Axiomatic here are the interrelationships between TV receiver intermediate frequencies, the range of TV channel frequencies to be received, and the geographical allocations of those channels.
In general, one might expect that channel frequencies would have been assigned first, based upon the ITU Atlantic City 1947 band allocations, then the geographical disposition of those channels, and finally the optimum IFs. But it has not always turned out that way, as shown in the following commentary.
In the US case, the FCC assigned the VHF TV channels in 1945. This was ahead of Atlantic City 1947, at which the US 1945 VHF broadcasting bands (minis TV channel 1) were then adopted for all of Region II. Very quickly the RMA developed its initial “low” IF recommendation in line with those channel assignments. This “low” IF turned out to be problematical, so the RMA withdrew it in 1948 and then developed a new “high” IF, released in 1949. Even though a second iteration was needed in respect of the IF choice, both iterations followed rather than preceded the channel assignments. The “high” IF did not impose any undue restrictions on VHF channel geographical allocations beyond what was anyway reasonable practice.
But the FCC then used the new “high” IF as the basis for its UHF channel geographical allocations. With the UHF channels, in-band images and other interferences were, short of upconversion, unavoidable, so allocations had to be made with these in mind. The FCC had no power to fix a standard receiver IF, but by basing its UHF channel allocations on the RMA standard, it did provide a strong endorsement. So in this case, the channel allocations followed determination of the IF.
In Europe, definition of the VHF TV channels, both within and in some cases without the Atlantic City 1947 band limits, was undertaken at the ITU Stockholm 1952 meeting. Initial geographical channel assignments were also made at that meeting. But at the time, no standard TV receiver IFs had been developed except in Italy.
As noted in the previous posting, it certainly looks as if the prior Italian choice of standard IF, modelled on American practice, determined its need for non-standard channelling in both Bands I and III, which meant that it had one fewer Band III channel than did the other countries in Europe that used System B.
The CCIR standard System B IF of 38.9 MHz was evidently developed circa 1954 to fit the channels assigned at Stockholm 1952.
In the UK case, it was the imminent use of Band III and the consequent advent of multichannel tuning that led to the development of the BREMA standard IF. This was based upon the System A channel frequencies already defined.
Both the CCIR and BREMA IFs did not impose any undue restrictions on VHF channel geographical allocations beyond what was anyway reasonable practice.
The French case was somewhat different, though. The tête-bêche channelling for System E was defined at Stockholm 1952. And this included a small number of Band I assignments, although originally it had been planned to use only Band III for the 819-line service.
The development of a standard IF, at least one that was practicable, inevitably created restrictions on the use of those Band I channels. The tête-bêche system required oscillator-high for some channels and oscillator-low for others, depending upon whether the chosen IF channel had the vision carrier at the bottom end or the top end. But oscillator-low – with an IF channel just below Band I - was not workable for the Band I channels, as for the most part, oscillator frequencies would have been within the IF channel. So depending upon which way around the IF channel was oriented, either channels F2 and F4, or channel F3 would have been unusable. As it tuned out, the standard IF channel was chosen with the vision carrier at the bottom end, meaning that channel F3 was unusable. Thus it seems at least possible that the IF channel orientation was chosen to minimize the disruption to Band I use. Apparently channel F3 was originally assigned to a planned Tours transmitter.
Whether the deliberations over the CCIR standard IF included the multistandard receiver case is unknown. It seems possible, as multistandard receivers were the norm in Belgium from the start. But whether considered or not, the 38.9 MHz number was evidently satisfactory for the Belgian four-system receivers. This put the System E sound at 27.75 MHz, meaning that the IF channel was reversed as compared with the French case. In turn that meant that Belgian receivers would have been unable to be configured to receive channels F2 and F4. But that did not matter, as the reception requirements were for channel F8A and perhaps some others of the Band III channels, but not the Band I F-channels. As recorded previously, Belgian practice then worked out suitable frequencies for the sound second IF.
