15-03-2018, 01:12 AM
Belgian TV receivers were four-system from the start in 1953, covering Systems B, C, E and F. The reason for System F with its overly narrow vision bandwidth was that all Belgian transmitters had to be able to broadcast either 625- or 819-line signals according to the incoming programme format, although 625 and 819 were nominally standard for Flanders and Wallonia respectively. For more detail, see Wireless World (WW) 1956 November pp. 559 through 562, “Four-Standards Television”. With the advent of UHF, five-system receivers were introduced, covering Systems B/G/H, C, E, F and L.
Typically, the Belgian multi-system receivers covered only a handful of Band III channels for System E, logically only those that were receivable within Belgium. Given that they used a vision-high IF, then including the Band I channels F2 and F4 in the tuning range would have been awkward to say the least. Channel F3 would have been possible, but although nominally allocated at ITU Stockholm 1952, that channel was rendered unusable by the French decision to standardize on a vision-low IF, in place of previously-used double-ended IF strips.
French border-area multi-system TV receivers appear to have started out with the so-called Strasbourg models in the mid-1950s, but as best I can determine design generally coalesced around the Belgian approach. But there were one or two that also covered System A, so those must have had IF arrangements that also accommodated inverted Band I channels. I suspect too that the French makers of multi-system receivers may have made more effort to obtain reasonable visions bandwidths (at least well above 5 MHz, say around 7 MHz or so) on their own System E. The Belgian makers may have seen less need to have the System E pictures any better than those of System F.
The Argentinean System N appears to have had its origins in the experimental American-origin 625-line transmitter installed at Torino, Italy in 1949. This operated in channel A6 (82 to 88 MHz) and basically followed the NTSC standard except that it was 625/50 instead of 525/60. So that set a precedent for Argentina, whose regular TV service started in 1951, ahead of that of most Western European countries. Evidently adhering to the same American channel allocation pattern throughout South America was considered to be of overarching importance.
At the time, the prevailing thought, derived from the 1941 NTSC deliberations, was that there was quite a bit of flexibility in the relativity between vertical and horizontal definitions, and that it was paramount to have a line count that was sufficiently high to avoid undue “lininess” and to provide adequate flatness of the field. Thus Donald Fink moved the NTSC thinking from 441 to 525 lines. The NTSC 6 MHz channel was evidently seen as attractive by some in Europe, but by others seen as not enough for 625 lines. The Philips 567-line proposal was an effort to provide an optimum line count for a 6 MHz channel with 4 MHz vision bandwidth. However reasonable it might have been, it was surely doomed as a lower line count than the 625 already used by the Russians was hardly likely to fly. As best I can determine the debate within the CCIR Gerber sub-committee was between a 6 MHz channel with 4.25 MHz vision bandwidth and a 7 MHz channel with 5 MHz bandwidth. The Russian 8 MHz channel with 6 MHz vision bandwidth seems to have been dismissed as probably “too expensive” in bandwidth terms and perhaps for political reasons as well. That the apparent lower option studied by Gerber was 4.25 MHz was interesting, given that NTSC was then 4 MHz. One may deduce that its proponents saw that 4 MHz was a “bit thin”, so as to speak, and wanted to push out to a barely possible limit. NTSC moved out to 4.2 MHz with the advent of colour in 1953. The Gerber decision seems to have been somewhat of the “political” art-of-the-possible kind, as the 7 MHz channel was really on the short side.
System N was also one of the contenders for Japan, where NTSC won the day. Italy adopted the 7 MHz channel, but the legacy of that experimental transmitter was that its channel frequency was more-or-less retained, adjusted to 81 to 88 MHz, as Italian channel C. Early on Italy also followed American practice by adopting a standard IF channel of 40 to 47 MHz with 45.75 MHz vision carrier (the American “high” IF channel was 41 to 47 MHz with 45.75 MHz vision carrier), and this meant that it could not use the lower end of Band I. I suspect that interference possibilities stemming from this choice of IF led to the non-standard spacings of its Band III channels.
As far as I know, System N retained the NTSC “6-pack” equalizing pulse structure until the end. System B started that way, but moved over to the “5-pack” in the early-to-mid 1950s. System D probably followed a bit later, but System C was “5-pack” from the start.
System N also had the NTSC FM sound parameters of ±25 kHz deviation and 75 µs pre-emphasis. These were the 1945 NTSC numbers; the original 1941 version having been ±75 kHz and 100 µs. The ±50 kHz and 50 µs numbers used in Europe might have come from the original Russian 625-line work. Certainly Russia used the same numbers for its Band I FM sound broadcasting (and for which combination the Zenith-GE stereo system apparently did not work well enough, hence the development of the alternative polar modulation system). Early FM broadcasting work by the BBC circa 1944-45 showed that 50 µs was better than 100 µs (with later work showing that 50 µs was still better than 75 µs) so that also might have been the origin of the 50 µs pre-emphasis number.
The UK TAC realized that the Gerber standard was a bit short on vision bandwidth, and was originally thinking in terms of the Russian 8 MHz channel with 6 MHz vision bandwidth. But the Russians appeared to have overlooked the desirability of proportionality between the main and vestigial sidebands, simply taking the established NTSC VSB number of 0.75 MHz and using it with a 50% wider main sideband. On the other hand, the French opted for a 2.0 MHz VSB to match their 10.4 MHz main sideband in the 819-line system. So the TAC opted for a 1.25 MHz VSB with a 5.5 MHz main vision sideband within an 8 MHz channel. The French combined the 1.25 MHz VSB with a 6.0 MHz main sideband for Systems L and K’, by dispensing with the outer guard bands, which is what they had done previously when the definitive tête-bêche channelling for the 819-line system adopted 13.15 MHz channel spacing in place of the original 14 MHz.
