Radio waves reflect off a large conducting plane as if it were a mirror. A coarse screen can serve as well. Reflector antennas are very common. The double bowtie in Figure 4-7 has gain of 5–7dBi. With a bigger screen, it would have more.

The parabolic reflector shown in Figure 4-8 focuses the signal onto a single dipole, but its bandwidth is a little disappointing. The corner reflector (in the same figure) has a little less gain but much greater bandwidth. The corner reflector has roughly the gain of three dipoles. It is a good medium-gain antenna, widely used for UHF.

Double bowtie reflector
Figure 4-7. Double bowtie reflector
Two reflector types
Figure 4-8. Two reflector types

If you need more than 25dBi, the paraboloid dish shown in Figure 4-9 is the only practical choice.

Log-periodic dipole arrays (LPDAs).

The LPDA, shown in Figure 4-10, has several dipoles arranged in echelon and crisscross-fed from the front. The name comes from the geometric growth, which is logarithmic.

This is a very wide-band antenna with a gain of up to about 7dBi. For any frequency, only about three of the elements are carrying much current. The other elements are inactive. As frequency increases, the active elements “move” toward the front of the array. Most VHF antennas are LPDAs.

Parabolic reflector
Figure 4-9. Parabolic reflector
LPDA antenna types
Figure 4-10. LPDA antenna types

TV LPDAs come in two types: straight and Vee. The Vee type has just a slightly higher gain for channels 7–13. But I usually favor the straight type because it has nulls 90° to each side that can be used to cancel out ghosts.

Yagi antennas.

A Yagi antenna has several elements arranged in echelon. They are connected together by a long element, called the boom. The boom carries no current. If the boom is an insulator, the antenna works the same. Figure 4-11 shows the overhead view of a Yagi antenna.

Yagi antenna, overhead view
Figure 4-11. Yagi antenna, overhead view

The rearmost element is called the reflector. The next element is called the driven element. All the remaining elements are called directors. The directors are about 5% shorter than the driven element. The reflector is about 5% longer than the driven element. The driven element is usually a folded dipole or a loop. It is the only element connected to the cable. Yet the other elements carry almost as much current.

The Yagi is the most magical of all antennas. I won’t attempt to explain why it works; the math simply gets way too complex. Suffice it to say that the more directors you add, the higher the gain becomes, and gains higher than 20dBi are possible. But the Yagi is a narrow-band antenna, often intended for a single frequency. As frequency increases above the design frequency, the gain declines abruptly. Below the design frequency, the gain falls off more gradually. When a Yagi is to cover a band of frequencies, it must be designed for the highest frequency of the band.

A UHF Yagi today is designed for channel 69. If you see an old Yagi, it might be intended for channel 82. In the future they will be cut for channel 51. It’s not possible to tell by looking at a Yagi which era it belongs to, so be careful. Often the reflector element is replaced by a corner reflector, as shown in Figure 4-12.

Corner reflector on a Yagi antenna
Figure 4-12. Corner reflector on a Yagi antenna

This corner reflector makes up somewhat for the poor performance on the lower-numbered channels. Although the Yagi/Corner-Reflector is not the best antenna, it is the most common UHF TV antenna, mainly because it can be mounted on the front of a VHF antenna without degrading the VHF antenna.

An antenna also has an aperture area, from which it captures all incoming radiation. The aperture of a Yagi is round (see Figure 4-13) and its area is proportional to the gain. As the leading elements absorb power, diffraction bends the adjacent rays in toward the antenna.

Comparing antenna types.

The graph in Figure 4-14 shows the gain functions for four TV antennas:

  • Plot A is the Channel Master 4228 8-Bay, a stacked dipole reflector antenna.

  • Plot B is the Channel Master 4248, a Yagi/Corner-Reflector.

    Aperture area
    Figure 4-13. Aperture area
    Comparing antenna types
    Figure 4-14. Comparing antenna types
  • Plot C is the 4248 with all of its directors removed, making it a pure corner reflector antenna.

  • Plot D is the 4248 with its corner reflector removed and replaced by a single reflector element, making it a standard Yagi. The D2 plot shows the backward gain where this exceeds the forward gain.

