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Old 6th Jan 2009, 2:30 am   #1
Synchrodyne
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Default 625-Line Television Broadcast Standards

Has anyone here ever come across a book or magazine article that provides a comprehensive account of the multiplicity of 625-line television broadcast standards that were developed, and the reasons, technical and otherwise, for such diversity?

Whilst one can piece together parts of the story from various sources, there are still some apparent gaps.

What might be called the “parent” 625-line broadcast standard, namely the Gerber standard, later CCIR System B, was promulgated by the CCIR in July, 1950. It was evidently derived largely from the US NTCS 525-line standard. However, I suspect that the Gerber standard had a long gestation period, and that its likely key parameters were known well in advance of 1950.

But contraindicating this “parent system” position is the fact that as far as I know, the Russian 625-line service was started before the Gerber standard was released, perhaps circa 1948. Assuming that the OIRT standard (later CCIR System D) was used from the start, one can wonder why the Russians chose 6 MHz video bandwidth and +6.5 MHz sound carrier spacing in an 8 MHz channel. Was it a case of “oneupmanship” over the anticipated Western European standard, or at the time, was the CCIR still deliberating over video bandwidth, etc., only later on opting for the 7 MHz channel parameters? Still, given the later choice of 8 MHz channeling for Western European UHF services, one might say that the Russians were a little prescient.

Then why did Belgium choose to do differently in 1953, with its own variants of the 625 and 819 line systems, particularly as it was one of the six countries (the others being Denmark, Italy, Netherlands, Sweden and Switzerland) that were heavily involved in the development of the Gerber system. That Belgium needed both 625 and 819 line systems was surely a political rather than a technical requirement, and given that, then “squeezing” the 819 line system into a standard 7 MHz channel was an understandable decision, even if technically questionable. Similarly understandable was the desire, to the extent possible, to have common parameters for both systems. This could have been done by using the Gerber system for 625 lines and developing a companion 819 line variant with negative vision modulation and FM sound. But instead, it was elected to use positive vision modulation and AM sound, which required a new 625-line variant as well as a new one for 819 lines. In the thread “Experimental 1029 line TV c.1949”, at http://www.vintage-radio.net/forum/s...ad.php?t=14741, ORTF & Co. suggests that there may have been US (RCA?) patent and royalty issues with the use of negative vision modulation and FM sound, which is why in 1948 France chose its own 819-line system with positive vision modulation and AM sound (System E). Perhaps the Belgian choice, like that in France, was made in order to avoid royalty payments? But then I understand that most early Belgian receivers were designed for four systems, namely B (Gerber), C (Belgian 625), E (French 819) and F (Belgian 819). So from the receiver design viewpoint, the benefits of the similarities of Systems C and F were not fully realized. As a digression, was it perhaps this early need for multistandard receivers that launched Belgian company Barco along the pathway to particular expertise in this field?

An interesting facet of the Belgian 625- and 819-line systems was that the AM sound channel had 50 microsecond pre-emphasis, something not used with the UK 405-line and French 819-line systems. Insofar as, unlike FM, AM does not have a triangular noise spectrum, there is no pressing need for pre-emphasis. Perhaps, though, it was thought that the required de-emphasis roll-off in receivers would mitigate the effects of any line frequency components that found their way into the sound channel, particularly in the 625-line case. More recently, though, 75 microsecond pre-emphasis has found its way into MF radio broadcasting, as part of the NRSC standard developed in the USA, and also used elsewhere, such as by the ABC in Australia.

When was it decided that the European UHF channels would uniformly be 8 MHz wide, regardless of system? I suspect that this would have happened somewhere in the 2nd half of the 1950s, which was why both BBC and RTF were both working within that channel width for their “new” 625-line UHF systems.

I recall reading somewhere many years ago that when the BBC was working on the development of what became System I – in the late 1950s I think – it determined that optimum use of the 8 MHz channel was obtained with 5.5 MHz video bandwidth, not 6.0 MHz as with the OIRT System D, but with the vestigial sideband extended from 0.75 to 1.25 MHz, and with +5.5 MHz sound carrier spacing. My memory is hazy here, but as I recall the rationale was that extended vestigial sideband made it easier to design IF filters (back in the days of distributed selectivity with LC filters) without too much phase distortion of the lower video frequencies, the benefits of which were greater than going from 5.5 to 6.0 MHz video bandwidth . On the other hand, in approximately the same time period, RTF, in the case of System L, felt that both 6.0 MHz video bandwidth and a 1.25 MHz vestigial sideband could be accommodated within an 8 MHz channel. Which came first, System I or System L? And was System H ahead of both?

