Wait until you look up QPSK modulation. Plus the bandwidth requirements are pretty intense. You just thought 6 megs was a lot. Every pixel has to have its value sent in real time.

I'm lazy - does HDTV use 5, 6, or 8 bit bits/color?

For a bit of perspective, those 525 scan lines looked really great on a 5" CRT back in 1927. I am pretty sure that was when the U.S. standards got set. The vestigal sideband for the audio was pretty cute, as was the color oscillator synch getting put in during vertical retrace blanking. NTSC does stand for "never the same color", though.

 

QPSK is actually pretty simple compared to QAM.

http://en.wikipedia.org/wiki/QPSK

Is that what you meant? Quadrature Amplitude Modulation?

http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation

 

I think it is the multiple carriers with QPSK for digital broadcast tv that got me going.

 

Isn't that OFDM. Orthogonal Frequency Division Multiplexing? Or is it just a coincidence that it also uses multiple carriers?

 

NTSC does stand for "never the same color",

For the benefit of newer viewers I thought it ran "never twice the same color"

 

Isn't that OFDM. Orthogonal Frequency Division Multiplexing? Or is it just a coincidence that it also uses multiple carriers?

OFDM or COFDM is Multiplexing. It uses a modulation like QAM. In the UK they use a version of COFDM that has 2000 carriers or 2K. They will switch to 8K AFAIK and then will be the same as most of Europe. This will allow for mobile better mobile reception.

In the UK the digital broadcast channels have an average of 3 kWs of power with maybe 20 channels as high as 2 kWs. They only have 80 transmitter sites I believe and still they have maybe 70% penetration of homes with OTA receivers and receivers are selling like mad. A high percentage of homes that have a receiver have more than one.

If the US had picked an 8K COFDM based modulation like the French have recently back in 2000 when the question came up we would now have over 150 million receivers sold, none of which would have been subsidized, IMO. And that is just super-imposing the growth rate that the UK has experienced so far.

If we had chosen DVB-T and allowed for an upgrade path to MPEG4 or similar codec the US transition would be virtually over since very few people would be using analog today.

As it is the US has the worst modulation in the world by far. And the way they plan on using it makes the worst worser. Since the US modulation will not work mobile and has major problems working with a fixed receiver, broadcasters are now talking about massively introducing a kludge fix called A-VSB or MPH that will work mobile and use MPEG4. The problem is that all current receivers will be able to receive the signal, though not while mobile, but will NOT be able to decode the MPEG4 codec.

The US DTV transition is a disaster and will only get much worse. No one has been on board with it since it started in 1998. Broadcasters, retailers and manufacturers have ignored it until the last minute. In the UK everyone was on board because they had a decent modulation and will upgrade it soon to a better one.

No one is talking about doing that in the US.

robmx

 

I should have said that you should compare the power levels in the UK, 3 kW on average and a maximum of 20 kW to US power levels that are as high as ONE MEGAWATT (One Million Watts).

The UK will see increases in power once their analog stations are off the air but not to anything like a MILLION Watts. More like a max of 100,000 Watts.

Anyone know better?

 

I can only say why digital technology is worse than analog. But since you are asking, I guess that is because of the marketing involved in promoting digital products. I wouldn't buy a class D amp, even if it costs 50 cents. Digital is only good for lawyers and attourneys.

Digital takes life from music, photographs and video. Analog preserves it.

For example, have you ever heard about analog computers? They sure are fast and almost precise. The problem with analog is because it doesn't deal well with errors, that is, it doesn't distinguish information from noise.

 

That is a megawatt ERP. Effective radiated power. The placement of radiator elements suppresses signal radiation upward and downward, so the actual power out resembles a dipole putting out 1,000,000 watts. Actual power is more like 200,000 watts.

 

you guys are awesome. thanks very much. i've learnt alot ...