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[Sticky] Television Receiver Intermediate Frequencies

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Synchrodyne
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Posts: 519
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Topic starter
 
Here are the Table 3 pages for:
 
Systems B & G, Italy
 
Table 3 Systems B,G Italy
Systems D & K, China
 
Table 3 Systems D, K China
 System I, South Africa
 
Table 3 System I   South Africa

 

This completes the planned set of Table 3 items.
 
Note that I have not issued separate pages for systems C, F and N.  Systems C and F were effectively covered by the systems B, G & H Europe & Worldwide page, and system N by the system M US & Worldwide page. 
 
Cheers, 
Steve
 
Posted : 28/09/2022 6:49 am
Nuvistor reacted
Synchrodyne
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Topic starter
 
Posted by: @synchrodyne

Thanks for the feedback, John.

Yes, I plan to compile a tabulation. In fact I have had several attempts at it so far, none with a satisfactory outcome. My thinking now is to have three tables. One would be a simple list in ascending VIF order, each entry with a comment to indicate with which system(s) it was used, where it was used if it was “geographical”, approximately over what period it was used, and whether or not it was an actual standard number.

The second list would be ordered by system, using the CCIR letter designations, and would show standard and other IFs used for each system.

The third would be a list of standard IFs and their direct and indirect derivatives.

 
After drafting up the second list, mentioned above, I realized that it turned out to be essentially a consolidated version of Table 3, with a reduced amount of information.  It would require nearly as many pages as Table 3 itself to present here.  Ergo I have not taken it to completion.  I think that Tables 1 and 3 between them provide a reasonably accessible summary.
 
There remains some unfinished business in respect of the tables, including:
 
- Second conversion sound IFs where used (mostly in early Belgian practice).
 
- Second sound carriers as used for Zweiton and Nicam.
 
- IFs for TV sound tuners and TV/FM receivers.
 
- IFs for (analogue) TV receivers with double conversion (vision and sound)
 
In respect of the last-mentioned practice, I have accumulated some, but by no means complete information.  I have yet to sift through it more than superficially.  The first step will be to develop the narrative, from which the tabular version may be derived.
 
 
Cheers,
 
Steve 
 
 
Posted : 05/10/2022 9:47 pm
Synchrodyne
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Posts: 519
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Topic starter
 
Multistandard TV Receiver Intermediate Frequencies
 
This thread has covered IFs for multistandard TV receivers to some extent, so this posting is intended as a something of a reprise.
 
The situations in which multistandard receivers were required may be classified thus:
 
1. Where two or more standards were extant in a country at the same time.  This applied in France, Belgium and the UK, for example.
 
2. Where reception of extra-territorial broadcasts of a different standard to national broadcasts was possible and desired.  This applied to many European countries, including but not limited to France, Belgium, Austria and Finland.
 
3. Where multistandard receivers were designed and built for their own sake, sometimes for use anywhere in the world, without priority being given to any one country or region.  Such had been required for shipboard installations quite early on, but became more common for onshore applications from about the 1970s onwards.  To some extent, receivers of this type may have displaced ad hoc multistandard designs during the 1980s.
 
 
 
As to how these cases affected IF choices, in brief:
 
Situation 1: Nominally, equal weighting would be given to the two (or more) national systems.  But where the second system was introduced much later than the first, the IF choice for the incoming system would need to take account of the existing IF in terms of simplifying, as far as reasonably possible, receiver design.
 
Situation 2: Here priority was generally given to the national system(s), and so the IFs for the extra-territorial systems were generally derived from the national system IFs, taking into account the need for receiver simplification.  That the extra-territorial IFs departed from the respective system optimums was of lesser consequence, given that only a small number of extra-territorial stations would be receivable in any given location.
 
Situation 3: This was basically the receiver designer’s choice, perhaps influenced by domicile.  In practice, the 38.9 MHz “CCIR” VIF was often used as the anchor point.
 
 
Receiver technology also affected IF choices where two or more standards were involved.  In the valve and early solid state era, when untuned diode demodulators were used for vision, it was not so difficult to have two different VIFs handled by the same demodulator.  Sound IF channels were usually narrow enough that separate tuning was required where more than one SIF was involved, although with AM sound a single diode demodulator could handle two or more frequencies.  With FM sound, tuned demodulators were used, typically requiring one per frequency.
 
Quasi-synchronous vision demodulators arrived early in the IC era, and these were tuned.  Thus they pointed to the use of common VIFs where reasonably possible.  Quite late on, there were some examples where the quasi-synchronous demodulator tank circuits were switched between two frequencies.  The same considerations applied to the use of quasi-synchronous AM sound demodulators, when they were designed to use tank circuits, but another facet was the use of ICs that did not require tank circuits (feasible with AM sound, but not with vision), which were therefore “frequency wild”.
 
Not long after quasi-synchronous vision demodulators arrived, the fully synchronous type appeared, and there was slow growth of their use so that by the 1990s, they were quite common.  These favoured the use of a single VIF, but some were switchable between two different VIFs.
 
The advent of SAW filters (SAWFs) in the mid/late 1970s also favoured the single VIF approach.  But later on were developed SAWFs that could be switched between two characteristics, with two VIFs if required.  As well, double-Nyquist SAWFs became available, so that combined direct and indirect IF strips could be accommodated.
 
In terms of case study examples, Belgium readily comes to mind in that from the start of TV broadcasting there, its TV receivers were multistandard (four standards initially), and situations 1 and 2 both applied.  However, in some ways, France makes a better starting point in that it embodied elements of both situations 1 and 2, with the details varying over time.  So I’ll address the French case first, then after that the Belgian case in a following post.
 
Situation 1 existed – in the Paris area only - from the start of system E (819/50) broadcasting in 1949, alongside the established 441/50 system until the cessation of the latter in 1956.
 
Situation 2 existed in the eastern border areas from 1953-54, when systems B, C and F became available from neighbouring countries.  
 
Another situation 1 was created with the commencement of system L broadcasting in 1964.  This also ensured the existence of situation 2 until the end of analogue TV broadcasting, even though system E was discontinued in 1984.  The arrival of system L’ was accommodated without any disruption to French IF practice, although it did create difficulties for multistandard receivers elsewhere.
 
Paris Area 441/819:
 
Notwithstanding that the 441/50 system had a limited life, there were available some dual-standard 441/819 line receivers.  That was recorded in WW 1951 November, p.459 in an article about the then recent Paris Television Show.  To quote:
 
“Altogether 81 different receivers were shown.  Most exhibitors had a standard chassis in different cabinets—some of these incorporated a broadcast receiver or a record changer, and others were for long-distance reception with one or two r.f, preamplifier valves.  Seventy percent of the sets were for the high-definition 819-line standard and included six dual-standard 441/819-line receivers.  The number of valves varied between 15 and 22 for 441 lines and between 14 and 23 for 819 lines.”
 
I have not found any information about those receivers.  To the best of my knowledge, there was never a standard IF for the 441/50 system, and the standard IF for the 819/50 system was several years away.  Thus receiver makers would have been left to their own devices.  The receivers would have been single-channel for 441/50, and quite probably also single channel for 819/50.  Given the latter was in Band III, then almost certainly superhet receivers were required.  Just how long 441/819 dual-standard receivers remained available is unknown.
 
Be that as it may, the French domestic TV receiver industry had an early, if short-lived introduction to production dual-standard receivers.
 
Cross-Border 625/819 (and 819/819): 
 
There was early interest in cross-border reception.  This was noted in the report from the 1952 EBU TV IF survey, summarized in WW 1954 July p.322ff.  From p.324:
 
“For the frontier regions it has been suggested that a receiver similar to the Belgian might be an answer, but the matter is still under consideration.  In the meantime, a receiver has been built for the Strasbourg region (where it is possible to receive German programmes) which employs two separate i.f. amplifier chains; one using 37.6 and 26.45 Mc/s for vision and sound, the other with 28.5 and 23 Mc/s.”
 
The reporting period for the EBU survey was 1953 and early 1954.  The “Strasbourg” receiver would have been designed before the French and CCIR standard IFs arrived, so the IF numbers for both systems were probably ad hoc choices.
 
The “Strasbourg” receiver had also been mentioned in a Wireless World 1954 June article, “French Television Progress’, p.261ff.  From p.263:
 
“In eastern France there are many localities where several programmes can be picked up, including the local programme.  As there is a difference between the French standard and the European standard, as used in Germany and Switzerland, special receivers arc needed—not only for the difference between the 819- and 625-line transmissions and their attendant variation in black-level percentage, but also the sound section of the receiver must he capable of receiving a.m. or f.m. signals.  One manufacturer is marketing a receiver of this type aptly named the " Strasbourg," since in this town the Baden Baden transmitter can provide adequate signal strength.”
 
The extent to which cross-border transmissions could be received in France, in the pre-UHF era, is illustrated in this map:
 
Tele Magazine 10 16 01 1960 p26 carte TV etrangeres 2
 
 
For eastern France, the following system combinations would appear to have been of utility in the specific areas:
 
1. E with C and F
2. E with F
3. E with B
4. Possibly E with B and F
 
The fourth combination would almost automatically embrace system C as well, so the result would be E with B, C and F.  That would produce a “universal” receiver for the eastern side of France, provided that it had full VHF channel coverage, Bands I and III, for system E.  
 
At first glance the B/C/E/F combination suggests that the Belgian four standard type of receiver would have been suitable.  However, it was limited to the Band III channels only for system E.  That would have been satisfactory in some parts of Eastern France where the local transmitter was in Band III, but not in all parts.  Probably Belgian type receivers had some application, but for wider use, a French solution was required.  A couple of basic premises could well have been that the receiver should be suitable for use on system E anywhere in France, and that it should have full or close to full system E vision bandwidth.
 
