07-07-2017, 09:19 PM
Some information on French border area multistandard TV receivers may be found at: http://tsf-schoser-2.e-monsite.com/pages...nes-page1/.
In the VHF-only era, the examples shown seemed to have followed the Belgian four-standard precedent, with a vision IF of 38.9 MHz for all systems, a sound IF of 33.4 MHz for systems B, C and F, and 27.75 MHz for system E. One would hope that system E, being the French national standard, was given a reasonable vision bandwidth, well above 5 MHz.
Also, as in the Belgian case, only the Band III system E channels were covered. The Band I channels F2 and F4, both vision-high would have been difficult to accommodate given that the IF was also vision-high.
In Belgium (and Luxembourg), there was no need to cover the French Band I channels, as no transmitters using these were near enough to the borders. But although the Band I channels were not much used in France overall, there were at least a couple of cases where they were assigned to transmitters in other border overlap areas. Thus, multistandard receivers for those areas would have required Band I system E coverage and consequently different IF arrangements. Different IF arrangements would also have been required for those multistandard receivers that also covered UK system A, since in that case the Band I channels would have been of primary interest.
When the VHF-UHF era arrived, again as in the Belgian case, system L had a vision IF of 39.9 MHz, thus allowing its sound IF to be at 33.4 MHz, the same as for systems B, C and F. But unlike the Belgians, who appeared to retain the 38.9/27.75 MHz IFs for system E, in the French case these were moved up to 39.9/28.75 MHz. Thus, the French systems E and L had the same vision IF. I can only speculate as to why this was done. In respect of the IF bandpass, the Nyquist slope at 38.9 MHz would have been based upon a 0.75 MHz vestigial sideband for systems B, C and F, and perhaps was not switched to a shallower slope for the 2.0 MHz vestigial sideband of system E. Thus, system E reception was compromised to some extent. The Nyquist slope at 39.9 MHz would have been based upon a 1.25 MHz vestigial sideband for System L. As this would have been less of a compromise for system E, one may see that there was some logic in using it for that, at least in France where it was a national system.
Two-system 819/405-line receivers probably would not have had the Band I channel difficulty. One may imagine that the standard IFs, 28.05 MHz vision and 39.2 MHz sound were used for 819, with then 35.7 MHz vision and 39.2 MHz sound being the easiest way to accommodate 405. In both cases oscillator-high would be used for the Band I channels.
With the Band III channels of any system, whether, regular or inverted, both oscillator-low and oscillator-high were workable, so that IF channels of the vision-low or vision-high type could be used. With the Band I channels in combination with IFs that were just below the bottom edge of that band, only oscillator-high was workable. So, regular channels, with vision low, required a vision-high IF channel, whereas inverted channels, with vision high (as for systems A, E and L’) required a vision-low IF channel. Where reception of both regular and inverted Band I channels was required, then either a “double-ended” IF strip was needed, or double conversion for the inverted channels (say up to the vicinity of Band III, and then back down again).
Cheers,
Steve
In the VHF-only era, the examples shown seemed to have followed the Belgian four-standard precedent, with a vision IF of 38.9 MHz for all systems, a sound IF of 33.4 MHz for systems B, C and F, and 27.75 MHz for system E. One would hope that system E, being the French national standard, was given a reasonable vision bandwidth, well above 5 MHz.
Also, as in the Belgian case, only the Band III system E channels were covered. The Band I channels F2 and F4, both vision-high would have been difficult to accommodate given that the IF was also vision-high.
In Belgium (and Luxembourg), there was no need to cover the French Band I channels, as no transmitters using these were near enough to the borders. But although the Band I channels were not much used in France overall, there were at least a couple of cases where they were assigned to transmitters in other border overlap areas. Thus, multistandard receivers for those areas would have required Band I system E coverage and consequently different IF arrangements. Different IF arrangements would also have been required for those multistandard receivers that also covered UK system A, since in that case the Band I channels would have been of primary interest.
When the VHF-UHF era arrived, again as in the Belgian case, system L had a vision IF of 39.9 MHz, thus allowing its sound IF to be at 33.4 MHz, the same as for systems B, C and F. But unlike the Belgians, who appeared to retain the 38.9/27.75 MHz IFs for system E, in the French case these were moved up to 39.9/28.75 MHz. Thus, the French systems E and L had the same vision IF. I can only speculate as to why this was done. In respect of the IF bandpass, the Nyquist slope at 38.9 MHz would have been based upon a 0.75 MHz vestigial sideband for systems B, C and F, and perhaps was not switched to a shallower slope for the 2.0 MHz vestigial sideband of system E. Thus, system E reception was compromised to some extent. The Nyquist slope at 39.9 MHz would have been based upon a 1.25 MHz vestigial sideband for System L. As this would have been less of a compromise for system E, one may see that there was some logic in using it for that, at least in France where it was a national system.
Two-system 819/405-line receivers probably would not have had the Band I channel difficulty. One may imagine that the standard IFs, 28.05 MHz vision and 39.2 MHz sound were used for 819, with then 35.7 MHz vision and 39.2 MHz sound being the easiest way to accommodate 405. In both cases oscillator-high would be used for the Band I channels.
With the Band III channels of any system, whether, regular or inverted, both oscillator-low and oscillator-high were workable, so that IF channels of the vision-low or vision-high type could be used. With the Band I channels in combination with IFs that were just below the bottom edge of that band, only oscillator-high was workable. So, regular channels, with vision low, required a vision-high IF channel, whereas inverted channels, with vision high (as for systems A, E and L’) required a vision-low IF channel. Where reception of both regular and inverted Band I channels was required, then either a “double-ended” IF strip was needed, or double conversion for the inverted channels (say up to the vicinity of Band III, and then back down again).
Cheers,
Steve
