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Mdoc
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DTV frequency allocation

How and where can I find out the list of frequencies allocated for DTV (and other) use?


ArthurS
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Is this what you're looking for?
»www.ntia.doc.gov/osmhome/allochr ··· chrt.pdf


88615298
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Mdoc
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reply to ArthurS
said by ArthurS:

Is this what you're looking for?
»www.ntia.doc.gov/osmhome/allochr ··· chrt.pdf
Very close. But it was published in Oct '03, so it doesn't contain any info on DTV. But thanks for the reference!


Mdoc
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Click for full size
Here it is, found it, it's close enough. The surprise is the bandwidth for each DTV channel is still the same as the old TV channels (I thought it was less), but there's fewer channels. That frees up some of the spectrum for emergency services use, which I think is part of the reason for re-allocation and for DTV transition. Maybe a major reason.


ArthurS
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Yes, DTV channels use the same bandwidth allocation as analog TV channels, however digital television practically uses up all the bandwidth of the channel, whereas analog television didn't. The spectrum from 746 to 806 MHz has been freed up and reallocated for police/fire/emergency/life safety use.


Mdoc
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OK, that leaves 695 (692+3) to 746 MHz. Do you know what that spectrum is allocated for?


ArthurS
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said by Mdoc:

OK, that leaves 695 (692+3) to 746 MHz. Do you know what that spectrum is allocated for?
That part of the spectrum was sold last year to the highest bidder for new wireless services.


Mdoc
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Do you know who the bidder was that won it?


ArthurS
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said by Mdoc:

Do you know who the bidder was that won it?
Several parties. Google "700 MHz Auction".

»wireless.fcc.gov/auctions/defaul ··· ry&id=73


Mdoc
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3 edits
Thanks, Authur, that's a lot of bidders, "several" is an understatement. While reading and following up, I found out that although the spectrum covering DTV looks used up, there's still a lot of "white space" between the DTV channel allocations that people want to use for unregulated use. »www.nytimes.com/2008/02/09/opini ··· f=slogin

This suggests a possibility for local interference with DTV signals.

Another one:
»arstechnica.com/news.ars/post/20 ··· fud.html

The most recent talk on white space:
»arstechnica.com/news.ars/post/20 ··· aby.html

edit: "unregulated use" = unlicensed use.


88615298
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reply to ArthurS
said by ArthurS:

Yes, DTV channels use the same bandwidth allocation as analog TV channels, however digital television practically uses up all the bandwidth of the channel, whereas analog television didn't.
You have our facts backwards.


Mdoc
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said by 88615298:

said by ArthurS:

Yes, DTV channels use the same bandwidth allocation as analog TV channels, however digital television practically uses up all the bandwidth of the channel, whereas analog television didn't.
You have our facts backwards.
How so?


ArthurS
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reply to 88615298

Analog Television Waveform

DTV Waveform
said by 88615298:

said by ArthurS:

Yes, DTV channels use the same bandwidth allocation as analog TV channels, however digital television practically uses up all the bandwidth of the channel, whereas analog television didn't.
You have our facts backwards.
In what way? Analog or DTV, it still uses the same 6 MHz bandwidth allocated for TV channels, only the DTV waveform packs in a lot more information because of it's more efficient use of the bandwidth allotted for the channel.


Mdoc
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Yes, for HD resolution, all 6 MHz must needs be used up. How much "white space" are there between two of the DTV channels?


ArthurS
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said by Mdoc:

Yes, for HD resolution, all 6 MHz must needs be used up. How much "white space" are there between two of the DTV channels?
Between adjacent DTV channels, hardly any "white" space at all. Typically, white space devices are supposed to seek out unused channels, and use those. Gets to be very challenging in major cities where it can get quite crowded with many TV stations.


88615298
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reply to Mdoc
said by Mdoc:

said by 88615298:

said by ArthurS:

Yes, DTV channels use the same bandwidth allocation as analog TV channels, however digital television practically uses up all the bandwidth of the channel, whereas analog television didn't.
You have our facts backwards.
How so?
Um because we aren't swicthing to digital just so the signals can be MORE ineffcient they are being switched because theyare more efficient? get it? Consdiering the nalog signal cna only carry anlog and just ONE signal at that and the digital signals can carry a HD and multiple SD signals I think digital is more efficient. The only way a digital signal uses more bandwidth is by using all these multiple signals. If all a station did was broadcast one SD signal there's no way it uses more bandwidth than an analog signal.


ArthurS
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2 edits
said by 88615298:

Um because we aren't swicthing to digital just so the signals can be MORE ineffcient they are being switched because theyare more efficient? get it? Consdiering the nalog signal cna only carry anlog and just ONE signal at that and the digital signals can carry a HD and multiple SD signals I think digital is more efficient. The only way a digital signal uses more bandwidth is by using all these multiple signals. If all a station did was broadcast one SD signal there's no way it uses more bandwidth than an analog signal.
Sorry, but you're confusing bandwidth allocation by the FCC of a television channel vs. what the broadcaster chooses to do with the bandwidth allocated. Furthermore you don't seem understand how DTV stations transmit their signal over the air.

Television channels here in North American are allocated 6 MHz, whether they are analogue or digital. As the waveforms I posted clearly show, there is a lot of unused space between the carriers in the analogue television transmission, a space often used by others for commercial two way communication, paging, even wireless microphones, etc. I know because I could fit multiple channels of wireless microphones between carriers within one television channel back in my theatre and broadcast days.

