Analogue Television Broadcast Transmission System Letter Designations
Another one of those questions that I first pondered many years ago was when, and under what circumstances did the letter designations for the various analogue TV broadcast standards originate. An approximate sense of the timing could be derived because the letter designations were not seen in 1950s publications, but were seen from the 1960s. But none of the books and magazine articles that I was able to access in the past mentioned the origins of letter designations.
Anyway, I thought to record my subsequent findings, in part as an adjunct to the Analogue Television Receiver Intermediate Frequency thread, https://www.radios-tv.co.uk/community/black-white-tvs/television-receiver-intermediate-frequencies/.
Sometime back I came across the Final Acts documents from the ITU 1961 European VHF-UHF planning meeting held at Stockholm, and referred to as ST61. This appeared to provide most of the answer in these two pages:
The ITU listed standards A through L, although yet without K1 within that sequence – that was still in the future. Standards M and N were not included, but then except for a small number of American Military stations, they were not used within the European area.
A reasonable inference was that the UHF standard letter designations G through L had been assigned as part of the ST61 work, as part of the planning exercise. So they date from 1961.
At first I took the reference to CCIR Report #124 to mean that the VHF standard letters A through F were actually assigned in that CCIR report, and therefore that they dated from 1959. More recently I found that report, which did not include any mention of those letters. Rather the descriptors included in the ST61 were used for differentiation. What the ST61 document really meant was that standards A through F were as defined in CCIR Report #124, but that the that the letter designations were assigned as part of the ST61 exercise. So they also date from 1961.
Here is Table I from CCIR Report #124.
In hindsight that the VHF standards letters derived from ST61 and not CCIR Geneva 1959 should have been obvious. Had the CCIR assigned letters designations in 1959, it surely would have included what became standards M and N as part of the logical sequence. But these were not added to the list until later on. The ST61 letter sequence applied only to those standards that would have ongoing use in Europe, whether at VHF or UHF.
One may deduce the logic of the VHF standards letter sequence development as follows:
Firstly, letters were assigned in ascending order according to line count.
Secondly, for systems with the same line count, letters were assigned in ascending order according to vision bandwidth.
Thirdly, for systems with the same line count and the same vision bandwidth, letters were assigned on the basis of vision modulation sense, with negative preceding positive.
An exception to this was that the French 819-line system, with 10 MHz vision bandwidth, assigned as standard E, preceded the Belgian 819-line system, with 5 MHz vision bandwidth, assigned as standard F. Possibly it was thought that as the French 819-line standard antedated the Belgian version, it should have the lower letter. But on that basis the Russian/OIRT 625-line standard, which antedated the CCIR 625-line standard, should also have had a lower letter. Whatever the reason, it would seem to that the French missed a happenstance but logically justifiable opportunity to have their 819-line standard labelled as “F”. Perhaps the reason for the exception is quite simple, though. That is that the letters simply followed the same order in which the standards were presented in CCIR Report #124 (excluding the 525-line standard), without further thought being given to the matter. Application of Occam’s Razor would certainly support that answer.
The UHF standards letter sequence – all for 625-line standards - followed the same logic as for VHF, with the addition of:
Fourthly, for standards with the same line count, same vision bandwidth and same vision modulation sense, letters were assigned in ascending order according to vestigial sideband bandwidth.
Thus the French 625-line standard (L) followed the Russian/OIRT 625-line standard (K) on the basis of both the third and fourth “rules”. Even had the Russian standard vestigial sideband been increased to 1.25 MHz, noted as a future possibility, the order would still have been right on the basis of “rule” 3.
It is also apparent that the ITU chose to keep the VHF and UHF standards in separate sets of letters, I should imagine more to have the five UHF standards in a sequential group. This resulted in one case of duplication, in that standard K was the same as standard D. Standard G was essentially standard B but in an 8 MHz rather than a 7 MHz channel, which difference alone probably justified their having separate letter assignments.
Nevertheless, standard I was also considered to be a VHF as well as a UHF standard from the start, being shown in the ST61 as that to be used Ireland on the VHF channels.
Standards I and L were new. Standard I was that recommended by the UK TAC in 1960, following a period in which the working assumption was that the UK would adopt the standard D parameters for its UHF 625-line service. Standard I traded 0.5 MHz of vision bandwidth for a commensurate increase in the vestigial sideband bandwidth, which was thought to offer optimum use of the available bandwidth with the domestic receiver technology of the time.
The French standard L was developed to offer maximum commonality with the existing 819-line standard E in order to simplify the design of dual-standard receivers, and so had positive vision modulation and AM sound, without pre-emphasis. Combining a 6.0 MHz vision bandwidth with a 1.25 MHz vestigial sideband with the customary guardbands it would have required an 8.5 MHz channel. But it was fitted into the 8 MHz channel by discarding 0.5 MHz of outer guardband space. This approach was not new to the French. Standard E had originally been designed for a 14 MHz channel, but the definitive channel plan had 13.15 MHz spacing obtained by discarding 0.85 MHz of outer guardband space. One possible reason for the choice of 6.0 MHz vision bandwidth was to allow enough room for a future colour subcarrier to have fully symmetrical sidebands. At that time it was generally accepted that a colour subcarrier would be placed at around 4.43 MHz in 625-line systems. The SECAM system that was being developed in France (originally for 819-lines with an 8.37 MHz subcarrier) initially used conventional AM subcarriers, so any sideband asymmetry would have caused distortion. I am not sure when the change to FM subcarriers was made, but again, sideband asymmetry in an FM system was perhaps seen as something to be avoided, although eventually it was accepted where SECAM colour was used for standards B, G and H.
