Hawes Mechanical Television Archive by James T. Hawes, AA9DT
DTV Changeover FAQ, Part 6

DTV Technology Questions

QUESTION. Will I be able to get all the same stations that I get now?

ANSWER. That depends on the distance and direction to each station. Terrain, buildings, weather and trees between you and the stations also affect reception. Here are two possibilities...

Maybe not. Suppose that you live a long way from a station. For analog reception, you're in a "fringe" or "deep fringe" area. In addition, maybe your antenna is inadequate, or isn't ideally aimed at the station. Due to the Cliff Effect, you might not get any digital pictures.

Maybe so. Suppose that you live near a big city. You receive several analog stations, and reception is fairly good. You'll probably get most of the same stations, and you might even pull in a few new ones.

Symbol for DTV conversion program

Frequency shift and coverage. Many stations are shifting to new frequencies. Some, but not all VHF stations will move to UHF frequencies. The local coverage area of the new frequencies usually matches the coverage of the old frequencies. (The typical match is 90 percent or better.) I suspect that fringe-coverage conditions of widely-separated frequencies probably don't match as well. For instance, lower frequencies tend to travel further. Higher frequencies tend to be less noisy. In an analog picture, noise makes "snow." Yet noise can destroy a digital picture. Add this fact into the bargain, though: Digital signals have a higher average signal strength than analog signals do.


QUESTION. How well do these DTV converters perform?

ANSWER. In Chicago-area tests, a Zenith DTT900, ATSC converter picked up 11 extra stations. Some of these are multicasters with three or more subchannels. Analog sets here receive about 19 stations. Our digital test pulled in 30. Add to those the UHF stations that we could never before see on this particular set. Now they come in fine. For the test, we never re-aimed the roof antenna. In fact, the test antenna is very old, and missing a few elements.

Despite our inadequate setup, the pictures seemed sharp, ghost-free and clear. The color was extremely saturated. Some might like this effect, but to us it seems unnatural. We also noticed frequent digital artifacts. The artifacts are a definite step down from analog. A common problem is that digital pictures often don't fill the screen. We were glad that the Zenith includes a "Zoom" button that fixes this problem. Yet the Zenith doesn't work through a switchbox. That's another minus.

Analog problem. Some stations might not convert to digital broadcasting. Of course, you won't see these stations through a decoder box. The Zenith doesn't have a passthrough switch to allow analog television viewing after conversion. An external switchbox would fix this problem, but the Zenith refuses to operate through a switchbox. Our test switch is a Radio Shack unit. The only way to watch analog shows is to reconnect the antenna to the TV.

Dealing with artifacts. On the artifacts, the Zenith converter is probably better than most. The Zenith picture seems better than what we saw when we tested a Digital Stream DTX9900 box. Neither box provides the picture quality of a Channel Master CM-7000 box. In quality, Zenith is closer than Digital Stream is. (With an excellent antenna, a nearby transmitter and no obstructions, you'll see the fewest artifacts.)

System crashes. Another problem is system crashes. So that we could record several shows, we left the Zenith box on for a few weeks. When the box is on for long periods, it sometimes crashes. Then you get a static scene. The scene consists of parts of a picture and some cryptic hex numbers. The box won't change stations or even turn off. It's completely locked up. Time to hit the big switch and reboot! Then everything's fine. In the first six months of converter use, I coped with four such crashes. My DTV recorder dutifully time-shifted one crash for me. Great: A half hour of digital gibberish.

Screen shot off TV when our DTV box crashed What a decoder box crash looks like.

The Upshot? After the fourth crash, the DTV box looks a little different to me: These converters work well. Yet they aren't as simple, reliable or easy to use as analog tuners are. At least converters aren't that expensive. Use your NTIA coupon and buy one. Try it out. Maybe you'll be satisfied with the result. You can always return the box for your out-of-pocket expense. In that case, you'll lose the coupon. But, if you venture nothing, you gain nothing.

For converter reviews, see these sites...


QUESTION. I want to upgrade to a DTV set. What should I do with my old TV, VCR, TiVo, DVD player, etc.?

ANSWER. Sell it to your uncle in Mexico. (Honestly, someone could make a good business of remarketing used TVs in Mexico!)

There are many other good uses for your analog TV set...

  • Use it to watch recorded shows on analog DVD or tape.

  • Use it to play analog video games.

  • Use it as a monitor with your home video security system.