It would appear that three types of French eastern border multistandard receiver were developed:
 
I.) System E, all VHF channels, with system F channel E7 only for reception from Luxembourg.
II.) System E with system B, all VHF channels (following the Strasbourg receiver precedent).
III.) System E with systems B, C and F, all VHF channels.
 
The third type may have superseded the second type.
 
The first type probably sustained because it was quite easy to do, given that systems E and F were both 819/50, and the Luxembourg transmitter had quite a large footprint in France (by design as I understand it.)
 
Given that E7 was a Band III channel, infradyne conversion could be used, and so it could be translated to a direct IF channel.  Thus it was simple to use the French system E standard SIF of 39.2 MHz, which put the VIF at 33.7 MHz.  The system F IF channel was then nested within the system E IF channel, with a common SIF at the upper end.  In respect of the IF strip, what was required for system F was the switching in, somewhere within the vision IF strip, of a narrow band filter that also provided a system F adjacent sound trap at 32.2 MHz and a 1.5 MHz wide Nyquist slope over 33.7 MHz.  System F adjacent vision at 40.7 MHz could be handled by having a trough between the existing 39.2 MHz sound and 41.2 MHz system E adjacent vision traps.
 
The second type, systems E and B, was more difficult.  For Band I system B capability, for example as required for the  Swiss Geneva channel E4 transmitter, which had a big footprint in France, then supradyne conversion with a resultant indirect IF channel was required.  This outruled the possibility of having a common VIF or SIF.  Nesting the system B IF channel within the system E IF channel was probably desirable to avoid any bandwidth extension.  But taking the 6 dB down points of the system E IF channel as being approximately 28 to 38 MHz, then the standard system B IF channel would not quite fit, unless a much steeper Nyquist slope were accepted, steep enough to get from 6 dB down at 38.9 MHz to a rejection notch at 39.2 MHz.  And with diode vision demodulators, such would have introduced unacceptable distortion.  Thus moving the system B IF channel downwards somewhat was desirable.  Given that there was anyway a 39.2 MHz sound trap, this could also serve as the system B adjacent sound trap, which then put the VIF at 37.7 MHz, and the SIF at 32.2 MHz.  This was lower by 1.2 MHz than the standard CCIR IF, but evidently satisfactory in context.
 
As intercarrier sound was most likely used, the non-coincidence of the SIFs was not a major issue, and the sound IF strip would have catered for 39.2 MHz AM and 5.5 MHz FM.
 
For system B, a switched narrow-band IF filter would have provided a system B adjacent vision trap at 30.7 MHz, and a sound shelf at 32.2 MHz.  The 1.5 MHz wide Nyquist slope over 37.7 MHz might well have been part of the switchable filter, but it could also have been a permanent feature perhaps combined with the 39.2 MHz sound trap.  A fixed 6 dB down point at 37.7 MHz would have given a system E vision bandwidth of 9.65 MHz, probably in the acceptable range.
 
The third receiver type, covering systems E, B, C and F, would have followed the E/B precedent with a 37.7/32.2 MHz system B/C/F IF nested within the system E 28.05/39.2 MHz IF channel.  The sound IF channel would have catered for 32.2 and 39.2 MHz AM, and 5.5 MHz FM.  Some switching of filters at the 32.2 MHz sound carrier frequency might have been needed to provide a shelf for system B but suppression for systems C and F.
 
I suspect that 37.7/32.2 MHz nested within 28.05/39.2 MHz was the modal choice for French border area receivers covering systems E and B and E and B/C/F.  But it is known for example, that Pye-Grammont did differently for its E/B receiver.  So there might well have been other departures.
 
From the post-demodulator video perspective, the E/B and E/B/C/F receivers were of the 625/819 line type.  The E/ F channel E7 only receivers were 819 line only.
 
The E/B and E/B/C/F receivers handled both positive/AM and negative/FM signals, the E/F channel E7 only handled just the positive/AM type.
 
Cross-Border 405/819 and 405/625/819:
 
Confirmation that the multistandard TV receiver was a fixture in France was provided in a WW 1959 October report on the Paris Radio Show, p.456ff.  From p.456:
 
“In certain parts of France reception of television programmes from other countries is possible. However, since these programmes have different characteristics, multi-standard sets have to be provided to receive them.  Among the numbers of such receivers on show we saw one, the Telemaster Super V5D FM, which could receive as many as five types of television transmissions-819 lines on French and Belgian standards, 625 lines on Belgian and European standards and even our own familiar 405 lines—not to mention f.m. sound broadcasts in Band II.”
 
My interpretation of that comment is that although four-standard receivers were relatively commonplace, the five standard type that included system A was quite rare.
 
As an aside, it would be interesting to know what IF(s) were used for FM reception in the Telemaster Super V5D FM, but I suspect that information would be very hard to find.  The designation “V5D FM” suggests that there might have been a version without FM, as the “V5D”.  In that case, FM was probably added as simply as possible, perhaps using the ostensible German approach of having the 5.5 MHz intercarrier double as the FM IF.  (As recorded in WW 1955 October, p.468.)  But one could also ask the question – were there “regular” French TV-FM receivers that handled system E only, and if so, how did they treat FM?  There would have been some similarities with the British pre-UHF TV-FM receiver situation.
 
Returning to system A reception in France, this section from the map above shows that it was possible in the Le Havre area, from the Channel Islands transmitter(s).
 
Tele Magazine 10 16 01 1960 p26 detail carte BBC Jersey
 
 
The BBC transmitter had opened in 1955.  In a WW 1962 October article on the opening of the ITA Fremont Point Channel Islands transmitter, “I.T.A’s Smallest Station”, p.482, it was said:
 
“It is understood there are some 2,000 dual-standard (405/819 lines) set-in use along the coast of the Havre peninsula, where viewers get a reasonable signal from the B.B.C. station on the island.  The I.T.A. station will, in fact, radiate a daily French news bulletin (intended primarily for the French-speaking section of the island’s population) and include some French manufacturers amongst its advertisers.”
 
Thus it has been established that the French border area TV receiver group included both system E/A and E/B/C/F/A receivers.
 
How the system A IF was addressed in these cases is unknown.  It would have been possible to nest the standard 34.65/38.15 MHz system A IF channel within the standard system E IF channel.  But much simpler would have been to adopt the common SIF approach, using the 39.2 MHz from system E.  That would have put the system A VIF at 35.7 MHz, coincidentally the same as the VIF used in some early French system E receivers with double-ended IF strips (28.05/39.2 and 35.7/24.55 MHz.)  From an IF strip viewpoint, this would have been analogous to the approach used for system E receivers that also covered system F from Luxembourg channel E7.  And it would have been applicable to both the E/A and E/B/C/F/A combinations.  Thus on the basis of simplicity, 35.7/39.2 MHz would be my best estimate for system A in French border area receivers.  In any event, the system A IF channel would have to be of the direct type in order to accommodate the Band I channels.
 
At the video end, the E/A receivers were 405/819 line, and positive/AM only, so conceptually not different in that regard to the 441/819 receivers of 1951.
 
The E/B/C/F/A receivers were more complicated in having a 405/625/819 line video section, and handling positive/AM and negative/FM.
 
Thus French border area multistandard TV receivers covered up to four extra-territorial systems in the pre-UHF era.  The need for full coverage of the system E VHF channels required a different approach to that used for Belgian four-system (B/C/E/F) receivers, although the latter type probably had a place in some parts of France.
 
In the French case too, there was a stronger need to provide full or near full vision bandwidth for system E, and the use of the standard 28.05/39.2 MHz IF facilitated this.  It could be done in Belgian receivers, but more often the system E vision bandwidth was truncated to around the system F level.  The importance of vision bandwidth was shown in this comment from the previously mentioned WW 1959 October article:
 
“Quotation of the vision bandwidth is also very common in France.  9Mc/s was the usual figure given but 10Mc/s was also quite often quoted.”
 
Domestic 625/819:
 
There was a return of situation 1 with the introduction of system L, 625/50, using the UHF channels in 1964, whereafter dual-standard receivers, covering systems E and L, became the norm in France.
 
Here both the system L details and its associated IF were chosen for simplify receiver design to the extent possible.  At about the same time, the French authorities and the industry had developed what became system K1 for use in the French territories and other Francophone countries in Africa.  In line with what by then was normal practice, this used negative vision modulation and FM sound, and was generally similar to the Eastern European system D/K, but with the vestigial sideband extended to 1.25 MHz in place of 0.75 MHz.  At the same time, a standard IF channel was derived from first principles, namely 40.2 MHz VIF, 33.7 MHz SIF.  Coupled with this was the choice of specific frequencies for the three Band I channels.
 
For domestic use though, system L had the same bandwidth parameters, but had positive vision modulation and AM sound, without pre-emphasis, by which means it was aligned with system E as far as possible.  Also, the standard IF, 32.7 MHz VIF, 39.2 MHz SIF, was based on a common SIF with system E, further easing receiver design at a time when a common SIF was of greater utility than a common VIF.  This IF was used for the planning of the French UHF geographical channel allocations.  System E/L receivers were probably amongst the simplest of the dual-standard types that had to deal with two different line rates, in this case 625 and 819.
 
Being derived from the system E standard IF, the system L standard IF channel was of the direct type, and that implied infradyne conversion, which was not a problem with the UHF channels.
 
