240, 405 & 625

[neon indicator]

What % Geographically had coverage by 1949?

What % of population had TVs by 1949?

It's a plausible argument, but has it a factual basis?

But in a short while UK was worse off than many countries. What actual real benefit was TV from 1946 to 1948, 1949 or even up till 1950?

How many Pre 1951 TVs were able to directly have BandIII or were adapted with Set boxes for ITV in 1954/1955?

Would the 1946 to 1949 TV market not have been tiny compare to Radio and other electrical equipment?

Would Cinema and Radio not been more important moral boosters than TV in 1946 to 1948?

Look http://en.wikipedia.org/wiki/Timelin...n_in_countries

Was 1946 TV in UK not just an ego trip for a rich minority and the BBC*?

The priority in Europe and UK was Food, Heat and Reconstruction.

(*I'm no BBC hater, I have fond memories working there as a Communications Engineer in latter half 1970s).

[neon indicator]

As an aside, for a normal room, 405 lines is fine up to about 21" TV. The reason to switch to 625 was not for screen sizes in 1969, but future Colour services.

Assuming a 20" visible diagonal 405 line, the same DPI is 30" 4:3 on 625 lines, or 56" 4:3 1125 line (1080 visible HD). Approximately same DPI as 65" 1920x1080 16:9 panel.

Very few people have 65". 42" would be the most common HD choice fast replacing 37" and smaller HDTVs for main TV.

The US had large screens up to 56" before HD or Digital on 525 lines.
There was even a UK prewar domestic back projection mechanical 405 Line TV and some post WWII 405 CRT projection TVs. Not common. 17" to 21" common sizes for 405 line era and 21" to 26" common for Colour 625 Era. Larger 28" 4:3 sets only common about the time WS analogue TV launched (32" WS is roughly same height as 26" 4:3 and it's the hieght that counts, not the diagonal when comparing different formats).

[neon indicator]

BTW I probably meant PAL M and N rather than just N earlier.

[tubesrule]

Originally Posted by neon indicator

Assuming a 20" visible diagonal 405 line, the same DPI is 30" 4:3 on 625 lines, or 56" 4:3 1125 line (1080 visible HD). Approximately same DPI as 65" 1920x1080 16:9 panel.

This only takes into consideration the vertical resolution. With a maximum bandwidth of 3MHz, a 20" 405 screen has a horizontal resolution of 30 DPI while the 30" 625 screen with a bandwidth of 5.5MHz would be about 24DPI.

Assuming the viewer is sitting the same distance from each screen, the 405 will actually appear sharper horizontally. If the viewer sits close enough to the 20" 405 set to make it's screen size appear the same as the 30" 625 screen, the horizontal resolution difference is small, less than 20%. Vertically it will appear more course, but the Kell factor needs to be applied to determine the perceived vertical resolution.

Darryl

[neon indicator]

The above was only approximate. Also very very few domestic CRTs or receivers ever did the full horizontal resolution. On horizontal you get also a smooth low pass filter action, a graduation. On vertical it's line structure, which has fixed sharp transitions rather than totally continuous variation on monochrome CRT line scan.

It's true that to get the same relative increase in Horizontal resolution you would need about 6.6MHz rather than 5.5MHz video bandwidth, but no domestic TV would ever have displayed it. Especially Colour tubes.

The point though of HDTV was never for better pictures, but larger screens. Thus for almost everyone there's no point on HDTV on a 32" WS (about similar to 26" 4:3) and 405 TV "window boxed" on a 26" 16:9 screen would look absolutely fine at normal viewing distance. I'm not sure why 625 was chosen rather than 441 or whatever. 819 always seemed somewhat ambitious. Why did France go for 625 SECAM rather than 819 SECAM? Why change to 625 at all from 819? That seems a more interesting question than 405 vs 625.

Interlacing is a neat trick to double the static resolution without doubling the bandwidth or double the refresh rate and reduce flicker dramatically for all image detail more than 1 line high. Easy to do on electronic system and very much harder on mechanical.

