Idea: Let's use ATSC TV for digital radio - Canadian TV, Computing and Home Theatre Forums
 
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post #1 of 13 (permalink) Old 2007-06-17, 02:05 AM Thread Starter
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Idea: Let's use ATSC TV for digital radio

Here's another "flowery idea"... I'll let you decide whether I'm a "budding genius" or a "blooming idiot". According to the webpage http://broadcastengineering.com/mag/...atsc_standard/ the typical ATSC 5.1 audio stream is compressed to 384 Kbits sec. That's 1/50th of the 19.2 Mbits used by the entire ATSC transport stream. Allowing for meta-data overhead, and slight separation to prevent adjacent-subchannel interference, it should still be possible to get 30 high-quality DD5.1 signals into a 6 mhz ATSC "TV channel".

This proposal has a couple of HUGE advantages over IBOC and DAB...
  1. It will not require you to buy a new technology that you wouldn't otherwise buy. It uses ATSC digital TV equipment, which probably even today, is found in more Canadian homes than IBOC and DAB receivers put together. After the digital cut-over, most homes in Canada will end up with ATSC tuners.
  2. An FM transmitter is expensive to set up and run. If costs can be split 30 ways, the economics look much better.

When an idea looks great on paper, I get this nagging feeling that I'm missing something glaringly obvious. Anybody see any technical problems?

I'm not getting into the politics of this right now. But, as a start, I suggest that the entire FM band be migrated to "ATSC radio". That'll free up 20 mhz of radio spectrum as an extra benefit.
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post #2 of 13 (permalink) Old 2007-06-17, 10:10 AM
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I assume these stations would only exist with 'a few words from our sponsors' since the commercial free subscription model is not possible. It would be nice to have another source of radio but chock full of commercials? What about the mobile market? Can you lock onto an ATSC signal when moving? As far as I know ATSC tuners only exist in TVs right now. MP3 players, clock radios, etc would have to catch up.
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post #3 of 13 (permalink) Old 2007-06-17, 12:43 PM Thread Starter
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Quote:
Originally Posted by Jake View Post
I assume these stations would only exist with 'a few words from our sponsors' since the commercial free subscription model is not possible.
I never meant to imply that. I did say "migrate the FM band", and I intended that to include the FM band's business model.

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Originally Posted by Jake View Post
It would be nice to have another source of radio but chock full of commercials?
Not so much "another source" as an updated FM band with native DD5.1 signal. Talk radio can remain on AM.

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Originally Posted by Jake View Post
What about the mobile market? Can you lock onto an ATSC signal when moving?
ATSC uses the VHF-HI and UHF bands.
  1. Mobile VHF radio does exist (taxi dispatch, etc).
  2. Sirius and XM both have ground-based repeaters for their radio signals, at higher frequencies than ATSC channel 51. And it's aimed squarely at the in-car market. That's actually the closest analogy to what I'm proposing.
  3. Haven't you ever seen anybody talking on a cellphone aboard a moving bus, or even worse, driving with one hand on the steering wheel, and the other hand holding their cellphone? Proof positive that you can lock onto a UHF signal in a moving vehicle. And remember that that's with just the cellphone's intenal antenna. Hook up a radio to your car's aerial, and you should easily be able to get very good reception.

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Originally Posted by Jake View Post
As far as I know ATSC tuners only exist in TVs right now. MP3 players, clock radios, etc would have to catch up.
And the other options for migrating to digital radio with DD5.1 are DAB and IBOC; not exactly low-cost either. You have to do SOMETHING to get digital radio to DD5.1. I figure the installed base of ATSC tuners in North America exceeds the installed base of IBOC and DAB tuners. Migrating to ATSC should be less painfull than migrating to IBOC or DAB.
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post #4 of 13 (permalink) Old 2007-06-18, 10:31 AM
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It is not a matter of frequency, but modulation. My understanding is 8VSB might not work well with mobile/portable receivers.

If you want all digital shared carrier portable radio, DAB is what you want, which I think has a mode that lives on the VHF/UHF bands
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post #5 of 13 (permalink) Old 2007-06-18, 11:14 AM
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My post about locking onto an ATSC signal is relevant.

Quote:
A-VSB or Advanced VSB is a modification of the 8VSB modulation system used for transmission of digital television using the ATSC system. One of the constraints of conventional ATSC transmission is that reliable reception is difficult or impossible when the receiver is moving at speeds associated with normal vehicular traffic.
Article on A-VSB.

Last edited by Jake; 2007-06-18 at 11:15 AM. Reason: fixed formating
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post #6 of 13 (permalink) Old 2007-06-18, 12:21 PM
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Yes Jake you are correct.

As I understand it, most mobile carrier signals use vertical polarization and ATSC standard uses horizontal polarization which is inherently crippled by the doppler effect.

There are two competing mobile ATSC standards currently in development for North America:
http://www.digitalhome.ca/forum/showthread.php?t=63639
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post #7 of 13 (permalink) Old 2007-06-20, 05:34 PM
 
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Another excuse to go HD lighter and lighter. Thanks but no.
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post #8 of 13 (permalink) Old 2007-06-20, 06:34 PM
 
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How's about digital video over DAB?

CBC English Radio, TV and web streaming: Retired
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post #9 of 13 (permalink) Old 2007-06-20, 07:10 PM Thread Starter
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Yes Jake you are correct.

As I understand it, most mobile carrier signals use vertical polarization and ATSC standard uses horizontal polarization which is inherently crippled by the doppler effect.
So? Use vertical polarization for a dedicated audio channel (6mhz bandwidth). Next question?
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post #10 of 13 (permalink) Old 2007-06-20, 07:32 PM
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Hmmm... That's why the Toronto CBC DAB ensemble has both CBLT and RDI as data streams?

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post #11 of 13 (permalink) Old 2007-06-21, 09:30 AM
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Use vertical polarization for a dedicated audio channel
Would that not mean new transmitters, antennas and receivers?
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post #12 of 13 (permalink) Old 2007-06-21, 11:20 AM
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Essentially, yes.
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post #13 of 13 (permalink) Old 2007-06-21, 11:59 AM
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Yes, and no.

You are talking about receiving an ATSC signal in a car, so a new receiver is needed regardless of polarization.

But the idea would have to piggyback onto existing broadcast infrastructure. I have a hard time believing the broadcasters would want to reinvest - there would have to be enough demand to justify the cost. This where the OP's question progresses - multiple broadcasters sharing the load - and a evaluation would have to be done.

Vehicles and home audio equipment are almost exclusively already outfitted with vertically polarized receive antennas. While it would be easy to put an additional antenna in homes the problem is for mobile reception.
The beauty of vertical polarization is a vertical whip receiving antenna is omni-directional - this is great for mobile devices. With a horizontal polarized signal, the existing receiving whip antenna (vertically polarized) may still receive some signal, but it is so weak as to be impracticable. A second omni directional horizontally polarized antenna would be required for the receive end. And it should be placed outside the vehicle (cost), due to the partial Faraday cage effect. I have a hard time seeing the auto manufacturers justifying a second antenna for an unproven technology.

A circular (dual) polarized transmitter would potentially overcome this need for secondary receive antennas, but the wasted power, and the RF hazard at the tower base would be show stoppers.

I would think the issue would be better addressed when a mobile OTA standard is finalized and then use that.
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