Border Area Receivers and System L:
 
The resultant situation with border area multistandard receivers after the debut of system L was summarized in the WW 1965 October 1965 report on the September Paris Radio Show, p.501ff.  From p.501:
 
“The multistandard receiver for use in frontier areas is, of course, a familiar object at European radio shows and at Paris most of the larger manufacturers had two or three sets in their normal range.  Several of the French-made sets will receive the French (14 Mc/s), Belgian (7 Mc/s) and Luxembourg (7 Mc/s) 819-line transmissions on v.h.f., the French 625-line second programme on u.h.f., the Belgian 625-line transmissions on v.h.f., and the European (7 Mc/s, f.m. sound) 625-line broadcasts from Germany, Switzerland, Italy and Spain.  British 405-line pictures can be received on some sets made by Grammont.”
 
The foregoing implies the more general use of combinations up to and including E/L/B/C/F, with E/L/B/C/F/A being less common.  Along with system B would have been its system G and H UHF counterparts.  Systems G and H would have required that the UHF tuner be arranged for supradyne conversion, as well as infradyne for system L.
 
Possibly there were intermediate combinations, such as E/L/F channel E7 only and E/L/B.  But given that domestic receivers were anyway 625/819, catering for positive/AM on 625, it may well have been logical for makers to focus on the E/L/B/C/F type.  Although systems B, G and G were treated as a single system from the receiver viewpoint, listing them separately in this sequence, as E/L/B/G/H/C/F gives rise to the seven-system designation sometimes used for such receivers.  Addition of system A would make it eight systems.
 
From an IF perspective, the only change would have been the addition of the 32.7 MHz VIF for system L.  Thus the modal structure could well have been:
 
28.05 MHz VIF, 39.2 MHz for system E as the basic IF channel.
32.7 MHz VIF, 39.2 MHz for system L as a truncated, common SIF version of the basic channel.
32.2 MHz SIF, 37.7 MHz VIF for systems B, C and F, as a nested IF channel within the main channel.
35.7 MHz VIF, 39.2 MHz SIF for system A, where required, as a further truncated, common SIF version of the basic channel.
 
From a video perspective, these receivers were of the 625/819, or 405/625/819 type, handling both positive and negative modulation.
 
The provision for systems C and F would have dropped away when these were discontinued, in 1978 and 1971 respectively.  The disappearance of system F would have had very little effect on receivers generally and the IF system in particular.  The loss of system C would have meant that the SIF could revert to single frequency, namely 39.2 MHz, and that filtering at 32.2 MHz could be fixed for the system B/G/H requirements.  Also, the audio section would no longer need to have switchable de-emphasis.
 
I imagine that the 405/625/819 type would have disappeared from the French inventory at about the same time that dual-standard 405/625 receivers disappeared from the UK inventory.
 
Late 625/819 Era:
 
Late in the system E era – probably in the later 1970s - another combination, namely 32.7 MHz VIF, 43.85 MHz SIF, appeared for that system.
 
Here, the rationale was evidently a common VIF with system L.  The driver there was most likely to facilitate the use of a common quasi-synchronous demodulator and/or a SAW filter for systems E and L.  Whether system E-specific SAWFs were ever actually produced I do not know.  A possibility is simply that the system L SAWF was used on both systems, with resultant truncation of the system E vision bandwidth to 6 MHz.  Also, many quasi-synchronous demodulator ICs of the time had a vision bandwidth that was somewhat less than 10 MHz.
 
With the 32.7/43.85 MHz combination careful screening was probably required, given that 43.85 MHz was within Band I, the channel F2 sound carrier being at 41.25 MHz.
 
Whether 32.7/43.85 MHz was used only for standard domestic receivers, or for those and border area receivers, is unknown.  On its face, its combination with 37.7/32.2 MHz would have resulted in an overall IF strip bandwidth that was wider than hitherto.  But of the system E vision bandwidth were truncated to the system L level, as could well have been the case, then only the tuner output would have been full bandwidth, to allow extraction of the 43.85 MHz SIF, after which the extreme carriers would have been at 32.2 and 39.2 MHz.
 
625 Only Era:
 
The end of system E in France meant the disappearance of the 28.08/39.2 and 32.7/43.85 MHz combinations.  The introduction of system L in band III required no change in IF practice, the existing 32.7/39.2 MHz combination being used.  However, VHF tuners needed to be configured for infradyne conversion in Band III, to suit the combination of direct transmission channels with a direct IF channel.  In band I, where only supradyne conversion was practicable, the solution was to use indirect transmission channels, thus allowing the use of the existing direct IF channel.  This Band I variation was informally referred to as system L’.  Thus domestic-only receivers became quite simple, being single standard, 625 with positive modulation and AM sound only, with a single IF channel of 32.7/39.2 MHz.
 
Border area receivers then would also have been 625 only, but able to handle both positive and negative modulation, and AM and FM sound.  It seems reasonable to assume that there was continued use of the 37.7/32.2 MHz nested IF channel for systems B/G/H.  But it may not have been long before the start of the incursion of non-country specific multistandard receivers, with non-French focussed IF choices.  Thus use of the 32.7/39.2 MHz IF channel in multistandard receivers may have progressively fallen away, and with it the use of the nested 37.7/32.2 MHz IF channel.
 
Apparent from the foregoing is that the French border area receivers, with the exception of the “domestic + Luxembourg only” and systems E + A typed, required the use of what might be called double-ended IF strips, one direct and the other indirect, the latter often nested in the former.  The same approach had been used with some early system E domestic receivers, so the French setmakers had prior experience with this technique.
 
Double-ended IF strips were used in British dual-standard receivers from 1964.  And they were also use in generalized multistandard receivers from c.1984 that included system L’, which required a direct IF channel.
 
 
This chart provides a summary of the foregoing.  It includes French domestic receiver IFs as reference points.
 
French Multistandard TV IFs
 
 
 
Next will be a review of the Belgian case.
 
 
Cheers,
 
Steve
 
Posted : 09/12/2022 9:58 pm
Nuvistor reacted
Nuvistor
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@synchrodyne 

There is a lot to take in in that post, I have made a start and will continue in the next few days.

Thanks, all intriguing, I didn’t realise the 405 signals being received in Le Havre from the Channel Isles would have been an interest to the French viewers, how wrong can I be.

 

Frank

 
Posted : 09/12/2022 11:04 pm
Synchrodyne
(@synchrodyne)
Posts: 519
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Topic starter
 
Thanks!  The French multistandard case does make for an interesting story when one puts it together sequentially in one place.
 
Still a bit murky are the timing and details of the apparent transition from more-or-less country-specific to Europe-wide (or worldwide) multistandard receivers, which saw a move away from the French system L standard IF.  That seems to have happened in a significant way in the 1990s, although with roots back in the 1970s.  Barco (Belgium) was an early player in that field, with semi-professional all-standard monitor-receivers, such as the CRM2631, offered in the mid-1970s.  I have never discovered the IF structures of those models.  One may infer that Barco’s presence in that field was a direct consequence of the fact that Belgian domestic TV receivers were multistandard from the start.  And that would suggest that the 1970s Barco models had Belgian style IF structures.  But it is apparent that the CRM2631 covered the system E Band I channels, normally omitted in Belgian practice and essentially excluded by the customary Belgian IF structure.  That made me wonder if Barco had not used a French multistandard IF structure, which prompted another close look at the French case, and so the above posting.  One could say that if the objective (in that period) was an all systems, all channels receiver, then French practice was the better starting point.
 
 
Cheers,
 
Steve
 
Posted : 11/12/2022 8:39 pm
Synchrodyne
(@synchrodyne)
Posts: 519
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Topic starter
 
Multistandard TV Receiver Intermediate Frequencies – The Belgian Case.
 
 
Early Years – Systems C, F, B and E:
 
The Belgian case was characterized both by the existence of two national TV transmission standards from the start, namely C and F, and the desire that all domestic receivers be able to receive cross-border system B transmissions from the Netherlands and Germany, and system E transmissions from France.  Thus these receivers were multistandard, covering 625 and 819 lines, positive and negative vision modulation, differing video bandwidths, and AM and FM sound, the former both with and without pre-emphasis, in various combinations.  The background to this was given in a WW 1956 November article, “Four-Standards Television”, p.559ff.
 
From an IF selection viewpoint, systems C and F were no different to system B, so that the standard developed for system B, 38.9 MHz VIF, 33.4 MHz SIF, was equally applicable.  Thus once it was available, very soon after the commencement of TV broadcasting in Belgium, it was logically used for the national systems B and F, and for cross-border system B.
 
Clearly some variation was required for system E transmissions from France.  Perhaps fortunately, those that could be received in Belgium were all from Band III transmitters, which certainly eased the problem.  Given that both infradyne and supradyne conversion was readily possible in Band III, then all of the French system E channels in that band could be converted to an indirect IF channel, by the selective use of both infradyne and supradyne conversion.  Odd-numbered channels required supradyne conversion, whilst those that were even-numbered required infradyne.  That was the opposite to the French domestic receiver case, where a direct IF channel was employed.
 
Thus for system E, Band III only, the same 38.9 MHz VIF as for systems B, C and F could be used, and that put the SIF at 27.75 MHz.  That could be compared with the French pre-standardization indirect IF channel, 35.7/24.55 MHz, which minimized interference possibilities in the presence of multiple system E signals.  But relatively few system E transmissions would have been receivable (at entertainment signal strength) in any given part of Belgium, so interference avoidance would have been less of an issue.  One consequence of this choice was the need for a dual-frequency, 27.75 and 33.4 MHz, SIF strip.
 
Some early receivers used a second conversion on the sound side, from 27.75 and 33.4 MHz to 7.0 or 11.8 MHz.  This was done mostly because FM limiting and demodulation was done much more easily and effectively at lower frequencies.
 
A subsequent move to intercarrier sound (at 5.5 MHz) for system B removed the need for the second conversion, and dual-mode SIF strips were then used, handling FM at 5.5 MHz and AM at 27.75 and 33.4 MHz.
 
