How does digital cable work?

[cjchaps]

I used to have Time Warner cable, bought about a year ago AT&T took over my cable(I live in a Chicago burb). Now they are offering digital cable. What happens to the cable signal when you get digital cable? Do I need a cable box for each TV I have, or does the cable still output a regular signal?

 

[rival]

you need a box for each tv i think, its a big old dvd size box too :| , also need a fone jack for it so it can download the tvguide and stuff

 

[Pepsi90919]

It's like a cable modem but usually it's just downstream data.

The box is a tuner that can decode additional digital data channels, as well as the standard analog channels, and will give you a prettied-up interface tailored to your cable company's needs (like a guide and stuff.)

If you want the digital channels on every TV, you must get a decoder for each TV.

 

[Hayabusa Rider]

I have att digital- You dont need a phone line at all. The remote has a guide button. Just press and you are there. It's better than analog cable, but ATT cheaped out and I cant get HDTV broadcasts. I hope they fix that.

 

[PrincessGuard]

I have AT&T Digital and have to use a phone line as well.

 

[Blayze]

<< you need a box for each tv i think, its a big old dvd size box too , also need a fone jack for it so it can download the tvguide and stuff >>



hmm... I have Adelphia Digital Cable and we do not have to use a phone jack to download. we do have to phone in our PPV's though

 

[pulse8]

I have AT&T Digital Cable and I don't have a phone line and can order my por-errrr PPV through the box.

 

[Blayze]

we used to have Benchmark and then Adelphia bought them out.

anyway when I select a PPV it gives me a 1-800 number to call. When I call it goes thanks for ordering and the movie comes on.
still would be better if I didn't have to dial the phone
yes Im a lazy mofo...

 

[helloedchen]

well...afaik...for digital cable, about 8-10 channels are packed into a packet of data, as opposed to the analog signal which can only carry 1-2? correct me if i'm wrong. to accomplish this, you need a digital convertor box for each tv set. The digi box also can accept analog signals for your analog chans. TW here does not use a phone line. I assume it is a two way communication since we can order PPV and stuff right from our remote. So a signal is sent back to log which programs we've ordered.

 

[cjchaps]

So for AT&T in Brookfield(outside of Chicago), will I get a mix of analog and digital, or purely digital signals? We have 3 TV's in the house, and if I choose to switch to digital, I don't want to pay to have 3 TV's on it.

 

[Electrode]

First, my understanding of how digital and analog cable works:

Analog cable uses a copper wire to simulate regular airwaves. TV channels are sent as plain old RF signals. PPV channels are scrambled, and the cable box (about the size of a small phonebook) descrambles them. I never did figure out how the cable co. authorizes a PPV channel for a particular box.
Digital cable uses data packets transmitted on a low frequency RF signal over a regular copper wire, or in some places, as a pure digital signal over fiber. Instead of each channel being an RF signal, they are digital video streams. The channel numbers have nothing to do with frequencies. Infrastructures capable of digital cable TV are also capable of carrying TCP/IP packets, which is how cable internet service works.

I am probably waaaaaaaaaayyy off on the digital cable description, but why does it matter?

Second, about the phone line requirement. I have Charter digital cable. They give customers a Motorola DCT box, which is about the size of a DVD player. It doesn't use a phone line, but instead retrieves TV listings over the cable network. PPV ordering is also done over the cable line, but premium channels must be ordered by phone.

Again, I have no idea what I'm talking about. I worked at a cable TV station once and learned quite a bit about the workings of analog cable, but I know nothing of digital cable.

 

[UFGator]

You dont need the phone line anymore.

I think for 2 reasons

1. With the phone line box you could get free ppv movies
2. A lot of people only have cell phones.

You need a box for all TVs...

 

[guyver01]

Digital cable is very similiar to analogue cable.

In 1989, General Instruments demonstrated that it was possible to convert an analog cable signal to digital and transmit it in a standard 6-MHz television channel. Using MPEG compression, CATV systems installed today can transmit up to 10 channels of video in the 6-MHz bandwidth of a single analog channel. When combined with a 550-MHz overall bandwidth, this allows the possibility of nearly 1,000 channels of video on a system. In addition, digital technology allows for error correction to ensure the quality of the received signal. The move to digital technology also changed the quality of one of cable television's most visible features: the scrambled channel.
The first system to "scramble" a channel on a cable system was demonstrated in 1971. In the first scrambling system, one of the signals used to synchronize the television picture was removed when the signal was transmitted, then reinserted by a small device at the customer's home. Later scrambling systems inserted a signal slightly offset from the channel's frequency to interfere with the picture, then filtered the interfering signal out of the mix at the customer's television. In both cases, the scrambled channel could generally be seen as a jagged, jumbled set of video images.

In a digital system, the signal isn't scrambled, but encrypted. The encrypted signal must be decoded with the proper key. Without the key, the digital-to-analog converter can't turn the stream of bits into anything usable by the television's tuner. When a "non-signal" is received, the cable system substitutes an advertisement or the familiar blue screen.