Quite some time back (early 1970s, I think), I set out to make a list of the standard television receiver intermediate frequencies associated with the major (terrestrial, analogue) broadcast transmission systems. There was no particular reason for so doing beyond idle curiosity. At the time I didn’t get all that far, but now with access to more information, I decided to complete the list to the extent that I can, although there are still some gaps and interesting questions. Having completed the summary, and this being the season for oddities and stepping out of the mainstream, it seemed reasonable to post it here.
My original list started with four of the better known examples:
1. North America, System M, 525/60: 45.75 MHz vision, 41.25 MHz sound (RETMA)
2. UK, System A, 405/50: 34.65 MHz vision, 38.15 MHz sound (BREMA)
3. Western Europe, System B (& later G, H), 625/50: 38.9 MHz vision, 33.4 MHz sound (CCIR?)
4. UK, System I, 625/50: 39.5 MHz vision, 33.5 MHz sound (BREMA)
Of the above, (1) through (3) were all established by late 1954, but all were introduced some time after their respective transmission systems were actually in use, following an earlier period in which lower, and usually non-standard intermediate frequencies had been used. Clearly, each was the result of careful tradesoff amongst the competing requirements including avoidance of beats whether internally or externally caused, and minimization of interference with other receivers and devices. Thus the choices would have taken account of the actual channel frequencies in use as well as the respective system parameters. All three had in common that they were placed just under the lowest Band I (low band) channel frequency, effectively as high as could be without invoking up-conversion, presumably to maximize image rejection inter alia. And all three were based upon “oscillator high” frequency conversion, such that the relative positions of the vision and sound carriers are transposed during frequency changing.
45.75 MHz arrived in US practice in 1950. Previously 25.75 MHz was a commonly used frequency. The higher number moved all VHF images out-of-band, and in the case of the VHF low band (Band I), above the FM band (Band II). In the UHF case, where images are unavoidably in-band, the FCC assumed a receiver IF of 45.75 MHz when it planned the UHF channel assignments in 1950-51, and at some stage thereafter it was adopted as a RETMA recommended standard.
The BREMA numbers for the UK 405-line system were as far as I know developed during 1954 in anticipation of the 1955 start of ITV Band III broadcasting. So as with the RETMA case, they were related to expansion of the channel frequencies used by an existing standard. Previously various lower numbers had been used for Band I-only receivers, such as 16.0 MHz vision, 19.5 MHz sound.
The CCIR IF numbers seem to date to somewhere in the 1953-54 period. Philips literature from 1953 associated with the original world series of TV valves gave an example receiver with IFs of 23.75 MHz vision, 18.25 MHz sound, so it seems unlikely to have been earlier than that. Whereas the US and UK standard IFs were promulgated by the respective receiver and allied equipment trade associations, RETMA and BREMA, as far as I can tell, although I am not completely sure, the European number of 38.9 MHz was established under CCIR auspices.
It would appear that the 38.9 MHz vision IF has been used worldwide wherever Systems B, C, F, G and H have been deployed, except that Australia had a different standard number. So one might say that it was a relatively robust choice when measured against the diversity of channelling systems actually used for Systems B/G/H, including the 8 MHz European UHF channelling which I doubt was in view back in 1953-54. In later years 38.9 MHz was also used to some extent for Systems D, I, K, K’ and L.
The BREMA and CCIR IFs were a little lower than those of RETMA, and this would appear to stem from the relativity of lowest frequency channels used for broadcasting. In North America the lower edge of the low band started at 54 MHz, whereas in Europe Band I started at 41 MHz, and in the early 1950s there was the possibility that channel E1, 40 to 47 MHz, might have been used. Thus European IFs needed to be below 40 MHz.
And so on to (4), the UK BREMA 625-line IF. This chosen in advance of establishment of the UK UHF TV network, and were developed in conjunction with the channel assignment plan, which included receiver image rejection as a defined parameter. I think it reasonable to assume that some account would also have been taken of the needs of the Irish TV network which also used System I in Band I and Band III channels, and the below-40 MHz positioning tends to support this. Anyway, here was a case where the optimum IF was chosen before transmissions started, not afterwards.
That the System I vision IF was 39.5 MHz as compared with the 38.9 MHz of Systems B/G/H is, on its face, simply the result of picking the best trade-off given the conditions prevailing. But then when South Africa adopted System I later in the 1970s, broadcasting in Band III and on UHF (European channel frequencies), it adopted standard IFs of 38.9 MHz vision, 32.9 MHz sound, the 38.9 MHz number aligning with that for Systems B/G/H. Assuming that 38.9 MHz was an appropriately considered choice, it certainly prompts a rethink of the basis for the UK choice of 39.5 MHz. Thus I wonder if it (the UK choice) was also influenced by the need for receivers to be dual-standard, which in turn would have made 38.9 MHz a less than ideal choice in terms of ease of receiver IF strip design, at least for those set makers pursuing maximum simplicity.
Consider that Mullard at least on occasion advocated dual-standard IF strips whose basic bandpass characteristic was 6 dB down at 34.65 and 39.5 MHz respectively, and so which included the Nyquist slopes for both the 405- and 625-line cases, additional system-specific shaping being provided by switchable traps, etc. This basic curve thus allowed a 625-line vision bandwidth of 4.85 MHz at -6 dB, which although short of the 5.5 MHz transmitted, was deemed to be adequate for most domestic receiver purposes. On the other hand, with a 38.9 MHz vision IF, the basic 6 dB bandwidth would have been 4.25 MHz, perhaps not enough for those setmakers who wanted 625 line horizontal definition to match that for 405 lines. Then the 405-line Nyquist slope would have had to be switchable. So it seems at least plausible that 38.9 MHz would have been found acceptable for 625-line reception alone, but that it was desirable to find another satisfactory number about half a MHz higher to more easily accommodate dual standard receivers, hence 39.5 MHz.