The often-used 0.75 MHz vestigial sideband width originated with the first NTSC in 1941, and was optimum in relationship to the other parameters, noting that the 6 MHz overall channel width was a fixed parameter within which the NTSC had to work. The vestigial sideband width was just short of a fifth of the main sideband width, originally 4.0 MHz. (The second NTSC in 1953 moved that out to 4.2 MHz to accommodate the colour subcarrier, and later that number became the norm for monochrome as well.)
That 0.75 MHz value was adopted without change for the Russian 625-line standard developed circa 1944, and again for the vestigial sideband variant of the British 405-line standard. In both cases there was no reproportioning to take account of the differing vision bandwidths. However, in the case of the French 819-line standard, which had a 10.4 MHz vision bandwidth (original number, later amended or perhaps rounded to 10 MHz), the vestigial sideband width was set at 2.0 MHz, again just short of a fifth of the main sideband, so aligned with the NTSC case. A proportional vestigial sideband for the Russian 625-line standard would have been 1.2 MHz. But evidently the issue was not reconsidered when the CCIR 625-line parameters were set. There total channel width was the issue, and with the 8 MHz adopted by the Russians considered to be unacceptable, the debate appears to have been between the 6 and 7 MHz channel options, of which the latter was chosen as the Gerber compromise.
In summary, the Analogue TV Standards designations A, B, C, D, E, F, G, H, K and L all originated at the ITU Stockholm 1961 European VHF-UHF Planning Meeting (ST61). They all referred to currently used or planned future standards for use in Europe, although at the time, some of these, particularly B and D, were also used outside of Europe.
Excluded from that list were the NTSC 525-line standard, widely used throughout the Americas and in parts of Asia, and what might be called the Argentinean 625-line standard, used in Argentina and some other South American countries. The addition of these will be addressed in the next posting.
The letter designations M and N, respectively for the NTSC 525-line system and the Argentinean 625-line system first appeared in CCIR Report #308 from the 1963 Geneva CCIR Xth Plenary Meeting, which was the first such following the 1959 Los Angeles meeting.
I have extracted Table I, which lists the various standards:
One could say that the CCIR completed the work started by the ITU in 1961 by assigning letters to the NTSC 525- and Argentinean 625-line standards. Given that letters A through L were already assigned, it used the next available in sequence, namely M and N, assigned on the basis of increasing line count.
Report #308 was also the first in the sequence of CCIR TV Systems Reports that included the Argentinean 625-line standard, even though it had been in regular use since the latter part of 1951.
It was also the first report to include European UHF standards G through L, which had been documented at ST61, i.e. after the CCIR 1959 Geneva meeting.
The tabular presentation of the standards in Report #308 does not follow their alphabetical sequence, but rather a logical sequence based upon system parameters, in order: line count, vision bandwidth, vestigial sideband width, vision modulation sense (negative ahead of positive). As a result, M and N were slotted in between A and B; D and K, previously identified as being the same, were grouped together; and F preceded E.
The CCIR Report sequence deserves more comment, to be part of a future posting. The next posting will address standard K1.
Probably this is something that should have been included in the opening post, and that is addressing the question as to why the ITU wanted a simple designation system for the various TV standards that were involved in the ST61 planning exercise.
No reason was explicitly given in the ST61 documentation, at least not that I have found. But self-evidently, with the addition of several new 625-line systems for UHF transmissions, the previous descriptive system used by the CCIR, namely line-count with a preceding differentiating descriptor where necessary, would have become unwieldy for use throughout the ST61 tables, etc. The letter designations were a lot simpler.
The simplicity shows up in this page from the ST61 Final Acts channel assignments section. Just a single column was needed to identify the TV standard for each transmitter.
That it was the ITU who defined the European UHF TV channel frequencies and corresponding channel numbers also simplified the UHF case, in that only the channel number, together with the TV standard, was needed to identify the vision and sound carrier frequencies in each case. In the European VHF case, the ITU had apparently not been involved with the VHF channel frequency assignments and numbering systems, which to some extent at least appear to have been developed by individual in-country authorities. So the ITU did not use those VHF channel numbers in the ST61 documentation, nor had it done so in the earlier Stockholm 1952 European VHF Planning meeting (ST52) documentation. For the VHF assignments, it listed both the vision and sound carrier frequencies as well as TV standard for each transmitter. There was some apparent redundancy there, in that say vision carrier frequency and standard letter alone would suffice in most cases, it would not have worked for standard E, where the sound carrier could be above or below the vision carrier, so needed to be included to avoid any ambiguity.
That was still simpler than for the ST52 case, where it had been necessary to list vison and sound carrier frequencies, channel width, sound modulation and line count to provide full channel and TV standard identification for each VHF transmitter.
TV Standard K1 evidently made its debut at the ITU 1963 Geneva African VHF-UHF Planning Conference, when it was proposed as the system for use in the Francophone countries in Africa. At the time, it was referred to as standard K*. That looks to have been a convenient interim designation for use until such time as the ITU assigned it a permanent designation within the existing sequence. Given that it was in essence a modified version of standard K, then K* was logical.