The point of this graph is that a Yagi/Corner-Reflector performs like a Yagi for the high-numbered channels, and like a corner reflector for the low-numbered channels. For the middle channels it outperforms the sum of the two types. Clearly, the 8-Bay and Yagi/Corner-Reflector are the favorites here.

Radiation patterns.

The last thing to be aware of is the radiation patterns of these antennas. First, Figure 4-15 is the overhead view of an 8-Bay antenna.

Overhead view of 8-Bay antenna
Figure 4-15. Overhead view of 8-Bay antenna

Figure 4-16 is the elevation view of the same antenna.

Elevation view of 8-Bay antenna
Figure 4-16. Elevation view of 8-Bay antenna

As you can see, the 8-Bay is a very directional antenna. If the aim is off by 5°, you can lose 1dB of signal. If the horizon is more than 5° above horizontal, you should tilt the antenna up to point at the horizon.

The overhead view shows nulls at 30° and 90° to both sides. These can be used to eliminate multipath (ghosts) or interference. You simply rotate the antenna until the offending signal is in one of the nulls.

Compare that to Figure 4-17, the overhead view of a Yagi/Corner-Reflector antenna.

Overhead view of Yagi/Corner-Reflector
Figure 4-17. Overhead view of Yagi/Corner-Reflector

Figure 4-18 is the aerial view of the Yagi/Corner-Reflector.

A Yagi also has some forward nulls that can be used as ghost killers. But a Yagi/Corner-Reflector acts more like a corner reflector for most channels, and has no nulls. At channel 60 you can finally see the Yagi pattern start to emerge.

I prefer the 8-Bay to the Yagi/Corner-Reflector for the following reasons:

  • It has high gain.

  • Its gain is evenly distributed over the channels.

  • It has nulls that can eliminate multipath.

  • It has a rectangular aperture that permits efficient stacking when more than eight bays are necessary [Hack #81] .

However, the high gain means it is hard to aim. In good-signal areas, avoid high-gain antennas.

Aerial view of Yagi/Corner-Reflector
Figure 4-18. Aerial view of Yagi/Corner-Reflector

Commercial Antenna Types

Antenna marketing is a racket in that the less honest you are, the more antennas you sell. Gain figures published by antenna makers are mostly useless, except maybe for comparing antennas by the same maker. The data for all the charts in this section came from computer simulations of the antennas that I performed.

UHF antennas.

Raw gain is the true gain of an antenna—using the"pure” definition of gain (as seen in Figure 4-19).

However, a fraction of the power is going to be rejected by the transmission line because of an impedance mismatch. This rejected power gets retransmitted. What is left is the net gain. Therefore, the graph in Figure 4-20 is the one you should pay the most attention to.

Here’s the legend for both graphs:

  • A: Channel Master 4228 8-Bay

  • B: Channel Master 4221 4-Bay

  • C: Channel Master 4248 Yagi/Corner-Reflector

  • D: Televes DAT-75 Yagi/Corner-Reflector

  • E: Winegard PR-8800 8-Bay

  • F: Winegard PR-4400 4-Bay

  • G: Channel Master 4242 VHF/UHF Combo

    Raw gain for common UHF antennas
    Figure 4-19. Raw gain for common UHF antennas
    Net gain for common UHF antennas
    Figure 4-20. Net gain for common UHF antennas
  • H: Channel Master 3018 VHF/UHF Combo

  • I: Zenith Silver Sensor indoor LPDA

  • J: Small indoor loops

  • K: Double-Bow

Some of these antennas are UHF-only. Although you might not need VHF presently, you probably will after 2006.

The 4242 and 3018 represent typical Yagi/Corner-Reflector UHF antennas that are part of a VHF/UHF combo. You can estimate any other unknown such antenna from these two. Just find the length of the UHF part of the boom of the unknown antenna (measured from the intersection of the corner planes to the frontmost director). Compare this length to the 4242 and 3018 to estimate where the plot for the unknown lies in the preceding graph. The 4242 has an 87-inch boom; the 3018 has a 57-inch boom.

VHF antennas.

Here are the same graphs, but for common VHF antennas. Figure 4-21 shows the raw gain for common VHF antennas.

Raw gain for common VHF antennas
Figure 4-21. Raw gain for common VHF antennas

Figure 4-22 is the net gain for these VHF antennas.

