French dual standard TV's.

[ppppenguin]

Though the decoder was only part of the problem. The IF was also tricky for multiple standards.

[Terry]

If you take 819-lines out of the equation, it isn't so bad. Stick to a common vision IF and arrange rejectors accordingly. It wouldn't do any great harm for System I, for example, to retain the System B/G/H bandwidth and mix the intercarrier sound with an 11.5MHz oscillator to convert the 6MHz to 5.5MHz.

Also, this is the era of the SAW filter. I've seen switchable DTV SAWs for 7/8MHz channel widths so it would probably be just as easy to produce a multiband version for analogue IF - or use more than one SAWF.

It would be interesting to see a service manual for one of these sets ...

[Synchrodyne]

For a multisystem but 625-only receiver, the IF strip complexity would depend somewhat upon whether one adopted a “lowest common denominator” approach or made an effort to get the vision frequency response and group delay right for each system.  The French System L’ channels, being inverted, presented something of a problem.

There were switchable SAWFs that provided various combinations of two IF bandpass characteristics.  And there were also dual-Nyquist SAWFs that accommodated a vision-low IF channel for L’ as well as a regular channel.  And some manufacturers did use frequency-switchable tank circuits for quasi-synchronous demodulators.

Second conversion in the sound channel required some care in frequency selection for the 2nd IF, although the better screening that was possible with solid state circuitry eased the problem of undesirable spurs.  Perhaps in that case it was better to convert directly from the sound IFs themselves to a common lower frequency than from one intercarrier frequency to another.  There is evidence that a 2nd sound IF of 10.7 MHz, taboo in valve days, was doable with well-screened solid-state circuitry.  But another possibility was to use a separate TBA120 or similar IC for each intercarrier frequency.  In later days, single ICs that covered multiple sound standards also became available.  Covering the Zweiton and NICAM (of which there was more than one variant) multichannel sound systems as well added more complexity.
  
There was some discussion of multistandard receiver IFs here:  http://www.forum.radios-tv.co.uk/viewtopic.php?f=5&t=3742&sid=dcb94559b472b4d63271abc091c6ba82.

I have a .pdf of the service manual for the Sony Profeel VTX-100M multistandard TV tuner, which covered Systems B/G/H, D/K, I, L/L’ and M, with Zweiton sound capability.  It was nominally a high-quality unit, but perhaps missed a point here and there.  Please PM me if you want a copy.

Cheers,

Steve

[colly0410]

Wonder why Belgium used pre-emphasis on it's AM TV sound Systems? & UK & France never did?

[Synchrodyne]

The definitive answer to that question may well be lost in history.

Historically, AM broadcasting systems did not have standardized pre-emphasis and de-emphasis curves, and that was probably the reason why the UK 405-line system (which predated FM broadcasting) did not have pre-emphasis.

The triangular noise structure of FM made pre-emphasis and de-emphasis highly desirable.  The original US number (evidently attributable to work by Crosby) was 100 microseconds, but BBC work showed that 50 microseconds was better.  I suspect that Russian work at the same time or perhaps even a bit earlier also supported 50 microseconds.  The US changed to 75 microseconds in 1945.

On the face of it, the same benefits of pre-emphasis as obtained with FM would not apply to AM with its square noise characteristic.  But some work was done, and Tibbs & Johnstone, in “Frequency Modulation Engineering”, recorded that a small benefit was available by applying pre-emphasis to AM systems:

   

That is from the 1955 2nd edition.  I don’t have the 1947 1st edition, but I imagine that it had the same commentary.

Against that background, one might infer that those who set the parameters for the French 819-line system did not regard pre-emphasis of the AM sound channel as bringing enough benefits to justify it.  Perhaps too there was some inertia in that the 441-line system then in operation did not have pre-emphasis.

The Belgians evidently saw it differently, and without any potentially constraining precedent decided that whatever small benefits came with AM pre-emphasis were worth doing.  That decided, then there was probably no good reason to use other than the 50-microsecond number already established for FM systems in Europe.  One possible benefit in TV receivers is that any extraneous line frequency signal that gets into the sound channel ahead of the AF section will be significantly suppressed by the de-emphasis circuit.  This was of greater significance for 625 lines, where the line frequency, 15 625 Hz, was just above the wanted AF range, presumed to extend to 15 kHz.  It would have been less of an issue with 819 lines, as the normal AF response could be expected to be quite a bit down at 20 475 Hz.  So, the Belgians, with 625 and 819 line systems, had more reason to use pre-emphasis than did the French for their 819-line system.    

The French 625-line system was designed to have maximum commonality with the existing 819-line system in order to make easier the design of dual-standard receivers.  That’s why it was a positive/AM system at a time when negative/FM was the norm.  Accordingly, the AM sound was not pre-emphasized in order to maintain commonality with the 819-line system.
 
Note that the French adopted negative/FM (System K’) for their Outré-Mer territories, where backward compatibility with 819 lines was not an issue.  The choice of a 1.25 MHz vestigial sideband for Systems L and K' was in line with thinking at the time.  But its combination with a 6 MHz main sideband, thus “overfilling” the 8 MHz channel, was an interesting one.   My guess, and it’s only that, is that it was done because it allowed enough room for symmetrical subcarrier sidebands for the SECAM colour system.  The original SECAM proposal, for 819 lines, used simple AM for the subcarriers, and I think assumed simple envelope demodulation.  As is well-known, simple AM demodulators produce significant distortion when presented with asymmetrical sideband signals.  The SECAM system was changed to FM subcarriers quite early on, but there could have been some reluctance to have asymmetrical sideband FM, at least with conventional FM demodulators of the period.