Standard K* was included in the table of TV standards included in the Final Acts documents for the 1963 Geneva conference:
The main standards planned for use or already in use in Africa were B/GH, I and K*. Standard E was already used by Algeria, and standard M was listed for possible use by Liberia.
CCIR Report #308-1 from the 1966 Oslo XIth Plenary meeting, which superseded Report #308, included standard K1:
K1 was the definitive designation for K*, and in the Oslo report it was shown in the same column as standards D and K. In many references standard K1 is also referred to as standard K’. The ITU and CCIR documents that I have seen consistently show it as K1. So unknown on the basis of available information is whether K’ was an authorized alternative or an informal version in common usage.
Standard K1 can also be thought of as being the negative vision modulation, FM sound counterpart to French domestic standard L, which had positive vision modulation and AM sound. On that basis it is not so surprising that it followed standard L in having a 6 MHz vision main sideband with a 1.25 MHz vestigial sideband. In the French domestic case, reducing the complexity of dual-standard receivers indicated that L should be aligned with standard E, and thus be of positive/AM form. That constraint generally did not obtain in the African case, so for French Africa it was possible to use the negative/FM form, thus aligning with majority practice, and with the other 625-line variants that were or were to be used in Africa. Certainly standard E was already used in Algeria, but by 1963 it could be observed that alignment with French practice was probably not a priority for that country. Perhaps somewhat improbably, Algeria had an unusual claim to TV practice fame in that it was the first country to start regular bilingual TV sound broadcasting (using the French AM TDM system.)
The 1963 Geneva conference documents are readily available at the ITU Portal, here:
There was some debate on the issue of 7 or 8 MHz channels for 625-line systems, and about standard K* itself. The case for the latter was expounded in Document 28-E, which I have attached. I imagine that this was the same reasoning that led the French engineers to the standard L parameters.
Mod Note: edited post to correct font formatting.
Tip: When pasting in text use the "T" tool (second to last icon on tool bar) this ensures correct formatting for forum is maintained.
As mentioned in the TV Intermediate Frequencies thread, I did some “dumpster diving” in the ST61 “documents” section. One of the finds was the very document in which the initial set of analogue TV system letter designations was “cast in stone”, as it were.
That was in ST61 Document 84-E, 1961 June 09, Item 4:
It was all quite simple, really. The VHF systems were lettered in the order in which they appeared in CCIR Report 124, after dropping out the 525-line system. Then the UHF systems went on from there, in the same order in which they had generally been treated in the ST61 deliberations.
For a while, the UHF systems had been labelled A through F, as shown in Document DT 23, dated 1961 June 07:
These followed the previously deduced logical sequence.
An interesting point was that because the OIRT countries were studying the possibility of extending the vestigial sideband of their UHF 625-line system from 0.75 to 1.25 MHz, the two options were then listed as separate systems, then labelled as “D” and “E”. Presumably as the decision to make the change had not been made by the end of the ST61 (I am not sure that it ever happened, in fact), the 1.25 MHz vestigial sideband option was dropped from the final classification system. Of course, the irony was that two years later that very system was required in French Africa, initially designated K*. then K1. One could say that the ST61 Committee 4 decision was convenient at the time but not prescient.
The intent to use coded TV system designation is apparent from these two pages from Document ST-30E, about the format of the eventual pan-European transmitter plans which would be the major output of ST61. Both include the comment: “The television system will be given in coded form, in accordance with a table to be established by Committee 4.”
So now we have drilled down far enough to find why the TV system letter classifications were required, how the actual sequence came about, and why some systems were not included in the original listing.
What was essentially an ad hoc system developed to simplify ST61 reporting then became the definitive means by which analogue TV systems were labelled. I’d say that a turning point in this regard was its adoption by the CCIR in its 1963 Geneva Report 308, “Characteristics of monochrome television systems.” Whilst I have identified the conference document that backed Report 308, namely #2329, it does not seem to be available at the ITU portal. It probably confirmed the adoption of the letter system for CCIR purposes and the addition of systems M and N.
The TV system letter designation system stemmed from the planning work for European UHF TV broadcasting at ST61, informed by the immediately preceding CCIR Cannes :Meeting of Experts”. But before that, much preliminary work had been done in particular with the objective of obtaining agreement on the use of common 8 MHz channels and vision carrier frequencies at UHF. Much of that work was encapsulated in Report #123 from the CCIR 1959 Geneva Plenary meeting, I have extracted the table from that report, which gives a reasonable overall picture:
Note that the vision-to-sound carrier spacings listed are 5.5 and 6.5 MHz – there was as yet no mention of the 6.0 MHz option. At the time, the UK 625-line planning envisaged the use of 6.5 MHz. 6.0 MHz was a late entry as it were, appearing in the 1960 TAC Report.
Nothing was indicated about vision modulation sense or sound modulation type, although one could reasonably guess that most countries were thinking negative/FM, as used at VHF, with France thinking positive/FM, as used for its 819-line system. That was largely clarified by the CCIR 1961 Experts meeting, wherefrom came the following table:
That confirmed the positive/AM choice for France, and negative/FM for most of the others, including Belgium, which used positive/AM at VHF. The surprise (to me, anyway) was that the UK was at that time apparently undecided between positive/AM and negative/FM. As I understand it, the UHF 625-line test transmissions from the Crystal Palace transmitter had all been of the negative/FM form, initially anyway with 6.5 MHz intercarrier. Perhaps the either/or was a “just-in-case we change our mind” exercise, in part driven by considerations of which might be easier for dual-standard receiver design.