Here’s the legend:

  • A: RadioShack VU-75XR VHF/UHF combo

  • B: RadioShack VU-90XR VHF/UHF combo

  • C: RadioShack VU-120XR VHF/UHF combo

  • D: RadioShack VU-190XR VHF/UHF combo

  • G: Rabbit ears – 40° 45°

  • H,H2: Getting the most out of rabbit ears

Net gain for common VHF antennas
Figure 4-22. Net gain for common VHF antennas

If all the elements are parallel (as in a straight-type LPDA), there will be nulls at +90° and –90° that might be useful for eliminating ghosts and interfering signals.

I realize that’s a lot of information, but I’d rather you make an informed decision than just take my word for it (or, even worse, some salesperson’s opinion). With these graphs and the other information in this hack, you should easily be able to determine which antenna is best for your house, location, and broadcasting needs.

—Kenneth L. Nist

Erect an OTA Antenna

Once you’ve got an antenna, there’s as much knowledge involved in mounting it correctly as there was in selecting i. If you don’t hire an installer, you’re going to need some basic knowledge to get things right.

Once you’ve got the right antenna [Hack #32] , you’ve got to put it up. I’ve separated selection of an antenna from installation, as many folks will allow someone else to take care of installation once the initial purchase has been made. Still, installation and mounting are common tasks, and assuming you understand the possible problems, you’re ready to get an antenna set up by yourself.

Proceed at Your Own Risk

There is a chance that the first antenna you install won’t meet your expectations. Once an outdoor antenna has been installed, the seller won’t take it back; even RadioShack won’t take back an installed outdoor antenna. The cost of a second antenna might wipe out any savings you hoped for by doing the job yourself. Further, an installer won’t charge you for two antennas if he is wrong on the first try.

If you aren’t a do-it-yourself type, you can find an installer in the Yellow Pages under “Antennas” (or possibly “Televisions—Dealers and Services”). The cost ranges from $100 for an easy install to $800 for a difficult install, with $300 being the most typical bill. If you do it yourself, you will pay almost $200 just for the hardware:

  • Antenna: $70

  • Amplifier: $70

  • 50 feet of RG-6: $30

You might be able to get some free advice or a free rough estimate over the phone or by visiting the installer’s shop. If he comes to your home, the estimate won’t be free, but it will be accurate.

And, it would be irresponsible to not mention the following:

  • Every year, people get killed while erecting antennas.

  • There are places within the station’s broadcast radius where reception isn’t possible, no matter how good your installation is.

  • There are places where reception is so difficult that the challenge can outwit the installer.

  • Although the dollar cost of an antenna system is modest, a lot of your time might be required.

With all that said, if you’re willing to be careful, patient, and diligent, it’s fun and inexpensive to install an antenna. So, take these warnings seriously, but don’t let them scare you off.

Choosing a Mounting Site

Once you’ve got these terms and concepts down, your first step in erecting an antenna is to choose a site to mount the antenna. There are several considerations; here’s the rundown.

Diffraction.

Diffraction is the ability of a wave to bend around into the shadow formed by an obstruction. It doesn’t matter if it is an absorbing or reflecting obstruction. Most OTA viewers depend on diffraction for their reception. The only exceptions are:

  • Where the transmitting tower can be seen.

  • Sometimes in cities with tall buildings, reflection is more effective than diffraction.

Low frequencies diffract efficiently, but VHF diffracts poorly (see Figure 4-23).

VHF diffraction
Figure 4-23. VHF diffraction

UHF is another 10 times worse (see Figure 4-24).

UHF diffraction
Figure 4-24. UHF diffraction

Tip

These diagrams use linear shading and thus are perhaps overly pessimistic. Reception might be possible where these diagrams show no signal. Logarithmic shading would convey more optimism.

To make up for the poor performance of UHF, the FCC allows UHF stations to broadcast a much stronger signal, as Table 4-5 shows.

Table 4-5. TV transmitting power allowed by the FCC

Channels

Flat region

Hilly region

2–6

50 kilowatts

150 kilowatts

7–13

150 kilowatts

500 kilowatts

14–69

500 kilowatts

1.5 megawatts

Tip

The numbers in Table 4-5 are approximate. Stations often argue for and get a higher limit. But the goal in most cases is a 60-mile reception radius

Trees.