Now to some other examples:
5. Japan, System M, 525/60: 58.75 MHz vision, 54.25 MHz sound
6. Eastern Europe, Systems D & K: 38.0 MHz vision, 31.5 MHz sound
7. China, Systems D & K: 37.0 MHz vision, 30.5 MHz sound
8. France, Systems L & L’: 32.7 MHz vision, 39.2 MHz sound
9. South Africa, System: 38.9 MHz vision, 32.9 MHz sound (SABS standard)
10. Australia, System B: 36.875 MHz vision, 31.375 MHz sound
The relatively high IF used in Japan stems from the fact that the lower edge of the lowest TV channel, J1, was 90 MHz. Whether the 58.75 MHz number was used from the start of the Japanese TV service in 1953 I do not know, but a history wherein the American 45.75 MHz number was used initially, followed by an upward migration, is quite plausible. Japan appears to have been the only exception to the use of 45.75 MHz for System M, which number was also used for System N in Latin America. Also, Japan was the only example of a country not using Band I/low band for TV channels that took advantage of the opportunity that the non-use gave to move to a higher standard IF.
The Eastern European 38.0 MHz number seems unlikely to have been used from the start of 625-line television in the USSR, but was more likely a standard introduced in the first half of the 1950s after earlier use of lower IFs. It would appear that in later years, 38.9 MHz vision, 32.4 MHz sound was also used.
I am not sure about the 37.0 MHz number for China. It is from a single datapoint and it is not immediately apparent why it would be different to the Eastern European number. But whether 37.0 MHz or 38.0 MHz, it was probably used from the start of TV broadcasting in China in 1958.
The French System L IF had the vision carrier below the sound carrier, which would have required having the local oscillator on the low side of the signal, evidently not a problem with the UHF and Band III channels. When System L was extended to Band I, it was as System L’, with the channels configured with the vision carrier high, thus allowing use of the standard IFs with oscillator high.
I have not come across any information on IFs for French 819-line (System E) receivers, but there is evidence that French dual-standard receivers used the same 32.7 MHz vision IF for both systems, which would put the System E sound IF at 43.85 MHz. Whether the 32.7 + 43.85 MHz combination was used before the dual-standard era I do not know, but it seems possible maybe probable, unless there was a complete rethink at the beginning of the dual-standard era. Given the tête-bêche channelling system used in French VHF practice, oscillator low would have been required for the odd-numbered Band III channels F5 through F11, and oscillator high for the even-numbered Band I (F2, F4) and Band III (F6 through F12) channels. I am not sure which channels were tête and which were bêche, but as F8A was the first used, it is probably not unreasonable to assume that the even-numbered channels were tête. At one time Band I bêche channel F3 was listed, but not I think actually used. If 32.7 + 43.85 MHz had been used from the inception of French 819-line broadcasts in 1950, then firstly it was an early start with a “high” IF, and secondly the sound IF was actually inside Band I, which seems odd at first glance. But then perhaps the original thinking was to use only Band III for the 819-line service, although 43.85 MHz was also within the Paris 441-line channel F1. As I understand it the French for a short while did toy with the idea of having regular (405 or 441 line) and very high definition services side-by-side. The F channel allocations bespeak of a rethink, too. The original, used at Paris and Lille, was at the lower end of Band III, 185.25 MHz vision, 174.10 MHz sound. Then there was a change, possibly connected with a decision to go with 819 lines only, that introduced the tête-bêche system, inclusive of Band I channels and in the Band III case, with allocations starting at 162 MHz, below the lower edge. Thus the original channel became a non-sequitur, and was numbered as F8A.
Mention of the Lille transmitter, which allegedly was sited to give good coverage into Wallonia, brings in Belgian multistandard TV receiver practice. At least based upon information on some of the Philips models during the valve era, these were designed to receive Systems B, C and F on all E-channels, and System E on channel F8A (Lille) only. The standard CCIR IFs of 38.9 MHz vision, 33.4 MHz sound applied to Systems B, C and F. System E used 38.9 MHz vision, 27.75 MHz sound. Early examples had a second down-conversion for sound on all systems, to 7.0 MHz. Later, intercarrier sound was used for System B with a dual frequency (33.4 and 27.75 MHz) AM sound IF strip. Unknown is whether the 38.9 MHz vision IF number had been determined before the start of Belgian TV in later 1953.
In more recent times, multistandard receivers have used 38.9 + 32.4 MHz for System L, with 33.4 + 39.9 MHz for System L’, although that implies separate IF filters for L and L’.
The 32.7 MHz vision + 39.2 MHz sound IF combination was also nominal for the French Outré Mer System K’, which used Band III channels only. But 38.9 + 32.4 MHz was likely also used. Notwithstanding the fact that Band I was not used, existing standard numbers were preferred to the somewhat higher numbers that could have been possible.
The same could be said of the South African case, which has already been mentioned in comparison with the UK case.
Australia seems to have been the only System B country to deviate from the 38.9 MHz standard. Possibly its choice of 36.875 MHz was connected with its use of Band II TV channels and the need to avoid interference with non-broadcast services. Australia was also the only System B country to use 7 MHz rather than 8 MHz UHF channelling.
Note that I have not attempted to add-in second sound carrier IFs where used. In IF terms these lay where they fell as the result of existing vision carrier-to-oscillator relationships, and did not cause any fundamental changes.
Last edited by CTV
on Thu Dec 27, 2012 10:29 am, edited 1 time in total.
Reason: Superb information