 
The UHF Era – Addition of Systems H, G and L:
 
The foregoing was the situation until the arrival of UHF transmissions in 1964.  Belgium adopted system H, which from an IF viewpoint was generally the same as system B, except that the adjacent sound rejector was 2.5 rather than 1.5 MHz away from the VIF.  The same applied to cross-border system G UHF transmissions from the Netherlands and Germany.
 
On the other hand, France adopted system L, a positive/AM system with a vision-sound spacing of 6.5 MHz, and using direct channels.
 
In IF terms, that was accommodated by using the same SIF, 33.4 MHz, as for systems B, C, F, G and H.  That put the VIF at 39.9 MHz.  The use of an indirect IF channel meant that supradyne conversion could be used for system L UHF transmissions, as with systems G and H.
 
The 39.9/33.4 MHz IF combination was also used for system B receivers in Austria and Finland which also had the capability of receiving system D transmissions from eastern Europe.  This used may well have preceded the Belgian use.
 
At the same time as 39.9/33.4 MHz was adopted for system L in Belgian receivers, system E was usually moved up 1 MHz from 38.9/27.75 MHz to 39.9/28.75 MHz.  One rationale for doing this would have been to keep the overall IF strip bandwidth the same as before, the 1 MHz increment at the top end being matched by a 1 MHz decrement at the bottom end.  Another may have been to provide a more favourable Nyquist slope for system E.  At 38.9 MHz, the slope would have occupied ±0.75 MHz to suit systems B, C, F, G and H.  In some cases, but I suspect not all, or even not many, it would have been widened out to ±2.0 MHz for system E.  For system L at 39.9 MHz, the slope could have occupied the full ± 1.25 MHz for this system, and that would have been better for system E than ±0.75 MHz.
 
The net result was that the SIF side was virtually unchanged, except that the AM frequency pair became 28.85/33.4 MHz rather than 27.75/33.4 MHz.  On the VIF side, there would need to have been switching to move the Nyquist slope midpoint (and associated traps) between 38.9 and 39.9 MHz.
 
During this era, both systems C and F were discontinued, system C in 1978, and system F earlier than that, 1968 in Belgium, and 1971 in Luxembourg.  This had but minor effect on receiver IF systems.  The 33.4 MHz AM SIF was still required for system L.   Some minor simplification of IF mode switching might have been possible given that 33.4 MHz extraction was then only required for one IF strip VIF mode, not both.  And it was no longer necessary to have switchable de-emphasis in the AM sound channel.
 
On balance, one could say that as long as system E capability was a factor, the Belgian situation, Band III channels only, allowed of slightly simpler – and so slightly lower cost - multistandard IF systems than did the French border area multistandard requirements, where Band I channels were also required.  Insofar as all Belgian receivers were affected, rather than a minority of special purpose models, cost of implementation was probably a significant issue.  That said, there may have been some French border areas where Belgian-type receivers were suitable, and such usable, and I think that such were offered by some French setmakers.
 
Whether there was any Belgian requirement for UK system A reception capability I do not know.  Adding system A, Band I channels to the standard Belgian IF structure would not have been easy, given that system A would have required a direct IF.  In that case the established French multistandard form, which was sometimes expanded to include system A, might have been the answer.  
 
 
Post-System E:
 
With the cessation of system E transmissions in 1984, the system list for Belgian receivers became B, G, H and L.  A continuation of previous practice would have seen an IF channel with systems B. G and H at 38.9/33.4 MHz, with system L at 39.9/33.4 MHz.  But given that by this time, the use of SAW filters and/or quasi-synchronous vision demodulators pointed towards a common VIF rather than a common SIF, it seems possible, even likely, that there was some use of 38.9/32.4 MHz for system L.
 
The extension of system L to Band III would not have created any problems for the Belgian receivers.  Given that the channels were direct, whilst the IF channel was indirect, supradyne conversion as used for systems B/G/H would have applied.
 
System L’ transmissions in Band I were potentially problematical.  The channels were indirect, and as only supradyne conversion was feasible, a direct IF channel was required.  Whether or not system L’ reception was required in Belgium I do not know.  This map suggests that none of the French L’ transmitters reached into Belgium, although there were overlaps in some other bordering system B countries.
 
French band I 819 to 625%20 channels switch over 1984
 
 
At this point though, stage though the stage was set for the wider use of pan-European multistandard receivers, in which system L’ was accommodated by the use of double-Nyquist IF strips.  Often these had a 38.9 MHz VIF for all systems except L’, but the VIF used for the latter did vary somewhat.  That can be a topic for another day, though.
 
Belgian Multistandard TV IFs
 
 
Cheers,
 
Steve
 
Posted : 11/12/2022 8:46 pm
Synchrodyne
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Multistandard Receivers – Post 1985
 
 
I have yet to obtain a clear picture as to how multistandard TV receiver IFs evolved after around 1985, but I have found some pointers.  This may be viewed as a growth era for pan-European (Euro) and worldwide type receivers.
 
The first pointer is provided by the Philips TDA2549 IC, described as an IF amplifier and demodulator for multistandard receivers.  The earliest datasheet I can find is dated 1985 April.  It would have been an addition to the established TDA254x series.  The latter included inter alia the TDA2540 and TDA2541, which addressed the needs of negative modulation TV systems, and the TDA2542, which covered positive modulation systems.  Accompanying those was the TDA2543, which was an AM sound IF channel.
 
The TDA2549 covered both the negative and positive modulation cases, with externally controlled switching between the two.  There was also a separate externally controlled AFC inverter switch.  The data show this providing opposite-sense AFC biases centred on 32.7 MHz and 38.9 MHz, reflecting the fact that the two frequencies were at opposite ends of the IF channel.  A single frequency demodulator tank circuit was shown, but it is possible that the tank frequency was switched internally by the AFC inverter switch.
 
Anyway, one may deduce that Philips saw the TDA2549 as being used with the standard 32.7 MHz VIF for system L/L’, and the standard 38.9 MHz for systems B/G/H (and also for systems D/K and I if required).  Probably it was assumed that L-C type IF filters would be used ahead of it, as with the earlier members of the TDA254x series.
 
In IF terms, this was essentially a continuation of established practice for systems L/L’ and B/G/H.
 
Nonetheless, the TDA2549 could probably have been used with the system L IF at 38.9 MHz, in which case the AFC inverter switch would be left in 38.9 MHz position.
 
 
Notwithstanding the above, a different approach was shown in 1985 November Philips Germany IEEE paper, “System and Realization Aspects of Multistandard TV Receivers”, by Wolfgang Weltersbach.
 
Here it was determined that a common 38.9 MHz VIF for all European TV systems, including L, was the best approach.  That put the system L SIF at 32.4 MHz.  The paper included this chart:
 
TV Sound Standards & IFs
 
Note that the author used “L” for system L with its standard 32.7/39.2 MHz IF, and L bar (sometimes L’), not for system L’ itself, but for system L when used with a 38.9/32.4 MHz IF.  I suspect that the paper may have been drafted before the designation L’ came into use for the Band I, inverted channel version of system L.  There is no indication that the IF complications introduced by L’ proper were considered.
 
Be that as it may, we see what was probably an early proposal that 38.9/32.4 MHz be used as the IF for system L in multistandard receivers.  It certainly would have been applicable in Belgian receivers, where there was no apparent need to cover the Band I L’ channels.
 
The required IF selectivity curves, vision above and QSS sound below, were shown as follows:
 
Multistandard Selectivity
 
 
 
The VIF selectivity curves, with SIF shelves, look as if they were drawn for a conventional intercarrier receivers, whereas the QSS type was advocated.
 
 
More to follow.
 
 
 
Cheers,
 
Steve
 
Posted : 17/12/2022 12:32 am
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Multistandard Receivers – Post 1985, continued
 
 
The next data point is a Toshiba patent, US4814874 of 1989 March 21, filed 1988 March 25, for a TV receiver IF processing circuit using a double-Nyquist SAWF in the vision IF circuit of a multistandard TV receiver.
 
Whether this was the first double-Nyquist SAWF proposal I do not know, but given that it was patented, it is reasonable to assume that it was an early example.  Clearly Toshiba was addressing the “system L’ problem”.
 
The basic IF strip layout was shown in this diagram:
 
Toshiba Double Nyquist
 
 
 
Both the vision IF IC, of the intercarrier type, and the AM sound IC, were shown with a switched two-frequency tank circuits.
 
Toshiba did not nominate specific IFs, but provided a chart to show the relationships, albeit as transmitted, rather than as inverted in the IF strip:
 
Toshiba B,G,L Bandpass
 
 
Point A, 6 dB down on one Nyquist slope, can be taken as the VIF for system B/G, normally 38.9 MHz.  Point C is then the SIF for that system, at 33.4 MHz.
 
Point B, at 6 dB down on the opposite Nyquist slope, is the colour subcarrier for system B/G, thus 4.43 MHz below the VIF, which put it at 34.47 MHz.
 
Points A and B were also used for system L, with point D representing the sound carrier rejection at 32.4 MHz.
 
Point B, at 34.47 MHz, was the VIF for system L’ (shown here as system L, VHF low band).  The SIF for system L was then 6.5 MHz higher, at 40.97 MHz, with the rejection filter at point E.  The colour subcarrier then fell at point A, 38.9 MHz, and the sound carrier rejection at point E, 
 
The AM SIF SAWF had two peaks, one at 32.4 MHz, and the other at 40.97 MHz.
 
The system L’ numbers could be rounded to 34.5 MHz VIF and 41.0 MHz SIF, so there we have the probable origin of this combination, which was one, but by no means the only one, used for system L’ in double-Nyquist SAWFs.
 
