Stories tagged broadcast

Jun
12
2009

High definition digital orcs are only hours away!
High definition digital orcs are only hours away!Courtesy Alexander Heinz
Heyo, Buzzketeers. Once more, today’s the day that regl’r TV switches completely and forever to digital TV. So get yourself a converter box. Or sit back and watch your newer TV, and, once again, forget everything else about the world. But Science Buzz will not be held responsible for your confusion.

Seriously, go to Science Buzz’s Digital Television Feature, and get your brain exploded with knoooowwwwleeeeedggggeee.

Also, we have here a question from one of the visitors to Science Buzz regarding what is called the “cliff effect” in digital broadcasting:

Why does digital TV and all types of radio technology experience the cliff effect? Is this caused by binary code packets that are corrupted or eliminated by natural and man made sources of over the air interference and signal reflections? Is this tied into the fact that any computer/translator of binary packets, back into analogue waves within our televisions and digital radios, must have this data to function? Is there any way to create computer technology to eliminate this malaise of digital broadcast technology? Why cannot we have a "dirty" digital signal that gets through without "drop-out" in all weather conditions, and through buildings and all sorts of structures just like with analogue? Why is analogue AM, FM and Pulse Modulation still able to be "copied" reasonably well through sources that block or corrupt a signal?
Hoping to read your response to these questions soon.

Sincerely Yours,

Rob

Weeelllll… first of all, Rob, I have the feeling that you know more about this than you’re letting on. In fact, I have the feeling that you know more about it than me, and I wrote the digital television feature linked to above. But let’s start from the beginning…

So, everybody else, the “cliff effect” is something a few of you will probably soon discover and react to with a big ol’ “But this is a brand new fancy TV! I. Can’t. See. Anything! W. T…. F!!!”

If you live a long ways from a television station’s transmitter tower, or have some large mountain-y, forest-y, building-y thingy in between you and that tower, you might not have gotten very good reception on your old TV (analog broadcast TV), but you still might have been able to see and hear something even if it was grainy or fuzzy or staticy, or whatever. That’s because analog signals could be picked up perfectly, or not at all, or everywhere in between. Digital signals, on the other hand, can more or less just be picked up perfectly, or not at all. So if you got slightly fuzzy reception before, you might get perfect digital reception. Or you might get no digital reception at all. But you shouldn’t get fuzzy digital reception, because at a certain point it’s like the signal just drops off a cliff—it’s there just great up to a point, and then it disappears.

This happens because of the nature of digital broadcasts.

Think about an analog signal (old TV) being like someone shouting a message to you. If you’re very near the shouter, or broadcaster, you’re going to hear them perfectly. If you’re a ways away, you can still hear the shouting, but the words are getting quieter. And as you move further and further away, you’ll hear less and less of the sounds of the shouting, until it’s so faint that you can’t hear anything at all. Analog TV is like this. Sort of.

Now think about a digital TV broadcast as still being like someone shouting a message to you, but they’re shouting it in a complicated, secret code. Nearby, you hear and interpret the code perfectly. A ways away, you hear the shouting pretty well, and if you miss a piece or two of the code, you can still put together the over all message. But after reaching a certain distance, you might hear so little of the code that you can’t understand any of what the message is supposed to be, even if you can still hear faint shouting. That’s sort of like digital TV.

See, analog TV really is kind of like listening to the broadcasting tower shout out signals. It’s not as nice to listen to (that is, watch) a faint and distorted signal, but it’s still something. But digital broadcasts send out packets of digital information (1s and 0s). The digital information is decoded on your TV and turned into a picture, and the TV can still make a pretty cool picture even if not all of the information is getting through, but if there’s enough interference, and not enough digital information is reaching the TV, at some point the decoding equipment in the TV will be all, “Screw it. I totally give up.” And you’ll be totally without a picture.

Does that make sense? Tell me if it doesn’t.

So back to Rob’s questions specifically:

“Why does digital TV and all types of radio technology experience the cliff effect?”

Interference and weak signals. Digital TVs don’t see the cup of information as half full, half empty, full, sort of empty, almost empty, nearly full, etc. They see the glass of information as “full enough” or “empty.” Oh, man, I liked that analogy.

“Is this caused by binary code packets that are corrupted or eliminated by natural and man made sources of over the air interference and signal reflections?”

Yep. Digital broadcasts still use radio waves, just like analog broadcasts, so the same stuff that would interfere with an old TV signal will interfere with a digital signal.

“Is this tied into the fact that any computer/translator of binary packets, back into analogue waves within our televisions and digital radios, must have this data to function?”

Um… yes? (When Rob says “binary packets” he’s talking about digital information. “Binary” is the basic language of computers—it’s the 1s and 0s I mentioned before.) Yeah, that data is what gets turned into images and sound, so if it’s not there, or if there’s not enough of it… no images or sound. BTW, with digital TVs, digital signals don’t necessarily get turned back into analogue waves. Mostly they go straight to being images, after being decoded. But on older sets with converter boxes, or on fancier CRT screens, yeah, they do get turned back into waves, because the display technology uses them. The waves are translated directly into a beam of electrons that “paints” the images on the back of the screen… actually, that’s a different topic, and remembering learning about it makes me sad.

“Is there any way to create computer technology to eliminate this malaise of digital broadcast technology?”

Er… maybe? At the moment, I think the best way to eliminate the problem of the cliff effect is to get a better antenna, or put your antenna in a different spot. Check out this section of the feature for some home made antenna plans. I made one of these myself, and it really does work well, even in my basement bedroom. (This also makes me sad.) I don’t know enough about it to give you a better answer, but… maybe if there was a new and more efficient way of encoding images on digital broadcasts, a TV (or whatever) might be able to construct a picture out of the information available on a weak signal. Maybe?

“Why cannot we have a "dirty" digital signal that gets through without "drop-out" in all weather conditions, and through buildings and all sorts of structures just like with analogue?”

For the reasons we went through above. Going through stuff makes a TV signal weaker, whether its digital or analog, and DTV needs a certain strength of signal to make a whole picture. So maybe if way more power was put into broadcast towers that would help? Or maybe if we broadcast TV on a higher energy wave than radio waves? X-rays would punch right through houses and hills, I bet, and deliver delightful reception all over. But they’d also give us cancer. Whoops!

“Why is analogue AM, FM and Pulse Modulation still able to be "copied" reasonably well through sources that block or corrupt a signal?”

I don’t know.

“Hoping to read your response to these questions soon.

Sincerely Yours,

Rob”

Word.

1928: W3XK, the first American TV station, begins broadcasting from suburban Washington, D.C.