Audio/Video Chat → Re: DTV frequency allocation

You have our facts backwards.

How so?

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.

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.

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.

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).

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".

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.

"White space" is created by skipping channels in local markets. They did the same thing with NTSC. Notice if you have several NTSC channels on VHF high band in the same market they will be on channels 7,9,11,13 or 8,10,12. They will do the same thing with the ATSC channels.

Yes, that's the impression I got. Didn't realize that about the missing adjacent channels though.