TV question for Nat

TV question for Nat

Ken
Ken

July 12th, 2010, 9:18 pm #1

Nat, this is Ken, you may know me from TFF. Got a question for you- I saw down below that youre a TV engineer. Can you tell me why if digital TV is suppose to be so much better why can't I see half the stations I could before they switched last year? And why do some stations come in at night but not during the day?

Thanks Ken
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Nat
Joined: January 1st, 1970, 12:00 am

July 13th, 2010, 1:57 am #2

Hi Ken, glad you found us at Potpourri. Digital TV is great- IF you have a good signal. The problem is the FCC greatly underestimated the amount of power it would take for a digital signal to replicate analog coverage. Many (including me) think this underestimation was deliberate because they had to squeeze all the stations that were in 68 channels into 45 channels because chs 52-69 were removed from TV service and chs 2-6 are unsuitable for digital. So with more stations sharing fewer channels the FCC limited power to prevent them from interfering with each other. Add to this- digital TVs are more fussy about the signal they receive- reception problems that only degrade analog TV will completely kill digital.

As for why you can't get some stations during the day- TV signals generally don't go as far during the day because propagation loses are higher and if a digital signal does not reach a certain threshold of strength you don't see (or hear) it at all. Some people have the reverse problem- they can get a station during the day but not at night. In this case it's because a more distant station on the same channel comes in stronger at night and the two signals interfere with each other. With analog the stronger one wins but two signals totally confuse digital decoders and you see nothing.

In short, digital TV can be beautiful when it done right- with a good clear signal, but with marginal signals we were better off with analog.
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Ken
Ken

July 13th, 2010, 7:45 pm #3

Well if digital is not as good as what we had why did they switch to it?
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Nat
Joined: January 1st, 1970, 12:00 am

July 14th, 2010, 1:02 am #4

Well I wouldn't say the change was a mistake, but the way it was implemented. With a good signal digital picture quality is much better- wider, more detailed and without many problems inherent in analog. It's just that it requires a good signal to make it work properly which many people aren't getting.

As to why we switched- it began back in the 1980s when Japan came up with a hi-def TV system as a way to sell new TVs in a stagnate industry. But Japan's system was analog and took too much bandwidth and could not be implemented here. But by the 1990s digital chips had become fast enough to work at video frequencies so a consortium of companies came up with a digital system that was much more bandwidth-efficient. In fact it possible to transmit 4 different programs in a standard 6-Mhz US TV channel.

And about this time the cellular and communication industries were screaming for more frequencies to use so it was decided by switching to digital, stations would need fewer channels and then many TV channels could be auctioned off to the telecommunication industry bringing considerable revenue to the government. It's also more energy efficient. Our digital transmitter uses about a third what the old analog did saving the station thousands of dollars in power bills.

I think in the future the current concept of central high power transmitters for radio and TV broadcasting will be replaced by some sort of super WiMax system.
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Cool beans boi
Cool beans boi

July 14th, 2010, 9:06 pm #5

The problem with digital is that any station that stayed on VHF (chs 2-13) stinks. Where I live near NYC, 3 stations Ch 7(ABC) 11(CW) & 13(PBS) are unwatchable, however the ones that moved to UHF are just fine.
I learned this the hard way. My cable company had a dispute a few months back with ABC. This resulted in WABC Ch 7 being pulled from our cable service the day of the Oscar Telecast. I bought a cheap digital antenna and could not see ABC at all, but CBS, NBC & FOX, which all migrated to UHF were fine. Ch 6 in Philly had to quadruple their power and their signal is still bad in the suburbs!!

Chris
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Nat
Joined: January 1st, 1970, 12:00 am

July 14th, 2010, 11:30 pm #6

Yes, it was well known that low-band VHF (2-6) was a no-go for digital but most engineers thought high-band V (7-13) would be ok- but a combination of impulse noise (which digital decoders hate), phase-shifting (also a problem with digital) and late-night tropospheric ducting- which brings in distant stations to interfere has been problematic for high-band-Vs. So UHF is the place to be- especially in metro areas. Ironic since broadcasters use to hate UHF- but times change. VHF's longer range is still advantageous for stations in rural areas where noise and reflection (which causes phase shift) are less of a problem.
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Bob
Bob

July 19th, 2010, 5:54 pm #7

Nat, this is Ken, you may know me from TFF. Got a question for you- I saw down below that youre a TV engineer. Can you tell me why if digital TV is suppose to be so much better why can't I see half the stations I could before they switched last year? And why do some stations come in at night but not during the day?

Thanks Ken
I just got a flat panel (LCD) television. I never owned one before. I was anticipating all the great pictures and am a bit disappointed. Set is name-brand, 1080p, 120 Hz and connection is HDMI, but the picture still doesn't look crystal clear (better on stationary image than with movement). My cable service is not HD (didn't go to that expense when I took out the contract, as I had no HD TV's). Think that could be it . . . the signal is not hi-def, so the TV cannot give hi-def?
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Nat
Joined: January 1st, 1970, 12:00 am

July 19th, 2010, 6:29 pm #8

Bob, you sound like the guy who bought a color TV back in the 1960s and then complained that most of the programs were black & white. No, you can not see a hi-def picture if you are not watching a hi-def signal! In fact, standard-def pictures look worse on a hi-def TV because it shows all the imperfections of a standard-def picture that you didn't notice on smaller tube screens. What's more, the quality of even so-called hi-def pictures varies a lot- some stations are blowing up SD video to fit HD-format- but it isn't really HD. And cable companies are notorious for compressing the bandwidth of digital video to squeeze more channels onto their system so even what they say is hi-def is not as hi-def at it should be. To see really good HD- you should watch a live or taped off-air broadcast using a antenna. Even then stations that are running subchannels may compress the video a bit. In short picture quality varies a lot- but when you see true uncompressed 19.39-Mbit/S video- you will be impressed!
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Bob
Bob

July 19th, 2010, 6:48 pm #9

Could I watch a blu-ray movie on suitable player, with HDMI connection, and see what you are referring too? (First, I'd have to buy a blu-ray player!)

(Speaking of HDMI, I didn't realize how expensive those cables are! I didn't expect to get the HDMI cable thrown in with the TV, given the price I payed, but neither was I expecting to see the prices for those cables be so high. "Cheap" cables -- $40 Mid-range price/quality -- $60-70 High end cables can run $90-$150! For a cable! Yes, the sales guy told me about all the individual wires in each cable, and about the insultation around each to shield from interference. He said the cheap cables allow more interference and degrade the signal, and he recommended against them. But, $90 or more?! That sounded crazy to me. I felt ripped off enough paying $60 for a "good, not great cable", and only did so when the sales guy pointed up, "You are going to spend several hundreds of dollars on a TV and then scrimp on the cable and not be able to see what the TV can really do?" They know they have you -- once you have the set, they know you will pay an exhorbitant price for cables to watch the TV)
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Nat
Joined: January 1st, 1970, 12:00 am

July 19th, 2010, 7:08 pm #10

Yes, Blu-Ray would look great too!

And HDMI cables are one of the biggest rip-offs around! They're akin to those "oxygen-free" speaker cables stores sell.

It's well known that these stores make their big profits on accessories.
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