Also in the above-mentioned thread, ORTF & Co. states that RTF chose positive vision modulation and AM sound for System L in order to maintain commonality with System E, and so ease receiver design. This seems to be reinforced by the fact that for its overseas territories, where System E had not been used, France chose System K1 essentially the “inverse” of System L, with negative vision modulation and FM sound.

Finally - for now, anyway - when was 625-line System N introduced? I would guess that Argentina was the first country to use this system, which “squeezed” a 625 line signal into a 6 MHz NTSC channel, I would imagine to ensure that the whole of South America (or nearly so, anyway) adhered to a standard channeling system. But the 6 MHz channel was perhaps a little ironic considering that in 1950, Channel E1, 41 to 47 MHz, was deemed unsuitable for 625-line television.

Cheers,
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Old 6th Jan 2009, 12:25 pm   #2
Mr Hoover
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Default Re: 625-Line Television Broadcast Standards

Hi

The Uhf channel numbers I believe were assigned by the European Broadcasting Conference at Stockholm in 1961.
W.Germany commenced some Uhf transmissions possibly earlier than this,
around 1960 according to old "Practical Television" magazines.Some early
Uhf tuners there didn't have channel numbers,just a scale.

Read somewhere the 625 line system was initiated in 1946 & some
experimental transmissions from Holland started around 1948/49.

Belgium ditched the narrow bandwidth 819 line variation around 1963
& dropped system C in the late '70's.

Luxembourg also used the narrower bandwidth 819 line system on band 3
till possibly the early 1970's when it changed to system C and then
system B in the late '70's(Band 3 Channel E7 which now puts put DTT
transmissions).

France had some 819 line relays of their first network on Uhf to
otherwise system L standard (positive modulation + 6.5 MHz audio)
& not the Vhf system E standard.

The BBC were experimenting with 625 line vision with + 6.5MHz audio
in the late '50's from Crystal Palace on Uhf around what would become ch 43/44.

No doubt system N was introduced sometime in the 1950's.Brazil had TV
from 1950 so sometime after that probably.

I heard a story that Cuba which uses system M experimented with Secam
colour as they weren't keen to use the American NTSC system but the
two FM colour subcarriers used with Secam wouldn't fit happily into the
fairly limited space & no doubt caused problems with the 4.5MHz intercarrier
sound.They ended up using NTSC in the end!

Interesting article in an old Practical TV magazine of someone living in
Belgium in 1963 & the channels/systems he could receive,using a UK Ekco
export TV set & various aerials.

Hugh

Last edited by Mr Hoover; 6th Jan 2009 at 12:33 pm.
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Old 7th Jan 2009, 12:08 pm   #3
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Default Re: 625-Line Television Broadcast Standards

Quote:
Originally Posted by Synchrodyne View Post

Belgium choose to do differently in 1953, with its own variants of the 625 and 819 line systems,
That's probably why Philips developed the KM2 multistandard colour chassis in the early 70s,

This set is able to display every possible version of of PAL and SECAM in both 625 and 819 lines, they were quite popular here in Italy in the mid 70s when politicians were fighting over PAL or 625 line SECAM as the official standard for colour broadcasts

I have two of them, it's a real monster, it uses an A66-410X delta gun CRT, the electronics are extremely complex and overcrowded, there are TWO convergence panels, miles of wiring and literally dozens of relays all over the place, but despite its complex nature, it was a reliable set.
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Old 7th Jan 2009, 8:21 pm   #4
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Default Re: 625-Line Television Broadcast Standards

As a general point, please distinguish between studio and transmission standards. The same 625 PAL studio kit is used in all 625 line countries. Including most of the SECAM ones because a SECAM vision mixer is an evil piece of kit. I know, I've been on the fringes of designing one. The SECAM countries, notably France, were enthusiastic early adopters of component signals in the studio. All studio stuff is now component, usually digital.