I'm re-watching B&W original series "The Saint" on DVD up-scaled by BD player to 1080 lines on a 42" TV. The last time I saw it was probably on a 17" TV on 405 lines! I presume though it's a transfer to 576 line DVD from B&W film as the quality is fabulous. A Colour "Rumpole of the Bailey" series on DVD is much poorer and looks like it has passed through something nasty as there is occasional colour flicker on fine detail, yet also shows film damage on the intro sequence. (Direct Composite to the TV shows no large area flicker/patterns on highly saturated colour, or colour flicker on fine details as the HDTV has superb DSP comb filter).

[peter_scott]

Originally Posted by neon indicator

Would the 1946 to 1949 TV market not have been tiny compare to Radio and other electrical equipment?

No matter what date you chose to re-start British television there would still have been a ramp up largely determined by the expansion of the transmitter network. In 1951 the number of television sets sold was approximately half the number of radios sold and of course televisions commanded a higher price tag.

If we had waited until 1951 to re-start television then perhaps the industry might have had to wait until the mid fifties for the same boost in sales relative to the largely static radio sales.

Peter

[neon indicator]

RTE solved the problem by having 2x TX on 405 line to suit people that already had got 405 for UK reception and the rest of network was 625.

They could have had just one TX in London on 405 in 1946 and added a 625 network nationally in 1949. N.I. Didn't have TV till 1952 I think.

I think 1949 would have been a more sensible date for major TV launch.

[Brigham]

The fact that the French took a backward step casts a different light onto the situation. It removes 'improved definition' from the debate entirely, leaving us with a political, rather than a technical motive.
It remains my firm view that the adoption of 625-lines was a consequence of Quisling-style politicians collaborating with an unseen body of internationalists, to instigate a pan-European television system for the forthcoming new reich.

[murphyv310]

The Demise of 819 was possibly political, but personally I believe that the restricted bandwidth that was used in system F and poor receiver design even with system E was actually the death knell for 819. 819 line pictures looked flat in comparison to 405, it was well documented that tourists from Belgium would comment on our "good" pictures. It was also difficult to align a system E set properly and still achieve good gain with the circuitry of the time.
So 625 was the obvious course and using positive modulation was too, yes I am sticking my neck out here, it was the correct way to go as it gives good quality whites with no crushing and solid black level.

[neon indicator]

Negative modulation can be equally good for Blacks, Whites and can be easier for sampling Sync pulses and thus AGC.

But it's down to receiver design rather than Positive or Negative really.

The main difference is that car ignition interference is white dots & dashes on Positive and black on Negative, which seems to be less noticeable. My memory is that ignition interference was more noticeable on 405 than 625, though the likelihood was higher probably due to VHF. In 1983 we moved from UK to VHF only 625 part of Ireland and suffered interference and Aircraft flutter on our fringe reception. But any ignition interference was less noticeable black dashes.

[murphyv310]

We often criticise receiver design and blame them for poor pictures and during early dual standard days with only BBC2 on 625 there were many complaints about the Grey pictures! The receiver always got the blame, but I do remember the area engineer (Henry Chmiel) in British Relay telling me the whites were crushed for a long time until all of a sudden the problem was rectified. We used receivers that were designed for broadcast standard monitoring made by Murphy R&D, MR754 & 756, the 756 had true synchronous detectors but still the step was crushed on the VIT signal. So without a doubt this was a transmission problem and it did eventually get sorted.
When I started this thread it was not about a debate on positive or negative modulation, both systems have advantages and disadvantages.
Regarding impulse interference UHF has made a big difference to that but also the legislation for the reduction in interference has made the car manufacturers get their act together, also mains borne interference from motors has reduced due to better suppression etc, so I doubt positive mod has that problem nowadays.

[German Dalek]

Hi to everyone,

I come a little late to this discussion, didn`read all posts, only
the latest.
I have to add some information , based on old radiomags from Belgium
and France.

1.) France decided in 1948 to go on 819 lignes in 1950 just to show
movies. They said, that a 441 ligne picture on a 22-31 cm CRT is not
good enough.
Not to use 625 lignes was based on the idea of the old postminister
(I think it was Mitterand,later a big european!) to save France against
the strong radio-industry from Italy, Germany and England (Why England
didn`t could sell their TVs in the late 40s to France?)
Going back to 625 lignes was a result of the high production costs of
studio equipment and the price of TV sets, because the market asked for
low budget TVs.