Toshiba expanded the concept to encompass systems D/K, I and M, all using the same VIF, as shown here:
 
Toshiba BG, DK, I, M Bandpass
 
 
Some additional traps were needed.  Assuming a 38.9 MHz VIF, this gave a 34.4 MHz SIF for system M, 32.9 MHz for system I, and 32.4 MHz for systems D/K.
 
The Toshiba approach was based upon the premise that the -6 dB points of the VIF passband should correspond on the one hand to the VIF, and on the other to the colour subcarrier.  Although having the colour subcarrier 6 dB down was at one time considered appropriate when diode vision demodulators were used, the need was probably less so with synchronous demodulators.  Not all double Nyquist approaches followed this pattern.
 
Early on in this thread, I commented upon the IFs used in the Sony Profeel VTX-100M multistandard TV tuner (see:  https://www.radios-tv.co.uk/community/black-white-tvs/television-receiver-intermediate-frequencies/#post-50370).   That unit used the 34.5/41.0 MHz combination for system L’.  At the time I thought that it was rather an odd ad hoc choice, but now I can see its origins.  The VTX-100M actually predated the Toshiba patent, so one wonders whether this combination was more of a “Japan Inc.” development.  Sony though did not appear to use a double-Nyquist SAWF.  Instead there was a switched trap ahead of the main VIF SAWF to provide the second Nyquist slope.
 
As an aside, I recall that in the 1980s, Sanyo was offering some worldwide all-standards TV receivers and VCRs.  (We had a set in the office where I then worked circa 1985-86.)  Perhaps Sanyo had used the Toshiba double-Nyquist IF concept.  But clearly, Japan Inc. was by then interested in multistandard TV receivers.
 
There appear to have been at least two other conventions when it came to the placement of the 6 dB down points on double-Nyquist TV IF systems and SAWFs.  More on these to follow.
 
 
Cheers,
 
Steve
 
 
Posted : 17/12/2022 12:50 am
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Multistandard Receivers – Post 1985, continued
 
 
The two other apparent conventions with respect to double-Nyquist IF strips for multistandard TV receivers were, in terms of the 6 dB down points:
 
33.4 and 38.9 MHz; and:
 
33.9 and 38.9 MHz.
 
In both cases, the vision carriers for all systems except L’ were placed at 38.9 MHz, as expected.
 
For L’, the vision carriers were placed at 33.4 or 33.9 MHz.
 
Looking at each case in turn:
 
 
33.4/38.9 MHz:
 
The earliest record I have found of the 33.4 MHz VIF for system L’ is in the developmental datasheet for the Philips UV815 TV tuner, dated 1989 February.  This also appears to be the earliest mention by Philips of 38.9 MHz as the VIF for system L.
 
Philips UV815 198902
 
Assuming the use of a double-Nyquist SAWF, this put the usable video bandwidth for systems L and L’ at 5.5 MHz, a little short of the 6.0 MHz that the systems were capable of.  But the 5.5 MHz separation of the VIFs was probably the greatest manageable if the single SAWF was to provide the appropriate bandpass for each, without additional switching being required.  The two SIFs were 32.4 MHz for L and 39.9 MHz for L’.  Thus the SAWF needed to have significantly reduced response at each of those frequencies.  That allowed a 1 MHz margin for each of the Nyquist slopes below the respective VIFs.
 
System L/L’ was transmitted with an extended vestigial sideband (VSB) of 1.25 MHz.  In the days of L-C IF bandpass filters, I understand that the resultant lower slope required made it easier to avoid phase distortion at the lower video frequencies.  With SAWFs, where the frequency and group delay responses could be set somewhat independently, that was much less of an issue, and so relatively steep Nyquist slopes could be used, at least from the vision perspective.
 
Here is the bandpass curve for a typical vision SAWF for the 33.4/38.9 MHz case:
 
Siemems G3957M Bandpass
 
 
 
The SAWF shown addressed the vision IF channel requirements alone.  A separate SAWF with peaks at 32.4 and 39.9 MHz would have been required for the sound channel.
 
It is also apparent that the vision SAWF shown above, although appropriate for a system L/L’ only receiver with 38.9 MHz VIF for system L, would be less suitable for multistandard receivers, although it would work for systems D/K/K’.  But for systems B/G/H and I, it would not by itself have provided adequate suppression at the sound carriers at 33.4 MHz for B/G/H, and 32.9 MHz for I.  Either a SAWF with internal switching, or switched filters external to the SAWF, would be required.
 
So it certainly looks as though the 39.9/33.4 MHz VIF/SIF combination might have been used for system L’ primarily in system L/L’ only receivers where for whatever reason it was desired to use the 38.9/32.4 MHz VIF/SIF combination for system L.  That does seem more complexing than using the French standard 32.7/39.2 MHz VIF/SIF combination for both, but in some cases there might have been a preference for keeping L/L’ receivers as close as possible to others in the same range.
 
From that it may be seen that closer spacing of the two 6 dB down points would be preferable for the multistandard case, and that was achieved with the 33.9/38.9 MHz combination, to be discussed in the next posting.
 
A curious correspondence is that the 39.9/33.4 MHz VIF/SIF pairing was used for system L in Belgian multistandard receivers in the 1960s.  Here the reverse was used for system L’.
 
 
Cheers,
 
Steve
 
Posted : 17/12/2022 4:39 am
Synchrodyne
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Multistandard Receivers – Post 1985, continued
 
 
The third of the three apparent double-Nyquist IF combinations was 33.9 and 38.9 MHz, which had a 5 MHz separation between the two 6 dB down points, this corresponding with the video bandwidth for systems B/G/H.
 
Thus the respective VIF/SIF combinations were 38.9/33.4 MHz for L, and 33.9/40.4 MHz for L’
 
 
The earliest record I have found of the 33.9 MHz VIF for system L’ is in the datasheet for the Philips FQ816MF TV front end, dated 1990 April.  In this context, “front end” meant and tuner and IF strip combination, delivering baseband video and audio.  The FQ816MF was intended primarily for systems L/L’, also with systems B/G and I capability.
 
Philips FQ816MF
 
The description of the series of units of which the FQ816MF was a member included the following:
 
“The IF section of the frontend has the vision carrier fixed at 38.9 MHz (33.9 MHz for FQ816MF using system L').  The units use QSS-SAW filter except for the F0816MF using system L' where a double Nyquist QSS-SAW filter is used in the vision channel.
 
“Quasi-synchronous vision IF demodulation is used and this is suitable for positive and negative modulation.
 
“The IF sound filtering is done by means of a QSS-SAW filter for systems B, G and I and via a separate bandpass filter for systems Land L'.”
 
 
Here is the bandpass curve for a typical vision double-Nyquist QSS SAWF for the 33.4/38.9 MHz case:
 
Siemens K3261K Bandpass
 
 
 
It may be observed that the Nyquist slope associated with 33.9 MHz is somewhat steeper than that associated with 38.9 MHz.  In the former case, the steep slope allowed the achievement of reasonably good rejection at 33.4 MHz, the system B/G SIF.  Above 38.9 MHz, the nearest rejection point was 40.4 MHz for the system L’ sound channel, also the system B (VHF) adjacent sound point.
 
This is the bandpass for a typical double-Nyquist, 33.9 and 38.9 MHz, intercarrier SAWF.  It shows a sound shelf at 33.4 MHz.
 
Siemens K2962M Bandpass
 
 
 
 
I suspect that 33.9/38.9 MHz was the modal choice for European multistandard receivers (that included L/L’ capability) in the 1990s and onwards.
 
 
Cheers,
 
Steve
 
 
 
Posted : 17/12/2022 10:05 pm
Synchrodyne
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Multistandard Receivers – Post 1985, continued
 
 
To recap, there appear to have been three conventions for double-Nyquist SAW filters for multistandard TV receivers.  In terms of the 6 dB down Nyquist slope points, these were:
 
1. 34.5 (more precisely 34.47)/38.9 MHz
2. 33.4/38.9 MHz
3. 33.9/38.9 MHz
 
All included the European standard system B/G/H 38.9 MHz VIF.
 
Toshiba patented the double-Nyquist SAWF approach.  It specified the spacing for the 6 dB down points, at 4.43 MHz, but it did not specify the actual frequencies of those points.  Set #1 above derives from applying the Toshiba spacing to the standard 38.9 MHz VIF.
 
Whether Philips pioneered sets #2 and #3 is unknown.  It may well be happenstance that Philips documents are the earliest references I have found for each.  These did not provide a rationale for the choices.  Rather that has been derived, although there are not many degrees of freedom.
 
Interestingly, Philips also made mention of the 34.47 MHz number, in the 1993 January datasheet for its TDA3845 QSS & AM Sound IC.  (This was mentioned recently in the Intercarrier thread, at:  https://www.radios-tv.co.uk/community/black-white-tvs/intercarrier-sound/paged/3/#post-114245).
 
The suggested AM sound SAWF characteristics showed a 32.4 MHz SIF (with 38.9 MHz VIF) for system L, as might be expected, but a 40.97 MHz SIF (with 34.47 MHz VIF) for system L’, not 40.4/33.9 MHz as might have been expected.
 
Philips TDA3845 AM Sound SAWF
 
 
 
As best I can determine, none of these three combinations were ever included in national or industry standards.  But they were all derived from 38.9 MHz, which was a standard number.  By the 1990s, the improved screening typically provided in TV receiver tuners and IF strips probably made the use of carefully determined standard IFs less important than it had been in earlier eras.  IF strips were sometimes mounted within metal enclosures similar to those used for tuners.  Concomitantly, one could argue that this also gave the receiver makers freedom to choose their own IFs.  Countering this though was that the use of standard SAWFs, and so industry-common IFs, was more economical than would have been custom-made types for individual IF choices.
 
