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HDTV & Cable  

post #1 of 4
Thread Starter 
I'm a DBS, PTV, Home Theater etc. enthusiast and I'm familiar with avscience forums because I own a TIVO. Sorry if this isn't quite the usual hobbyist chat.

I have been appointed to my towns Cable TV Advisory Committee because they want to beef it up with tech people. This would be great, if we weren't under huge time pressure because the previous committee has done nothing for two and a half years of our three year renewal period, so now we're scrambling and have lost a lot of leverage.

I'd like to make sure that our rebuilt system will be capable of carrying HDTV signals and I'm concerned that they will build a system for today not for tomorrow--which is what happened last time around.

The big technical question is how much bandwidth do these take up. Contracts are phrased in terms of a "750mhz system capable of 77 NTSC Channels" or the old one is a "550mhz" system etc. What kind of a system are we going to need to accomodate HD signals.

So my questions are more specifically phrased:

Anyone know of cable systems currently doing HDTV or municipalities with HDTV written into their contracts? Any with specifications for full passthrough (ie, not stripping multicasting) or for analog conversion of multicasting?

Technically, how many NTSC equivilent channels does a full HDTV signal take up--does it require greater bandwidth?
post #2 of 4
Lets start with your last question first. Bandwidth, an HD channel is the same as a NTSC channel, 6 Mhz wide. The HD channel, when transmitted by the broadcaster is also an analog signal, just like NTSC. But is modulated as 8VSB. The signal does not become digital until it is encoded in the receiver. So an analog cable system can carry (pass through) the HD signal.

The question is mostly must carry, the cable system is not obligated to carry the HD simulcast signal.

Now if a cable system goes full digital then one 6 mhz channel can carry up to 10 or more standard definition (NTSC or digital) programs. If a cable system used 256 QAM for its modulation scheme then it can carry as 2 HD ch in the equivalent 6 mhz band width. So 77ch times 10 would be up to 770 standard def ch. More than enough to cover many HD ch. lets say 40 HD 6 mhz ch 256 QAM modulation thats (77-(40/2))x10=570 that leaves 570 SD ch.

As you can see there is no excuse for not going digital.

Hope this helps.

I think the actual number of channels that most digital systems will carry is about 300, but the math is still the same.

P Joy
post #3 of 4
Don't know the technical specifics but you want to check out Time-Warner Cable as they seem to be the most progressive in getting HDTV rolled out in various markets. Here in Houston I have been using TWC for about 9 months and it is decent service -- all the local HD OTA channels and 2 HBO and 2 SHO HD channels. They are in other markets too. I am sure if you asked for a tech consult they would see it as an opportunity.

There have been occasional TWC people participating in the HDTV programming forum -- do a search for TWC Houston and you will find one guy -- bryan.gann@twcable.com -- who assisted me in getting some HD issues sorted out.
post #4 of 4
Thread Starter 
Thanks, I really appreciate the information! Gives me what I needed.
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