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Old 11th Jun 2018, 5:57 am   #10
Synchrodyne
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Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
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Default Re: Tuners in Philips G6-G11 CTV chassis

Quote:
Originally Posted by Synchrodyne View Post
The system designations A through F were promulgated at the CCIR 1959 Los Angeles meeting. There was some order to them, based upon line count. I.e. A for 405, B,C,D for 625 and E,F for 819. Within the 625 group, they appear to have been ordered by increasing channel width, with negative/FM preceding positive/AM at a given width. With E and F it looks to have been a time-based ordering, in that E preceded F.
Not so. I have since found Report 124 from the CCIR 1959 meeting. It did not include the system letters. It simply described seven systems as 405, 525, 625, Belgian 625, IBTO 625, 819 and Belgian 819 respectively.

I had previously misread the statement in the Technical Annex to the Stockholm 1961 meeting, which was:

2.1 The television standards for Bands I, II and III (see C.C.I.R. Report No. 124) are designated in the Plans as
follows:

A – 405-line system
B – 625-line system
C – Belgian 625-line system
D – l.B.T.O. 625-line system
E – 819-line system
F – Belgian 819-line system


What appears to have been meant is that the whilst the systems had been described in CCIR report 124, the letter designations were developed at and for the purposes of the ITU ST61 plan, and were not part of that report. Thus, the A through F designations were assigned in 1961, essentially at the same time as the G through L designations were assigned. It seems obvious now, but my misapprehension has existed for quite a long time. One may imagine that with so many systems to consider, a simple designation system was highly desirable for those doing the planning.

Given that ST61 was concerned only with European matters, it seems reasonable that only systems of interest to Europe were included in the list.

These system designation letters were included in Report 308 from the CCIR 1963 Geneva meeting. Report 308 replaced Report 124. Additionally, Report 308 used the letters M and N for the 525- and Latin American 625-line systems respectively.

Report 308-1 from CCIR 1966 added system K1 (written that way rather than as K’), which as already mentioned, had first appeared as K* from the ITU 1963 Geneva African VHF-UHF planning meeting.

The detailed history of those CCIR TV system reports would be another topic.

Quote:
Originally Posted by Synchrodyne View Post
In the mid-to-late 1950s, European UHF transmitter network planning was heading to a common 8 MHz channel with fixed vision carrier position. This was in order to maximize utilization of the available channels. Countries using the existing CCIR 625/50 system would simply replicate this at UHF, albeit in 8 MHz rather than 7 MHz channels.

Without existing 625/50 services, both the UK and France, who were heading towards the use of 625/50 for future services, were free to fully exploit the possibilities of the 8 MHz UHF channels.
Report 123 from CCIR 1959 Los Angeles, referring to a 1958 Moscow meeting, include the following in respect of the UK and France:

The UK had yet to make a decision on what standard to use in Bands IV and V, but in any event would adopt the 8 MHz channel if that was generally adopted in Europe. And if it did chose 625 lines, it would be with 6 MHz vision bandwidth and 6.5 MHz vision-to-sound spacing.

France was similarly undecided, but accepted the 8 MHz channel if that were the majority choice, and stated that any 625-line system should have at least 6.5 MHz vision-to-sound spacing.

Quote:
Originally Posted by Synchrodyne View Post
France opted for both the 1.25 MHz vestigial sideband and the 6 MHz main sideband for 625/50, this requiring utilization of the outer guardbands, as it had done with its 819/50 tête-bêche channelling. Why 6 MHz for the main sideband I do not know. My speculation is that it was done in consideration of the future adoption of SECAM colour. The initial SECAM proposal used AM (DSB) colour subcarriers. With DSB AM and the use of simple envelope detectors at the receiving end, any single-sidebanding caused by restricted vision bandwidth would have caused quadrature distortion which was potentially deleterious. A 6 MHz vision bandwidth allowed plenty of room for colour subcarrier upper sidebands without truncation.
The ITU 1963 Geneva African VHF-UHF documents included a submission on the benefits of the K* system. Argued therein was that the 1.25 MHz vestigial sideband was “right-sized” for minimizing quadrature distortion, and that the 6 MHz vision bandwidth allowed for a symmetrical ± 1.5 MHz colour subcarrier bandwidth (about 4.43 MHz), preferable for NTSC colour as well. I imagine that the same arguments had previously led the French to the System L parameters.


Cheers,
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