Transmission standards are another matter. There's a whole alphabet soup of them with many minor differences.

Quote:
Originally Posted by Synchrodyne View Post
Finally - for now, anyway - when was 625-line System N introduced? I would guess that Argentina was the first country to use this system, which “squeezed” a 625 line signal into a 6 MHz NTSC channel, I would imagine to ensure that the whole of South America (or nearly so, anyway) adhered to a standard channeling system. But the 6 MHz channel was perhaps a little ironic considering that in 1950, Channel E1, 41 to 47 MHz, was deemed unsuitable for 625-line television.
System N was a bodge. Argentina has 50Hz mains and so naturally used basic 625/50 TV. The channels planning however was American giving narrow channels. This didn't matter too much for monochrome, you just lived with a bit less resolution, but colour was a nuisance. Ended up with a roughly 3.5MHz subcarrier (as used for NTSC) but using PAL. Totally non-standard. Studio systems used ordinary PAL-B 4.43MHz subcarrier and transcoding to PAL-N was done at the inputs to transmitters.

South America is the home of oddball standards. Brazil uses PAL-M which is a properly engineered PAL 525/60 system. Not surprsingly the studios use NTSC and transcode at the tranmitters.
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Old 8th Jan 2009, 7:41 am   #5
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Default Re: 625-Line Television Broadcast Standards

BBC R&D has posted dozens of reseach documents here:

http://downloads.bbc.co.uk/rd/pubs/r...60s_70to96.pdf

You may find some clues if you dig about.

Regards,

Ian
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Old 16th Jan 2009, 10:31 am   #6
Synchrodyne
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Default Re: 625-Line Television Broadcast Standards

Thanks to all for your responses.

ppppenguin: thanks - yes, I should probably have entitled the thread “625-line Television Broadcast Transmission Standards”, but I am not sure if I can amend it now. Initially anyway, I was focusing on the basic monochrome systems; the permutations and combinations start building up when one adds the various colour systems, and then the diversity of stereo sound systems.

I have used Alan Pemberton’s excellent site at: http://www.pembers.freeserve.co.uk/W...rds/index.html as my primary reference, and I imagine that it is not going to be so easy to find answers to any questions that are unanswered therein. Still, it’s always worth a try.

Ian – G4JQT: that BBC is full of fascinating information. It’s a pity that it doesn’t go back to the late 1950s, as I suspect that it was then that the BBC decided upon the 625-line system parameters that became System I. In that connection, though, I have since found this comment in the Volume 1 of the book “Colour Television” by Carnt & Townsend (*):

“For 625 lines the suggested chrominance bandwidths are the same as for the American system. If an 8 Mc/s channel is available for each station, as in the U.S.S.R., the optimum utilization of the extra megacycle of bandwidth is probably to increase the luminance pass-band by 0.5 megacycle and use the other 0.5 megacycle to increase the vestigial sideband of the vision carrier to 1.25 Mc/s. The latter reduces the effects of vestigial sideband distortion, particularly on negative modulation. If the sub-carrier frequency is left unaltered, the extra luminance bandwidth can be used to increase the chrominance bandwidth and to ease the problem of providing a sharp luminance and chrominance cut-off at the sound channel frequency.”

Also, later in the same book is the interesting comment, supported by a preceding detailed analysis:

“It would appear that while some schools of thought may regard the difference between N and P monochrome systems as being marginal, or even in favour of N systems, there is overwhelming evidence in favour of positive modulation, A.M. sound systems for N.T.S.C. use.”

