technical questions

#1
Hello

I am french (and living in France) and have interrest on DTV technical choices in all teh countries.
I tried to find any technical information on DTV in the US, but didn't find any answers.

I hope this forum and members could help me.

First . France started DTV for terrestrial transmission 2 years ago. but the analog signal is still there to let people find their DTV box.
Analog TV should begin to shut down in 2010.

In the US, I understand that analog is switched off when DTV starts , is this the 12th of june ?

My technical questions :
How many channels channels are transmitted in one frequency ? in france there are 6 channels on one frequency
If there are more than one channel, who choose the channels to be sent on the same frequency ?

Are all the DVT frequency in UHF band ?
What is the spectral bandwith of one frequency , 7 or 8 Mhz ?
What is the DVB-t modulation choosen , 2K or 8K ?
What is the Mpeg standard used for the video channels ? MPEG2 or MPEG4 ?

perhaps, you will have answer on these questions only the 12th of june ?

Thank you !

Philippe
 

Trip

Moderator, , , Webmaster of: Rabbit Ears
Staff member
#2
There are large differences in the European and American systems.

First of all, we're transitioning to digital. Most stations already have digital signals on the air. The correct terminology (despite all the advertising) is to say we're shutting off the analog signals, because the digitals are already present.

America does not use the DVB-T system, we use a system called ATSC. It uses 6 MHz channels and chokes horribly on a lot of common interference problems. It uses MPEG-2, as the standard dates to 1996. Receiver boxes are not required to decode MPEG-4, even though it's now a part of the standard, so I don't expect any movement in that direction. If you want more technical information on the ATSC standard, you might look it up on Wikipedia.

The American system supports HDTV whereas I don't think the European system does yet (that might be in DVB2-T), so the number of channels transmitted on a frequency varies. Some stations, like WCBS in New York, transmit only a single HDTV feed to ensure best picture quality. Other stations without HD transmit 5 or 6 SD channels. Some stations even attempt to balance an HD with one or more SD feeds, and some very stupid stations attempt to air 2 HD feeds plus an SD. Your picture quality may vary.

I hope that answers your questions. If not, I can try again. :)

- Trip
 

bicker

DTVUSA Member
#3
How many channels channels are transmitted in one frequency ?
As indicated, above, each channel in the United States is 6 MHz, and due to the nature of the technology used for broadcast television here, the limitation on how many signals can be carried on each channel is a bit stricter than for some other specifications. For example, (doing this from memory, so I might be off by a little) while a broadcast channel in the United States can probably safely carry 1 HD signal and 1 SD signal (or 4 or 5 SD signals), on a 6MHz channel, a cable channel in the United States can probably safely carry 2 HD signals; or 1 HD signal and 2, 3 or perhaps even 4 SD signals; or 8 or 9 SD signals.

in france there are 6 channels on one frequency
I echo the speculation, above, as to whether the 6 signals you are referring to are HD signals, ED signals, or SD signals. I suspect one of the latter. I seem to remember that broadcast channels in Europe support a bit more data per channel than here in the United States, but that would not account for such a large difference in capacity. In other words, it makes sense to me that a digital channel in Europe carries 6 SD signals, not 6 HD signals.

If there are more than one channel, who choose the channels to be sent on the same frequency ?
Here in the United States, the channel is what is allocated to a broadcaster. Effectively, the broadcaster decides how many signals to carry, and which ones.

Here in Boston, some of our digital channels carry just the "main" signal of the broadcaster (in HD, of course). Other digital channels carry the "main" signal of the broadcaster, plus one additional signal (in SD). That additional signal has, at times, either been a 24-hour automatic weather telecast (two or our channels did this for a while, but neither is still doing so), an SD simulcast of the HD signal (one of our channels is doing this), or an alternative programming channel (SD, of course), typically sub-contracted from another company. Right now, we have "This TV" as a sub-channel on one of channels. It shows (basically) old movies and old television shows. Another has (and may still be -- I don't know) presented a 24-hour music videos channel, called Tube. Another common sub-channel network is ION, which presents syndicated runs of old television progams, and movies.

Are all the DVT frequency in UHF band ?
The vast majority are, now, but some still are on VHF, both VHF High, and VHF Low, though clearly many are avoiding that lower band. It should end up being relatively unused.

What is the spectral bandwith of one frequency , 7 or 8 Mhz ?
As noted above, 6 MHz.

What is the DVB-t modulation choosen , 2K or 8K ?
As noted above, we use 8VSB, not DVB-T. For more details, see 8VSB - Wikipedia, the free encyclopedia

What is the Mpeg standard used for the video channels ? MPEG2 or MPEG4 ?
As noted above, MPEG-2.

perhaps, you will have answer on these questions only the 12th of june ?
Nope...all the information is available now.
 