2.) The belgium 819 ligne television had a smaller bandwidth than the french 819 ligne
system!!!!!!! This picture was minor sharp than the belgium 625 ligne system!!!!!
Both with AM sound and positive picture modulation.
Also this was a result of an agressive political situation between the dutch and french
spoken people, and the politicians , which tried to save there industry against the rest
of europe.

3.) The Belgium Company PRISMA (Antwerp) wrote in their manual for 1958 TV sets, that
positve modulation leads to poor contrast when showing night views on the screen.

4.) Australia (as a partner of the commonwealth/englishspoken) had a good reason to decide
in 1956 for the european TV standard, and against the US and GB 405 ligne standard.
But british and US companies were able to sell them (partly build in AUS) 625 ligne TV sets.

Best regards,

German Dalek

[German Dalek]

Yepp,
I forgot to add this:

France, the main reason to move from 819 to 625 lines was because of
the UHF band could cover more 625 line channels than 819 line channels
according the used bandwidth.
Plans for a second and a third program were in the desk in the early 60s.
This time "lines" in english.

Best regards,

The German Dalek

[Synchrodyne]

Originally Posted by neon indicator

The above was only approximate. Also very very few domestic CRTs or receivers ever did the full horizontal resolution. On horizontal you get also a smooth low pass filter action, a graduation. On vertical it's line structure, which has fixed sharp transitions rather than totally continuous variation on monochrome CRT line scan.

That’s an interesting point. The evidence would suggest too that is more flexibility in determining horizontal resolution (video bandwidth) than vertical resolution (line number), but even so, that there is some trade off available between the two.

The NTSC (1941) system is a good example. The video bandwidth, 4 MHz, the aspect ratio, 4:3, and the field frequency, 60 Hz were fixed before the line number was determined. I think it was recognized that there was a range of line numbers that would work with this video bandwidth. 525 lines was evidently chosen as a compromise between the quasi-established 441 lines and the higher numbers advocated by some participants in the debate. Roughly calculating on the basis of gross lines (and recognizing that net or active lines is more accurate), 4 MHz video bandwidth for 525/60 corresponds to 2.6 MHz for 405/50. So in 1941 the NTSC was happy with a system that had a lesser horizontal resolution than the British 405-line system. Or one might say that it traded horizontal resolution for vertical resolution. Again using rough gross line calculations 441/60 at 4 MHz would have given horizontal resolution a tad better than the 405-line system. The inference is that first and foremost there had to be enough lines, the choice of horizontal resolution thereafter being a bandwidth tradeoff. Any choice such as that made by the NTSC is to some extent arbitrary, but it did stand the test of time, 525/60 being one of the two “Goldilocks” standards of the analogue TV era that is being replaced by digital systems, and not another analogue system. Incidentally, applying the NTSC’s choice of vertical/horizontal definition tradeoff to the British 3 MHz video bandwidth would have pointed to something around 473/50. (I haven’t checked to see if there are any nearby numbers that factor into 3s, 5s and 7s.)

Looking at 625/50, matching 405/50 in horizontal resolution would require 4.6 MHz bandwidth. The CCIR chose 5 MHz, whereas the Russians chose 6 MHz for the OIRT system. Argentina used an NTSC 6 MHz channel, so video bandwidth was only 4.2 MHz. This equated to 2.7 MHz in the 405-line system, but gave about the same horizontal resolution as the American 525/60 system.

The UK later chose 5.5. MHz for what became System I. Around the same time the French chose 6.5 MHz for System L, but later reduced this to 5.5 MHz to accommodate a 5.85 MHz NICAM carrier.

Relative to the 405-line system, to obtain increases in horizontal resolution to match those in vertical resolution would have required video bandwidths of 6 MHz for 525/60 and 7.1 MHz for 625/50. Quite clearly such improvements and the increased bandwidths they demanded were viewed as either unnecessary or not readily achievable/justifiable in terms of the cost and complexity involved. Arguments supporting the actual bandwidths chosen for 525/60 and 625/50 invoke the Kell factor, and suggest that either it wasn’t used or assumed to be unity when the 405-line parameters were determined. But that is not really relevant on a comparative basis where the 405-line system is the baseline. Whatever the arguments for or against 405 lines per se, the UK system was no doubt adequate in horizontal definition terms.