Although Toshiba had patented the double-Nyquist SAWF, the double-Nyquist IF strip was not a new concept.  As noted upthread, the standard IF choice for UK dual-standard receivers allowed for the use of a double-Nyquist IF strip (using L-C filters), at the cost of restricted system I vision bandwidth, and it is known that this was done.  Possibly some early French system E receivers, with double-ended IF strips, also used the double-Nyquist approach, to avoid some switching.  In that case the 6 dB down points would have been at 28.05 and 35.7 MHz, allowing for a 7.65 MHz vision bandwidth, well short of 10 MHz, but more than was typically provide for system E in Belgian multistandard receivers.
 
 
An interesting point is that the Philips FQ816MF TV front end also made provision for system I, which was also covered by some of the multistandard SAWFs available at that time.  The IF combination used was 38.9 MHz VIF, 32.9 MHz SIF, which was the South African standard.
 
The inclusion of system I in a full multistandard receiver, intended to be usable anywhere in the world, is understandable.  Its inclusion in a European multistandard receiver suggests system I reception (from the UK or Eire) was possible in some parts of Europe.
 
That makes me wonder whether or not system I capability was included in any pre-1985 French or Belgian domestic receivers, and if so, how it was fitted into the prevailing IF patterns.  Certainly, the Barco CRM2631 (CT-31 chassis) of circa 1976 covered it, but this was intended to be a worldwide receiver, and probably differed somewhat from the typical Belgian domestic receivers.  Its IF structure, if such can be found, could be quite instructive.
 
 
Cheers,
 
Steve
 
Posted : 17/12/2022 10:16 pm
Synchrodyne
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Topic starter
 
An interesting aspect here, in respect of system L, is the migration from the erstwhile 32.7 MHz standard IF to the European 38.9 MHz standard.
 
When planning to extend system L to Band I, the various French interests, both at the transmission and receiver manufacturing ends (the latter represented by SCART) evidently elected to stay with the established 32.7 MHz standard VIF, and so the Band I channels were accordingly specified to be indirect, viz vision carrier high.  This might have been done to allow some existing TV receivers to cover the Band I, system L channels.  Insofar as existing receivers had system E, channels F2 and F4 capability, some might have had the fine-tuning range to cover the new system L Band I channels.  Of course, this would work only if the Band I channels were indirect.
 
Without that consideration, then system L, Band I capability would have applied to new receivers only, which could have been specified with a different IF configuration.  In particular, 38.9 MHz VIF, 32.4 MHz SIF would have allowed the use of direct Band I channels for system L.  It would also have worked for Bands III and UHF, albeit with supradyne rather than the customary infradyne conversion.  That this IF channel was not that originally used for geographical channel allocation planning would have been of less moment in the mid-1980s, when much better screening of individual receiver circuit modules was possible and in fact routine.
 
A reasonable deduction is that the shift to 38.9 MHz VIF for system L did not come so much from the French industry, but from external influences.
 
The earliest reference I have found to the use of 38.9 MHz for system L was in the 1985 Philips Germany paper on multistandard receivers, referred to in a recent post, https://www.radios-tv.co.uk/community/black-white-tvs/television-receiver-intermediate-frequencies/paged/7/#post-114246
 
As noted, this suggestion did not appear to take account of the Band I channels.
 
A slightly later Philips Netherlands IEEE paper had on multistandard receivers had a somewhat different approach.  The paper was:
 
“Processing of IF Television Signals in a Multistandard Environment”, by M. Trzyna, H. Apeldoorn, V. Frequin, J. Inghels, H. Schmidt, 1986 June.
 
This was primarily about the development of a suitable IF processing IC, including the various conditions it had to cater for:
 
In respect of the incoming IF, it was said:
 
“The bulk of European receivers use either Low Intermediate Frequency - 32.7 MHz or High Intermediate Frequency - 38.9 MHz (or the close proximity of it).  The U.S.A. uses 45.75 MHz and Japan uses 58.75 MHz.
 
“Taking into account, that the performance of the I.F. processor depends on the phase relations of internal signals at those frequencies, it sounds reasonable that the processor is provided with (external) info about the (Low or High) intermediate frequency being used. It stands to reason, that the ref. circuit combination of the synchronous demodulator must also be kept informed.”
 
The terms “low: and "high” in respect of VIF I should take to refer to their relative positioning in the IF channel, i.e. low end for 32.7 MHz and high end for 38.9 MHz, rather than their positioning in the sub-41 MHz spectrum.  That contrast with, for example, the earlier American convention when low IF referred to the early 25.75 MHz standard, and “high” to the subsequent 45.75 MHz standard.
 
Anyway, it was evident that the new multistandard IF processing IFIC would need to cater for 32.7 as well as 38.9 MHz.
 
“Close proximity” of 38.9 MHz probably meant the 38.0 MHz standard that applied for systems D/K, and the 39.5 MHz standard that applied to system I in the UK and Eire.  In particular, with the demise of the UK 405-line transmissions, and so the need for dual-standard receivers, the raison d’être for 39.5 MHz disappeared, meaning that reversion to 38.9 MHz was possible and logical.
 
AFC Polarity was another consideration, about which it was said: 
 
“Conditions in France dictate the use of both the infradyne and supradyne mixing in the channel selector.  This implies, that both positive and negative slopes of the A.F.C. voltage versus frequency have to be delivered, again on command from an external control device.”
 
Clearly this was a reference to the fact that the French Band I channels required supradyne conversion, as opposed to infradyne for the Band III and UHF channels.  This is also consistent with a view that the multistandard IF channel had to deal with the 32.7 MHZ VIF as well as 38.9 MHz.
 
One may deduce that at the time, Philips NL was not thinking in terms of moving to the 38.9 MHz VIF for system L, notwithstanding Philips Germany’s prior suggestion.  It could have been that Philips NL took account of system L’, whereas Philips D had evidently not done so.
 
The Philips NL paper did not specifically mention system L’.  Perhaps at that time the designation was not in play.  As previously mentioned, L’ was never adopted as formal name by CCIR or ITU-R.  Perhaps it was introduced at some stage by other groups, such as SCART in France.  That kind of thing happened later.  E.g., the EBU coined “B1” for the 8 MHz VHF channel version of system B.  But in that case the EBU used it as an anticipator name, one that was later adopted by the ITU.
 
Nonetheless, the IF IC development that was the subject of the Philips NL paper effectively prepared the way for the dual-Nyquist IF strip era, in that it could be switched between two VIFs, at opposite ends of the VIF channel.  Instead of 32.7 and 38.9 MHz as originally envisaged, 33.4 or 33.9 and 38.9 MHz would have been easily accommodated.
 
One could also gain the impression from the two papers at interest that Philips NL and Philips D were not always fully synchronized, and that the latter sometimes pushed its own agenda.  (In a transnational, multifaceted organization it would be unusual if some subsidiaries did not endeavour to operate quasi-independently at times.)
 
So far, I have not identified the Philips TV IF IC that was the subject of the 1986 paper.  It retained quasi-synchronous vision, albeit in an improved form.  That feature would seem to have placed it as being subsequent to the TDA2579.  Philips seems to have been a relatively later mover to PLL fully synchronous demodulation; that came with the TDA98xx series ICs of the 1990s, although perhaps there were earlier examples.
 
Anyway, we may see that:
 
- The use of the 38.9 MHz VIF for system L was suggested at least as early as 1985;
 
- The advent of system L’ may have slowed down the start of a migration to 38.9 MHz, but it did promote the development of VIF-agile TV IF processing ICs; .
 
- The eventual solution was the dual-Nyquist IF strip and associated SAWFs, established by 1990.
 
 
Cheers,
 
Steve
 
 
Posted : 28/12/2022 1:38 am
Synchrodyne
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Just after writing and placing the preceding post, I discovered an earlier example where 38.9 MHz was used as a system L VIF in a multistandard receiver, namely the Philips Netherlands KM2 chassis.
 
The KM2 dated from 1975, perhaps a little earlier, and was a derivative of the Philips NL K9 chassis, which was single standard, systems B/G/H, with PAL colour, and as far as I know, dated from 1972.  The KM2 was essentially in a Belgian configuration, coverings systems B/G/H, C and F, E (almost certainly Band III channels only) and L (UHF and Band III only), with PAL and SECAM colour.
 
The question then arises, was the KM2 a harbinger, a bellwether or simply an anomaly.
 
My best guess is that it was an anomaly.  The K9 and KM2 certainly predated the use of SAWFs.  They were on the cusp of the widespread adoption of quasi-synchronous demodulation.  As fa as I know, the K9 had conventional envelope demodulation.  The Philips TCA270 quasi-synchronous demodulator dated from 1972, but it was configured for negative vision modulation.  Thus there was no apparent compelling technical reason for Philips top have departed from the established IF set for this type of receiver, namely 38.9 MHz VIF, 33.4 MHz SIF for systems B/G/H, C and F, 39.9/28.85 MHz for system E and 39.9/33.4 MHz for system L.
 
A possible explanation is that Philips wanted to maximize the use of existing K9 circuit modules without modification, including that for the vision IF.  That would have dictated the use of the 38.9 MHz VIF for all systems.  It would have been short of bandwidth for system L, and a lot short for system E, but that was evidently not a major concern.  Thus the IF set was 38.9/33.4 MHz for systems B/G/H, C and F, 38.9/27.75 MHz for system E, and 38.9/32.4 MHz for system L.
 
From the available information, it appears a video polarity inversion switch module was inserted between the vision IF and luminance modules, to enable the receiver to deal with positive as well as vision modulation.  The existing 5.5 MHz sound intercarrier module was retained, and an AM sound module was added, this dealing with three SIFs, namely 33.4, 32.4 and 27.75 MHz.
 
