The Light At The End Of The Tunnel
8VSB chipsets for terrestrial digital television are now in their 5th generation. Have they finally become plug and play?
THE TRANSITION to digital television is well under way. More than 600 terrestrial digital TV stations were fully licensed with many more conducting tests and operating under temporary authorizations. Cable companies have expanded their digital plants to include more HDTV channels. Direct broadcast satellite (DBS) operators DirecTV and Dish Network have also expanded their HDTV programming. Newcomer VOOM, still struggling to add subscribers, recently announced plans to launch another satellite in 2005 and pack 70 more channels of HD programming into its lineup.
While satellite and cable digital program distribution is not very complicated, terrestrial broadcast digital TV continues to be. The reason? With a DBS or cable provider, all of the channels come down one pipe from one location. But with terrestrial stations, many channels of programming can come from two or more locations, which makes choosing, installing, and aiming antennas a real bear at times.
The 8VSB or Eight Level Vestigial Sideband modulation system used by terrestrial broadcasters has been controversial since its adoption by the FCC in the mid 1990s. Early tests with 8VSB vs. a competing scheme (Coded Orthogonal Frequency Division Multiplexing, or COFDM) showed that 8VSB receivers had a long way to go to provide reliable reception in areas with moderate to high signal reflections and multipath.
In early side-by-side tests, COFDM receivers were able to reliably hold DTV signals in urban environments while 8VSB receivers simply gave up the ghost. Broadcasters, networks, and other industry pundits claimed that the FCC had picked the wrong standard and had better fix its mistake before the Jan. 1, 2007, analog TV shutoff date.
Like any new technology, there's always a breaking-in period during which systems that were designed, tested, and proven 100 percent reliable in laboratories must go out to the field to fail (at which point most of the lab results can be tossed out the window). Plenty of bugs are found and it's back to the drawing board. The 8VSB system was no exception in its evolution.
Fast-forward five years later, and it appears that perhaps the sky isn't falling after all and maybe the FCC did indeed make the right choice for digital TV. Throughout 2004 LG Corp. held demonstrations of its 5th-generation 8VSB chipsets, and the results are amazing. Using pre-recorded multipath sets based on real-world environments, LG has been able to lock up on 8VSB signals in environments so chock-full of echoes and multipath that no analog TV reception is possible. More surprisingly, some of the 8VSB system's most vocal critics in the early days have now become its biggest and most enthusiastic supporters.
That's a far cry from the days of the 1st-gen 8VSB receivers from Panasonic, RCA, and Zenith (vintage 1998), which were finicky, expensive, and bulky boxes that required lots of signal and as little multipath as possible. Slight changes in weather, interference from nearby computers and TVs, snow, reflections from icy surfaces — you name it, these receivers had problems with it.
Today's terrestrial DTV receivers are using mostly 3rd-gen and some 4th-gen chipsets, and while they run circles around those 1st-gen boxes, they still have problems with moderate (14 dB or greater) echoes and signal notches, plus they can't handle what's known as close-in echoes. These annoying pests don't even register on a spectrum analyzer, as the difference between them and the desired signal is almost non-discernable.
The 5th-gen silicon changes all that and makes reception of digital TV a lot simpler. Case in point: A simple $3 UHF bow-tie antenna was all it took for successful reception in one well-known uptown New York City apartment location that has regularly stumped the best DTV receivers and design engineers for years.
The timing couldn't be better for these new chips, as more and more integrated digital TV sets are coming to market. Manufacturers of these sets have bet their sales forecasts on the new CableCARD system; all integrated sets with the DCR logo can receive digital cable programming with the addition of a special PCMCIA plug-in card from the cable company.
But as integrated digital TVs using 5th-gen 8VSB receivers start coming to market, more and more consumers will likely appreciate getting CSI, Monday Night Football, and The Tonight Show with Jay Leno in HDTV for free, whether or not they activate the CableCARD function.
Over the past five years, I've conducted numerous tests of antennas and VHF and UHF signal propagation around the United States to see which models of antennas deliver the goods. As each successive generation of 8VSB chips makes it to market, I've found that the choice of antenna becomes less critical, although it's still a good idea to have lots of signal from the digital TV station with little multipath.
In a recent review, I tested a 42-inch plasma TV from LG (DU-42PY10X) that was purported to carry the hot new 5th-gen ICs, but actually turned out to have 4th-gen product aboard. Even so, I could see an improvement in reception over a 3rd-generation LG set-top tuner (and it's no slouch, either). At one point, I simply connected that ubiquitous $3 UHF bow-tie antenna to the DU-42PY10X' RF input and did a DTV channel scan. Even though the antenna was dangling flat against the rear cover of the plasma TV, three more channels were captured than on LG's older set-top receiver using the same antenna in the same position.
It appears that the writing is on the wall and the day is coming soon when antenna testing will become moot. (That's particularly good news for me because one part of the attic over my garage is now 3 feet deep in aluminum from my reception tests.)
LG's tests have shown that all kinds of compromises can be made to the 8VSB reception environment with nary a hiccup by those 5th-gen chipsets, including severe signal notches from out-of-phase antennas and dynamic multipath, such as you'd see from planes passing overhead or trucks cruising by on the street.
The big question now is this: Can consumers be persuaded to give terrestrial digital TV a whirl, now that more than 70 percent of all TV viewers appear to have forsaken the old rooftop antenna for cable TV connections to their primary TV set? The common wisdom these days appears to be that TV antennas are old-fashioned and ugly, and restrictive covenants in townhouses, condominiums, and neighborhood associations have made erecting antennas a difficult proposition.
Of course, the FCC has pre-empted many of those restrictions with their Over-The-Air Reception Devices (OTARD) Rule, enacted in 1996. OTARD makes it possible for folks to put antennas in non-common areas (such as balconies) or on roofs up to 12 feet in height to pick up DTV programs over the air.
Until now, very few people wanted to bother. But with the availability of integrated digital TV sets with receivers that actually work in the crazy, mixed-up RF environments of cities and suburbs — and an expanding schedule of free HDTV programs to watch — perhaps they'll once again want to put a “stick” up on the roof, in the attic, on a rail, or in the most old-fashioned position of all — atop the TV.
Pete Putman is a contributing editor for Pro AV and president of ROAM Consulting, Doylestown, PA. Especially well known for the product testing/development services he provides manufacturers of projectors, monitors, integrated TVs, and display interfaces, he has also authored hundreds of technical articles, reviews, and columns for industry trade and consumer magazines over the last two decades. You can reach him at firstname.lastname@example.org.