With the digital transmission signal, apart from the shoulders above and below the transmission, practically all of the 6 MHz allocated is being used by the broadcaster, it's one big data stream, essentially occupying the same amount of spectrum no matter how much they squeeze into that transmission. Within that digital transmission, can be multiple data streams containing separate SD and HD channels, along with data, multichannel audio, etc. Or for that matter, it could be a full resolution HD transmission. It's up to the broadcaster to choose what to do with that 6 MHz, whether one channel or many data streams, as long as they follow FCC regulations. A more efficient use of that *allocated* space is the result because the station is no longer constrained to the limitations of the analog transmission waveform requirements.


Mdoc
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Arthur, I got another question: are the carrier center frequencies for DTV channels the same as the analog channels? If so, that may mean I could continue to use the Telecaption Decoder 4000 or an RF demodulator (connected to a cable TV feed through F connector, not pulled from OTA).


ArthurS
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DTV carrier? What carrier?

With HDTV, hi def closed captioning is encoded in the metadata within the HDTV signal itself. On the old analogue TV sets, closed captioning was contained on line 21 of the vertical blanking of the picture. Now if the TV station continues to broadcast a standard definition picture on their DTV transmitter, there may be a chance they continued to put the closed captioning on line 21 of the picture to make things backwards compatible with your TV set, but YMMV. Upgrading to HDTV captioning is an expensive proposition for most TV stations, and the standard is still evolving (at least the last time I checked about a year ago).

So to answer your question, "maybe".


Mdoc
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1 edit

DTV Haystack
said by ArthurS:

DTV carrier? What carrier?

This carrier (see above).

That's right [snap], I forgot about the fact that you can have more than one channel in the 6MHz space.

Kearnstd
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OT but then how does cable put say two channels on one 6mhz channel when they go digital? or is that what QAM does.
--
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Matt3
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reply to Mdoc
Good thread guys, I'm learning a lot of interesting stuff.


ArthurS
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reply to Kearnstd
said by Kearnstd:

OT but then how does cable put say two channels on one 6mhz channel when they go digital? or is that what QAM does.
Well, depending on the resolution, a channel may not occupy the entire 6 MHz bandwidth, particularly standard def channels. So a broadcaster might have one 720p channel, and several 480i channels squeezed in there.


toups

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1 edit
reply to Kearnstd
said by Kearnstd:

OT but then how does cable put say two channels on one 6mhz channel when they go digital? or is that what QAM does.
Try reading »en.wikipedia.org/wiki/QAM_tuner

and

»en.wikipedia.org/wiki/Modulation

and

»en.wikipedia.org/wiki/QAM


Mdoc
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Your last to me forces another question:
At the transmitting station, are channels within the DTV channel multiplexed? If so, that in part explains how they are selected at the receiver for further processing.

If not, how are they selected?


ArthurS
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said by Mdoc:

Your last to me forces another question:
At the transmitting station, are channels within the DTV channel multiplexed? If so, that in part explains how they are selected at the receiver for further processing.

If not, how are they selected?
I guess you can call it multiplexing. Let's put it this way, the broadcaster has 19.39 Mbps of bandwidth to play with in one 6 MHz channel, they can choose to send a single program that consumes all of that bandwidth, or divide it into several different streams or sub channels, each containing something different. Digital TV standards have several different formats, each consuming different amounts of bandwidth: 480i, 480p, 720p, 1080i. So they choose the right combination, compress each stream using MPEG-2 compression, modulate the data to fit the 6 MHz channel bandwidth. So at 1080i, the entire 19.39 Mbps can be consumed, however a 480p signal only consumes around 3 Mbps, depending on source material. Some broadcasters are even exploring sending data with a show to enhance the viewer experience.


Matt3
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Arthur, has there been any desire to move to a more efficient compression scheme, like MPEG-4?


ArthurS
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said by Matt3:

Arthur, has there been any desire to move to a more efficient compression scheme, like MPEG-4?
I'm sure the desire is there, and ATSC has approved MPEG-4, but that would involve customers getting additional decoding equipment (read set top coverter boxes) to be able to view those streams. I know there was one company out there that was encoding MPEG-4 subscriber based streams on regular OTA television channels, but it went bankrupt before it could expand beyond a few markets. Let's hope that whatever the future holds for MPEG-4 on OTA channels, it doesn't suffer the same poor quality that we see on satellite and digital cable presently.


Mdoc
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1 edit
reply to ArthurS
said by ArthurS:

said by Mdoc:

Your last to me forces another question:
At the transmitting station, are channels within the DTV channel multiplexed? If so, that in part explains how they are selected at the receiver for further processing.

If not, how are they selected?
I guess you can call it multiplexing. Let's put it this way, the broadcaster has 19.39 Mbps of bandwidth to play with in one 6 MHz channel, they can choose to send a single program that consumes all of that bandwidth, or divide it into several different streams or sub channels, each containing something different. Digital TV standards have several different formats, each consuming different amounts of bandwidth: 480i, 480p, 720p, 1080i. So they choose the right combination, compress each stream using MPEG-2 compression, modulate the data to fit the 6 MHz channel bandwidth. So at 1080i, the entire 19.39 Mbps can be consumed, however a 480p signal only consumes around 3 Mbps, depending on source material. Some broadcasters are even exploring sending data with a show to enhance the viewer experience.
Yes, that's multiplexing. I'm familiar with video encoders and receiver/decoders as well as multiplexers and satellite communications equipment. But my understanding is that MPEG4's use is limited to the computer arena, not video broadcasting, unless that standard has been modified for video industry use.