Cheers,


(*) Colour Television
Volume 1, Principles and Practice
P.S. Carnt & G.B. Townsend
Iliffe, 1961, 2nd Impression 1968
No ISBN, SBN or LCC
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Old 17th Jan 2009, 11:09 am   #7
ENGLISH VICTOR
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Default Re: 625-Line Television Broadcast Standards

Other advantages for adopting System I is near full chrominance bandwidth to be transmitted in both chroma sidebands, it also enables the chroma /sound beat to occour outside the the chroma bandpass limit i.e. 1.566MHz. as compared to system B/G with a 1.067MHz. beat. The result can look like coloured herringbone interference. Also Quadradure envelope distortion is minimised during chroma transients as a result of equal bandwidth non vestigial chroma sidebands.The problem is best seen during the transistion between the green and magenta bars on standard colour bars when receiving systemB/G. The P.A.L. system certainly helps minimise the problem however.
Victor.
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Old 23rd Feb 2009, 8:40 am   #8
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Default Re: 625-Line Television Broadcast Standards

It would be interesting to compare systems B/G and I side-by-side with receiving equipment that is optimized for each case. I have a multistandard Philips receiver that I have used in South Africa, the USA and Australia. I doubt that it takes full advantage of the bandwidth possibilities of system I, but my assessment is that it was directionally better in South Africa (system I) than here in Australia (system B/G). In the USA (system M) I used it as a monitor, fed from a Luxman T407 outboard tuner. By the way, once one is well-accustomed to the 60 Hz field frequency of system M, it takes quite a while of watching 50 Hz systems before the flicker goes unnoticed.

Back to the origins of the various 625-line broadcast transmission systems, and with reference to the narrow-channel system N, according to Wikipedia, Argentinean television started in October, 1951, see: http://en.wikipedia.org/wiki/Canal_7_Argentina. So assuming that it was used from the start in Argentina, system N arrived quite early in 625-line history, about two years ahead of the Belgian system C. On the other hand, from the same article, PAL-N was quite late, in 1978.

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Old 14th Mar 2009, 8:20 am   #9
Synchrodyne
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Default Re: 625-Line Television Broadcast Standards

Quote:
Originally Posted by Mr Hoover View Post
Hi

Read somewhere the 625 line system was initiated in 1946 & some
experimental transmissions from Holland started around 1948/49.
The 1946 timing is confirmed in a comment I have since found at:

http://www.bvws.org.uk/405alive/faq/405_hist.html

To quote:

"The rest of Europe opted for 625 lines, a system devised in 1946 by two German engineers, Möller and Urtel (it appears that the Russians came up independently with a very similar system and if you had set anyone else the problem - to Europeanise the American 525-line standard - they would have come up with something pretty similar). In Geneva a Mr W. Gerber proposed this as a European system and it has remained in use until the present day."

It seems, then, that the Russian version of the 625 line system was more the result of synchronicity than imitation. And that the Russian choice of 6 MHz video bandwidth could simply have been an engineering decision, there being no precisely "right" number for this parameter.

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Old 19th Apr 2009, 11:12 am   #10
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Default Re: 625-Line Television Broadcast Standards

A sidebar issue here is the origin and timing of the various CCIR television transmission system letter designations, particularly for the diversity of 625 line variants. I see that the topic has already been discussed in other threads, such as: http://www.vintage-radio.net/forum/s...ad.php?t=26968. In an effort to pinpoint the time when the letter designations were first used, I looked through the likely materials on hand. The best I could do was somewhere between 1966 and 1969.

Firstly, Hutson (1), in 1966, has a chapter on television signal standards, which goes into considerable detail, and covers most of them (although OIRT 625, Argentinean 625 and French 625 are not mentioned). Nowhere is there any reference to system letter designators. As one assumes that Mr. Hutson would have been “in the know” on such matters, it is reasonable to deduce that the CCIR had not assigned them at the time the book was written.

Secondly, Carnt and Townsend (2), in 1969, do refer to Systems G and I in their discussion of the PAL colour system. So by the time they were writing their book, the letter identifiers had been assigned.

Anyway, it seems that the letter identifiers were assigned after all of the various systems were in service, in which case they appear to be a combination of logic and arbitrariness. The UK’s pioneering efforts seem to have been recognized by the assignment of the letter A to the 405-line system. Then not surprisingly, the letter B went to CCIR’s own standard Gerber 625 line system, with the other early 625 line systems following as C (Belgian) and D (OIRT), although not including the Argentinean 625 line system, early though it was. Next were the two 819 line systems, E (French) and F (Belgian). So A for 406, B, C, D for 625, and E and F for 819, covering all of the early VHF systems used in Europe, does have a certain logic, although the order of the 625 line systems suggests a certain “political” input, given that the OIRT system was the first in service. Or one can impute the logic that for any given line standard, they are ranked in order of increasing video bandwidth, with N-type systems preceding P-type systems. That works for B, C and D, but fails for E and F, though.

