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Putting the TV Broadcast Spectrum to Better Use?
KoshClassic asks: "Recently, on the NPR show All Things Considered, an interview was broadcast with Thomas Hazlett, formerly the chief economist of the FCC. Although short on details, Mr. Hazlett raises the point that, with the high penetration rate of cable / satellite TV into American homes, broadcasting television over the air has (or soon will) become superfulous and that this portion of the radio spectrum could be better utilized for other purposes. What do Slashdot readers think of this idea and, for those who agree, what alternative uses of the broadcast spectrum would you like to see?"
I think the airwaves are still good for HD content (cable company here doesn't throw any our way). Over the air hdtv is still a reason to use the airwaves.
Erm. No. You've got that completely wrong.
It was decided years ago that digital TV broadcasts (whether HD or not; that hadn't been decided at that point) would occupy the same slices of spectrum we used for analog broadcasts: 6 MHz channels. So a single HD channel occupies the same amount of spectrum as a single analog channel. Which is why HD has to be so highly compressed for broadcast. (HD starts out at over 1.3 Gbps, and gets MPEGged down to 19 Mbps.)
The 6X figure comes in when you start talking about subchannels. Inside a 6 MHz channel, you can broadcast as many subchannels as you want, dividing up the channel's bandwidth among them. A SD broadcast can be squeezed down to about 3 Mbps (1 MHz) and still look acceptable, so you can put 6 SD subchannels inside a single digital broadcast channel.
This is not HDTV, however. In order for a broadcast to be called HDTV, it has to have a vertical resolution of at least 1,000 lines. (That's the ATSC's definition.) Broadcasting SD digitially is not the same as HD.