06-06-2021, 12:40 AM
(05-11-2020, 10:06 AM)ppppenguin Wrote: I think our antipodean friend, Synchrodyne, explored this in some detail a while ago.
That was quite some time back – see: https://www.vintage-radio.net/forum/show...hp?t=83653.
That article at: https://medium.com/@ReflectiveObserver/f...d02007e22a seems to capture the essence of the story.
I am not sure that the reason given for the 7 MHz Western European channel is quite right, though. Band I easily accommodated three 7 MHz channels, but was slightly short in respect of a fourth channel. Evidently there some early plans, not realized, to include four channels. The lowest would have spanned 40 to 47 MHz, the lowest 1 MHz thus out-of-band, but the vision carrier, at 41.25 MHz, would have been in-band. But if three channels were the desideratum, then three 8 MHz channels could also be accommodated, fully in-band. See: https://www.radios-tv.co.uk/community/bl...numbering/, 5th post.
My take on the channel width issue was that there was a cohort in favour of using a 6 MHz channel, following the NTSC precedent. The Italian experimental 625-line transmitter at Torino, of American origin, had used a 6 MHz channel. Against that, 7 MHz was a compromise, attributed to Gerber of the CCIR, between those who wanted the 6 MHz channel on one hand and those who wanted the technically better solution of an 8 MHz channel, with 6 MHz vision bandwidth. The Russians had chosen the latter parameter to provide 16 mm movie quality equivalence.
It is interesting to note that the NTSC 6 MHz channel was not an ab initio choice for the 525/60 system. Rather it was an imposed initial condition, carried over from the RMA 441/60 system. Within the available bandwidth, the tradeoff between line-count and horizontal definition was chosen to be somewhat in favour of line count, enough lines to ensure flatness of field according to Fink, who was evidently a major proponent of the 525 number. Interestingly though, Fink was later on record as saying that the 6 MHz channel was not a good choice; rather 8 MHz would have been better.
Cheers,
Steve
That article at: https://medium.com/@ReflectiveObserver/f...d02007e22a seems to capture the essence of the story.
I am not sure that the reason given for the 7 MHz Western European channel is quite right, though. Band I easily accommodated three 7 MHz channels, but was slightly short in respect of a fourth channel. Evidently there some early plans, not realized, to include four channels. The lowest would have spanned 40 to 47 MHz, the lowest 1 MHz thus out-of-band, but the vision carrier, at 41.25 MHz, would have been in-band. But if three channels were the desideratum, then three 8 MHz channels could also be accommodated, fully in-band. See: https://www.radios-tv.co.uk/community/bl...numbering/, 5th post.
My take on the channel width issue was that there was a cohort in favour of using a 6 MHz channel, following the NTSC precedent. The Italian experimental 625-line transmitter at Torino, of American origin, had used a 6 MHz channel. Against that, 7 MHz was a compromise, attributed to Gerber of the CCIR, between those who wanted the 6 MHz channel on one hand and those who wanted the technically better solution of an 8 MHz channel, with 6 MHz vision bandwidth. The Russians had chosen the latter parameter to provide 16 mm movie quality equivalence.
It is interesting to note that the NTSC 6 MHz channel was not an ab initio choice for the 525/60 system. Rather it was an imposed initial condition, carried over from the RMA 441/60 system. Within the available bandwidth, the tradeoff between line-count and horizontal definition was chosen to be somewhat in favour of line count, enough lines to ensure flatness of field according to Fink, who was evidently a major proponent of the 525 number. Interestingly though, Fink was later on record as saying that the 6 MHz channel was not a good choice; rather 8 MHz would have been better.
Cheers,
Steve
