What makes digital broadcast transmission (like over-the-air TV) need less power (as little as 25%) to cover the same area as the previous analog transmitter?
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Digital signals are like images made from only two colors: full black and full white. You can make out such an image even if it is very noisy. So you can send a signal at a level that would be extremely fuzzy on an old analog TV, but the digital circuitry can still pick out the data reliably.
Instead of an actual image, a string of ones and zeroes (black and white color) representing an image is transmitted, and as long as the TV can make out each of them, it can recreate a pristine image.
This is a simplification, but it illustrates the basic premise.
Let’s imagine it as you having a shortwave handheld radio. You and your friend can speak back and forth over it. At some distance the interference from other signals and just the atmosphere in general will make the meaning of the speech unrecognizable. You’ll be able to recognize it as human speech but the actual words will be garbled beyond recognition. This is much like an analog signal.
Now let’s say you and your friend are fluent in Morse code. Just a series of beeps. The beep itself conveys no information other than the fact that it is a beep. So as long as the reciever can clearly hear the beep they have received a part of the message. The tone of a Morse beep can clearly be distinguished even through a ton of static. Thus using the same handset with the same amount of power, you’re able to transmit clear messages over much greater distancea because the same amount of interference has a lesser effect on the information being transmitted.
It also means that you can drop the power of the transmitter to only be understood at the same range as the voice message. Now you have the same information, over the same range, using less power.
I got a some questions. I’m NOT challenging or arguing, I know enough about RF to know I DON’T know much at all, but I’m genuinely curious:
Same 6mhz wide channel, optimize each transmitting antenna differently if it matters, but you gotta be covering the same area.
Can you really get away with only 25% as much transmitter power out requirement for ATSC 1.0 as would be needed for analog NTSC? To cover the same approximate area with a sufficiently useable signal? For ATSC let’s say one physical 6mhz channel and not “cheat” by dividing the power up per sub channel or “stream”. ATSC is certainly way better use of SPECTRUM…
“IT’S digital, ons and offs, blips” may be ELI5 but it seems woefully inaccurate here. That transmitter signal is doing a whole lot more than just existing and not existing rapidly. 8VSB diagrams look to be “just a bit” more than “blips”.
On the analog side, actual power needed can vary a lot based on the content. I mean I don’t understand it, I have heard it’s inverse; dark = high power, bright =low power. I do understand the concept of analog video being a single continuously varying signal, with a bunch of extra “sync stuff” so the TV can “steer” it. Then you gotta jam color and audio in there. And we are Presented in Stereo (where available) aren’t we?
OK so when theoretical TV station WXYZ threw the switch from analog to digital, did their transmitter power bill go down by 75%? None of that power factor stuff, they’re shooting out the consumption with capacitors and inductors and stuff.
Fundamentally the reason is that digital video can be compressed to use lower bandwidth than analogue video. Digital compression is very advanced whereas analogue signals are essentially uncompressed, unless you count interlacing and chroma subsampling. So you can send several video streams, some in high definition, on the same channel that used to support a single standard-definition channel, and do it with less power. Because the great majority of video frames are almost exactly the same as the frame before, and pixels are mostly the same as their neighbouring pixels, yet analogue TV takes no advantage of that.
Also, analogue might use a modulated carrier wave for transmission with a greater duty cycle in regard to power efficiency.
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