By that time of course the UK had opted for 5.5 MHz vision bandwidth, with 1.25 MHz vestigial sideband, and 6 MHz intercarrier, and Belgium had included this as a possibility, although not preferred. And there was significant interest shown in the 1.25 MHz vestigial sideband. This may well have been generated by the UK TAC’s viewpoint. However, what cannot be outruled is that the French had previously decided to use the 1.25 MHz vestigial sideband.
CCIR Television System Reports:
Reports on the characteristics of the various TV transmissions systems were generated at the CCIR Plenary meetings starting with the 1951 Geneva VIth Plenary, and running through to the 1990 Dusseldorf XVIIth Plenary. The documentation for these meetings may be found at: https://www.itu.int/en/history/Pages/ConferencesCollection.aspx.
After 1990, similar information was found in ITU-R reports, about which more in a later post.
The TV system reports included convenient tabular data, which I have extracted for the purposes of this thread. There was much else in these reports, such as waveform data, and they may be used to track detail changes. For example, one may follow the various 625-line systems in their (gradual) migration from a 3H to a 2.5H equalizing pulse interval.
In this post I’ll include and comment upon the first six of the subject CCIR reports, covering the period 1951 through 1966.
From CCIR Report #15, “Television Systems”, Geneva VIth Plenary, 1951:
This showed just four systems, identified simply as “405”, “525”, “625” and “819”, and presented in line-count order.
For the 405-line system, the aspect ratio was shown as 4:3. It had been changed from 5:4 to 4:3 during 1950, as recorded in “Wireless World” (WW) 1950 March, p.99. Also, the details shown applied to the vestigial sideband version, which was being used for all new transmitters and had been announced in connection with details of the planned Birmingham transmitter in WW 1948 November p.411. The double sideband was still used by the Alexandra Palace transmitter, but was presumably seen as being obsolescent, so was not listed by the CCIR.
For the 525-line system, the vision bandwidth was shown as 4 MHz, its original (NTSC 1941) value.
“625” referred to the Gerber system. There was no mention of the earlier Russian 625-line system. The Argentinean 625-line system was not yet in regular service, although of course that variant had its start with the 1949 experimental transmitter in Torino, Italy.
“819” referred to the French 819-line system, the Belgian version being still in the future. Vision bandwidth was shown as 10.4 MHz, and the aspect ratio as 4:3. The latter may have been a change from the original, which for example Kerkhof and Werner reported as being 4.12:3. The sound carrier is shown as being 11.15 MHz below the vision carrier, which was the original arrangement within the nominal 14 MHz channel.
The French 441-line system, although still in use, was not included. That would appear to be because it was effectively obsolescent given that there was to be no expansion of the service and the Paris transmitter was slated for eventual closure.
From CCIR Report #35, “Television Systems”, London VIIth Plenary, 1953:
Here, notwithstanding the heading “Details of Four Television Systems”, the table had been expanded to included six systems, the same four from the 1951 report plus two more, identified as “Belgian 625” and “Belgian 819”, placed in additional columns to the right-hand side. The two Belgian systems were slated for regular use from later in 1953, and had been the basis for Belgian channel allocations at the ITU 1952 Stockholm (ST52) European VHF Planning conference.
For the (French) 819-line system, the sound carrier was still shown as being 11.15 MHz below the vision carrier, and the channel width as 14 MHz channel. This was despite the fact that the tête-bêche channelling arrangement, using both sound-carrier-low (inverted) and sound-carrier-high (normal) channels, with 13.15 MHz channel spacing, had been the basis for the ST52 allocations.
Neither the OIRT 625-line system, nor the Argentinean 625-line system were included, although the latter had been in regular use since the later part of 1951.
From CCIR Report #83, “Television Systems”, Warsaw VIIth Plenary, 1956:
The OIRT 625-line system was added, identified as “O.I.R 625”. Considering that the CCIR meeting was held at Warsaw, that was hardly surprising. I am not sure whether “OIRT” or “OIR” is the correct designation, as both seem to have been used.
The columns were restored to line-count order, with what were regarded as the basic systems of the “625” and “819” systems preceding variants. However, historical accuracy would have required that the OIRT 625 system be placed as the basic or original 625-line variant.
Footnotes were added to indicate where the Japanese version of the 525-line system (in use in 1953) differed from the NTSC original.
From CCIR Report #124, “Characteristics of Monochrome Television Systems”, Los Angeles IXth Plenary, 1959:
The report name was changed to “Characteristics of Monochrome Television Systems”. Whilst as yet the CCIR had not issue any reports specifically about colour television systems, there was mention of colour subcarrier frequencies in Report #123, “Television Standards for Bands IV and V”.
No new systems had been added, but the O.I.R. 625 system was renamed as the I.B.T.O 625 system.
For the 525-line system, the vision bandwidth was shown as 4.2 MHz, although it was still 4 MHz for the Japanese variant. The 4.2 MHz number had been introduced with the NTSC (II) colour system of 1953, and later this was also transferred to the monochrome system, although I am not sure exactly when that happened.
A footnote was added to indicate where the Australian version of the 625-line system differed from the Gerber original.
For the 819-line system, the vision bandwidth was shown as 10 MHz. Whether was an actual reduction or simply rounding of the 10.4 MHz original number is unknown. The sound channel was shown as being 11.15 MHz from the vision channel, which thus allowed for the positive and negative separations that were part of the tête-bêche channelling system. The channel width was still shown as 14 MHz, though.
