Digital Cable Boxes

My aunt asked elsewhere,

I don’t understand – the cable company at home says they are changing to digital transmission and we are not going to get reception unless we get a digital adapter. Maybe my smart nephews, nieces and children can explain why we need a digital adapter for a digital TV????

“Digital TV” refers to being able to receive digital over-the-air (with an antenna!) TV channels and implies being able to use the newer devices like DVD players that use digital formats, not analog formats, for providing the TV the signal.

“Digital cable” refers to the signal the cable TV company sends to the home. Almost any contemporary TV or video recorder can process an analog TV signal reasonably easy and well, but the cable TV companies are converting to digital networks for one reason: they can send (and receive) more data over a digital network than an analog network.

We don’t think of TV signals having a speed or a bandwidth, but they do. Thirty times a second, they transmit 240 lines that are 360 positions wide and having three values that have a range like 1-1000 (red, green, and blue). This is for standard (analog) TV.

For HD TV, it becomes 720 lines that are 1280 positions wide or 540 lines that are 1920 wide, again, every 30 seconds. That’s nine times as much data in every screen shot than was in the old channels.

Add to that the explosion in the numbers of channels. Bruce Springsteen sang of “Fifty-Seven Channels (and Nothing On)”, but that was twenty years ago. These days, any cable operator with that few of channels would be laughed out of the market in no time at all. My cable company’s starter package is 200 channels, but their network has to be able to handle 500 or so channels. The old analog cable systems couldn’t handle nearly that many channels. For a while they used a system where they’d choose only some of those channels to a given neighborhood; cable boxes would signal the local relay station which station was just tuned in to make sure the relay station would send that channel down the cable, presumably replacing another channel that was the least recently chosen. However, even that wasn’t enough, so they’re going digital more and more now.

So, even if you don’t want the additional channels, the cable company thinks your neighbors do, and they worry that if they don’t upgrade to offer that many channels, your neighbors will switch to satellite TV or even “just the Internet.”
I’m sure my cousin the Honda Whisperer has similar stories about automotive technologies marching on so that old techniques and tools are now just quaint and old.


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