The next group, G, H, I, K, K’ and L covers 625 line systems that were developed mostly with UHF transmissions in 8 MHz channels in mind, although some have also been used at VHF, as with System I in Ireland. G was essentially the same as B, H was G with the vestigial sideband extended from 0.75 to 1.25 MHz, I was the UK (1960 TAC Report) system with video bandwidth extended to 5.5 MHz and with a 1.25 MHz vestigial sideband, K was essentially the same as D, and L was the French P-type 625 line system with video bandwidth of 6 MHz and vestigial sideband of 1.25 MHz. So here the letter progression does follow the increasing video bandwidth rule from G through L. I suspect that K’ (D/K, but with a 1.25 MHz vestigial sideband) may have been a later addition that had to be shoehorned into the system, there being no free letters in the appropriate part of the system. Maybe the CCIR was not anticipating any further variants of the existing transmission standards when it developed its letter system.

Then came M (NTSC 525, NTSC here referring to its early 1940s work, not its later colour work) and N (Argentinean 625). The inferred rationale here was that the CCIR was a European organization, so it would list the European systems ahead of the others. Evidently it saw system N as being a rather ersatz 625 line variant, and more American than European, hence its inclusion in the American group, following the 525 line system. (Although compressing the Gerber system into a 6 MHz channel was surely a no greater act of cruelty than squeezing the 819 line system into a 7 MHz channel, as was done for System F.)

Clearly there is more than some guesswork in the above commentary, but it is difficult to make a logical country connection with the letters, such as I = Ireland. And perhaps the good folk of that country might have preferred E for Eire anyway, but the surely if the CCIR were open to such allocations, the French would have claimed F for the original 819 line system. (And reversing the E and F letter designations could have been justified on a video bandwidth basis.) G for Germany is another possibility, but even here, I think that Italy might have been earlier with the implementation of UHF TV broadcasting, and therefore use of System G.

Cheers,

(1) Television Receiver Theory, Part 1
G.H. Hutson
Edward Arnold, 1966
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(2) Colour Television, Volume 2
PAL, SECAM and Other Systems
P.S. Carnt & G.B. Townsend
Iliffe, 1969
SBN 592 05946 4
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Old 20th Apr 2009, 12:53 pm   #11
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Default Re: 625-Line Television Broadcast Standards

Generally speaking the Irish don't like the term "Eire" being used in English for political reasons that are not appropriate to discuss here. I suspect that System I was named as such as Ireland was the first country to use the standard in 1962, two years before the BBC. Telefis Eireann's implementation of System I was different insofar that it was used on VHF (with letters A-I for the channel numbers) rather than UHF.

Had the UK adopted VHF 625 line TV the channels would have used the same letters as the Irish I suspect.
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Old 2nd May 2009, 4:53 am   #12
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Default Re: 625-Line Television Broadcast Standards

Thanks very much for the education on Ireland vs Eire – I was previously unaware of that.

Re the Irish adoption of what later became known as System I, is there any information available on the process by which it came to be chosen, rather than say System B? As far as I know, the first public proposal of the System I parameters was in the May, 1960 TAC (Television Advisory Committee) Report, although I haven’t seen the report itself. I think that the same report also proposed that the UK should adopt 8 MHz UHF television channels if the rest of Europe did the same, the latter aspect seeming to have come to fruition at the 1961 Stockholm meeting. But actual adoption of the TAC proposed 625-line standard in the UK would not have been reasonably certain until the 1962 Pilkington Report, and I suspect that it may have taken some time for the recommendations to be translated into confirmed action. So the Irish decision to take up System I must have predated any finality about adoption of the TAC 625 line system in the UK.

Re the lettered VHF channels, I think that I’ve read somewhere that they were used in the UK by some cable or wired relay services, which would tend to confirm that they had been pencilled-in should Bands I and/or III be recast for 625 line TV. A curious aspect of the Band I channels A through C is that the carrier frequencies are 0.5 MHz higher than one might have expected, e.g. 51.75, not 51.25 MHz for channel A vision carrier.

Cheers,
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