  • Donate it to charity.

Or recycle your equipment the green way. See...


QUESTION. My converter worked when I installed it. Now all I get is snow. What should I do?

ANSWER. Follow these steps...

  1. Get the TV remote (not the converter remote).

  2. Set the TV to Channel 3. (Some areas use Channel 4. Try channel 3 first.)

  3. Put the TV remote away. From now on, don't use it to change channels. To change channels, only use the converter remote!

  4. Get the converter box remote. You'll need it for the rest of the steps.

  5. Turn on the converter.

  6. Check the converter LED to see that the unit is on.

  7. If you have "passthrough," switch it off.

  8. Tune in the station that you want to see.

Still doesn't work? Check these connections...

  • The cable between your antenna and the converter.

  • The cable between the converter and your TV set.

  • On converters with separate supplies: The cable between the converter and its power supply.

  • On converters that connect to the wall: The cable between the converter and the wall outlet.


QUESTION. After the analog stations shut off, my converter stopped receiving a few digital channels. How can I get these stations back?

ANSWER. Rescan your channels. To do that, follow your converter's instruction manual. If you lost the manual, click the <MENU> button on the remote control. Then follow the onscreen instructions.

Before the analog station shutdown, some digital stations operated on temporary channels. After the shutdown, these temporary digital stations went off the air. Afterward, the channels that you miss moved to their final locations.

Rescanning the stations allows your converter box to find the new channel locations. In about five minutes, you'll be watching your favorite stations again.

Oh, one more item: When you tune in those new channels, you want the picture to fill the screen. Don't forget to reset the <ZOOM> control. (On some sets, this is the <ASPECT RATIO> control.)


QUESTION. My converter only displays a still picture. The TV screen is full of numbers. Did I break this thing?

ANSWER. Your converter probably isn't broken, but it definitely crashed. Computers do that, and your converter is a computer. You'll notice that none of the controls work, either. I've seen crashes where you can't even turn off the unit!

Unplug the unit and leave it unplugged for 30 seconds. Then plug it back in again. Turn it on, and tune in a show. If you're lucky, everything will be normal again.

To reduce the chances of a crash, connect your converter to a surge suppressor. Some people even use an uninteruptible power supply (UPS). Also when you aren't using the converter, turn it off.

Converters use CMOS parts that are very static-sensitive. Computer programs operate the converters, and these programs have bugs. Everything is built for economy, not reliability. Let's face it: DTV is less dependable than analog TV. In that respect, our government cut us a bad deal. We needed the chance to vote on this change. How about a chance to vote in compatible digital TV? We deserved the chance to buy what we want to buy. And to watch what we want to watch.

Screen shot off TV when our DTV box crashed What a decoder box crash looks like.


QUESTION. What are some drawbacks to DTV?

ANSWER.

  • Cliff effect. There is no "deep fringe reception" or "TV-DX." You get a picture, or you don't.

  • Digital artifacts. At picture transitions and during movement, the picture breaks up. Sometimes the screen freezes. Afterward, you temporarily lose synchronized sound.

  • TV remotes won't work anymore. The converter assumes the remote control functions. The converter remote might not have all the features that you depend on.

  • VCR, DVD-R or DVR won't be able to change channels anymore. This problem is only cause for concern when you record off the air.

  • Coverage area isn't the same. In most cases, the coverage area is 90 percent or more of the analog coverage area. If you're in the "90-percent area," that's great. If you're in the "10-percent area," that's not so great. Rural locations might have more difficulties than urban areas will.

  • Stations change numbers. In some cases, digital tuners can switch to the new numbers for you. Otherwise, memorizing new numbers is inconvenient, but not difficult.

  • Channel 3 inconvenience. Channel 3 is the converter box's "output channel." Your DTV box translates all DTV channels to an analog signal on Channel 3. Still, a new digital channel might move to Channel 3. In that case, you must switch your converter box and TV to Channel 4. The converter box switch is on the back of the unit. After you flip the switch, select stations with the converter remote. Don't try to select stations with the TV remote.

  • Channel surfing is more difficult. Analog TV channel changes are instantaneous. Digital TV channel changes are slow. Also, with multicasting, you must remember to surf both channels and subchannels.

  • Changing channels takes more time. Somehow, in this case, progress means slowing down. Slow channel changes are an obvious flaw that will obsolete this product generation. The idea is probably to persuade you to buy the next version.

