Digital Television 101 01010101

Bruce Jacobs' (Twin Cities Public Television) "How To Buy A TV" has proven to be by far the most popular post in the nine-month history of this weblog. Henry Ruhwiedel, Chief Engineer of WYIN, Gary-Merrillville, Indiana, has written another essay on this theme. While some of it is specific to the Chicago market, the essay in the continuation area below has lots of helpful general information on the topic of digital television reception. --Dennis

Digital Television 101 01010101
By Henry Ruhwiedel

Somewhere out there you may have noticed advertising for HDTV, Digital TV, or programs that start with a logo or banner saying available in HDTV. There is a whole new TV system, and your old TV sets will be obsolete soon. Here’s what you need to know to be smart about digital TV and the future of Broadcast television.

When I was a kid, FM radio was just beginning and we all had AM radio, 45 RPM records and LP’s. And some of us still had 78’s. Many cities only had VHF TV stations and we had to buy a converter box to put on the top of the TV to get the new UHF stations. If you lived in Ft. Wayne, South Bend or other UHF only areas you bought a set top box to get the VHF stations from Chicago, Grand Rapids, Indianapolis or Champaign. Eventually we all bought AM-FM radios, and later stereo FM radios, and color TV sets with all channel tuners covering channels 2-83. Some of us also got cable TV, and a new box was added to get the “cable channels.” Over time we went from receiving only a few local stations to a hundred or more via satellite, cable and over the air. The transition to digital TV broadcasting is going to be the same.

In Chicago there are 15 over the air TV stations that can be received by any TV set. 2, 5, 7, 9, 11, 20, 26, 32, 38, 44, 50, 56, 60, 62, 66. There are also a few low power TV stations that cover small areas, 4, 13, 23, 28, 36, 68 and if you live close to their transmitter you can also receive them free over the air as well. These are all what we call NTSC or analog television stations. But there are also 15 digital TV stations, each paired with its full power station. Just as FM was often introduced by simulcasting the better known AM stations, the digital TV stations transmit the same programs as the analog stations, and a whole lot more. Each digital TV station can send several programs at the same time, providing up to 6 channels of information per station. It’s magic and in a bit I’ll tell you about how it’s done. The important part to know is that the analog TV stations will soon have to turn off their transmitters and to get free over the air TV you will need to have a new digital RECEIVER, which can be a whole new TV set, or just a converter box to convert the digital TV signals to analog TV signals your current TV can receive. You really should get one now, and begin enjoying the perfect pictures and sound and added programming only available on digital broadcast TV. I’ll tell you what to look for a little later too.

If you have cable or satellite, you do not get the extra digital channels. Cable and satellite are not required to carry the additional programs DTV stations send out. So to get all the local programs, you can only watch them on a new digital TV receiver, they are not available on cable or satellite. Only free over the air TV stations provide these extra programs to you. Cable and satellite only carry the free over the air analog signal. So keep your antenna to get more free TV viewing! Do not allow the cable or satellite people to disconnect and remove your TV antenna, it is your only way to receive the new digital high def channels in pristine condition.

What is digital?

Even for us in the business it is confusing. There are several “flavors” of digital. Most people have heard of high definition TV or HDTV. That is one flavor. Not all digital TV is “high def” and even a lot of TV sets sold as HDTV are not fully high def. It’s a jungle out there and you need a road map, so here it is!

All of the over the air digital TV stations transmit a digital signal. Sort of makes sense, but it’s what the digits mean that makes the difference. We all send exactly the same number of digital bits. Just like your computer has bits and the floppy drive and hard drives have a maximum number of bits they can hold, but the bits can represent anything we want. In digital TV we all send exactly 19.39 million bits per second. It’s how we divide that number to provide different programs in the same channel that is the magic part.

TV stations, just like your computer, sort out the bits into files. Each file can be anything; it’s just a collection of digital information. In digital TV, we create a file for each program transmitted, and the digital TV set sorts out the data so you can view each file as a separate program. Right now TV stations in Chicago are sending as many as six different programs. Your computer allows you to name each of your files. In Digital TV, the TV station puts a label on each program file and generally it is a simple numbering system, 56-1, 56-2, 56-3 etc. The digital TV set reads the file name, called PID or PSIP and displays the information as a channel number and a program guide.