If the antenna is behind a tree, it is in overlapping fields: a weak field that passes through the tree plus a weak field that is diffracted around the tree. Overlapping fields are complicated, with strong spots and weak spots. If you get a UHF antenna to work behind a tree, you likely will see dropouts when the wind blows because the strong and weak spots will move around.

Many people install antennas in the winter and think they were successful. Then in the summer they wonder why the antenna totally quit working. It’s the trees!

Is a higher antenna always better?

For VHF, higher is always better. An antenna should be four wave lengths above the ground to be unaffected by the ground. For channel 3, this would be 70 feet (see Table 4-2 to check the wave length for each channel). Of course, for most houses, 70 feet is unreachable.

The rules for UHF are a little more complicated than for VHF, though. UHF is affected more by obstructions and less by height. For UHF, four wave lengths is only about seven feet. However, a UHF antenna should be higher than this in the following cases:

  • If at all possible, get the antenna above any obstructions.

  • If your horizon is less than 200 yards away, raising the antenna makes a significant difference. (You would be a candidate for a tower.)

  • As Figure 4-25 showed, even if you can see the transmitting tower, if the signal skims over the top of some obstructions, there is a stronger field just a few feet higher.

You probably will want to attach a VHF antenna to your chimney. That is also likely the best place for a UHF antenna. But if your chimney mount is still obstructed (by trees, etc.), an unobstructed site closer to the ground will work better for UHF. The essential goal is to find a spot where your UHF antenna can see the horizon in the direction of the station (see Figure 4-25).

Obstructions and their effect on antennas
Figure 4-25. Obstructions and their effect on antennas

Keeping the antenna above four wave lengths minimizes the effect of the ground reflection. Actually, the ground-reflected signal could either add to or subtract from the direct signal, so being close to the ground is not always a disadvantage. I’ve seen a situation where the strongest UHF signal was found 3 feet off the ground.

Adding to the confusion.

Diffraction over the horizon ridge often results in overlapping fields. Overlapping fields will result in weak signal spots (cold spots) and strong spots (hot spots), arranged in a regular pattern. For UHF, the hot and cold spots are often 5 to 20 feet apart.

If you are in a neighborhood with overlapping fields, moving your antenna a few feet can make a huge difference in signal strength. The chimney might seem like the perfect site, but if the chimney is in a cold spot it’s a mistake.

To make matters worse, the pattern of hot and cold spots are different for different frequencies. You will want to find a spot that is hot for all the channels you want, but such a spot might not exist above your roof. In this case you need an antenna with higher gain than is otherwise recommended.

To make matters even worse, you likely won’t discover that you are in such a neighborhood until after you have purchased and installed the antenna. To prove that you have hot and cold spots, you move the antenna (forward and backward, left and right, higher and lower) while keeping it perfectly pointed at the signal and watching the DTV signal strength indicator. It is hard to keep a large antenna pointed correctly while devoting half of your attention to not falling off the roof, but a smaller antenna might not achieve a digital lock.

At this point a professional installer starts to look like the smart choice. But will he stick with it, or will he, too, quickly declare further improvements impossible and walk away? He will hesitate to raise his estimate, but he will not work at a loss.

These problems are all UHF problems. VHF does the same thing, but with hot and cold spots 50 to 200 feet apart they aren’t evident and there usually isn’t much you can do about them.

Attic antennas.

If an indoor antenna isn’t as reliable as you want, an attic antenna is the next step up. If you are in a neighborhood with moderately strong signals, an attic antenna might work. But you are wasting your time installing an attic antenna in a poor-signal neighborhood. Most successful attic antennas are within 20 miles of the transmitter.

Tip

Thirty miles often works if you are on the crest of a hill.

The problems with attic antennas are:

  • The antenna might not be high enough above obstacles outside the house, such as trees.

  • It is hard to estimate the signal loss caused by wood and other construction materials.

  • Metal objects in the attic can block the signal.

Estimating the signal loss in ordinary construction materials requires knowledge of their water content. Exceptions are aluminum siding, stucco (which has an embedded metal screen), and foil-backed insulation, all of which totally block all signals. Concrete and most bricks have moderate water content, but their thickness is enough to block all signals. In a desert, plywood becomes so dry that it causes no signal loss at all, even for UHF. In any other place, there will be some moisture. Exterior wood is generally always wet inside, especially in north-facing surfaces. The amount of water varies with the weather. Asphalt shingles are mostly transparent to UHF, but the way they overlap encourages water to persist between them. The vapor barrier is often wet on one side or the other. The bottom line is that there is no way to quantify the signal loss in these materials.