How the introduction of the French standard IF affected French multistandard receivers, developed quite early on for the border areas such as Strasbourg, is unknown. One assumes that these would have been required to cover the full French VHF channel set, so would have had a System E IF channel with vision carrier-low. On the other hand, vision-carrier high would have been required for channels E2 through E4, to allow oscillator-high operation. Actually though, a tête-bêche IF channel whose basic bandpass shape was determined by a pair of Nyquist slopes centred respectively on 28.05 and 38.9 MHz might have worked. For the System E case, a 39.2 MHz sound trap would have been switched in, and for the Systems B/C/F case, a 33.4 MHz sound trap and a high pass filter at around 33.9 MHz would have been switched in. That way the standard IFs for each system could have been used.
The European UHF channels were defined and initially allocated at the ITU Stockholm 1961 (ST61) meeting. The uniform use of 8 MHz channels helped. As with the US case, it appears that channel allocations were based upon existing standard IFs from VHF TV receiver practice. At least, that is the impression that one obtains from this excerpt from the ST61 Technical Annex. Thus were developed transmitter co-siting patterns such as n, n+3, n+6, n+10, avoiding the “taboo” combinations.
Unfortunately the IFs used in development of the ITU table were not stated, but one may make reasonable deductions. For the Systems G and H case, almost certainly it would have been the CCIR standard 38.9 MHz. That correlates with the image at channel n+9, and oscillator at n+5. Then the Italian System H case looks to have been calculated at both the CCIR standard and the Italian standard of 45.75 MHz. For the latter, the image was at n+11 and the oscillator at n+6.
The System K (OIRT) case was evidently calculated at both the then-Russian standard IF of 34.25 MHz and also at the CCIR standard IF or something proximate to it. The Russian standard IF put the image at n+8 and oscillator at n+4. Perhaps the Russians were by then pondering their later upward move to 38 MHz, in order to align with the general European pattern.
System I was more likely worked out on the basis of a 38.9 MHz IF, as I don’t think that the BREMA 39.5 MHz number had yet been debated or promulgated.
For the French System L case, the standard IF of 32.7 MHz might have been decided before ST61. For this, the oscillator would have been at n-4, and the image at n-9.
Whereas most of the European countries could, for UHF reception, continue using their existing TV receiver IFs established in the VHF era, both the UK and France were faced with new 625-line UHF systems and the need for dual-standard receivers, which would continue to use the established IFs for VHF reception, but needed “new” IFs for UHF.
In the French case, for simplicity at the receiver end, the System L IF channel was chosen to have the same sound IF as for System E, namely 39.2 MHz. A common sound IF was probably advantageous with AM sound on both systems. Since the IF channel should not encroach on Band I, this in turn meant that the vision IF was at the lower end of the channel, at 32.7 MHz. That required oscillator-low, not a problem at UHF, and not for Band III. But it had implications when System L was extended to Band I, where oscillator-low working was infeasible. The solution was to use inverted channels, with the vision carrier at the high end, for the Band I channels, which then allowed oscillator-high working. Hence System L’.
In the UK case, a common sound IF would have been of less value given that most receivers would have been expected to use the intercarrier technique for System I. Also, System I was to be used in VHF Bands I and III in Ireland near-term, and possibly in the UK in the more distant future. Allowing for Band I use meant oscillator-high working, and so an IF channel with the vision carrier at the high end. Effectively then UK dual-standard receivers would have a tête-bêche IF channel. As noted earlier in this thread, this could have been done with respectively 34.65 and 38.9 MHz IFs for 405 and 625 lines, but the 625-line number was moved up to 39.5 MHz to allow wider 625-line vision bandwidth whilst still using a basic double-Nyquist IF bandpass. This in turn created a requirement for much better receiver image rejection performance, given that the previously defined requirement for co-sited n+10 channels remained.
In the Australian case, the standard IF channel, with 36.0 MHz vision IF, was chosen more-or-less at the same as and to be compatible with the (unusual) VHF channel allocations, something that the CCIR standard number would not have done. Elsewhere outside of Europe with System B, the CCIR standard IF appeared to be satisfactory.