Just when the sky is falling...
Senate to Hear Update on Switch to Digital TV
By ROY FURCHGOTT
A test in Wilmington, N.C., of the coming nationwide switch of over-the-air TV signals to digital from analog went well, but some politicians are worried that the rest of the country’s transition will not go as smoothly and that many people will find themselves with no TV signal.
The country will make the transition on Feb. 17, when TV stations will no longer broadcast analog signals. Older TVs will not be able to use the new digital signal, and a person who does not buy a new digital-ready TV or a converter box will not receive TV programs.
At a hearing scheduled for Tuesday, the Senate Committee on Commerce, Science and Transportation plans to review a Government Accountability Office report questioning the ability of a federal agency, the National Telecommunications and Information Administration, to manage its part of the transition. The agency oversees the distribution of discount coupons for the converter boxes, which make it possible for older TVs to receive over-the-air digital signals.
The coupons, available at dtv2009.gov, give consumers a $40 discount on a converter box. The coupons expire after 90 days, and nearly half of those issued have not been redeemed.
Last week, the agency appeared before a House committee to explain why it needed to direct $7 million earmarked for its other programs to cover the anticipated additional administrative costs of the coupon program.
Kevin J. Martin, the Federal Communications Commission chairman, is scheduled to appear at the hearing. In a statement to the House committee, he said, that “with the national transition about five months away, much remains to be done.”
But he was upbeat about the changeover in Wilmington, seen as a test, saying that complaint calls represented 1 percent of homes in the market, a quarter of a percent were from homes that lost at least one station they should still have received.
Those figures are complaints only to the F.C.C., not to the stations themselves. They do not count people who decided to switch to cable or satellite service rather than use converter boxes.
Time Warner, the largest cable provider in Wilmington, said about 500 households subscribed for service in the months approaching the switch, but declined to specify that time period. The company did not know how many were linked to the changeover, said Alexander Dudley, a company spokesman.
Critics say it was not a representative test market because it is a flat region. Digital signals are more easily blocked than analog signals. Analog signals degrade slowly, so pictures are snowy but still viewable at distant reaches. They are also able to ricochet off buildings and hills to fill in signal gaps. When a digital signal gets weak, the picture breaks into unviewable blocks or disappears completely. Engineers call that the cliff effect — good reception or none at all.
Senator Bernard Sanders, an independent of Vermont, in a letter on Friday to the F.C.C. commissioners, asked that the commission begin an education campaign alerting over-the-air households of the possible need for a sensitive rooftop antenna. He also said the federal government should consider subsidies for antenna replacement.
He cited a study by Centris, a consulting firm, that said the F.C.C. had underestimated the homes that would need antennas to receive over-the-air signals. He also cited a study of the digital transition in Britain that said that 35 percent of consumers would need to buy new antennas.
“Americans should not be forced to pay for cable, satellite or other telecommunications video services to get their free broadcast channels,” he wrote, “because the government did not properly plan for this transition.”
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Most every station is already digital. I live in rural western PA - 75 miles from Pittsburgh. I get all the majors over the air in hi-def, with an antennae in my attic and an amplifier.
I live in a hilly area; and I get the digital stations better than the analog, fwiw.
Loss of television availability probably would spark off a violent uprising.
The DTV signals are also better than analog in north Austin, though I have only A/B-d it with my laptop's tv card.
....of EPIC proportions.
Nevermind we're being swindled for billions (trillions?), take Deal or No Deal off the air and every American monkey would be, quite literally, up in arms.
Looks like the liberals in congress might be worried their liberal brothers and sisters in the media will lose viewers. They might have to get their news from talk radio!
Everyone will just ignore or put of getting the converters until the analog signals are cut off.
Then they will .
Then they will get the converters.
Then they will about the rebates.
Then it will all be over.
I agree, but there may be areas that the converters don't work. At least the cheap ones that will be available. Television currently uses AM and FM encoding for the picture and sound. The signal to noise ratio is noticable when the noise is at levels that will show no distortions with a digital broadcast. However, the current signal simply gets worse picture and sound as the signal level decreases as a ratio to the noise. Some people in some areas tolerate poor quality signals. It is possible that this signal to noise ratio isn't sufficient to keep a digital broadcast signal being decoded right. Some outlying areas may completely lose the ability to get television without a satellite reciever.
Now, like I say, that might happen. I haven't been involved with communications electronics for a few years now, but we were using a T3 signal over microwave using QAM. This was 20 years ago. QAM is actually rather forgiving for noise levels, more so than analog. This is the same format the new digital tuners use. I'm surprised they don't use something newer, but maybe QAM quality for signal rates and signal to noise has never been exceeded?
Also see:
QAM Tuner
QAM Defined
No. The over the air tuners are ATSC Tuners and use 8VSB modulation. The QAM modulation and tuners are used in digital cable.
Last edited by ElNono; 09-23-2008 at 05:25 PM.
Well, Trellis encoding modulation...
That sucks. It seems to me that 16 level QAM would be far better than 8 level Trellis. At least with cable, we can use 256 level QAM.
I'm no expert on the topic, but I think Trellis packs more data? I seem to recall modems were tied to 9,600 bps using QAM until Trellis was discovered.
There's actually a 16VSB specifically designed for digital cable, but getting rid of QAM was too expensive, AFAIK.
In the end, over the air digital tv's bandwidth is restricted to 6 Mhz. If you take out the Reed-Solomon overhead, it's really restricted. Specially since they broadcast all those HD channels.
My understanding was that QAM was selected over 16VSB because it is capable of being expaned to the 256 data points easily, carrying far more data than VSB can. Remember now, cable and LOS microwave doesn't suffer the same signal to noise problems as regular terrestrial broadcasts. Ding a little searching around, it appears that VSB is better at noise rejection. Good enough that VSB actually can work with less power than the current NTSC broadcasts.
My concern was based on knowing QAM was susceptible to noise levels that NTSC isn't. I was unaware that QAM was used in modem usage, I don't recall ever seeing it. The fact that 8VSB is used instead is understood. It is less susceptible to noise. I don't even recall why I thought it was used in terrestrial broadcasts. Maybe because I knew my HDTV has a QAM receiver, and never hooked it to an antenna.
The inherent problems for QAM on two wire 135 ohm unshielded twisted pair are longitudinal distortion and envelope delay. This severely impairs the ability to discriminate the signal. When different encoding methods were first utilized in the past, the envelope delay could be corrected, but that was expensive to do at audio frequencies. Modern DSP's do it real cheap now allowing tightly packed QAM signals on cable and LOS microwave. Even 20+ years ago, microwave transmissions were easily kept under 1 nanosecond of envelope delay at the baseband with internal LC and/or wavequide tuning. Still, QAM radios normally tightened this maximum delay up farther. There is no way to fix longitudinal distortion for twisted pair. It's inherent to the quality of the wire and insulator dimensions and length. There is no longitudinal distortion in cable or radio.
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