Metals reflect signals. A metal object eight inches long is big enough to reflect UHF. Smaller objects, such as nails, are of no concern. Wires and metal pipes effectively reflect VHF, as do plastic pipes containing water. If these reflecting objects are positioned to the side, to the rear, above, or below the antenna, they will have little effect on it, provided they aren’t too close. These objects should be further away than two feet for UHF, four feet for VHF-high, or six feet for VHF-low, and an even larger separation can help a little.

Tip

You might wonder why these numbers aren’t proportional to the wave length. It is because the lower-frequency antennas are lower in gain. An antenna’s aperture depends on the gain as well as the wave length.

There should be no horizontal or diagonal wires or pipes in front of the antenna. A perfectly vertical metal vent pipe is invisible to TV signals, but its flashing at the roofline might not be.

—Kenneth L. Nist

Don’t Use Portable Signal Strength Meters

When working with an OTA antenna, you’ll waste your time by trying to use a portable signal strength meter. Understand why, and avoid this common mistake.

Sometimes readers ask where they can get a portable signal strength meter, thinking this will allow them to make objective studies of the signal from their OTA antenna [Hack #33] . However, a signal strength meter is not as useful as you might think. It will work fairly well for normal standard-definition broadcasts, but the fact that you’re here probably means you’re looking for HD broadcasts.

For HDTV, a strong meter reading is no guarantee that you have found a good reception spot. The ultimate arbiter of where the signal is good for your receiver is the HD receiver or set top box [Hack #30] itself. Therefore, I recommend that the signal strength readout provided by the receiver—not a meter—be used to search for the best antenna spots. The quality of the result justifies finding ways around the small problem you will discover when you try to do this: your antenna is rarely located where your receiver is! This means you (obviously) can’t see the signal readout while mounting the antenna. This is still fairly simple to solve, though. A spouse and a mobile phone, or a buddy with a walkie-talkie is more than sufficient to get around this issue.

This same principle applies for pulling in signal from a satellite dish, such as when installing DirecTV or DISH Network. There are some great gadgets that will help you get things pointed in the right direction, but there’s no substitute for checking the receiver to ensure you’re getting signal.

Tip

Keep in mind that “receiver” in this hack always refers to the cable or satellite receiver, and not an audio receiver. All cable/satellite receivers will have some sort of system menu where you can check the signal strength.

—Kenneth L. Nist

Resolve Problems After Buying an HDTV

There are a handful of tips you can follow and tweaks you can make to your setup after adding HD-capable devices. These are fairly random but all together they can make a huge difference in quality and operability.

No matter how much research you do before buying a TV, you’re still almost guaranteed to have a few surprises and problems when you break the set out of its box. This hodgepodge of tips and technical explanations will help you solve the most frequent issues you’ll run into.

Bridging Component Video and VGA Connectors

You’ve just brought home a new unit, and you’ve discovered that your HDTV requires a VGA cable, while your receiver offers only component video connections (or the other way around). Some manufacturers have anticipated this situation, and have designed their sets to break the rules, in a manner of speaking. That is, some VGA ports might allow syncs on the green wire.

Tip

For VGA, Hsync and Vsync are the fourth and fifth wires (remember that VGA connectors have five cables). In component video, these syncs are multiplexed onto the green wire (labeled Y in a Y-Pr-Pb system).

For example, my TV set will accept component video force-fed into its VGA port. There was nothing in the set’s instructions about this, but I found a menu item that allowed the set to accept green-wire syncs.

If the unit literature says nothing about this, ask the “expert” at the store where you bought the TV. If the sales staff doesn’t know anything about such an option, you can experiment. Adapters that might work are available via the Internet. An alternative to the adapter is to get a VGA cable that has five BNC connectors on one end, and then get three BNC-to-RCA adapters from RadioShack. These cables probably will cost around 50 bucks, but you can often return the cables if things don’t work out.

Understanding Subchannels

Let’s say the FCC has given the NTSC station on channel 3 permission to use channel 41 as a digital (HD) channel. So, you tune to channel 41, and your new receiver says you are now on channel 3-1. To add to the confusion, you also have discovered there is a channel 3-2. What are these channels and how did they get there?