Piggie

Super Moderator
#6
I'm going to defer to Trip with regard to the relative merits of the two modulation technologies. I really don't know much about DVB-T.
Its some opinion, but most people think the Euro Standard is better over all. If you search on Wikipedia, they keep it pretty simple as to the difference and merits, though many you have to pull yourself by reading, as opposed to a list.
 

divxhacker

DTVUSA Member
#7

Trip

Moderator, , , Webmaster of: Rabbit Ears
Staff member
#8
The way I hear it, the European system is not without its issues. Whereas our system has impulse noise concerns on the low-VHF channels, apparently DVB-T has problems with it all the way up to the lower UHF channels. I've heard that DVB-T might be a decent system in some respects but also has its share of issues.

The people I've spoken to think the Japanese ISDB-T is probably the best system.

- Trip
 
#9
HI

Thank you for all your answers. Now it's more clear for me.

I have to check the technical points on ATSC and 8VSB.

One remaining questions. I understand that actually the HD channels are transmitted in MPEG2. Any studies to move to mpeg4 to decrease bitrate uses ?

In france, 5 HD channels started in Nov 08.
3 HD channels on one frequency . this allows 8Mbit/s average bitrate. As statistic compression is used, a channel can go to 14Mb/s when needed. Transmission is in MPEG4 and with 1440 pixels x 1080 lines.
1 HD channel (mpeg4) is transmitted with other SD channels (mpeg2) one same frequency

I have a technical web site for french DVT , but I have to translate it before putting the url here (if you want to take a look of course).

regards

Philippe
 

Piggie

Super Moderator
#10
HI

One remaining questions. I understand that actually the HD channels are transmitted in MPEG2. Any studies to move to mpeg4 to decrease bitrate uses ?

I have a technical web site for french DVT , but I have to translate it before putting the url here (if you want to take a look of course).

regards

Philippe
I think Trip said MPEG4 is in the standards, but even like me, I have an ATSC TV so old it won't decode MPEG4 nor MPEG2 audio.

So breifly how to change to MPEG4 is on hold except in the back rooms of people thinking of ways the US might be able to change. The dumb part is MPEG4 came out before 95% or more of the US had not converted stations nor TV sets. It could have happened here, even without all the delays we have had.

========

That would be great if you had the time to translate your site and run dual languages. And congratulations to you for being so good in both languages. Even after 4 semesters of German in college I can't speak it. They teach us other languages too late here in the US.
 
#11
The dumb part is MPEG4 came out before 95% or more of the US had not converted stations nor TV sets. It could have happened here, even without all the delays we have had.

========

That would be great if you had the time to translate your site and run dual languages. And congratulations to you for being so good in both languages. Even after 4 semesters of German in college I can't speak it. They teach us other languages too late here in the US.
Thank you Piggie.
As you, I don't speak German. even after 2 years of school training.

I have translated the French DTV part of my website. Some parts are still not translated, but I think everything is there to understand the webpage.
Please note that the multiplex that handle the DTV in france are called R1 to R6 and are the same in all the country. L8 is a local multiplex for Paris.

French Digital channels bitrate.

My dream would be to have the same page for the US , for New york or other big city for example. I had a special tuner for these measurements, but I need to modify it for 8VSB as it was DVB-T. Not sure it will be easy.

If some users of this forum want to work on this type of webpage for the US, I am ready to help !

Regards

Philippe
 
#12
Thank you Piggie.
As you, I don't speak German. even after 2 years of school training.

I have translated the French DTV part of my website. Some parts are still not translated, but I think everything is there to understand the webpage.
Please note that the multiplex that handle the DTV in france are called R1 to R6 and are the same in all the country. L8 is a local multiplex for Paris.

French Digital channels bitrate.

My dream would be to have the same page for the US , for New york or other big city for example. I had a special tuner for these measurements, but I need to modify it for 8VSB as it was DVB-T. Not sure it will be easy.

If some users of this forum want to work on this type of webpage for the US, I am ready to help !

Regards

Philippe
That's an elaborate site. Hopefully your digital transition will go better than ours. Is the French Government offering monetary assistance for upgrading TVs?
 

Piggie

Super Moderator
#13
Thank you Piggie.
As you, I don't speak German. even after 2 years of school training.

I have translated the French DTV part of my website. Some parts are still not translated, but I think everything is there to understand the webpage.
Please note that the multiplex that handle the DTV in france are called R1 to R6 and are the same in all the country. L8 is a local multiplex for Paris.

French Digital channels bitrate.

My dream would be to have the same page for the US , for New york or other big city for example. I had a special tuner for these measurements, but I need to modify it for 8VSB as it was DVB-T. Not sure it will be easy.

If some users of this forum want to work on this type of webpage for the US, I am ready to help !

Regards

Philippe
You need to talk with Trip. He even answered you first post in this thread. His website is RabbitEars.Info. He uses people all around the USA with TSReader program to capture statistics on their local stations.

He would be the one to talk with.

Thanks for the translation. I need to look at you site earlier in the evening, as my eyes are getting blurred here..

Danke Schön !
 

Trip

Moderator, , , Webmaster of: Rabbit Ears
Staff member
#14
Yes, RabbitEars does keep bitrate measurements. I've got almost 850 individual stations now, which brings me close to half-way through the nation's full-powered stations. I know I will have more than that before the summer is out as there are some people who will be sending me data from trips they take.

Take a look around and let me know if you have any questions.

- Trip
 

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