Broadcast frequency between Digital and Analog: Is it the same?

bicker

DTVUSA Member
#2
Analog and digital are broadcast on the same spectrum frequencies: 55 MHz - 88 MHz (VHF Low), 174 MHz - 216 MHz (VHF High), and 470 MHz - 806 MHz (UHF). Of course, you cannot broadcast both an analog channel and a digital channel on the same frequency at the same time, no more than two people can stand in the same spot at the same time.

The government auctioned off just channels 55 and up (698 MHz - 806 MHz). Once the digital transition is complete, all of television will be broadcast in less space, but will have more room for programming signals, because digital is more efficient.

(Note that this in not the first time that a portion of the spectrum for television has been reallocated. Until the 1980s, UHF went all the way up to 890 MHz. 806 MHz - 890 MHz were reallocated for public safety and cellular telephones in 1982.)
 

1inxs

DTVUSA Member
#4
Efficient? There's heaps of data thrown out. (quite visible during scenes that use a lot of fast-motion transition effects.)
That has nothing to do with it being a digital signal. It is due to the filming techniques and your HDTV video scan rate. If your HDTV is only a 60 hz you will see more blurring with high speed scenes than a HDTV with 120 hz video scan rate unless it is part of the films special effects. If the film was purposefully produced with blurring during the high speed scenes there would be nothing you could do. Like some black and white films, blurring is part of the special effects and would lose the artistic intent and vision of the movies producer.
 

Trip

Moderator, , , Webmaster of: Rabbit Ears
Staff member
#5
First of all, bicker's post is 99% correct. He gave the correct spectrum for the auctioned off spectrum, but that spectrum is channels 52-69, rather than 55-69.

Efficient? There's heaps of data thrown out. (quite visible during scenes that use a lot of fast-motion transition effects.)
That doesn't make it any less efficient.

Analog can transmit a single 480i image on a 6 MHz stream. It cannot be compressed, so even if you're showing a static image, it takes the same 6 MHz.

Digital allows for more to be included. A single uncompressed SD is 15 Mbps on digital, which still leave 4 Mbps of unused space. Since most SD signals do not use the full 15 Mbps at a given time, in digital it is compressable such that you can fit 4 or more SD streams into that 6 MHz signal.

To do high definition programming in analog, it would take a 20 MHz channel. In digital, it is pulled off with 6 MHz. It is certainly more efficient.

The problem you cite is overcompression. If you put a single 1080i HD in a 6 MHz channel, it can look pretty good, depending on the encoder used and some other variables. If you start trying to compress it further to add subchannels, then you start running into motion artifacts. This is nothing that's directly digital's fault. Without digital TV, you wouldn't have HD at all.

That has nothing to do with it being a digital signal.
Yes it does. It's related to overcompression of the video feed. Many stations do it in an attempt to jam in an HD and multiple SD subchannels.

- Trip
 

bicker

DTVUSA Member
#7
Yes, efficient. You can broadcast the same amount of data (i.e., same resolution) via digital in about 1/6th as much bandwidth that analog would require for that much data.

There's heaps of data thrown out. (quite visible during scenes that use a lot of fast-motion transition effects.)
You're comparing HD, which is actually 6 times as much data, to old analog SD.

HD = 2,070,000 pixels
analog = 337,920 pixels

Besides, analog threw data out as well -- it was called snow.
 

Piggie

Super Moderator
#9
Yes, efficient. You can broadcast the same amount of data (i.e., same resolution) via digital in about 1/6th as much bandwidth that analog would require for that much data.
I guess it's in the eye of the beholder. If you run 6 SD programs on a single RF channel giving them each equal bandwidth, you end up near 3 mbps per program.

That is "barely" enough to imitate a good analog picture using ATSC and MPEG2 currently in use on OTA.

In my opinion you can fit 4 SDs in nicely on an RF Channel.

Five can be crammed into a channel if 2 of them are limited again back to 3 mbps. But to me anything under 4mbps is sub par to a solid clear analog signal.

So to my eyeball it's closer to 4.5 times as efficient as analog, which is a huge improvement. And like Trip says without digital we would never had HD in the RF space allotted for TV.
 

bicker

DTVUSA Member
#10
I guess it's in the eye of the beholder.
The question of efficiency is a matter of math and physics.

If you run 6 SD programs on a single RF channel giving them each equal bandwidth, you end up near 3 mbps per program. That is "barely" enough to imitate a good analog picture using ATSC and MPEG2 currently in use on OTA.
Now that is in the eye of the beholder. :)

In my opinion you can fit 4 SDs in nicely on an RF Channel.
Which still makes it a lot more efficient than analog.
 
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