You’ve discovered virtual channels. A virtual channel is a physical channel with a different name or number. The physical channel refers to the actual RF spectrum being used. The virtual channel could be called almost anything. In this example, 3-1 and 3-2 are virtual channels, and also are referred to as subchannels of virtual channel 3, which is physical channel 41. And just to confuse matters a little more, these virtual channel 3s have absolutely nothing to do with an analog station that is on the physical channel 3.

The data stream of DTV channel 41 has data blocks called PSIP data. The PSIP data tells the receiver that channel 41 has two subchannels: 3-1 and 3-2. The channel 3 people choose these subchannel names to remind you whom you are watching. However, not every station follows the example of this hypothetical channel 3; a different management might choose 41-1 and 41-2 for physical channel 41’s subchannels.

Your remote control will let you key in either the physical or the virtual channel number, but there are some differences between manufacturers. For example, some cable/satellite receivers will assume 3-0 means analog channel 3, while others will try to locate a virtual channel 3 for the same key sequence.

Why Can’t I Get My Local DTV Station?

Your first days with your new HDTV can be a very confusing and frustrating time, particularly where OTA stations are concerned. You can’t tell your receiver that a channel is digital; the receiver has to figure out for itself whether a physical channel is analog or digital. If the antenna is getting a marginal signal or is mis-aimed, the receiver often guesses incorrectly. You then can’t aim the antenna because the receiver thinks the channel is analog, and you can’t convince the receiver to switch because the antenna is mis-aimed. In strong signal areas, the receiver might eventually right itself. Otherwise, you might have to figure out how to make the receiver unlearn a channel (consult your menus and documentation). Even if you get this fixed, though, you’re still going to have a mis-aimed antenna.

Nearly all DTV receivers have a signal strength meter of some type. Most of these meters read zero until the signal is good enough (or almost good enough) for reception. In weak signal areas, these meters won’t tell you much about whether you need your antenna to aim more to the right or to the left. When you get no reception, you are left not knowing whether your antenna is just mis-aimed, or if the signal strength is inadequate. As you might guess, this leaves a lot of room for guesswork and can lead to plenty of frustration.

The good news is that once the receiver has learned all the channels correctly, these problems are gone forever. In fact, people in areas with strong signals will never see most of these problems to begin with. All receivers have a channel learn sequence, in which the receiver will search for and learn all available OTA channels at once.

Tip

When you initiate this learning sequence, some receivers will forget everything they learned previously, which creates problems for users who use a rotor or who switch between two antennas. These users will need to learn how to add channels manually.

Picture Quality

The image quality of an HD picture isn’t affected by a low to moderate level of noise in the signal. This is true for both satellite and OTA DTV. Yet some people can’t resist wondering whether some antenna tweaking would improve the signal strength and result in a better picture. The answer, without any hedging, is that this sort of tweaking will have no effect on picture quality.

When the signal for a channel becomes too weak to display, you will see macro-block errors—parts of the screen will be shifted or out of place—and you will experience sound dropouts lasting a few seconds, as well as image freezes lasting a few seconds. All of these errors are crude, unsubtle errors. If these are not present, your image is perfect. You either get the picture, or you don’t.

Once you’re at this stage, there is still one reason you might want to try to improve the signal: you might be able to decrease the chance of dropouts in bad conditions, such as heavy rain. Rain can affect DBS and UHF reception, but not VHF. In some places, wind can affect UHF.

Warning

If you get sound dropouts but not image dropouts, or vice versa, the fault is not a reception problem. Usually the station is at fault, but occasionally it is the set top box [Hack #30] .

Determining Display Resolution

It’s often hard to tell if you’ve got a picture in full-blown 1080i, or if you’re seeing 720p [Hack #1] , or just plain old 480 (progressive or interlaced). When a TV station decides to provide an HD subchannel, that subchannel is normally 1080i (or 720p) all the time at the transmitter, even if some of the programming originates from NTSC cameras that can’t capture HD images. There is no technical requirement for this, but it seems to be nearly universal practice. Thus, your receiver’s HD detector is not a reliable indicator of whether the program is actually HD. It will pick up the transmitter’s information rather than the format of the source material.