As mentioned in earlier posts, CCIR Report 124 was used by the pertinent ITU ST61 committee for the allocation of system designation letters for existing VHF TV systems.
From CCIR Report #308, “Characteristics of Monochrome Television Systems”, Geneva Xth Plenary, 1963:
Here we see some major changes. Firstly, the CCIR had adopted the letter designations developed at ST61, expanding that sequence to included systems M and N.
The table has the various systems arranged column-wise in logical sequence, with the result that the letter designations are not in alphabetical sequence. This shows up the apparent short-sightedness of the original ST61 letter designation system, in which what became system M was deliberately excluded, and systems E and F were assigned contrary to logical order. However, the ST61 committee involved probably was working under a narrowly-defined brief as well as time constraints that in combination did not allow of addressing anything outside of immediate requirements.
For the 525-line system M, the vision bandwidth is now shown as 4.2 MHz without exception, indicating that the Japanese had by now move their version up from 4.0 Mhz.
The Argentinean 625-line system, extant since 1951, was included for the first time as system N. Its vision bandwidth was shown as 4.2 MHz, the same as the 525-line system M. Originally it would have been 4 MHz, and the change to 4.2 MHz probably followed the corresponding change for system M.
The European UHF systems G, H, I, K and L were included for the first time. D and K being the same, they were listed jointly in what was the “K” column.
Another output from CCIR 1963 Geneva was: Report 309, “Choice of Standards for Colour Television in the European Area”, quite brief and mostly qualitative.
From CCIR Report #308-1, “Characteristics of Monochrome Television Systems”, Oslo XIth Plenary, 1966:
Here a significant change was the addition of the African system K1, included parenthetically in the same column as systems D and K. Again this shows up the short-sightedness of the original letter assignments. Tentatively this system had had its own letter (“E” in the initial UHF sequence) but it was not included in the definitive 1961 listing. Thus it had to be shoehorned in as K1. But if G and H, which differed only in vestigial sideband size, justified separate letters, then arguably so did K and K1, which differed in the same way. But then classification systems in any field are seldom pristine, and even if they start out that way, with human nature involved, they soon become corrupted by happenstance or otherwise.
System K1 had been designated as K* for the purposes of the ITU 1963 Geneva African VHF-UHF Conference. I think we may assume that somewhere in the documents supporting the Oslo meeting is recorded the decision to adopt the K1 form for its permanent designation. It is often written a K’, but thus far I have found no indication that this was officially supported.
CCIR 1966 Oslo reissued Report 309 from the Geneva meeting without change, and also issued a new Report 407 “Characteristics of Colour Television Systems”. This was quite comprehensive, covering the NTSC, SECAM and PAL systems as they then were and running to 20 pages.
Later CCIR Reports will be reviewed in a subsequent posting.
The system L’ situation in respect of multistandard receivers was well described by Jackson and Townsend, pertinent page attached:
One may find “hard” evidence that the dual-purpose or double-ended IF strip was used in practice.
Firstly, double-Nyquist SAWFs were available, apparently as standard items. Some VIF pairs that were used for these were 33.4 and 38.9 MHz, and 33.9 and 38.9 MHz, per the attached examples.
Thus the VIF for system L’ would have been 33.4 or 33.9 MHz, with SIF at 39.9 or 40.4 MHz.
The VIF for system L (and others) would have been 38.9 MHz, with SIF at 32.4 MHz.
Secondly, there were “multistandard” tuners, such as the Philips UV815/816, which provided 33.4 MHz VIF for system L’ and 38.9 MHz VIF for system L (and others).
Whether double-conversion for system L’ was used in practice I do not know. More generally, from the ST61 proceedings, it is apparent that the Russians at least contemplated double-conversion for the UHF channels, using a Band I channel as the 1st IF. In the USA in the 1990s, Mitsubishi advertised its TV receivers (and VCRs, I think) as having double-conversion tuners. I don’t have any details, but I have a vague recollection that initial upconversion, to somewhere above the top end of the UHF band, was used.
Oops! The immediately preceding post was intended for the TV IF thread, where I have now put it. I am not sure that I can delete it from this thread though.
The next CCIR Report in the TV systems series was from the 1970 New Delhi XIIth Plenary meeting.
This was Report #308-2, the Table I from which is attached:
No new systems had been added. So the list, in presentation order, remained as systems A, M, N, B, C, G, H, I, D/K/K1, L, F, E.
In this, System A, C, E and F were referred to footnote (1), the wording for which was: “These systems are given for information only. They are not recommended for adoption by countries setting up a new television service (see Recommendation 470).”
So these four systems could now be considered as being obsolescent.
Another change was that – at last – System E was shown as having a sound carrier that was ±11.15 MHz from its associated vision carrier, with footnote (10): “This system is used both normally and reversed on the frequency scale in a tête-bêche arrangement.”
It was odd that, despite this having been the case since 1952, it was not recorded until the system itself had reached obsolescence.
As had been the case since Report #308 from CCIR 1963 Geneva, it included an Annex with a list of which countries used (or planned to use) which system(s).
Up until 1963 Geneva, each issue of the report had its own number, #15 for 1951 Geneva, #35 for 1953 London, #83 for 1956 Warsaw, #124 for 1959 Los Angeles, and #308 for 1963 Geneva. From there the subsequent reports, if of broadly similar format, retained the same basic number, with a suffix number to indicate reissue, thus #308-1 for 1966 Oslo and #308-2 for 1970 New Delhi.
