24-06-2017, 11:39 PM
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
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
