Aiming at Nothing

In February of 2009, under Federal Communication Commission (FCC) directive, all terrestrial television broadcasts in the U.S. will be digital. Unless you subscribe to cable or satellite service, your old analog TV will no longer work for over-the-air signals without an external digital television (DTV) tuner after that date. If this sort of news puts you into a panic, fear not— the “drop dead” date for analog TV has been moved out several times and it might be moved again. But in preparation for this transition, most television broadcasters have already set up new transmitters and switching equipment to provide DTV content and most of the television networks have begun producing their prime-time programs in HDTV. This digital content is available for “free” if you have purchased the equipment necessary to capture it.

For this project, I installed a DVICO Fusion Gold 5 PCI card to act as tuner (I forgot to snap a picture.) The card was bundled with a short coaxial cable and an inexpensive directional indoor UHF antenna. The card contains all of the circuitry necessary to tune in local broadcasts and to hand off the content in a DTV Transport Stream format. From there BeyondTV software converts this stream into a viewable picture, but I’ll cover the software components in another post later on. This time I’ll be discussing the nature HDTV signals and equipment I use to pull these signals out of the air.

Over-the-air (OTA) DTV signals in the U.S. are transmitted (by way of the wildly popular “8-level vestigial sideband modulation” method the kids are so crazy about) in the same UHF band that was once used for analog TV signals. The channel allocations haven’t changed at all, only the content has. DTV signals occupy the same 6MHz space but, thanks to innovations in compression technology over the last 20 years, more information can be packed into the same space. As a matter of fact, the specification allows for as many as six standard definition (SD) channels to be transmitted within one stream. About half of the stations in my area include one or two SD channels along with their main high definition (HD) channel.

On KOPB-DT KOIN-DT the SD channel carries a duplicate of what they transmit on analog VHF channel 10 6. In addition to video, the stream also contains a rudimentary electronic program guide (EPG) for use with set-top boxes and DVRs such as the one I’m building. Each station in this market allocates their resources differently, but they all seem to follow a 1[CH][S] nomenclature for the channel number—a 1 followed by the two digit number representing the station’s analog channel number followed by a single sub channel number.

For example, KGW-TV Channel 8‘s main DTV channel number becomes 1081; channel 49, KPTV, becomes 1491, and so on. The local Public Broadcasting Service station in town, KOPBDT, identifies itself as channel 1101 for the HD picture and 1102 for the SD channel. Other markets may follow other patterns or no pattern at all. Obviously I can only report on what I can receive locally. The displayed channel number and the “old” UHF number don’t correspond at all—. KATU Channel 2 is carried on UHF channel 40 but the channel number is displayed as 1021. Got it? No? Don’t worry; if you don’t live in my town, your results may be completely different.

DVICO included a software and driver CD with the card. One of the programs allows a user to scan for local broadcasts and to evaluate the signal strength of each in order to best orient the antenna. I am very fortunate to live close enough to the major transmission towers (about eight miles away) but far enough away that the towers are grouped into a 35-40 degree arc to the east. Television signals—UHF signals in particular—are highly directional so having a relatively small “footprint” at which to point the antenna is a happy accident. Using the signal strength software, I was able to orient the antenna so that it pointed roughly in the middle of that footprint with indicated signal strength readings between 75% and 100% …some of the time.

Aside: If you’re thinking about building one of these systems and you don’t have access to a DTV tuner, you might consider installing an HDTV card into a computer you already own. With a small initial investment, you can determine how many DTV signals are available to you and how well they can be picked up where you live. If it doesn’t work out, you can always sell the card to someone else. That’s how I came into possession of the DVICO card. Get to know an early adopter and then buy his handoffs. (Thanks, Paul.)

My initial results were sub-par; signal strength was inconsistent, generally weak, and not at all dependent upon the direction of the antenna. The inconsistency turned out to be caused by a bad solder joint at the antenna’s connector. This was easily fixed. The relatively weak signal would have been more difficult to fix if I were not a packrat. Years ago when analog cable was the rage, I purchased a signal amplifier so that TV pictures would look passible on a set in room far removed from the utility pole out in front of the house where we lived at the time. Although I have had no need for it in almost ten years, it was packed away in a box I rarely see in a closet I rarely open. The amplifier provided about a 3db gain; just enough to bring all of the local stations to within 90-100% strength. So remember: never throw anything away. Just keep moving it from house to house, up and down the coast or wherever you happen to land.

Adequate signal strength is important with DTV. If you have ever watched a scratched or dirty DVD, you already know the results a poor data source can have on a digital picture. If the data is good you get a nice, sharp picture. If the data is inconsistent you might get a picture with artifacts (little boxes of solid color where none should be), a series of still pictures (great for slide shows, not so much for television) or nothing at all (go read a book!). My particular tuner card was unhappy with signals that dipped below 80% strength. Once I attached the amplifier to the repaired antenna, I was able to watch all of the stations in town without interruptions. I’ve even been known to watch tennis.

Yes, everything looks that good in HD.

In my next post on this project I’ll talk about PVR software. If you have any questions about this project, drop a note in the comments and I’ll do my best to make something up in response.