FCC phase-in begins
This is the first article in a two-part series about over-the-air digital television reception technology, which is being added to TV sets in accordance with the FCC's tuner mandate, and plug-and-play order.
FCC Broadcast DTV Tuner Phase-in TimetableBased on the FCC's DTV Tuner Phase-In Act adopted last summer, televisions and other electronic devices equipped with over-the-air analog reception technology must also be equipped with ATSC receivers, according to the timetable below.
Televisions equipped with cable plug-and-play cards, arriving in stores now, must also have ATSC reception.
• July 1, 2004: 50 percent of TVs 36 inches and above.
• July 1, 2005: 100 percent of TVs 36 inches and above; 50 percent of TVs 25-to-35 inches.
• July 1, 2006: 100 percent of TVs 25 inches and above.
• July 1, 2007: 100 percent of TVs 13 inches and above; All other devices that receive broadcast television signals.
SOURCE: FCC 02-230
Ever since the government rubber-stamped 8-VSB as the digital television transmission standard in 1997, questions about its receivability plagued broadcasters.
Now, the true test is nigh. The first phase of the FCC's order requiring new TVs to include off-air DTV tuners kicked in July 1, and cable-ready sets, which must also include the tuners, are already appearing in electronics showrooms. The intention is that new, digital-reception capable sets eventually will supplant old analog sets in the market.
ATSC Recommended Receiver Performance GuidelinesThe ATSC's receiver performance guidelines include numerous measurements:
Sensitivity: A transport stream bit-error rate of no worse than 3x10-6.
Multi-Signal Overload: Accommodation of more than one undesired high-level received NTSC and ATSC signal.
Phase Noise: Tolerance of phase noise levels at a threshold of visibility (TOV) of -80dBc/Hz at a 20kHz offset from signal source.
Selectivity: Multiple thresholds for taboo, first-adjacent and co-channel rejection.
Burst Noise: Tolerance of a noise burst of at least 165ms duration and a 10 Hz repetition rate without visible errors.
Multipath: Multiple parameters
Smart Antenna Interface
SOURCE: ATSC Working Draft, Recommended Practice: Recceiver Performance Guidelines
"We've always said, if you can't receive this indoors with a simple antenna, it ain't gonna work," said Nat Ostroff, vice president of New Technology at Sinclair Broadcast Group.
So tenacious was Sinclair's criticism of 8-VSB receivability that it became the stuff of industry folklore. In the meantime, a handful of engineers quietly applied their intellects to 8-VSB reception-commonly referred to as ATSC, named for the Advanced Television Systems Committee, from whence the standard came.
Sinclair called for the FCC to define DTV receiver performance standards, but the commission declined. At press time, the ATSC membership was voting on voluntary performance guidelines, which were expected to pass. (See "ATSC Recommended Receiver Performance Guidelines" sidebar.)
Then last month, Sinclair blessed the latest ATSC reception technology from Zenith, an 8-VSB patent holder and subsidiary of LG Electronics.
To understand Sinclair's trajectory, it helps to know the basics of ATSC reception, a three-stage operation involving not just a tuner, but a demodulator and signal decoders as well. Only the third stage of the process has been nailed down with any consistency.
Ideally, the tuner grabs the desired channel and rejects the rest, but there is concern about how well current devices do the job. The problem lies not in the technology, but with economics and spectrum policy.
Digital tuners are similar to analog tuners, except in price, which is simply a function of volume. Having been fabricated for some 50 years, analog tuners run about $3 to $4 apiece, where a digital tuner may cost $15 to $20, according to Richard Lewis, chief technology officer at Zenith. Additionally, there are two types of digital tuners-single and double conversion.
"What we've seen industry-wide, is people moving away from double-conversion tuners," Lewis said. "They're better at rejecting unwanted signals, but they cost more than single-conversion tuners."
Tuner reliability may be further complicated if the FCC farms out unused TV frequencies, said Bob Rast, president of Linx Pro Electronics, a Palatine, Ill. firm recently purchased by Zurich-based Micronas.
"The more people putting out signals, the greater the risk for interference," said Rast, who's worked on ATSC demodulation for years.
Another problem for tuners involves the simulcasting.
"It's partly a transition issue," Rast said. "in which there's a digital low-power channel next to an analog channel. The analog channels are wiping out the digital channels. If you overpower the tuner, the IC can't fix it."
The IC is engineer shorthand for integrated circuit; in DTV reception, it refers to the demodulator.
The evolution of digital television demodulation will be examined in Part 2 of "Tuner Time" in the July 21 issue of TV Technology.
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