As mentioned above, I have also delved a little into the origins of and reasons for quasi-split sound (QSS). Of the various references on hand, Benson & Whitaker (1) turned out to be the best starting point. In particular it pointed to a 1981 August IEEE paper, “Intercarrier Buzz Phenomena Analysis and Cures”, by Fockens and Eilers of Zenith (2). This was quite detailed. One conclusion was that to minimize buzz when audio subcarriers were used, it was desirable inter alia to eliminate the Nyquist-slope-caused IPM of the vision carrier, which thus outruled the conventional intercarrier technique. Various alternatives that avoided the problem were suggested, including quasi-split sound, also referred to as quasi-parallel sound. It was noted that there had been reports of dual-output SAW devices that could provide the required output.
This puts 1981 or perhaps a little earlier as the likely time in which the QSS was first developed and named as such. This timing is supported by the Plessey Consumer Integrated Circuit Handbook, March 1981 edition (3). This included advance information on a new SAW filter, the SW185 that had two output ports, one being suitable for QSS. The SW185 was shown paired with the developmental XL1441 IC, which appeared to be a dual-channel device handling both the vision IF and the QSS IF, and providing both video and intercarrier outputs. In that sense it followed the pattern of the SL1440, about which more later. The SW185 was also shown paired with the TDA2541 (for vision IF) and the TDA440 (for QSS IF). The TDA440 was itself a vision IF IC, but given that its normal deployment would include provision of the intercarrier as well as video baseband, its use for the QSS IF channel would seem to have been reasonable. A logical inference is that at the time, there were no industry-standard dedicated QSS IF ICs available. The TDA440 was on Plessey’s list of TV IF ICs, although the TDA2540/TDA2541 was its preferred type. The choice of TDA440, not TDA2541 for the QSS IF channel might have been because it was better in this role, or perhaps because unlike the TDA2541, it did not include the AFC function, which would have been redundant. Plessey used the term “parallel sound”, not QSS, in respect of the SW185. Perhaps the QSS term had not been coined in early 1981, but the Plessey had previously used “parallel sound” in connection with its SL1440 IC. Curiously the Plessey Television IC Handbook, April 1981 edition made no mention of the SW185 or the XL1441, although it did include the SL1440.
Plessey seemed to be a reasonable “place” to look because it seemed to have “majored” in SAW filters, which are a key part of QSS. But clearly Philips/Mullard was likely to have been an early mover with QSS circuits, as well. The Mullard Technical Handbook Book 4, Part 2, “Bipolar ICs for Video Equipment”, January 1983 edition confirms this. Both the TDA2545 (QSS IF) and TDA2546 (QSS IF with 5.5 MHz demodulation) were listed as development items, and in both cases the pages were dated May 1981. The term QSS was used, and one suspects that there is some chance that it was actually coined by Philips/Mullard. Possibly then the latter also introduced the idea of using the reference in phase quadrature for intercarrier generation, something that did require a dedicated IC.
Benson & Whitaker also referred to an August 1982 IEEE paper, “New Color TV Receiver with Composite SAW IF Separating the Sound and Picture Signals”, by Yamada and Uematsu of Hitachi (4) as an example of QSS. But this was around a year later than the European developments. The paper focussed on the two-output-port SAW filter; the sample circuit used an HA11440 vision IF IC and a µPC1366C QSS IF IC. I think that the latter might have been a vision IF IC pressed into QSS service, similar to one of Plessey’s approaches, which suggests that at the time, the Japanese industry was yet to produce a dedicated QSS IC.
Another Japanese example was the Sony Profeel VTX100ES component TV tuner, which covered Systems B/G/H and Zweiton stereo sound. The schematic from March 1982 shows the use of separate SAW filters for the vision IF and QSS IF channels. The vision IF used a TA7607AP IC, whereas the QSS used a TDA2840. The latter was a Siemens IC that appears to have been functionally similar to the Philips/Mullard TDA2545, although I have not been able to trace any detailed information on it. I should imagine though, that Siemens would have been an early mover in the QSS IC field. Sony’s use of a European IC for QSS would seem to confirm the lack of a Japanese supply source at the time. As an aside, I have seen it stated that the (Toshiba) TA7607AP was essentially the same as the Philips TDA2544, a probably lesser known variant in the TDA254x series that was the same as the TDA2540/1, except that the RF agc output was configured for mosfet vhf tuners, which were common in Japanese and North American practice. Possibly so, as that was an era when Japanese ICs were often developments of western counterparts; one thinks of the Hitachi and Toko works that were based upon the CA3089 (FM IF subsystem) and MC1310 (PLL MPX decoder), and as recorded in the Ambit catalogues of yore.