Tip

NTSC 4:3 images often have black bars on the side that you might not be able to eliminate because they are part of the 16:9 transmitted image.

So, what is the most reliable way to tell if you are seeing true HD? If the image is 16:9, the image is not stretched, and there are no black bars on the sides, you’re almost certainly looking at an HD image. ABC and ESPN typically are sending in 720p, and most other carriers are sending 1080i images.

Waiting on Local Networks to Broadcast in HD

All DTV transmitting equipment can handle HD at no extra cost. The only extra cost associated with passing on HD information is that associated with staffing two sets of transmission procedures. However, the cost of the DTV transition has hit the local stations hard, and some are resisting even this small expense.

Also, many of the newest DTV stations are rural stations. Rural stations often don’t have HD taping equipment, let alone a staff that can operate this higher-end gear. So, if you’re not in a larger city or television market, you might be stuck pulling in HD from a satellite provider for a while.

Grabbing HD Local Channels Through Satellite Providers

As you’ve no doubt figured out, most satellite providers give you local channels through their feeds, usually for a nominal cost. It would stand to reason, then, that HD versions of these local channels would soon follow. That turns out not to be the case, though, and probably won’t be for several years. An HD channel requires about five times the bandwidth of an SD channel. To convert all their local channels to HD, DirecTV and DISH Network would each have to launch several more satellites.

Tip

Both companies are very secretive about their future plans

Another seemingly good idea would be for satellites to simply pass through local channel HD feeds, supplying consumers with a single source for all programming (the satellite dish, as opposed to requiring both a dish and an OTA antenna [Hack #33] ). However, the National Association of Broadcasters lobbies effectively for local stations. As a result, Congress has legislated that these stations continue to enjoy their monopolies, and disallows satellite providers from passing on their feeds. In most cases the satellite operators are forbidden to offer viewers feeds or stations that would compete with the local channels.

The only exception in this area, at least right now, is CBS. CBS-HD is available on DirecTV and DISH Network. But to qualify for this, you probably will need a waiver from your local CBS station.

Getting Rid of Artifacts

In image processing, an artifact refers to any predictable flaw in the image that results from shortcuts or shortcomings in the processing technology. In HDTV, most artifacts result from compromises that have to be made when the picture changes too rapidly and requires more than the allowed band-width. Sometimes the solution to these bandwidth limitations is to delete frames, while other times the choice is to randomly delete 16x16 macro-blocks. There are also a number of common artifacts that result from converting 24 frames/sec films to 30 frames/sec TV broadcasts; this category of artifacts generally is not something related to bandwidth, and probably will be solved as conversion processes improve.

Tip

Snow and interference generally aren’t called artifacts.

It’s also not uncommon for a particular HDTV set to introduce some artifacts of its own. If you see these consistently, on multiple channels, contact your set manufacturer and see if you can get some resolution. You might also be trying to view broadcasts at a higher resolution than your set supports (although this is rarely the case with any but the first-generation HDTV sets).

The Problem with SD Programming

In cases where SD programming is pushed out via an HD broadcast, you can get an almost unheard of phenomenon, at least in HD programming: snow. Remember I mentioned earlier that either you get an HD picture, or you don’t. That’s true, but SD programming over an HD transmission is a bit of an exception. This is a consequence of the change in the bandwidth between recording and playback. Although the bandwidth of SD is said to be 5 MHz, it is not a sharp cutoff. The roll-off starts before 5 MHz, but some image information above 5 MHz survives the recording process, albeit mixed with electrical noise (which shows up as snow). The broadcaster has to decide if she wants to filter out this snow or leave it in. If the broadcaster decides to filter out the snow, some image information is lost, resulting in increased blurriness. Because this is a trade-off, different broadcasters will make different choices.

There has been a significant improvement in the average quality of NTSC broadcasts over the last three years. There are two reasons:

  • True SD resolution (640 x 480) used to be a target TV production crews believed they had to aim for but didn’t really have to meet. Their product often was well below 640 x 480, for a variety of reasons. But now, with large, high-definition sets becoming common, these production people are seeing how bad their product can look, and are paying more attention to the details (camera focus, circuit noise, cable reflections, filter circuit selection, etc.).

  • Many people are watching NTSC broadcasts of shows that were shot with high-definition equipment. These situations always reveal any deficiencies in the SD source material.

—Kenneth L. Nist

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