Digital TV for Dummies
The 1980’s gave us the last real change to analog TV. It was the addition of stereo sound. The standard was decided on as MTS. Multichannel Television Sound. It was invented by dbx labs, and used 2 AM sub-carriers of the original FM audio transmission. A third mono channel was added for second language or description services. It was called SAP, or Second Audio Program. Many stations used it for a Spanish audio sound track. TBS network used it for Description TV. This is a special sound track for sight impaired people. It provided more descriptions of what was on the screen than the regular track gave.
Analog TV had improved over the years with better technology but it was still the same system and room for improvement was running out. We had done about as much as we could do to make it better. The one problem that has plagued analog TV forever was noise. The TV receiver was designed to pick up anything on the channel it was tuned to. That meant noise, ghosts, and all types of electrical interference. It was unavoidable.
Now we have a new TV standard called digital TV. Since analog is out, the old NTSC was disbanded, and a new ATSC Advanced Television Standards Committee was formed to decide the technology standards of digital TV. Digital means that the signal is transmitted in bursts of 1’s and 0’s. Binary codes like a computer uses. There is no steady signal from the transmitter. There is one burst of packet information for a few seconds, then nothing for a few seconds. Each burst has enough information to provide your TV with picture and sound for the few seconds there is no signal.
Then another burst, then nothing. Then another burst, then nothing. Your TV receives these bursts and puts them all together to form a continuous seamless stream of video and audio. With digital, the audio and video are combined with all of the broadcast information, and sent as one bit-stream. The TV decodes the 1’s and 0’s, separates all of it, and converts it all back into video and audio.
The big deal about digital is it is interference free. With digital, the receiver in the TV only looks for the 1’s and 0’s. Digital is a specific language. The station transmitter, and the TV’s receiver talk the same exact binary language. The TV receives the 1’s and 0’s, and reconstructs the picture and sound perfectly. The TV ignores noise, ghosts and interference, because those things are not transmitted in a language of 1’s and 0’s. So the TV does not recognize it and ignores it. The result is a crystal clear picture and pin dropping clean audio.
Digital TV still uses the same 6MHz channel as analog used, but the digital signal is narrower and can carry a lot more information. And they can do it all with far less power than their old analog signal needed. An old analog UHF station that transmitted 2,000,000 watts to reach their audience, now only needs 400,000 to 700,000 watts with a digital signal to reach the same distance. One quarter the power to reach the same distance. It saves energy and lowers the electric bill.
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