So the foregoing establishes 1981 as the year in which the QSS technique arrived in commercially usable form, and that it was an essentially European development. That was also, I think, the year in which the IRT Zweiton TV stereo sound broadcasts started in Germany, so it does suggest that the two are linked. The reasons for using QSS (or at least not using the conventional intercarrier technique) are well covered in the Fockens and Eilers paper, although I imagine that there were European papers that covered the same ground. TV stereo sound arrived a little later in the USA, and it would appear that where QSS was used, European practice was followed (5).
TV stereo sound started in 1978 in Japan, using the FM-FM system, which raises the question as to what was done there prior to the arrival of QSS in the way of overcoming the conventional intercarrier sound problems, which per the above-mentioned Hitachi paper were known to exist. I don’t have definitive information, but from what I can glean, one approach, by Matsushita, was to adopt PLL fully-synchronous vision demodulation with a very narrow reference bandwidth, the latter effectively disposing of the Nyquist slope problem, and so allowing the production of a “clean” intercarrier from the vision demodulator. In the US, National Semiconductor, who developed a set of ICs for the US BTSC TV multichannel sound system, advocated the same approach. Another approach was to revert to the split sound technique. Sony did this for the VTX-1000R US version of its Profeel TV tuner, which I imagine was based upon a Japanese domestic model. The sound carrier was separated ahead of the vision IF SAW filter, and then down converted to 10.7 MHz for amplification and demodulation. The down conversion frequency changer included a VCO that was “steered” by afc from the FM demodulator. But the VTX-1000R also included a secondary, conventional intercarrier sound circuit for use when receiving cable and other transmissions significantly contaminated with incidental phase modulation (IPM) on both vision and sound carriers, this being self-cancelling with conventional intercarrier (and QSS) but not with split sound, nor with intercarrier derived from narrow-band PLL vision demodulation. I wonder if Japanese TV transmissions of the era were generally very “clean” in an IPM sense, such that split sound was usable without the intercarrier backup.
Now returning to Plessey’s endeavours, it seems to have had something of a false start in 1978 or thereabouts with its SW180 SAW filter and SL1440 IF IC. As I recall, these were covered in a Television magazine article of the time – which I no longer have or at least cannot find - that also announced the SL1431/2 if preamplifier ICs that were intended to drive SAW filters. The SW180 separated the vision and sound carriers which had separate output ports, that for sound containing only the sound carrier. The SL1440 IF IC had two channels, one each for vision and sound, the former producing video baseband and the latter intercarrier. Each channel was described as having a wideband, switching demodulator, which I should take to mean that they were of the quasi-synchronous type without tank circuits. The sound demodulator was switched by limited carrier from the vision channel. Thus the SL1440 did not solve the Nyquist slope problem. Possibly Plessey thinking was that avoiding co-processing of the vision and sound carriers in the later IF stages was a key desideratum. Anyway, it would appear that the SL1440 was not taken up by the setmakers in a significant way, and faded from the scene. The XL1441 mentioned above appears to have been a true QSS development of the SL1440, also with the apparent addition of a tank circuit on the vision side. Interestingly though, the SW180 type of SAW filter reappeared with the later advent of single-reference QSS systems, out-of-scope for this posting.
An interesting reference included in the Fockens and Eilers paper was another IEEE paper, “A System Approach to Synchronous Detection”, by Rzeszewski of Quasar, 1976 (6). This studied the errors, primarily in respect of vision demodulation, that arose from the wideband, Nyquist slope-affected reference in conventional quasi-synchronous demodulation. Although the primary recommendation was to use a narrow band reference channel as could be achieved with PLL fully synchronous demodulation, it was noted that the quasi-synchronous system could be improved by re-establishing the double sideband integrity of the vision carrier in the reference channel before amplitude limiting. And that was exactly what was done with QSS, but then only in respect of the sound channel, established practice being retained as far as the vision IF channel was concerned.
It is interesting to note that the 1969 Motorola paper (7) on the original vision synchronous demodulation IC, the MC1330, it was noted that given the separation of the signal and the switching channels, it was possible to operate on the latter by the use of selective circuits, and a diagram was shown with such selective circuits both ahead of and behind the limiter. Although not elaborated as such in the paper, the pre-limiter selective circuit provide the opportunity to neutralize the Nyquist slope in the reference channel. In practice though the MC1330 made provision only for a post-limiter selective circuit, in practice the customary tank circuit, as the connection from the vision IF amplifier to the limiter was fully internal. In hindsight it looks to have been an opportunity missed, but the same arrangement was repeated on subsequent vision quasi-synchronous demodulation ICs, including the TBA440 et seq, the TCA270 and the TDA254x et seq.