Updated and reissued in 1970 as Report 407-1 was Report 407 from 1966, “Characteristics of Colour Television Systems”.
CCIR Recommendation 470 was mentioned in footnote (1) to Table I. This was quite short, and a straightforward recommendation for any country planning to start a new TV service.
The CCIR 1974 Geneva XIIIth Plenary meeting resulted in a change of format for the TV systems report. This year it was Report 624 “Characteristics of Television Systems”. It covered both monochrome and colour systems in much detail, and ran to 32 pages. The expanded tabular data was presented in several tables, so that it is not possible to extract a single table that providers representative data. Instead, a simple summary is appropriate.
The system list was: A, M, N, B, C, B&G, H, I, D&K, K1, L and E, with systems A, C and E annotated as being obsolescent.
Systems B and G were combined into one column, following that for system C, presumably because system G had a wider channel width (8 MHz) than system C (7 MHz).
System K1 now had its own column, just to the right of the column for D & K.
System F had been deleted.
CCIR 1978 Kyoto XIVth Plenary produced Report 624-1, with the same systems list as for Report 624, thus:
A, M, N, B, C, B&G, H, I, D&K, K1, L and E, with systems A, C and E annotated as being obsolescent.
Likewise CCIR 1982 Geneva XVth Plenary saw no change of systems list in Report 624-2.
CCIR 1986 Dubrovnik XVIth Plenary produced Report 624-3.
Here, systems A, C and E had been deleted, so the list was: M, N, B&G, H, I, D&K, and L.
Report 624-4 from CCIR 1990 Dusseldorf had the same list as Report 624-3.
That was the last of the CCIR reports. After that CCIR became ITU-R, with a different series of reports.
The short recommendation for new TV installations progressed without major change through Recommendation 470-1 at 1974 Geneva, 1978 Kyoto and 1982 Geneva to Recommendation 470-2 at 1986 Dubrovnik and 1990 Dusseldorf.
Looking back, the ITU and CCIR between them had, since 1961 and through 1990, allocated systems letters A, B, C, D, E, F, G, H, I, K, K1, L, M and N.
Nowhere in the ITU and CCIR documentation can I find any reference to the use of K’ as an alternative to K1. Temporarily the ITU had used K* for what became K1, and that was documented. Thus we may deduce that notwithstanding its apparent lack of status with the ITU and CCIR, either it [K'] was nevertheless used by one or other of the administrations to describe that system, or it was an informal version of K1.
Neither was there any mention of system L’ (or L1 as one might have expected from the CCIR). L’ was the commonly used designation for the Band I version of French system L, for which the channels were inverted with vision carrier high, and which had been in use since 1984. It is debatable whether a separate designation for this variant was warranted. It could be argued that system E, at the time of its “lettering”, as it were, in 1961, was assigned a single letter even though it was used in both normal and inverted channels. This channel orientation duality had existed since 1952, whereas the original version, promulgated in the CCIR 1951 Report, had only the vision-carrier-high form. But there was some delay before it was recognized by the CCIR.
Through to 1990, the system L parameters shown by CCIR included only the normal channel version, with sound carrier at +6.5 MHz relative to the vision carrier, but the lack of a -6.5 MHz option from say the 1986 report might have been simple inertia. Perhaps the L’ designation was coined by the French administration, and never formalized with the CCIR, or perhaps it was simply an informal industry designation. Distinguishing between L and L’ was less important in French domestic receivers, for which the L’ channels were inverted for ease of design, but it was of greater importance for the makers of multistandard receivers and the components therefor. So there was, as it were, an operational need to separate the two systems.
In summary we can say that TV system lettering arose out of a specific need that the ITU ST61 working groups had for simple coded labels for the multiplicity of systems that would be included in the tabular channel allocation data that was to be the main ST61 output. The system devised was ad hoc, and included only those systems that wee included in the final report. For the VHF systems, the list was based upon CCIR Report 124 from 1959, less the NTSC 525-line system that was not used in Europe, and this took the first set of letters, A through F, in the same order as the systems were presented in Report 124. The UHF systems were the major activity of ST61, and an initial working assignment of the letters A through F was used. This was translated to G, H, I, K and L for the final assignment, with what had temporarily been system E left out because it was not planned for near-term use.
Thus ITU ST61 developed the system strictly for its own purposes, and apparently without regard for its possible wider use. But whatever its shortcomings, it was evidently seen as a system with high utility, and so was adopted by the CCIR for its 1963 TV Systems report, for which it also backfilled the gaps that ST61 had left, adding systems M and N. At that point CCIR appeared to have taken ownership of the TV systems lettering system. In the 1963 Geneva African VHF-UHF planning meeting documents, ITU used the interim designation K* for a system to be used by Francophile African countries (in fact the same one that ST61 had initially labelled E but which was not included in its definitive list), but this was formalized as K1 by the CCIR in Report 308-1 of 1966.
In 1992 “ownership” of the lettering system passed to ITU-R, under whose aegis some further changes were made, more information to follow.
thanks a lot, as always a very informative overview.
With respect to the use of L' or K' (or any other form thereof): like you already suggested, the reason for this is the difference between a broadcast STANDARD and a receiver system OPERATING MODE.