  • The environment. The DTV changeover will cause Americans to discard working TVs, VCRs, DVD players, games and TiVo units. This nouveau trash will foul landfills all over the country. A few years from now, landfills will also absorb millions of defunct converter boxes. Most of the converters will still function, too. Future archeologists will laugh at our folly.

  • Reliability. Digital devices aren't as dependable as analog devices. Compare your AM radio to your PC. Which one crashes more? Which one stalls? Which one comes on instantly, and which one takes forever? By the way, this isn't just theory. A DTV converter box can and will crash.

  • Planned obsolescence. Unlike analog devices, digital devices tend to become obsolete every few years. How many versions of Windows have we seen since the beginning? Ten? Eleven? An analog TV probably could outlast all of them. Expect manufacturers to obsolete your digital TV every two, three or four years.


QUESTION. I watch sporting events, and I'm concerned about digital artifacts. What does an artifact look like?

ANSWER. You have reason for your concern. Sporting events are among television's finest programs. These programs push the limits of the technology, and they provide some of the best pictures. This point is especially true of live events such as football and automobile races. Sports enthusiasts are television's "power users" and also its strongest critics.

A digital artifact might involve the whole screen, or just a part. In the worst digital artifacts, the picture freezes and breaks up into a panel of squares. The screen might stay this way for several seconds. Of course, you miss the action. You might have seen such digital artifacts with analog reception of digital shows, such as shows from a satellite. (In these shows, the program is digital up until the transmitter.)

Digital artifacts tend to occur when a large part of the picture changes. For example, when a foreground football player dashes across the screen. Or when the scene changes. Since sports involve a lot of motion and scene changes, expect to suffer through many digital artifacts.

In sports television, the worst problem of artifacts is that they obscure rapidly- changing events. Such events are the essence of sports! Also during and after a digital artifact passes, the sound often goes out of sync.

Except for digitally-originated shows, analog TV has no digital artifacts. We might as well say it: Digital artifacts are a terrible drawback of digital TV. The lack of digital artifacts is a serious advantage of analog TV.


QUESTION. What are the digital channel assignments for my area?

ANSWER. For the national list (by state), click Digital Channels.

The links below help you to find all the stations in your area. You can also find the distance to the station antenna. This information will help you to aim your receiving antenna for the best picture...


QUESTION. My converter has two (or three) types of outputs. Which connectors do I use?

ANSWER. The coax output is the one that most people use. That's why most manufacturers provide a coaxial cable. Connect the coaxial cable between the converter box output and the TV's antenna input.

The RCA jacks provide an AV output that bypasses part of the TV. Result: A better picture. Very few qualifying converters (such as Channel Master) provide a DIN jack output. This jack is for S-video. The DIN output bypasses more of the TV circuit and offers you the best picture. Of course, your TV must also have an AV or a DIN jack. Here's a summary...

Good Better Best
Coax RCA (AV) DIN (S-video, Y/C)


QUESTION. Will the new ATSC, digital standard last as long as NTSC did?

ANSWER. Not likely. Digital devices become obsolete much faster than analog devices do. Think about how many PCs or cellphones you've had in the past 10 or 15 years. Other digital devices have come and gone, too. For example...

  • Several times, manufacturers have updated DVD player software. Today, not all players can play all commercial discs. For home-recorded discs, the number of compatible players is even smaller.

  • Sony wants Blu-Ray® to succeed conventional DVDs. Expect Blu-Ray to last only a few years. Development on holographic DVDs proceeds.

  • The HDMI standard in many of today's DTV products has already been through many upgrades.

  • Manufacturers introduced first-generation DTV converter boxes only a few months ago. These are already giving way to Generation 2 boxes. Can Generation 3 be far behind?

  • Today's DTV depends on the MPEG2 standard. Many years ago, MPEG4 surpassed MPEG2's compression abilities. DivX® uses MPEG4. One DivX DVD can hold up to seven movies.

DTV didn't just pop up. Engineers began designing it in the 1980s. By the 1990s, the standard was complete. DTV is 20-year-old technology.

Due to Moore's Law and economics, the digital product design cycle is about three months long. For example, as soon as they hit the assembly line, PCs are obsolete. By then, three generations of replacements are well developed. Your new PC might serve you for 18 months. By then, you've installed a couple of service packs to keep the software alive. Eventually, the memory becomes insufficient. Or the feature set is incompatible with the rest of the world. The same will happen for DTV (ATSC) products.