The TV set manufacturers also decided the consumer would be confused if the digital TV station was not numbered the same as the analog TV station, so when the digital TV is programmed to receive all the channels, the channel ID will usually show as the same channel for analog and digital. The TV set is “smart” enough to know that even though the signal is really on two different radio frequencies. For example WYIN analog is on RF channel 56 and the WYIN Digital signal is on RF channel 17.

Magic happens here.

Back to the bits. Except for a small part of the 19.39 mbits that are used to tell your TV set to display information, such as channel number, program name, captioning, V chip ratings and other technical stuff, the rest can be used to send anything. During the transition period, between now and when the analog TV stations are ordered to shut down, every TV station is required to provide one primary TV service, which is duplication (simulcast) of the analog signal. That primary TV channel can be of any DTV flavor, from standard definition to high definition. It can have mono, stereo or full 5.1 surround sound. There is no requirement other than the picture and sound need to be equal to the analog signal. If a station chooses to send a standard definition signal, it takes as little as 3 mega bits per second, and a full high definition signal can take up to 18 mbps. Now you don’t need to know that when you go into a store, its just a way to explain how the TV station can send more than one program at the same time, just as your computer can store more than one file on a floppy, CD or hard drive. Its all just bits and bytes. The more bits, the higher the quality of the signal you receive.

In very simple terms think about it as shopping for groceries. At the check out you can only get one water melon in the bag, or several cantaloupes, or a whole lot of grapes. It’s how you divide up the space in the bag. In digital, it’s how you divide up the available number of bits that determines how many and what size (SD, ED, and HD) each channel can be.

We already did this in analog TV, first we sent black and white TV and monophonic sound, then we added the color information, then a second audio channel for stereo, then another audio channel for SAP (second audio program), and another for station use called PRO, (professional channel) then closed captioning, and a whole bunch of other stuff you may not even know we send, such as time of day to stop your VCR from blinking 12:00! We just made more room by going to digital signals.

DIGITAL it’s not just for computers.

There is a massive marketing campaign by everyone to identify themselves as digital. It’s the buzzword of the decade. There is digital cable, digital TV, digital satellite, digital antennas, and digital everything else.

Being digital does NOT make it better. And even the label is being used to promote products that are not digital. A Digital Ready TV is not digital. A Digital TV antenna is not digital. Digital cable just means they took the analog signals, converted them to data and then in your cable or satellite box, the data is converted back to an analog signal. It is nothing but confusion and you can ignore most of it as simply a sales gimmick. In most cases, the perfect analog TV signal is converted to digital so the cable or satellite TV provider can squeeze more channels into the same cable. They do this by throwing away a lot of the bits, reducing the picture and sound quality.

You may have noticed, especially in dark picture areas, visible contours, blocks and ragged edges, or stutter motion, soft edges and lack of detail, picture freezes and other artifacts. These are all the result of removing information from the original signal in order to deliver the signal with just enough information to be viewable. This is called data reduction or compression. Some times it is good, and others it is not. The technology of cable and satellite TV is limited in how much it can send in a data stream. In order to get more channels, the signals are compressed to get more into the same data stream. Just as I explained above, it can take 3 to 18 mbps for one TV program. Satellite and cable try to get this down to as little as 1 mbps. The result is often poor picture quality well below good analog broadcast TV, and closer to 6 hr VHS tape. Broadcast TV delivers the best quality TV picture, after all this is where it all starts. Everything else is a processed version of what we send out.

Analog vs. Digital

Believe it or not, nearly all of the TV you watch was created in analog form and converted to digital. Even on the “digital” channels most of the material is converted analog TV. It’s only in the past few years that program creation, transmission, and storage has been converting to digital. Even the many programs sent on the “high definition’ HDTV channels are converted from analog tapes. So for the next decade or so you will see a variety of picture quality as the mix of programming goes from all analog to all digital. Just as there used to be a mix of mono and stereo or color and black and white programs, TV stations have spent billions of dollars in conversion efforts to bring you digital TV, and billions more will be spent to complete the transition. That is why some DTV or HDTV programs from broadcast TV, DVD, cable or satellite will look great, and others not so great.

TV stations have been converting to digital also. Most began by changing from analog cameras and analog news tape to digital cameras and digital news tape. All of our local news is produced and edited in digital format to provide the best possible picture and sound quality.