Interestingly, Donald Fink, in one of his later writings, suggested that 8 MHz would have been the optimum analogue TV transmission channel width. But the American 6 MHz was one of the fixed parameters handed to the first NTSC, so was not up for reconsideration.
Cheers,
Typically, the Belgian multi-system receivers covered only a handful of Band III channels for System E, logically only those that were receivable within Belgium. Given that they used a vision-high IF, then including the Band I channels F2 and F4 in the tuning range would have been awkward to say the least. Channel F3 would have been possible, but although nominally allocated at ITU Stockholm 1952, that channel was rendered unusable by the French decision to standardize on a vision-low IF, in place of previously-used double-ended IF strips.
French border-area multi-system TV receivers appear to have started out with the so-called Strasbourg models in the mid-1950s, but as best I can determine design generally coalesced around the Belgian approach. But there were one or two that also covered System A, so those must have had IF arrangements that also accommodated inverted Band I channels. I suspect too that the French makers of multi-system receivers may have made more effort to obtain reasonable visions bandwidths (at least well above 5 MHz, say around 7 MHz or so) on their own System E. The Belgian makers may have seen less need to have the System E pictures any better than those of System F.
The Argentinean System N appears to have had its origins in the experimental American-origin 625-line transmitter installed at Torino, Italy in 1949. This operated in channel A6 (82 to 88 MHz) and basically followed the NTSC standard except that it was 625/50 instead of 525/60. So that set a precedent for Argentina, whose regular TV service started in 1951, ahead of that of most Western European countries. Evidently adhering to the same American channel allocation pattern throughout South America was considered to be of overarching importance.
At the time, the prevailing thought, derived from the 1941 NTSC deliberations, was that there was quite a bit of flexibility in the relativity between vertical and horizontal definitions, and that it was paramount to have a line count that was sufficiently high to avoid undue “lininess” and to provide adequate flatness of the field. Thus Donald Fink moved the NTSC thinking from 441 to 525 lines. The NTSC 6 MHz channel was evidently seen as attractive by some in Europe, but by others seen as not enough for 625 lines. The Philips 567-line proposal was an effort to provide an optimum line count for a 6 MHz channel with 4 MHz vision bandwidth. However reasonable it might have been, it was surely doomed as a lower line count than the 625 already used by the Russians was hardly likely to fly. As best I can determine the debate within the CCIR Gerber sub-committee was between a 6 MHz channel with 4.25 MHz vision bandwidth and a 7 MHz channel with 5 MHz bandwidth. The Russian 8 MHz channel with 6 MHz vision bandwidth seems to have been dismissed as probably “too expensive” in bandwidth terms and perhaps for political reasons as well. That the apparent lower option studied by Gerber was 4.25 MHz was interesting, given that NTSC was then 4 MHz. One may deduce that its proponents saw that 4 MHz was a “bit thin”, so as to speak, and wanted to push out to a barely possible limit. NTSC moved out to 4.2 MHz with the advent of colour in 1953. The Gerber decision seems to have been somewhat of the “political” art-of-the-possible kind, as the 7 MHz channel was really on the short side.
System N was also one of the contenders for Japan, where NTSC won the day. Italy adopted the 7 MHz channel, but the legacy of that experimental transmitter was that its channel frequency was more-or-less retained, adjusted to 81 to 88 MHz, as Italian channel C. Early on Italy also followed American practice by adopting a standard IF channel of 40 to 47 MHz with 45.75 MHz vision carrier (the American “high” IF channel was 41 to 47 MHz with 45.75 MHz vision carrier), and this meant that it could not use the lower end of Band I. I suspect that interference possibilities stemming from this choice of IF led to the non-standard spacings of its Band III channels.
As far as I know, System N retained the NTSC “6-pack” equalizing pulse structure until the end. System B started that way, but moved over to the “5-pack” in the early-to-mid 1950s. System D probably followed a bit later, but System C was “5-pack” from the start.
System N also had the NTSC FM sound parameters of ±25 kHz deviation and 75 µs pre-emphasis. These were the 1945 NTSC numbers; the original 1941 version having been ±75 kHz and 100 µs. The ±50 kHz and 50 µs numbers used in Europe might have come from the original Russian 625-line work. Certainly Russia used the same numbers for its Band I FM sound broadcasting (and for which combination the Zenith-GE stereo system apparently did not work well enough, hence the development of the alternative polar modulation system). Early FM broadcasting work by the BBC circa 1944-45 showed that 50 µs was better than 100 µs (with later work showing that 50 µs was still better than 75 µs) so that also might have been the origin of the 50 µs pre-emphasis number.
The UK TAC realized that the Gerber standard was a bit short on vision bandwidth, and was originally thinking in terms of the Russian 8 MHz channel with 6 MHz vision bandwidth. But the Russians appeared to have overlooked the desirability of proportionality between the main and vestigial sidebands, simply taking the established NTSC VSB number of 0.75 MHz and using it with a 50% wider main sideband. On the other hand, the French opted for a 2.0 MHz VSB to match their 10.4 MHz main sideband in the 819-line system. So the TAC opted for a 1.25 MHz VSB with a 5.5 MHz main vision sideband within an 8 MHz channel. The French combined the 1.25 MHz VSB with a 6.0 MHz main sideband for Systems L and K’, by dispensing with the outer guard bands, which is what they had done previously when the definitive tête-bêche channelling for the 819-line system adopted 13.15 MHz channel spacing in place of the original 14 MHz.
Interestingly, Donald Fink, in one of his later writings, suggested that 8 MHz would have been the optimum analogue TV transmission channel width. But the American 6 MHz was one of the fixed parameters handed to the first NTSC, so was not up for reconsideration.
Cheers,