So in a Standard it is very acceptable to say (e.g. in the case of standard L) "in band IV/V the LO is below the picture carrier to produce a VIF of 32,7 and SIF of 39,2MHZ, in band I the transmitted spectrum is inverted with picture carrier above, and an LO above the pc is used to produce a VIF of 32,7 and SIF of 39,2MHZ."
However, for a tuner or TV designer these are two quite different operating modes, with completely different rules for determining the required LO-frequency depending upon the reception in band I or IV/V. This was solved by calling the VHF-I mode/standard L'. Which was not a engineering-only internal thing, but also ended up in the official data sheets. So although not a formal standard, L' was effectively used as such in most tuner and TV set documentation.
Thanks for that.
As a practical matter, I think that the CCIR (and ITU-R) would have done better to recognize L’ (or L1) as a formal standard. But it is not clear whether it (they) declined to do this, or whether no-one made representation to the appropriate committee to have L1 included. To the end, ITU-R showed system L as having the sound carrier at +6.5 MHz relative to the vision carrier, with not even a footnote to show that -6.5 MHz was also used. In later days at least, system E was shown with the sound carrier at ±11.15 MHz. Perhaps recognizing system L’ was one of those activities of which it was said “we must get to that”, but the collective “we” involved always had other more pressing matters to attend to.
I doubt that CCIR/ITU-R could have made a persuasive technical argument for the non-inclusion of system L’ had the case been pressed. The position of the vision and sound carriers within the channel was an integral part of the specifications. If the separate designations B and G were justified simply on the basis of different channel “dimensions”, then you could argue that L and L’ were more different than were B and G, so separate designations were even more justified. The later appearance of B1 (to be mentioned in the next posting) reinforces that. Going further down this pathway, one could argue that E should have been split into say E (sound at -11.15 MHz, being the original version) and E1 (sound at +11.15 MHz).
As previously mentioned, ITU-R replaced the CCIR, and so assumed responsibility for the TV systems letter designation system.
In 1993 November ITU-R issued Recommendation BT.470-3 “Television Systems”.
Ostensibly this was simply an update of the previous CCIR Recommendation 470-2, which had been reissued in 1990.
Certainly the main page followed the same format as the previous CCIR 470 series. But added to it was Annex 1, “Characteristics of Television Systems”, which embodied the contents of the previous CCIR Report 624-4. Appendix 1 to Annex 1 was the list Television systems used in different countries/geographical areas, last published as Annex 1 to Report 624-4.
The lettered system list remained unchanged, as: M; N; B&G; H; I; D&K; K1; L.
ITU-R Recommendation BT.470-4 “Television Systems” was issued 1995 October with no change in the lettered systems list.
In 1998 February, ITU-R Recommendation BT.470-5 had a change of name, to “Conventional Television Systems”. By this time, non-conventional systems were being proposed.
There was also a change to the alphabetical list, in that system B1 was added, in the B, B1, G column.
So the amended list was: M; N; B, B1 & G; H, I, D&K, K1, L.
B1 was system B in an 8 MHz Eastern European VHF channel.
Background to its addition was provided by an EBU document: Information I33 -1997 - Changes to the terrestrial television systems in Central and East European countries. Here is the pertinent excerpt:
Of note is the comment: “For the VHF transmitters this situation creates a new emission standard with a draft designation “B1” which has not been yet incorporated to the relevant ITU-R Recommendation. The intercarrier-frequency is 5.5 MHz, channel width 8 MHz and vision carriers the same as in system D.”
EBU evidently recognized that ITU-R was in charge of the TV system letter designations, hence the description of “B1” as a draft designation. ITU-R ratified it in Recommendation BT.470-5.
One could ask, why was the B1 designation needed as well as G, given that the latter was essentially system B in an 8 MHz channel. One possible argument is that when the G designation was assigned, was specific to UHF transmissions. But so were I and L, and they were also later used at VHF. So that approach is not very persuasive. Another argument is that system G referred to regularly spaced 8 MHz channels, which situation did not obtain for all of the Eastern European VHF channels. Not all that strong, but in its favour was that the separate designations D and K had been used for the identical system at VHF and UHF respectively, thus creating a precedent for the use of B1 at VHF and G at UHF.
ITU-R Recommendation BT.470-6 was issued 1998 November. This added another system, namely D1, which was system D, still in an 8 MHz channel, still with 6.5 MHz intercarrier, but with video bandwidth reduced to 5 MHz. (I am not quite sure why this was done, though.) In Table 3, Characteristics of Radiated Signals, D1 was placed in the same column as D and K. Given that vision main sideband width was a key parameter in the letter designation process, then the assignment of D1 was quite reasonable, although it was the first example where a different vision bandwidth was not also associated with a different intercarrier spacing. On the other hand, when system L was operated with the vision main sideband reduced from 6.0 to 5.1 MHz to make room for a NICAM sound carrier at 5.85 MHz, no separate designation was allocated, and the change was covered by a footnote. That was an inconsistency.
The new list was thus: M; N; B, B1 & G; H; I; D, D1 & K; K1; L.
More changes came with ITU-R Recommendation BT.470-7 of 2005 February. Its name was changed to “Conventional Analogue Television Systems”, reflecting the fact that digital TV transmission was now a reality. It also reverted to the simple, single page format that was used for the CCIR Recommendation 470 series. For detail, it referred to two other ITU-R recommendations, namely:
Recommendation ITU-R BT.1701 – Characteristics of radiated signals of analogue television systems; and
Recommendation ITU-R BT.1700 – Characteristics of composite video signals for conventional analogue television systems.