Tape libraries have thousands of programs on analog tape, but as stations acquire new ones, they are now usually acquired and stored on digital tape or as digital computer files. Soon all stations will be recording their programming in digital format. But it all takes time and a lot of money for new equipment. Public stations, such as WYIN fund the costs via member donations and grants. Commercial stations rely on advertising income to convert to all digital.

DTV to you!

Digital broadcasting began in Chicago about 1999. Local station WYIN began transmitting its digital signal in early 2004. They have a new solid state transmitter and a new antenna that send out the signal on UHF channel 17. They can send up to four programs at the same time, and have been experimenting with multi channel transmissions. Remember TV stations are only required to transmit one primary DTV signal. DTV stations can use all the rest of the bits for anything: additional programs, or data for businesses, digital paging, private data channels, music, services for the handicapped, “radio” signals for emergency services (police, fire, etc) or just nothing.

Each channel has a digital identification signal called a PID or PSIP (Program Identification). Your home digital TV receiver decodes this information and displays it as a channel number on the screen. There are differences between manufacturers on how this is displayed, so a signal may show up as 17-1 or 56-1. Some TV sets will show the call letters such as WYIN DT-1 for example. It’s a brave new world and not everyone agrees on what the consumer (you) need to see.

If there are additional channels programmed into the system, they will show as 17-2, or 56-2, 17-3 or 56-3 etc. Just because there is a channel ID, does not mean there is an actual program you can receive. Channels can be open broadcast (anyone can watch) and some can be closed broadcast (only those subscribed can watch). Or there may be nothing being transmitted on the added channel. So if you get a blue or black screen, it just means that channel is not sending out a program at that time.

The consumer electronics industry has not decided what to do with part time channels yet. Some stations will switch their regular signal to the empty channel; others put up still pictures, slides, or just leave it blank. Still others will program the PSIP or PID identification signals to “turn off” and “turn on” the channel as programming is sent or not. Yes this causes confusion since your TV set programs itself for channels, and if it is not there, the TV can lock up or if the channel was off when your TV set scanned for channels, then it may be on but your don’t know it! Its not easy being digital!

RECEIVER BASICS

A true digital TV set has an analog and digital tuner. This is called an ATSC receiver. (Advanced Television System Committee) compliant receiver. That means all by itself it can receive the new digital channels. If it does not have an ATSC tuner, it is not a complete digital TV set (receiver) and it requires an external set top box to receive the off-air digital TV stations. Some stores sell digital monitors, or digital ready, or digital compatible TV displays. These are NOT DTV TV sets. They simply are a computer monitor dressed up for the living room, and require an external tuner or converter and are great for watching a DVD or the analog output of a cable or satellite box. If you buy one of these, you also have to buy the set top box to receive the off-air analog or digital broadcast channels. You may also need another box for cable and another box for satellite. Talk about clutter! A true DTV Receiver will receive all off-air digital signals, plus all off-air analog signals no set top box needed, just a regular TV antenna.

HIGH DEFINITION TV

Everyone wants to claim they are HDTV, very few are truly HDTV. The FCC did not settle on one flavor of HDTV. There is only one version of color analog TV, so it looks the same on any TV set. DTV has 19 flavors. Technically they are called SD, ED and HD for standard, extended and high definition (High def). What those labels mean is the format that your set displays as its best possible picture or “native display.” Your analog TV set is SD, and displays about 480 lines from top to bottom. This converts directly to digital SD. ED is a digital format with 720 lines and HD is 1080 lines. There are minor differences in how they are counted, from a consumer perspective the technical differences are unimportant and do not affect what you see.

The best HD is known as 1080I with 1080/1920 resolution. That means 1080 horizontal lines, and 1920 pixels (picture elements) per line. A display with his resolution is currently very expensive, typically in excess of $10,000. Most TV sets of the flat thin screen variety, LCD, TFT, that are called HDTV are in fact lower than the maximum, typically 1080/1280. So the display, while it looks great, still leaves out about 40% of the horizontal information being transmitted.

