US Cable Support > Comcast Cable TV > Comcast BASIC Cable (no digital box) and Upcoming Digital TV

reply to cypherstream

Re: If you don't like Marketing then say you don't like Marketin

Cable plants are built out to have a certain amount of bandwidth. The most common size plants are 750Mhz and 860Mhz. Most Comcast systems are 750Mhz, and have analog channels or digital carriers between 54-750Mhz (some plants like mine go up to 760-770Mhz).

OK, cable plants, I presume you mean cable companies, like Comcast. Am I correct? Do you know the channel bandwidth (analog/digital)?

Yeah, cable companies.

Each analog channel takes up 6Mhz of bandwidth. Digital QAMs vary. You can fit 12-15 digital SD channels on 6Mhz, or up to 3 HD channels.

It's my understanding a full resolution HD takes up the entire 6MHz bandwidth. Is this correct?

Not that I know of.

Each QAM is 38.8mbps. No quality loss at 19.9mbps HD MPEG2 (which would be a 2:1 HD mux). On a 3:1 mux, they have to strategically place what channels would go together to have minimal PQ impact. 2 1080i channels and a 720p channel are perfect.

Thanks. One more question: How many analog signals could practically fit in a 6MHz band?

Ouch, not two?

Dang, that means in the new DTV freq allocation, the max number of HD channels in a 6MHz band will have tripled, although the DTV allocation bandwidth is shorter than analog (54-692MHz for DTV, 54-860MHz analog).

DTV transition has no effect on cable frequencies. Cable will be able to use the 54-860Mhz (or whatever the plant is built out to).