ITU-R BT.1701 of 2005 February, “Characteristics of radiated signals of conventional analogue television systems” had a single main page that was much like the BT.470 series, followed by Annex 1 “Characteristics of radiated signals of conventional analogue television systems”. This was fairly short as compared with the previous “Characteristics of Television Systems” Annex 1 sections.
New to the list was system I1, which was system I with the vestigial sideband reduced from 1.25 to 0.75 MHz, as required when a system I transmission occupied the upper adjacent channel to a DVB-T transmission. This was fully consistent with the precept that vision vestigial sideband width was a key parameter, and had previously been used to differentiate G and H, and K and K1.
So the list was now:
M; N; B, B1 & G; H; I & I1; D, D1 & K; L.
BT.1701 did not include the country-by-country system list, previously Appendix 1 to Annex 1 in the earlier editions of ITU BT.470. Instead it was issued as a separate report, ITU BT.2043, the initial and still current issue being dated 2004.
ITU-R Recommendation BT.1701-1 was issued 2005 August. It remains current today, as shown at: https://www.itu.int/rec/R-REC-BT.1701-1-200508-I/en.
The alphabetical list was unchanged from the previous issue. I have extracted and reassembled the parts of Table I from this recommendation:
(For best readability of this attachment, I have found that right-clicking to open in a new tab, and then left-clicking to enlarge works well. But I can also upload the several smaller parts as separate items if required.)
This brings us to the end of the run-through of the various CCIR and ITU-R reports and recommendations. More comments to follow.
From the foregoing, it may be seen that the full list of analogue TV transmission system letters allocated by the ITU/CCIR/ITU-R comprised:
A UK 405/50, vestigial sideband version.
B CCIR 625/50.
B1 CCIR 625/50 in 8 MHz Eastern European channel.
C Belgian 625/50.
D OIRT/IBTO 625/50.
D1 OIRT/IBTO 625/50 with vision main sideband reduced to 5 MHz.
E French 819/50.
F Belgian 819/50.
G CCIR 625/50 in 8 MHz UHF channel.
H CCIR 625/50 in 8 MHz UHF channel with vestigial sideband extended to 1.25 MHz.
I UK/Ireland 625/50.
I1 UK/Ireland 625/50 with vestigial sideband reduced to 0.75 MHz.
K OIRT/IBTO 625/50 in 8 MHz UHF channel.
K1 French Outré Mer 625/50.
L French domestic 625/50.
M NTSC 525/60.
N South American 625/50.
Also as previously noted, K’ appears to have been an informal rendering of K1, and L’ (or L1) was an informal designation that was applied to the inverted-channel version of system L used in Band I.
This letter sequence covered most of the analogue TV systems that were used post-WWII for regular broadcasting. One exception was the French 441-line system, use of which ceased in 1956, well before the letters were first assigned. Probably because it was slated for discontinuation by 1958, this French system had not been included in any of the series of CCIR TV System Reports that started in 1951. To recap, the original (1951) list included just four systems, namely those identified from 1961 as A, M, B and E.
In that sequence, system A referred specifically to the vestigial sideband version of the UK 405-line standard, which dated from 1948. So one could also say that strictly speaking, the system A designation should not be applied to the original double-sideband version of the UK 405-line system, use of which ceased in 1956. The ITU/CCIR/ITU-R consistently differentiated between otherwise similar systems, with the same intercarrier spacing, that differed in respect of the bandwidth of one of both vision sidebands, and which co-existed. That shows up in the D and D1, G and H, I and I1 and K and K1 designation pairs. From that one may reasonably infer that had a letter designation been given to the double-sideband 405-line system, it would have been different to that of the vestigial sideband version.
It is worth reiterating that this letter designation system had very ad hoc origins, hence its somewhat erratic nature. The pertinent ITU ST61 working group need a shorthand way of identifying the six different 625/50 variants that were being proposed for UHF use in Europe. Initially these were assigned the letters A through F in what was a logical sequence. Inter alia, these letters were to be used in the tabular UHF geographical channel assignment lists that were a major output of ST61. Quite late on, it was evidently realized that the European VHF systems, would need to be similarly identified, as tabular VHF geographical frequency assignments were also to be an ST61 output. Thus, and rather summarily it appears, only those VHF systems pertinent to Europe (hence excluding NTSC 525/60) were assigned letters in the same (not entirely logical) sequence as they had appeared in CCIR Report #124. These took up the letters A through F, with the result that the UHF systems were reassigned with letters starting from G. What had been initially assigned as system E, a proposed variant of the OIRT/IBTO 625/50 system with vestigial sideband extended to 1.25 MHz, was omitted from the definitive list as it was not nominated for actual use. So there were five UHF systems that were assigned the letters A through L excluding J (presumably because J was not in the Italian alphabet).
This expedient-at-the-time approach by ITU proved to be short-sighted. Shortly thereafter it was necessary to expand the letter sequence to include NTSC 525/60, and also the South American 625/50 variant, which had not appeared in any CCIR list. These were “tacked-on”, as it were, at the end of the list as systems M and N. Then the modified OIRT/IBTO 625/50 variant that had been dropped from the definitive 1961 list resurfaced as the French Outré Mer system in 1963, and had to be “shoehorned” into the sequence as system K1. That established the precedent of using the suffix number 1 attached to the letter as a variant differentiator.