Picture tube HDTV sets, can produce the full 1080/1920 resolution, but some consumers think it is a softer picture, even though it has more detail. That is because the solid state displays have black stripes between the rows to improve contrast and reduce glare, and most picture tube sets do not. The other difference most people notice is the thin screen TV sets seem to have more contrast. In fact in the LCD TFT and other displays, the black and dark portions of the picture are darker than the actual picture because technology today just does not allow a nice gradual change from black to white, as a picture tube does. We call this gamma compression, a nice term you can toss at the salesperson as in “what is the gamma correction of this display?” At that point you likely know more than they do about DTV! At a minimum to get a realistic HDTV picture the TV set must have 720 or 1080 native display.

The important point of this is your TV set is the limiting factor of how good a picture you receive and view. The native display should be as high as your budget allows in order to get the greatest benefit from digital TV’s superb pictures. Think of it as going from that early 6 transistor AM-FM pocket radio to the 27” stereo color console with 360 watts of stereo sound to huge room filling speakers you have now.

NOISE and Antennas

DTV is supposed to go as far as analog TV. Analog TV pictures slowly degrade as the distance from the TV transmitter increases. We all know that as “snow.” If you live in Warsaw, Rochester, or other towns more than 35 miles from the TV station’s antenna, you have snow. Typically the picture is considered watchable with some snow (which is noise) up to 65 miles away. There is an actual grading system to measure this. Having a tower and big antenna or preamp can extend the viewing distance to 80 miles or more. Out west, with little to interfere to the signal, reception at 150 miles is not uncommon. Digital TV has no snow. The digital technology provides a perfect picture to the limits of reception, after that all you get is the famous blue screen and the message “NO SIGNAL.” With the analog TV set you could turn the antenna, usually with a rotator, to clean up the picture and get the strongest signal. With DTV, there is no way to do that. Most digital TV sets have a menu item called SIGNAL LEVEL or SIGNAL QUALITY. Some are bar graphs, some a simple three color bar to help you get the best signal. You can use these to adjust your antenna to get the best picture. There are no ghosts or noise in a digital TV signal. It’s perfect, or nothing.

WHERE TO POINT

The DTV signals are being transmitted from the same locations as the analog signals. But there is an advantage! With analog signals, if your antenna was not pointed at the transmitter you could get ghosts or noise. Often you have to choose between pointing at one station or another. With DTV there is no noise and no ghosts! The digital processing makes it impossible to see noise or a ghost.

If you are getting ghost or noisy signal it may be because you are pointing your antenna at the Sears or Hancock buildings or Tinley Park, or Crown Point for the stations, there is good news. With DTV you can re-aim your antenna and get perfect pictures on all the DTV stations. I actually point my TV antenna on my house south, which is the only direction I can get CBS DTV channel 3, which is 35 miles north of me. So when you get your DTV receiver, take some time to experiment with where you are aiming and you should be able to get all the DTV stations perfectly.

HINT: a low gain (small) antenna may be better than a big high gain antenna because a high gain antenna is much more critical in aim. The DTV signal can be received with a much lower signal level than the analog station, so it is easier to receive in most locations.

HINT: Your present TV antenna will work just fine. Important hint: Nearly all the Digital TV stations in the country transmit on UHF channels. In Chicago, only CBS channel 2 was unfortunate enough to be assigned VHF channel 3 for DTV. We say unfortunate because the low VHF channels (2-6) have a lot more noise interference and UHF has nearly none.

When the FCC orders the analog TV stations to be turned off, the stations on channels 2-50 may elect to use their analog channel for DTV, or remain on their new DTV only channel. We won’t know for several years what they will decide to do. Each TV station will make its own selection, so don’t throw that VHF-UHF antenna away. If you live in a UHF only market, such as South Bend, You only need a UHF only antenna for analog and digital stations. There is no difference in antennas for analog or digital, any will work.

Comments

[Dennis Haarsager]

The CEA has one at http://www.antennaweb.org/.

Good luck.

--Dennis

[Matt Kitterman]

I used to have a link to a site that would draw a TV signal direction and strength map for a given street address but I have lost the url. I thought it might be linked from this fine site but can not find it. Any ideas?
M@

[Joe]

Can anyone recommend the top 5 tvs in the 40-50" screen range. I'm confused on whether to purchase an LCD, DLP, LCOS, or Rear Projection. When I finally think I've settled on the right one, I read some negative reviews, and am back to square one. I've been spoiled by the Mitsubishi 35" tube tv I purchased 17 years ago. I have not put one cent into this tv since I've had it and the picture is as good as the day I got it. I'd just like to step up to the new technology.
Thank-you