8VSB vs. OFDM - Page 1
Forum section: electronics / general

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 06, 2012, 03:46:09 am
content: Why is it that the US uses 8VSB for digital TV whereas just about every other country uses OFDM? Those who live in the US probably know just how digital TV is sensitive to signal levels, while WiFi (which uses OFDM) continues to work even with a weak signal. (Yes, I did ask Tiffany Yep, a long time ago at that. She summarized that OFDM cuts up the channel into many subchannels, so that narrowband noise would only affect some of the subchannels and result in more graceful degradation. She agrees that OFDM is superior to 8VSB but couldn't answer why the US is not using it for TV!)Interestingly, OFDM hardware is actually cheaper than 8VSB hardware since it is more common. WiFi adapters commonly go for under $10, sometimes as little as $5. Digital TV receivers (the USB stick type), however, rarely go for under $20.

author: slateraptor
author_rank: Frequent Contributor
timestamp: May 06, 2012, 06:46:20 am
content: Pure speculation, but likely the same reason why the US has an interstate system as opposed to the rest of the world who depends on public transportation: before anyone gave a shit, we could and we did...and now it's much too cost prohibitive to make a transition.

author: BravoV
author_rank: Super Contributor
timestamp: May 06, 2012, 07:21:35 am
content: Its all about money, never about technical superiority nor optimal/cost efficiency.Its no secret that most US regulatory boards are run by themobbig enterprise 's puppets that any established standards must be unique and secured such way to ensure they will generate big money as long as posibble.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 06, 2012, 11:19:06 am
content: Quote from: slateraptor on May 06, 2012, 06:46:20 amBoth of these systems are contemporaries,so there was "no before anyone gave a shit!"Of course,you had a different analog TV system as well,but the differences between NTSC & PAL are fairly minor when you really look at them.Whats this about the rest of the world depending on public transport?Most interstate transport & a lot of passenger miles in Australia depend on the road system.A lot of people fly,of course,& some few travel by train,but for the rest,it's roads---not as fancy as yours,but they do the job!And our States are bigger,so a lot of Intrastate trips are as long as those through several of your States.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 06, 2012, 11:44:26 am
content: Quote from: BravoV on May 06, 2012, 07:21:35 amHardly fair!The original NTSC system was definitely technically superior to the old British 405 line system & other similarsystems of the time.The system was a remarkable achievement,considering it was a product of the 1940s when there were a few other things for Engineering people to be involved in.PAL,which was a 1950s design, is basically a modified NTSC,however,the concept of Phase Alternation of the lines(Dr Bruch et al )makes it a superior system.France,just to be different, introduced SECAM,& convinced the old Warsaw Pact countries to adopt it too.When the time came to introduce Stereo sound to TV,many countries introduced different systems,so it is not just the USA which has to be different!FM Stereo,which was introduced first in the USA,is used throughout the world,using the original American system.Unique systems are no barrier to competing manufacturers in other countries,as the standards are published freely,so what advantagewould that give to "big enterprise" in your country?

author: BravoV
author_rank: Super Contributor
timestamp: May 06, 2012, 02:54:25 pm
content: Quote from: vk6zgo on May 06, 2012, 11:44:26 amAh.. you're right, but only at those good old days.But these days ? I think I don't need to remind you of what was happened in 2007-2008 era when they're hit by the financial crisis there, thesemob..errr... I mean huge corporations even made the government/regulatory body to alter the financial "law" that made many Americans wholeheartedly understand the deep meaning of the word "foreclosure".Since even the law can be altered so easily, this so called pesky electrical "standard" is simply nothing, this kind of thingy is just way too easy.