In more recent times, standardized pre-emphasis has been applied to MF AM broadcasting.  In the USA, the NRSC standard, published in 1986, was adopted in 1987.  This applied 75 microseconds pre-emphasis, with a shelf at 8.7 kHz and a cutoff at 10 kHz (whereas previously 15 kHz was allowed).  This was predicated on the basis of obtaining the optimum results in the conditions then prevailing.  Part of the thinking seems to have been that the 75-microsecond de-emphasis roll-off could be included in the receiver IF filter curve, thus allowing better overall selectivity than would be conferred by an IF curve that was flat to plus/minus 10 kHz.  Though the bandwidth restriction to 10 kHz was not welcomed by some “quality” AM broadcasters who had previously transmitted out to 15 kHz.  The NRSC standard was adopted elsewhere, such as by the ABC in Australia.

Sometime before the NRSC standard was promulgated, NHK in Japan was using 100 microseconds pre-emphasis for its MF broadcasts, but I don’t know the background to this.  Perhaps this number was chosen to offset somewhat the narrow IF selectivity curves of typical AM receivers.

In summary, whereas for FM systems, pre-emphasis is de rigueur, with AM systems its benefits are essentially situational, which probably accounts for its selective use.

Cheers,

Steve

[Geordie McBoyne]

I believe a certain French TV manufacturer made a 405/819 line receiver for viewers living in Northern France and possibly the Channel Islands. To make such a receiver would certainly impose difficulties in the design of the line output stage.
Many later production 819 line receivers were only good for 7Mhz bandwidth.

Geordie McBoyne.

[ppppenguin]

People who lived on the south coast could pick up 819 TV on their 405 sets. You got 2 pictures side by side and no sound but it must have been exciting at the time.

The reason it worked is that 819 is almost exactly twice 405 so the line scan frequency was also almost double that of 405.

On the one occasion I saw 819 TV "for real" it was in Brussels with mediocre reception. Probably c1969. I was struck by the lack of line whistle. The programme was "The Forsyte Saga" dubbed into French.

[Synchrodyne]

Such 819/405-line dual-standard receivers were mentioned in this Wireless World (WW) article from 1962 October:

   

Presumably the French setmakers had already had some practice with a 2:1 or thereabouts line frequency ratio, because in the early days (1951) there were some 819/441-line dual-standard receivers:

   

819/625 line multistandard receivers for the border areas arrived quite early, by 1954.  Thus, the French setmakers gained some experience in this area well before 819/625-line dual-standard receivers became the norm in the early 1960s:

   

   

And by the end of the 1950s, 819/625/405 line multistandard receivers were available:

   

   


Cheers,

Steve

[Synchrodyne]

On the one occasion I saw 819 TV "for real" it was in Brussels with mediocre reception. Probably c1969.  I was struck by the lack of line whistle. The programme was "The Forsyte Saga" dubbed into French.

Ah yes, the original Forsyte Saga with good performances from Eric Porter and Nyree Dawn Porter, and a memorable one from Susan Hampshire as Fleur; perhaps with even more of the chienne when translated into French.  We have the DVD in our yet-to-be-watched stack of "let's see how well they travelled" older dramas.  A few years back we looked at "The Lotus Eaters" and "Who Pays the Ferryman", and both remained as good as I remembered them. 

Anyway, I digress.  Back to 819 lines; 7 MHz receiver vision bandwidth for the System E receivers does seem a bit rude.  Horizontal definition would be no better than 625 with 5.5 MHz.

Cheers,

Steve        

[Terry]

The programme was "The Forsyte Saga" dubbed into French.

In 1980, I was doing acceptance testing at Barco's factory in Kortrijk on some special receivers they were making for us and we were invited round to the factory manager's house one night together with a couple of young lads from their UK distributor.

During the course of the evening, one of these lads asked "What is the difference between the Flemish and the Walloons?"

Anything could have happened at this point but Joel just switched on the TV! He started going round the Dutch and Flemish channels and came across an episode of "Soap" on one of the Dutch channels in the original American with Dutch subtitles. One of the Flemish channels was showing a BBC programme - I can't remember which - in English with Dutch* subtitles.

He then moved onto the French language channels and found something which he couldn't have possibly planned. A western, with Lee Marvin marching down the sidewalk, crashing through the bat-wing doors as he strode into the saloon, marching up to the bar and smashing his fist down on the bar. At this point he opened his mouth and this squeaky high-pitched French voice came out! 

It was so out of character that we all just roared with laughter at such an inappropriate choice of voice.  

The point Joel was making was that the Dutch language networks would show any imported material with subtitles and the original sound whereas the French language networks on both sides of the border refused to buy imported material unless it had been dubbed into French. 

One small difference but an interesting way of neatly sidestepping an innocent question which could open up a veritable minefield!

* Flemish is actually a number of dialects of Dutch. There are considerable differences between them so all Flemish broadcasting uses the high level language, Dutch.

Last year there was a big awards ceremony in Antwerp which was hosted by a local celebrity who'd been a winner of Belgium's Got Talent or some-such.

She did the entire programme in the local dialect which two thirds of the TV audience couldn't understand and BRT was inundated with angry phone calls!