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Stephen Tu · 04-04-2008, 06:35 PM

Why two channels? One is the old analog channel that's been operating for however many decades. The other is the digital channel that's only been transmitting for maybe 9-10 years or so depending on your area. They can't transmit on the same channel because the signals would interfere with one another. But OTA signals usually contain so-called "PSIP" data, so that digital tuners will often display say the old analog channel as "5", with the new digital channel as "5.1", even though the digital channel is actually on physical channel "29" or whatever. 29 corresponds to real physical channel frequency, "5.1" is the virtual channel #, they came up with this scheme so people didn't have to learn all new channel #s. For cable & satellite, they can move either channel to whatever arbitrary channel #, but they usually try to come up with an easy scheme for people to remember. Like in my area Comcast, the old channel is 5, HD is 705, old channel 2, HD is 702, etc., they put all the HD channels in the 700 block.

They had to keep the old analog channel around because there are some millions of people with old equipment that can't tune the digital channel & they don't want to lose those viewers during this transition from analog to digital broadcasting. 9-10 years ago digital TVs/receivers are really expensive, can't expect everyone to go out & buy new stuff right away.

Early next year though, the analog channel goes away (because the government wants to sell the use of those frequencies for other purposes, like wi-fi communication). Some of the TV stations will move their digital channel back to the old analog frequency & give up their digital frequency instead.

Satellite will probably downconvert the digital channel for older receivers that can't get the current HD channel.

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04-04-2008, 06:35 PM	#5 of 23
Stephen Tu Member Join Date: Apr 1999 Local Time: 03:39 AM Local Date: 10-13-2008 Posts: 1,049	Re: HD programming Why two channels? One is the old analog channel that's been operating for however many decades. The other is the digital channel that's only been transmitting for maybe 9-10 years or so depending on your area. They can't transmit on the same channel because the signals would interfere with one another. But OTA signals usually contain so-called "PSIP" data, so that digital tuners will often display say the old analog channel as "5", with the new digital channel as "5.1", even though the digital channel is actually on physical channel "29" or whatever. 29 corresponds to real physical channel frequency, "5.1" is the virtual channel #, they came up with this scheme so people didn't have to learn all new channel #s. For cable & satellite, they can move either channel to whatever arbitrary channel #, but they usually try to come up with an easy scheme for people to remember. Like in my area Comcast, the old channel is 5, HD is 705, old channel 2, HD is 702, etc., they put all the HD channels in the 700 block. They had to keep the old analog channel around because there are some millions of people with old equipment that can't tune the digital channel & they don't want to lose those viewers during this transition from analog to digital broadcasting. 9-10 years ago digital TVs/receivers are really expensive, can't expect everyone to go out & buy new stuff right away. Early next year though, the analog channel goes away (because the government wants to sell the use of those frequencies for other purposes, like wi-fi communication). Some of the TV stations will move their digital channel back to the old analog frequency & give up their digital frequency instead. Satellite will probably downconvert the digital channel for older receivers that can't get the current HD channel. Last edited by Stephen Tu : 04-04-2008 at 06:37 PM.