QUESTION. What's the evidence of DTV's coming demise?

ANSWER. Of course, we don't have a crystal ball. But note these facts...

  • The existence of DivX®. ATSC digital TV depends on MPEG2. DivX uses the superior MPEG4.

  • The lack of flashable EPROMs in many DTV decoder boxes. These would allow upgrades and bug fixes on the fly. Too bad. Instead, manufacturers have built in obsolescence.

  • The announcement of Ultra HD. This television system offers a far better picture than HD. NHK has already demonstrated the system to the press. Of course, the company representative denies that this system will obsolete the current system. (Remember Eric Idle in the old Monty Python skit: "Nudge, nudge. Wink, wink. Need I say more?") See... Ultra HD.

  • The announcement of Digital 3D. This television system offers television in 3D, without the bothersome glasses. The press has already seen demonstrations. Several major manufacturers have announced research or even manufactured systems. Philips, HP and Sharp are some of the companies that are pursuing 3D. See... 3D TV .

  • The energy demands of current display technologies. The color CRT was no slouch, but flat-panel displays have far surpassed CRTs in energy siphoning. Consumer Reports notes that some flat-panel displays use as much energy as a refrigerator. Engineers are working on this tremendous new household cost. Just as they tamed color TV, they'll find more efficient flat-panel technology.

  • The continuing invention and improvement of display technologies. On the forefront are new technologies such as FED and OLED. We'll see many more.


QUESTION. What's inside my DTV box?

ANSWER. A digital computer. For those who know computer hardware: The computer includes an MC68360 microprocessor, SDRAM, ROM, an I/O port and a bus system. The processor divides down the crystal clock frequency to produce necessary outputs. One of these is the 3.58 MHz color burst frequency.

Computer system. The LG converter boxes use a 32-bit computer system. The MC68360 microprocessor is a descendant of the famous, Motorola MC68000 processor. The 68000 was the brains of the original Apple Macintosh and Commodore Amiga computers. Today, Freescale manufactures this processor family.

Processor design. Engineers designed the MC68360 for communications. Its other name is QUICC, for quad integrated communication controller. Onboard the chip are four serial communications controllers (SCC). The chip also includes two serial-management controllers (SMC) and a serial peripheral interface (SPI).

Peripherals. Your converter box includes some very useful peripherals...

Inputs Outputs
  • RF detector

  • MPEG-2 decoder

  • Infrared remote interface

  • Digital-to-analog converter

  • RF modulator for analog TV

  • 3.58 MHz subcarrier modulator

  • Sound subcarrier modulator

Details. The RF modulator transmits its AM carrier on Channel 3 (61.25 MHz). This composite signal includes vertical and horizontal sync, plus the monochrome or Y video signal. The 3.58 MHz subcarrier modulator is also on the output side. The subcarrier modulator transmits a QAM-SC (quadrature amplitude modulation, suppressed carrier) signal. Two multiplexed signals ride the subcarrier: The red (Pr or R-Y) and blue (Pb or B-Y) signals. The sound carrier modulator is another peripheral. This FM modulator operates at 65.75 MHz, 4.5 MHz above the picture carrier.

Block diagram of LG, 
      5-chip DTV box

Chipset. Your DTV box might include either of two versions of the LG chipset. The first-generation version uses five video-processing chips. (On the block diagram at left, these chips appear in red. The microprocessor, in blue, is in the lower-left corner.) The second-generation chipset uses only two chips. Besides these chips, the box includes the standard computer hardware and television peripherals.

Here are the names of the five video-processing chips...

• VDP • VD • Transport
• VCD • Sym EQ


QUESTION. Is the box hackable?

We haven't investigated inside the box, and don't know if the factory potted the components. We also don't know how much proprietary hardware is in there. I've read that at least the early boxes don't include writable flash memory. Too bad. But, hey, a converter's a computer, and computers are universal machines. Then in some sense, these boxes are hackable! Plus, in a few years, converters will start turning up at resale shops and rummage sales.

By now, hackers are planning to replace the converter program with their own code. Maybe they'll figure out how to play converter Pong, Space War or Tank. After all, if the firmware is accessible, the box could run other applications. Food for thought, you guys: Since it includes video peripherals, the box is particularly well suited to graphic-display applications.

At one time, Agilent produced an emulator for MC68360 applications. Amateur developers might have some use for the Agilent manual. See... Agilent book.





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