As would be expected, SECAM chrominance modules were added, and presumably the line timebase was modified to handle 819/50 as well as 625/50.
 
 
Cheers,
 
Steve
 
 
Posted : 01/01/2023 1:07 am
Synchrodyne
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Another, and a quite late approach to TV-FM receiver design was shown by Thomson R&D Americas in a 1991 IEEE paper (*).
 
Here is the block diagram for the receiver, which as well as TV and FM, was also equipped to receiver the US National Weather Service (NWS) NBFM broadcasts in the 162 MHz range.
 
 
Thomson TV FM Rx
 
 
 
From the TV perspective, it followed standard US practice, and although not stated, it is reasonable to assume that it used a standard SAW filter with the standard 41.25 MHz SIF and 45.75 MHz numbers.
 
The tuner and its associated PLL system were modified to include the FM band (88-108 MHz) and the 162 MHz NWS channels.  These were converted to a 1st IF of 43.3 MHz, which was roughly in the middle of the TV IF band.  This was tapped off ahead of the SAW filter preamplifier, and then downconverted, supradyne, to the standard FM IF of 10.7 MHz for final processing.
 
Originally, Thomson had planned on an FM/NWS 1st IF of 44.0 MHz.  However, this was unsatisfactory at the lowest FM channel, 88.1 MHz, where the tuner produced a spur at 44.1 MHz, which was within the FM/NWS IF channel bandwidth.  Although not stated, it looks as if the 2nd harmonic of the 1st IF, 88.0 MHz, was beating with the LO at 132.1 MHz, to produce the 44.1 MHz spur.  Thomson noted that moving the 1st IF down by at least 200 kHz was the solution.  The chosen 43.3 MHz was 700 kHz away from 44 MHz, so that its 2nd harmonic, 86.6 MHz, beating with the 131.4 MHz LO, would have produced a spur of 44.8 MHz, far enough away from the 43.3 MHz IF channel not to be troublesome.  It also looks as though 43.3 MHz specifically might have been chosen to allow a 2nd conversion LO frequency of 54.0 MHz exactly.  This was at the bottom edge of the lowest US TV channel 2 (54- 60 MHz) and its 2nd harmonic, at 108 MHz, was at the top edge of the FM band (88-108 MHz), which would have kept it out of harm’s way.  
 
The 43.3 MHz 1st IF channel also included a 48.85 MHz trap, to minimize the “half-IF” response.  This is a key parameter used to assess the linearity of FM front ends.  It arises because an unwanted signal that is removed from the wanted signal by half of the IF (i.e. usually 10.7/2 = 5.35 MHz), in the direction of the LO, can cause severe interference.  What happens is that the 2nd harmonic of the LO beats with the 2nd harmonic of the unwanted signal to produce a 10.7 MHz IF signal, overlaid on the wanted signal.  Insofar as linearity considerations often focus on third order products, some which are inherently in band, second order effects, usually expected to be well out-of-band, might be overlooked, including the half-IF case.  With many FM receivers, RF selectivity alone would not have provided significant rejection of signals at the half-IF point, hence the need for adequate linearity in the mixer.  For the receiver at interest, 48.85 MHz is of course 5.35 MHz above 43.3 MHz.  In respect of the 1st IF half-IF response, the front end itself would have provided adequate rejection of signals 43.3/2 = 21.65 MHz above the desired signal.
 
Thomson had an interesting approach to NWS reception.  As said, this is NBFM.  I don’t know the exact parameters, but my best guess is ±5 kHz maximum deviation, a 3 kHz maximum audio frequency, and phase modulation, i.e. a constant 6 dB/8ve pre-emphasis across the AF range.  (This corresponds to the marine VHF parameters after the change from ±15 kHz deviation and 50 kHz channelling to ±5 kHz deviation and 25 kHz channelling in the 1970s.  NWS might well have been ±15 kHz in the early days.)
 
The NWS uses seven channels, at 162.400, 162.425, 162.450, 162.475, 162.500, 162.525 and 162.550 MHz.  The Thomson receiver, when switched to NWS, was set to the centre channel, 162.475 MHz, with the others then at ±25, ±50 and ±75 kHz relative to it.  The FM IF channel bandwidth of ±100 kHz was wide enough to allow all seven channels to reach the demodulator.  Capture effect was then relied upon to select the strongest channel and reject the others.
 
As an aside, one may wonder what happened when two NWS signals of approximately equal strength were available, as is the case in say parts of the Dallas-Fort Worth area.  (And where one might want to selectively access both transmissions.)
 
Thomson stated “Switched-gain amplifiers are needed to volume match the weather band audio to that of FM radio”, and these are shown in the block schematic.  Given the large difference in deviation, ±75 kHz for FM against ±5 kHz for NWS, then the latter would certainly have needed more AF gain, nominally about 16 dB, although subjective volume matching may have produced a somewhat different number.  Nothing though was said about switching the de-emphasis.  For NWS, assumed to use PM, that would have required 6 dB/8ve across the band.  Sometimes that kind of de-emphasis was done with a 750 µs filter, with turnover at around 210 kHz, satisfactory given that the actual AF bandwidth was probably 300 Hz to 3 kHz.  Using the 75 µs curve for NWS would have resulted in a rising response to 2.1 kHz, and flat thereafter, which may well have been deemed fit-for-purpose.  Still, at least Thomson attended to volume matching.  In some portable combined FM-TV sound-NWS receivers, that was not done, with the result that much higher volume control settings were needed for NWS.
 
In its introduction to the paper, Thomson said:  “In the past, a radio in a TV consisted of a seperate radio module mounted in the TV cabinet that used the TV's power supply and speakers. When using these radios, the TV was usually turned off when the radio was in use. This created a "delay", for the user, when going from the radio mode to the TV mode. The integrated radio offers the advantages of no changeover delay and significant cost savings at the expense of giving up AM reception.”
 
That statement was true in the context of the relatively recent past.  For example, the combined receivers often found in American hotels in the 1980s and 1990s had separate, and separately tuned radio sections, sometimes with their own volume controls.  But it was not accurate if one goes further back.  The earliest American TV-FM receivers, in the later 1940s, and into the very early 1950s, typically used the same tuner unit for both TV and FM, sweeping from 44 (later 54) MHz right through to 216 MHz, and the same IF strip, with FM sharing the TV sound IF, usually to the early “low” standard of somewhere in the 21.25 to 21.9 MHz range.  This type of receiver soon died out, for several reasons, including the swing to intercarrier sound, the advent of standard third party turret tuners, and then the move to the “high” IF, where the 41.25 MHz TV sound number was probably viewed as being on the high side for good FM performance, as well as more difficult for split TV sound.
 
Also, in the second half of the 1950s and into the early 1960s, most British TV-FM receivers were fairly well integrated in front end and IF strip terms, although the use of separate FM front ends and/or separate FM IF strips was not unknown.
 
Clearly, this case is a curiosity, well away from the mainstream.  But it does well illustrate some of the points about IF selection and consequent receiver performance characteristics, such as the 2nd harmonic issues.  Also, with the inclusion of NWS it effectively mixed both broadcast and communications type reception in the one unit.
 
 
(*) “TV, FM Radio and Weather Band Receiver with Integrated Tuning”, by Gary D. Grubbs, William L. Lehmann, and Larry S. Wignot, Thomson R&D Laboratories, Americas, IEEE 1991 June.
 
 
 
Cheers,
 
Steve
 
 
Posted : 10/04/2023 3:56 am
Synchrodyne
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Upthread, about a year ago, and in respect of multistandard TV receiver IFs, I said:
 
“Barco (Belgium) was an early player in that field, with semi-professional all-standard monitor-receivers, such as the CRM2631, offered in the mid-1970s.  I have never discovered the IF structures of those models.  One may infer that Barco’s presence in that field was a direct consequence of the fact that Belgian domestic TV receivers were multistandard from the start.  And that would suggest that the 1970s Barco models had Belgian style IF structures.  But it is apparent that the CRM2631 covered the system E Band I channels, normally omitted in Belgian practice and essentially excluded by the customary Belgian IF structure.  That made me wonder if Barco had not used a French multistandard IF structure, which prompted another close look at the French case, and so the above posting.  One could say that if the objective (in that period) was an all systems, all channels receiver, then French practice was the better starting point.”
 
Information on Barco multistandard TV receiver IFs as they were in the 1960s and 1970s remains elusive.  I have though found an interesting comment in the Barco Timeline at:  https://www.barco.com/en/about/this-is-barco/timeline, as follows:
 
“1962 We start to produce multi-standard television sets. From now on, our TVs can receive no less than five different transmission standards, which propels TV setmaking to higher levels.”
 
There was some exaggeration in that.  Belgian domestic TV  receivers were, from the start, equipped for four standards, namely B, C, E and F, although with limited channel coverage for system E.  Thus multistandard was inherent in Belgian practice.  Whether or not, up to that time, Barco had made single-standard receivers for use in other European countries is unknown.  My take on the Barco statement is that from 1962, it made only “wide range” multistandard receivers, and that these were suitable for widespread use in Europe (and perhaps elsewhere) and had commensurately full channel coverage.  In 1962, the five standard minimum could have been B/G/H, C, E, F and L.  Or it might have meant A, B, C, E and F.  Be that as it may, given that Barco was the producing only multistandard receivers, it could well have chosen its IFs accordingly.  Other setmakers who produced a few multistandard models alongside much larger runs of single-standard models were probably more constrained in their IF choices.
 