author: slateraptor
author_rank: Frequent Contributor
timestamp: May 07, 2012, 07:25:11 am
content: Quote from: vk6zgo on May 06, 2012, 11:19:06 amFrom a technical perspective, there are indeed minor differences between NTSC and PAL...but what the technologically literate consider "minor" translates to a show stopper for the average consumer.You'll have to excuse me for forgetting about Oz and NZ when I refer to "the rest of the world"...must like how the rest of the world forgets too. If you've ever seen public transportation systems in Mexico City, China, Japan, or Europe, you'll know what I'm talking about. As another example, imagine how much it would cost if the US were to change every speed limit sign and speedometer across the nation for the sake of complying with the SI standard.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 07, 2012, 09:10:04 am
content: Quote from: slateraptor on May 07, 2012, 07:25:11 amRe the difference between NTSC & PAL,consumers don't normally build TVs,so all they need to know is which one works in their country.The last few generations of analog TVs have mostly been multi-system,in any case.Disregarding your sneer:-Mexico City is acity---how does that have any bearing on your "Interstates"?I haven't heard of any great public transport systems in Mexico,outside the cities!China--A very large country,& outside the cities,quite a lot of it's day to day transportation relies on roads.OK,they have good Railways,but my point still holds.India has enormous traffic problems,due to road vehicles occupying every inch of inadequate roads.They have a large railway system,too,but the emphasis is largely on road transport!In the UK,the use of public transport has decreased in recent years,due to the closing of rail lines,& reduction in the number of services.The UK also has an extensive system of Motorways which are heavily used .Europeans? Well,the Germans built Autobahns before your Interstates,Italy has Autostradas.Again their public transport system is good,but there is still a lot of road transport!South Africa has a fairly good rail system,but again,much transportation is by road.Why would you have to change the speedometers,except on those vehicles manufactured after the changeover?Americans aren't stupid,they would soon get a handle on what the equivalent readings are,just like all the people in the US services did when they were posted to Europe,& had to drive US military vehicles over there!Brits went for long road trips in Europe,drivingRH driveMPH speedometer cars,& very seldom got into trouble.According to other Americans I have talked to,some cars have dual calibrations already,which is what happened in Australia.OK,the Odometer would have to be changed in the new cars,but it wouldn't be that difficult to work with a mixed system for a while!Roadsigns also could be progressively changed,as they needed replacement.

author: Kremmen
author_rank: Super Contributor
timestamp: May 07, 2012, 10:36:26 am
content: Quote from: slateraptor on May 07, 2012, 07:25:11 amSince i am one of those Europeans, allow me to comment.Firstly, i don't know that we "depend" on public transportation. One gets the impression that this would be somehow inferior to private transportation or dictated by some authority. Not so. It is available for whoever wants to use it, but there is no reason why you can't use your car / other private vehicle if you feel like it.The Nordic countries where i come from are considered welfare states where taxation is relatively heavy but the society then largely sees that no one is left behind. General availability of public transport is one aspect of this thinking. There are other, in my opinion far more important consequences like social equality (think free University education for starters; the fact that you can walk through any part of any city at any time of the day and not be especially worried about getting mugged second). But back to traffic - changing the speed limit signs should be a piece of cake. At least here in Finland we do it 2 times a year. You see, we generally have separate winter and summer speed limits for main roads and only major highways have electronic speed limit displays. The rest need to be changed physically, but i haven't heard anyone complaining about the cost or effort.

author: SeanB
author_rank: Super Contributor
timestamp: May 07, 2012, 05:57:46 pm
content: SA has public transport? That is news to me, and I live here. If you mean overloaded, unsafe, poorly maintained deathtraps driven by unskilled, illiterate, arrogant and obnoxious asshats then yes, there is public transport.Every accident has one minibus taxi involved, last week there was a collision where 65 were killed or injured, only vehicles involved were 4 minibus taxis ( with a certified load capacity of 16 including the driver and conductor) and a truck. One was stopped with 80 schoolkids inside.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 08, 2012, 01:52:52 am
content: Quote from: SeanB on May 07, 2012, 05:57:46 pmPerhapsslateraptorhas a very limited definition of what constitutes "the rest of the world"!Oz,SA,& NZ "need not apply"

author: slateraptor
author_rank: Frequent Contributor
timestamp: May 08, 2012, 11:30:45 pm
content: This discussion has completely digressed into a retarded tangent.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 09, 2012, 12:44:29 am
content: OK,without going into who sent us down this "retarded" path,commenting on the first posting:The advantage of CODFM in Digital TV service is more "apparent" than practical.In practice,CODFM goes from,solid,to zilch quite quickly with reduction in signal,with the intermediate condition giving fairly unusable pix,& especially,sound.It certainly does not offer the kind of "graceful degradation" which is commonly seen with analog TV,where you can have a very noisy picture,perfectly locked,& with good sound.Where it does shine,is in that it is pretty much unaffected by RF reflections,which would cause severe "ghosting" in analog.It is not completely immune,as reflections may cancel the wanted signal,reducing it below useable level.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 09, 2012, 01:59:35 am
content: OFDM won't help much if the entire signal is starting to fall into the noise floor, but it works well if only some subcarriers are lost to non uniform noise. They probably could skew the power distribution so that some subcarriers disappear into the noise before others, adding some graceful degradation to the signal falling into a uniform noise floor.

author: saturation
author_rank: Super Contributor
timestamp: May 09, 2012, 12:59:54 pm
content: http://en.wikipedia.org/wiki/8VSB#8VSB_vs_COFDM