The French 819-line system had a video bandwidth of 10.4 MHz, equivalent to 5.1 MHz for 405-lines. So as might have been expected in what was intended to ne a “stepout” system, there was quite an increase in horizontal definition, although measured against the 405-line system, it didn’t match the increase in vertical resolution, which would have required 12.3 MHz. Using NTSC 525/60 and CCIR 625/50 as the starting points, video bandwidths of 8.1 and 8.9 MHz respectively would have been required for proportionate increases in horizontal definition, so by these standards the French parameters look good. The Belgian decision to squeeze an 819-line signal into the CCIR 7 MHz channel with 5 MHz video bandwidth meant that in horizontal definition, System F was equivalent to 405-lines with 2.5 MHz bandwidth, 625/50 with 3.8 MHz, and 525/60 with 3.1 MHz. It was probably at the edge of the acceptability band in terms of the ratio of horizontal to vertical resolution, maybe beyond it.

But as has already been outpointed most domestic receivers had video bandwidths that were below the applicable transmission standard. I suspect that proportionately, typical 405-line receivers got closer to transmitted bandwidth than did typical 525- and 625-line receivers. Somewhere I have seen the video bandwidth number 4.25 MHz for 625 lines in respect of early UK dual-standard receivers. And for French dual-standard receivers, I have seen quoted 9 MHz bandwidth on 819 as typical for better quality models, and the same bandwidth as used on 625 line for lower quality models. Belgian practice I know nothing about, but one hopes that some effort was made to get the video bandwidth very close to 5 MHz for System F 819-line reception.

Just how important was horizontal resolution from the viewer perspective is hard to determine. The very good (in absolute as well as relative terms) horizontal resolution of the 405-line system, and reasonable realization in practice of its potential might have been a saving grace judging by earlier comments in this thread. On the other hand, when home video recorders arrived, their relatively low video bandwidths and consequent loss of horizontal definition were hardly inimical to their widespread uptake, which suggests that it didn’t rank all that highly overall. And perhaps many users were quickly conditioned to the resultant picture quality as being reasonable and normal. Maybe there is an analogy with AM broadcasting, wherein the receiver makers started reducing audio bandwidths (for their own convenience) decades before the broadcasters did, to the extent that even 1950s and 1960s texts included erroneous statements to the effect that restricted bandwidth was an inherent property. Another way of looking at, and I think really just another way of saying what neon indicator has already said, it is to see horizontal resolution as more like an analogue parameter that decays gracefully, so as to speak, whereas vertical resolution, dependent upon line count, is more digital in nature, and so will go from good to not-so-good very quickly.

Turning back to the main theme, the debate as to whether the UK should have stayed with 405 lines or moved to 625 lines will no doubt go on. But change it did, and taking the eventual change as a given, the question then is should it have waited as long as it did or should it have “bitten the bullet” earlier. In the latter case there were two fairly obvious nodal points at which the change could have been started, one being the extension of the TV service to the provinces in 1949, and the other being the advent of ITV in 1955. Whatever reasons may be advanced in support of the status quo decisions made at those times, there do not appear to have been serious technical impediments to change.

Originally Posted by German Dalek

Hi to everyone,

4.) Australia (as a partner of the commonwealth/englishspoken) had a good reason to decide
in 1956 for the european TV standard, and against the US and GB 405 ligne standard.
But british and US companies were able to sell them (partly build in AUS) 625 ligne TV sets.

I don’t at all disagree with what you say – Australia and New Zealand surely made the right decision in choosing 625 lines. But I am curious as to the German perspective on what the “good reasons” were.

Cheers,

[ppppenguin]

Originally Posted by neon indicator

.... On vertical it's line structure, which has fixed sharp transitions rather than totally continuous variation on monochrome CRT line scan.