Motorola’s next effort was the MC1331 in 1974 (8). This was essentially an MC1330 with detailed improvements, and with the addition of a separate multiplier for intercarrier generation, the idea being that the sound carrier was trapped out ahead of the vision demodulator, so reducing the sound-colour subcarrier beat in the vision channel. But both the vision demodulator and the sound carrier multiplier were still fed internally by the vision carrier limited without prior correction of the Nyquist slope, so there was no step forward in that direction.
I am not sure that Nyquist-slope-corrected quasi-synchronous vision demodulation, as advocated by the Quasar paper, was ever widely adopted for consumer TV receivers. Rather the more general use of PLL fully synchronous vision demodulation in the later analogue years addressed the issue.
Nevertheless, a professional example is provided by the BBC RC1/511 receiver, as shown in block diagram form in Wireless World July 1984, p.39, copy attached. Here there was a separate vision carrier reference channel that was appropriately tailored and used both for vision demodulation and generation of what is called a “true intercarrier”. Evidently a similar approach was used for the RC5M-503 UHF Rebroadcast receiver (see: http://www.bbceng.info/EDI%20Sheets/10548.pdf
), for which it was stated: “Selectivity and Nyquist shaping are obtained by the use of a specially developed surface acoustic wave (SAW) filter, and no IF alignment is required. A second SAW filter extracts the vision IF carrier, and the amplitude modulation is removed by low-phase-shift limiters; the resulting carrier is used to demodulate the vision signal. This "exalted-carrier", or "pseudo-synchronous", demodulation means that the effect of any incidental phase modulation (IPM) present on the input is greatly reduced.” Interestingly the RCM-503 replaced earlier rebroadcast receivers, RCM-501 and RCM-502, that had used fully synchronous vision demodulation.
It may also be noted that occasionally, the Nyquist slope issue in respect of intercarrier generation had been addressed in the past in the pre-IC days. The Bang & Olufsen 3000 series was an example. It had a discrete bipolar vision IF strip with a side chain that branched off after the 2nd main IF stage, and led to the separate diode demodulator that provided the chroma and intercarrier signals. The overall frequency response of the sidechain was peaked on the vision carrier with the colour subcarrier about 12 dB down, and the sound carrier further down (9). I think that the main objective was to keep the vision carrier sufficiently higher than the subcarrier to minimize single sideband distortion, but the sound also benefitted because the intercarrier was formed with a “reference” that was devoid of the Nyquist slope.
(1) K.B. Benson, revised by J.C. Whitaker; “Television Engineering Handbook”, Revised Edition; McGraw-Hill, 1992; ISBN 0-07-004788-X
(2) “Intercarrier Buzz Phenomena Analysis and Cures”; P. Fockens & C.G. Eilers, Zenith Radio Corporation; IEEE Transactions on Consumer Electronics, Vol CE-27, No. 3, August 1981.
(3) Plessey Consumer Integrated Circuit Handbook, March 1981 may be found on-line at: http://archive.org/details/ConsumerInte ... itHandbook
(4) J. Yamada & M. Uematsu, Hitachi Ltd; “New Color TV Receiver with Composite SAW IF Separating the Sound and Picture Signals”; IEEE Transactions on Consumer Electronics, Vol CE-28, No. 3, August 1982.
(5) See: S. Prentiss; “AM Stereo & TV Stereo New Sound Dimensions”; TAB Books, 1985; ISBN 0-8306-1932-1.
(6) T. Rzeszewski, Quasar Electronics Corporation; “A System Approach to Synchronous Detection”; IEEE Transactions on Consumer Electronics, May 1976.
(7) G. Lunn, Motorola, Inc.; “A Monolithic Wideband Synchronous Video Detector for Color TV”; IEEE Transactions, Vol. BTR-15, No. 2, July 1969.
(8) M.E. Wilcox, Motorola, Inc.; “A New TV Video/Sound Detector IC”; IEEE Transactions on Broadcast and Television Receivers, Vol. BTR-20, Issue 1, 1974.
(9) As described in: G.J. King; Colour TV Servicing Manual Volume One; Newnes-Butterworths, 1973; ISBN 0 408 00089 9.