Thus it would seem important to include a commentary on Barco IF practice in this series, if and when the requisite information can be found.  Whether it throws up anything different to what has already been discussed remains to be seen.  As already said, probably the most difficult aspect for all-channel multistandard receivers was accommodating the system A and E Band I channels, given that these were indirect (inverted) and that supradyne frequency conversion was necessary, resulting in a direct (non-inverted) IF channel.
 
 
Cheers,
 
Steve
 
Posted : 30/11/2023 10:57 pm
Synchrodyne
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Not yet treated in any detail in this series is the subject of double conversion (of both vision and sound) for analogue TV receivers.  It was strongly associated with cable TV (CATV), but was also used for off-air reception.  I have found a limited amount of pertinent information, which I’ll develop into future postings.
 
Already considered are examples where, for various reasons, the sound channel has been subjected to a second conversion, whereas the vision channel had but a single conversion.  Intercarrier sound actually fell into this category, the “local oscillator” source for the second conversion being the vision carrier itself.  That made it a drift-cancelling “loop”, in that any drift in the main local oscillator did not appear in the intercarrier.  The basic intercarrier system was somewhat flawed, but later implementations, using PLL recovery of the vision carrier, could approach and even come close to matching split sound quality, and could be used for AM was well as FM sound.  That has been covered in a separate thread, “Intercarrier Sound”, see:  https://www.radios-tv.co.uk/community/black-white-tvs/intercarrier-sound/.
 
Taking a broad view, probably the earliest use of double conversion was in the USA, at the beginning of the UHF era.  There were some VHF-UHF tuner units that used double conversion on the UHF channels only.  These were initially converted to a spare low-band VHF channel, typically A5 or A6, but sometimes a high-band VHF channel, such as A9, A10 or A11.  The output channel was typically selectable or tuneable so that a locally unused channel could be chosen.  The resultant “1st IF” was then fed into the normal VHF tuner circuitry for conversion to the standard IF.  The first conversion was necessarily infradyne, so that the “1st IF” retained the VIF low orientation.  This approach was fairly quickly superseded by UHF tuners (or combined VHF-UHF tuners) that had direct conversion to standard IF.  Double conversion increased the possibilities for interference problems as compared with single conversion.  Also, the use of mass-produced relatively simple but precision single-conversion UHF tuners feeding into VHF tuners with an additional selectable “channel” at the standard IF was probably more economic.
 
A similar double conversion approach was used in the USA for outboard UHF adaptors.  These seemed to have remained available until the end of the 1950s at least.
 
Similar UHF converters were used for a while in the early days of UHF TV broadcasting in Europe, very late 1950s and early 1960s.  Typically the incoming UHF channels were converted to VHF channels E3 or E4.
 
In the above cases, double conversion applied only to the UHF channels.  These were infradyne converted to a “1st IF” that corresponded to one or other of the established VHF channels, the second conversion to the applicable standard IF being done by the VHF tuner (or VHF side of the combined tuner).  The VHF channels were subject to the customary single supradyne conversion.  This method was used only where the essentially the same TV system was used for UHF as had been established  at VHF.  (Systems B, G and H would be regarded as being the same system for this purpose.)  In countries where a different system was chosen for UHF (e.g. France, UK), it was not applicable.
 
A broadly parallel situation arose in the UK in 1955, with the advent of Band III transmissions.  Most existing receivers were Band I only, and were either fixed tuned to a single Band I channel, or where adjustment was possible, it was usually a service activity, not a consumer control.  Various means were used to adapt/convert existing Band I-only receivers to accept the new Band III channels.  One of those was the use of an adaptor, outboard or mounted within the receiver, that converted a selected incoming Band III signal to a suitable Band I channel.  With single-channel receivers, that meant using the same channel as for the local Band I transmission, which certainly created the opportunity for mutual interference.
 
Existing receivers could be of the superhet or TRF type.  With the superhet type, the combined adaptor/receiver was double conversion only on the Band III channels.  These were infradyne converted to a “1st IF” of one of the Band I channels, with the second conversion done in the receiver proper.  The Band I channels were subject to single conversion only.  At that time, receiver IFs had not been standardized, so varied somewhat, both in frequency and orientation, with infradyne or supradyne conversion used according to the latter.  With TRF receivers, the combination was single conversion (infradyne) on the Band III channels, and TRF on the Band I channels.
 
 
Thus one could say that double conversion had made an appearance quite early in the TV era.  Next will be a look at a 1973 RCA layout for a “cable ready” TV receiver.
 
 
Cheers,
 
Steve
 
Posted : 30/11/2023 10:59 pm
Nuvistor
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Hi Steve,

In the UK some communal aerial systems, in my district local authority flats, down converted BBC2 UHF Channel 62 to an unused VHF Channel. For dual standard TV sets that couldn’t accommodate 625/VHF,  Labgear produced a Televerter to up convert the VHF BBC2 signal to UHF. 
I installed a few of them but can’t recall the exact details, my excuse, it was 1965. 

Frank

 
Posted : 01/12/2023 8:04 am
Synchrodyne
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Thanks, Frank – I had missed that case.  I suspect that it was a very early example of both upconversion for domestic TV receivers, and a UHF band frequency as the “1st IF”.
 
I imagine that the BBC2 signal distribution was done on one of the designated 8 MHz VHF channels (Band I, A through C and Band III, D through I) so as to suit those receivers whose VHF tuners could be used for System I signals.  Thus, infradyne upconversion would have been used to translate to an appropriate UHF channel for the receiver input whilst retaining the vision-carrier-low orientation.  That UHF channel was then effectively the 1st IF in what overall was a double-conversion system.
 
 
Cheers,
 
Steve
 
Posted : 01/12/2023 11:10 pm
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Nuvistor
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@synchrodyne Photo of one, photo from UKVRRR. They were also used when the communal system put BBC1 and ITV 625 onto  the VHF channels, it allowed us to install UHF only sets to customers in the flats.

IMG 2956

Frank

 
Posted : 01/12/2023 11:22 pm
Synchrodyne
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As mentioned, double conversion TV receivers were strongly associated with cable television TV (CATV), which was a growth industry in the USA in the early 1970s.  Although CATV could be received by using external adaptors that converted the incoming cable signals to a suitable VHF channel for then feeding into a regular TV receiver, there was a desire for receivers that were capable of being directly connected to cable systems, and able to access all channels thereof, without the need for an external converter.
 
At the time, US CATV systems were of two types, namely single cable and dual cable.  The dual cable type used the existing VHF TV channels A2 through A13, and thus were able to provide a total of 24 channels.  These could be received by standard receivers, albeit that a means of switching between the two cables was required.
 
The single cable systems also used all 12 of the VHF broadcast channels, plus additional channels both above and below the VHF high band.  Channels A through I (nine of) occupied the range 120 to 174 MHz, and J through N (five of) the 216 to 246 MHz range.  Thus the range 120 to 246 MHz was continuously occupied by 21 TV channels.  With the five VHF low band channels, a single cable could provide a total of 26 channel choices.
 
Full coverage of the 120 to 246 MHz range was likely beyond the reasonable capability of typical VHF TV tuners.  Perhaps 246 MHz was not too much of a stretch with modern devices such as dual-gate mosfets.  But a high band tuning range of greater than 2:1, with performance well maintained over the whole band, probably was a big stretch for the then-incoming varactor type tuners.  One way of avoiding the problem was to use double conversion with an initial upconversion.  That allowed the whole 54 to 246 MHz band to be covered without bandswitching, and without the need for a tuned input circuit, as upconversion to a suitably high 1st IF ensured that images were removed to well above the highest input frequency.  Another benefit was that the lack of an input tuned circuit ensured that the impedance presented to the incoming cable (nominally 75R) did not vary over the band as different channels were selected, and so did not create undue VSWR problems.
 
RCA chose that approach for its KRK-212 cable tuner of 1973, as shown in this block schematic:
 
RCA KRK 212
 
As may be seen, there was no RF amplifier, the incoming signal going direct to a balanced mixer fed by a varactor-controlled oscillator.  The latter was variable over the range 640 to 830 MHz, a fairly narrow span of 1.3 to 1.  The resultant 1st VIF was 587.75 MHz.  The conversion was necessarily supradyne, given the input signal range of 54 to 246 MHz.  This produced channel inversion, with a 1st SIF of 583.25 MHz.
 
The 1st VIF was between the vision and sound carriers for US UHF channel 33 (585.25 and 589.75 MHz) and the 1st SIF was just below the sound carrier of channel 32 (583.75 MHz).  Presumably the 1st IF was chosen to minimize any interference effects from the UHF broadcast channels.
 
The second conversion was necessarily infradyne, in order to avoid another channel inversion.  With a local oscillator frequency of 542 MHz, it produced a 2nd IF at the Norther American standard numbers of 45.75 MHz VIF and 41.25 MHz sound.
 
 
The RCA TV receivers in which the KRK-212 cable tuner was used also included a KRK-211 VHF tuner and a KRK-194 UHF tuner for off-air reception.
 
For use with single-cable systems, the KRK-212 was of course used for cable reception.  With two-cable systems – which used only regular VHF broadcast channels though, the KRK-212 was used for one of the cables, with the KRK-211 used for the other.  In the latter, as filter network was used at the input to ensure that the impedance presented to the incoming cable was reasonably constant over the frequency range.
 
As best I can determine, this 1973 RCA case was a very early example double conversion being built-in to a domestic TV receiver.  I am not aware that it set a strong precedent for TV receivers as such, but it would appear that set-top cable converters did follow this pattern, although probably with different 1st IFs.  As the range of the cable channels was extended upwards into the lower UHF region, higher 1st IFs would have been necessary anyway.
 
More to follow.
 
 
 
Cheers,
 
Steve
 
Posted : 02/12/2023 1:06 am
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