I've seen pixelation occurs with satellite transmissions all the time during bad weather. I attribute it to noise in the transmission path, from a lightning storm.

It was worse in areas with high isokeranic levels.

DTV wasn't immune and neither were the cable system's dishes.

 

I've seen pixelation occur regularly in perfect weather. We live in a noisy universe.

 

Nevertheless a system that produces output through a switch that addresses each individual dot separately is purely digital. This is the basis of the Texas Instruments DLP system. (Digital light processor).

I find it amusing that DLP uses a motor for the color wheel. Sometimes technology steps backwards to older solutions. I wonder how many people realize in the beginning of TV, before CRTs became popular, prototype TVs were almost all mechanical.

For what it's worth (which ain't much) I think the transition was motivated by greed, and wasn't in the best interest of the public. They could have easily allowed the systems to be used with satellite and let the market take over, but all that bandwidth was valuable real estate, and people who can't afford new electronics are going to be left out in the cold. They talk about coupons for converters, but that doesn't really help all the recording devices such as older VCRs, now does it? Somehow I suspect the coupons are not going to be as prevalent as promised either.

 

I wasn't decrying either system, just adding some information.

 

Sorry, my version of a rant. Is Britain and/or the EU going though something similar?

 

Sorry, my version of a rant. Is Britain and/or the EU going though something similar?

Yes, Digital Switchover is supposed to happen by 2012 (likely chance! They may have push this back now). And IIRC there is a town (I'm thinking Workington?) has gone totally Digital. The problem with DTT in the UK is that the coverage is pretty poor, although when you take into account that Digital can include Sky Digital and the new Freesat satellite service, then coverage is considerably better. Digital has been generally accepted here - more channels, which is particularly good because you can get all the BBC channels which everyone pays a license fee for (there is certainly a perception of value for money).

Dave

 

I've seen pixelation occur regularly in perfect weather. We live in a noisy universe.

It is worst when it is very hot - in my experience more so than when it rains (heavily). But that's ok for us Brits because it rains considerably more than it is sunny!

Dave

 

Digital Television has been a big success in the UK. the latest figures I've seen have been over 60% penetration and rising.
Coverage is pretty good with only outlying and 'problem' areas unable to receive nowadays.
Picture quality is generally more reliable than with the older systems, although problems do occur and some useres find the problems with the sound /picture synchronisation. Most users had some good and some poorer channels with analogue, most find they are all pretty much the same (picture quality not content) so have gained that way.

Digital Radio has been rather less successful.
Firstly the sound quality transmitted is slightly less than good quality FM.
Secondly coverage is very patchy, even in larger towns and cities.
Thirdly it is competing with internet radio, which offers time shifting from stroed broadcasts.
Fourthly the associated gadgetry is poorly designed and a pain to use so many users have trouble selecting a station, even if they can tune in to them.

 

Any idea how compatible the systems are between the USA and UK? NTSC and PAL has been a PITA historically speaking, so if they are the same system at least something is working right. I'd bet they aren't though, given other differences between our standards.

 

'Digital' refers to the transmission system, not the works at the other end. The first introduction were 'digiboxes' - add on external tuner/decoders for existing televisions. More recently these have been incorporated into TV and video equipment.

But the decoder still outputs the good old PAL signal.

HDTV has achieved little penetration and they are still arguing over standards.

In any case NTSC or its successor needs to be synchronised to your 60HZ mains, justs as our PAL needs to be synchronised to our 50HZ.

 

In any case NTSC or its successor needs to be synchronised to your 60HZ mains, justs as our PAL needs to be synchronised to our 50HZ.

Not as I understand it, although I'll be the first to admit my understanding is weak. We already have a form of digital sitting right in front of you, in the form of the monitor. 50Hz and 60Hz systems are basically old standards, and don't apply to high res systems. The only reason they were used is back in the beginning stable clocks were hard and expensive, which is not the case today.

The converters will output PAL and NTSC, but that is for older TV sets. Somehow I doubt the new TVs and standards will incorporate them, except as a back standard to be supported for a little while. A lot like computer monitors. XP doesn't support 600 X 480 anymore either.

As I understand it the old 640 X 480 is the NTSC equivalent, and the 800 X 600 is the PAL equivalent on the monitors for PCs.

 

I did say 'or its successor' and I did say that HDTV takeup is low over here.

However the point of the 50/60 Hz is not one of a stable oscillator. The mains frequency is nowhere near stable enough. The PAL, SECAM or NTSC signal contains sync pulses, broadcast as part of the signal to indicate to the local oscillator in the TV when the scan line should start and finish.

The point of the close relationship between frame rate and mains frequency is to avoid interfence patterns on the picture.

 

Screen refresh rates are rarely 50 or 60 hertz nowdays, I doubt if digital TVs will be either. Just did a check of my monitor, it is 75 hertz.

 

Black and white transmissions (remember them?) using NTSC had the vertical sync at the same frequency as the 60Hz mains.
NTSC colour TV uses a 3.58MHz colour sidebands frequency so the vertical sync is at a multiple of 3.58MHz which is a little different from the mains frequency.

 

Actually the only difference between B&W and Color is the color sideband signal (which is analog of course), which is why old TVs don't have any heartburn with modern signals.

I don't think any modern electonics cares about line frequencies anymore, regulators and power supplies being what they are. Anytime you see something like that you can bet it has it's roots in really old tech.

 

There is a big difference between a TV signal and an PC monitor signal. Interlacing is one obvious difference.

There is also a difference between a monochrome CRT and a colour one. On a monochrome CRT the phosphor is one continuous film, similar to that on a CRT for a scope.

Thus it is possible to actually write a continuous trace on one with an analogue signal. The picture is not made up of dots it is made up of lines of continuously varying intensity.

With a colour CRT there are three phosphors, one for each colour, as close to being 'at a point' as practicable, without overlapping. Thus , of necessity, the phosphor films are discontinuous - they really are made up of dots. Illumininating the space between the dots with the scanning beam produces no light.

this is also why may viewers see monochrome as actually 'sharper' than colour.

 

This I know, we're talking basic signals. There is no difference between a B&W and color luminosity signal. Come to think of it, not much difference in later generation color guns either, don't they use a shadow mask in front of the phosphor to block a color gun from a mismatched color phosphor dot?

 

Yes the colour information (chrominance) is added in a frequency shifted carrier to the basic monochrome brightness (luminance) signal. This preserves compatibility with monochrome, whose circuits reject the chrominance portion of the signal. The luminance signal carries much more information than the chrominance. The chrominance has been squeezed into the bandwidth originally available, at the expense of resolution. This is OK because the eye is less sensitive to colour error than brightness error.

 

This has actually turned into a useful thread inspite of the OPs original question. Way to go guys.

 

Problem is, we're all talking tech that will obsolete in less than a year, although it will still be out there. I'd like to learn more about the digital signals myself, frequencies and modulation schemes among other things. This is going to affect antennas, bandwidths, and things I can't even think of yet.