Digital TV Question w/ DBS

NTSC is an analog signal.

DBS and ATSC are digital MPEG-2 encoded signals. DBS is 480i which is what the NTSC digitizes into (approximately), which in fact is an ATSC standard signal. ATSC has a bunch of formats ranging from 480i to 1080p. The common HDTV ones are 1080i and 720p.

Now the thorny issue is the transmission. Over the air HDTV uses a modulation of 8vsb which is just a method of sending a digital signal through the 6Mhz spectrum that the station uses.

Dishnetwork uses QPSK (an old satellite standard), and will be putting in 8PSK for newer signals for HDTV transponders. There are even faster standards available, but the limitation on the standard is the power per satellite transponder and the size of the recieving dish. Dish satellites have gotten much more powerful so they are now able to pack in more bits and your small dish can distinguish them from background noise. The next step up in power they could use 16QAM.

Cable companies use modulations such as 16QAM and 64QAM. This is because they have a nice sheilded cable and can pack in even more bits.

Another thing to note is that the spectrum for over the air TV is not contiguous. There are big gaps between some channels for things like FM radio.

Now the problem is that there is no standard established yet for cable reception of HDTV without using a cable box yet, since each cable box would use its own private method. One of the main holdups of this has been copyright holders wanting copy protection on everything.

Hopefully soon they will have a standard for "Cable Ready" ATSC that TV makers can use to make TVs that will work without a cable box. What is the point of having a digital tuner in your set if you cannot use cable without a box doing the tuning for you.

----
Another note: even though DBS is digital television at 480i, it does not mean that they do not overcompress the signal and give a bad picture. You may not have analog snow, sparkles, ghosting, etc, but your picture can now have digital artifacts such as blockiness, soft picture, etc.

The claim is that 4mb/sec is what it takes for broadcast quality for a 480i picture. This is about 8 channels per transponder. But, over time they have crammed 12 channels per transponder dropping the bit rate down to about 2.5mbs. Although they claim that the compression is better now (improvement in compression technology), the picture is suffering right now as they pack them in (in my opinion). Hopefully they will be able to unpack them as they get more satellites in the air with spot beams to give them the capacity they need now that they have to carry every tiny station in every local market that they cover.