The vertical structure may have fixed sharp transitions on an LCD or plasma display but the spot is fuzzy (approx gaussian) on a CRT so the vertical spatial frequency response isn't as good as the number of lines might indicate. This may account, at least in part, for the notorious Kell factor.

Originally Posted by Synchrodyne

Just how important was horizontal resolution from the viewer perspective is hard to determine. The very good (in absolute as well as relative terms) horizontal resolution of the 405-line system, and reasonable realization in practice of its potential might have been a saving grace judging by earlier comments in this thread. On the other hand, when home video recorders arrived, their relatively low video bandwidths and consequent loss of horizontal definition were hardly inimical to their widespread uptake,

When colour was introduced the CRTs had limited resolution due to the dot structure. Also the Y bandwidth was often heavily limited by the chroma notch. A typical UK colour TV in the 1960s/70s had little useful luminance above 3.5MHz. That may well have been true into the 1990s when comb filter decoders started to become feasible in domestic kit.

[murphyv310]

Originally Posted by ppppenguin

When colour was introduced the CRTs had limited resolution due to the dot structure. Also the Y bandwidth was often heavily limited by the chroma notch. A typical UK colour TV in the 1960s/70s had little useful luminance above 3.5MHz. That may well have been true into the 1990s when comb filter decoders started to become feasible in domestic kit.

Hi.
3.5MHZ on 625 is very poor, far worse than 3.0MHZ on 405. PIL tubes were better but still not in the same league for resolution as a good mono tube.
I have stated before that my experimental 405 line NTSC set was as good as a 625 line colour set, and from Jeffrey's statement it seems to sum it all up!

[ppppenguin]

I ought to make it clear that the 2 losses in H resolution are very different.

The dot pitch is nothing to do with bandwidth, it will limit the cycles per picture width regardless of standard. Y bandwidth may or may not be a limiting factor compared to the CRT limitations.

[murphyv310]

Yes I am aware of that, but if you have a 5.5 meg bandwidth that is available at the CRT cathodes and it is limited to a perception equivalent of 3.5 megs then on both standards the overall resolution will "look" approximately the same.
Even on 405 on a delta gun CRT it was hard to see the line structure, and one forum member and engineer thought I was having a laugh and thought the set was running 625!

My next 405 line NTSC set will utilise a more up to date CRT with inline gun, as yet though its still on the drawing board!

[ppppenguin]

The whole business of vertical vs horizontal spatial resolution is a bit fraught. For the real world and old fashioned film, resolution is the same in both directions. AFAIK likewise for the human eye. So the aim for a TV system is to give equal subjective H and V resolution. I stress subjective because there's a fair bit of fudging that goes on. Ranging from CRT spot profiles to the Kell factor. Actually the Kell factor is simply an empirical fix to allow for the fact that the perceived vertical resolution differs from what you might predict. It's lower for interlace systems than progressive. I suspect it's near enough unity for a CCD camera and LCD monitor.

Some systems, such as 405, have excess H resolution. Others such as Belgian 819 are clearly deficient. It's pretty obvious that viewers hardly notice, within pretty wide margins.

[Electrical]

I have just taken two pictures of a 625 and 405 line test pattern from a Philips pattern generator displaying a grey scale and frequency multiburst on a Ferguson 1400 chassis dual standard set. The 625 line signal from the pattern generator via its UHF RF modulator to the UHF aerial input and the 405 line signal from the pattern generator video output to the input of an Aurora and from the Aurora the VHF aerial input on the set.
The Multiburst contains eight frequency ranges and from left to right is, as follows: -
0.8, 1.8, 2.8, 3.0, 3.2, 3.4, 3.8 and 4.8Mhz.
The 625, line picture clearly resolves all frequencies to 3.8Mhz which, is the seventh bar from the left. The 405, line picture clearly resolves all seven bars, but am I correct in thinking that the 3.8Mhz bar on the 405 line picture is only around 2,5Mhz and the 4.8Mhz bar, number eight would be 3.1Mhz, which is beyond the bandwidth of the 405 line system?
From the pictures on the set, it is hard to tell the difference between the two systems, as the photographs do not do justice to the screen images.
P.S. The 405 line photo has the slightly elongated circle.
Regards Stan.