23-07-2017, 07:07 AM
Perhaps in some cases the horizontal-only countries took their lead from the NTSC’s 1941 decision in favour of horizontal polarization. Overall, the NTSC’s conclusions were quite influential when it came to the development of worldwide analogue TV transmission standards.
In the USA, the use of orthogonal polarization might have created difficulties. In the more populated northeast, some viewers were likely in range of the transmitters of two (or more) urban centres, so having some horizontal and some vertical, a difference likely between adjacent centres, would have created unwelcome difficulties for them. Also, perhaps inevitably, horizontal and vertical would not have been seen as equal alternatives, with horizontal most likely seen as the better option. So, in a competitive market, broadcasters assigned vertical polarization may have seen this as being saddled with a disadvantage. Hence channel assignment planning was done on the basis of all transmitters being horizontally polarized, with physical separation and offsets being the means by which co-channel interference was minimized.
In Europe with its generally higher population density and more closely spaced urban centres, co-channel interference was likely to be a bigger problem, to the extent that the benefits of orthogonal polarization were sufficiently desirable to overcome any perceived disadvantages. As far as I know, and the UK excepted, those countries adopting orthogonal polarization saw horizontal as primary and vertical as secondary. In the New Zealand case, I’d guess – and it’s only a guess – that orthogonal polarization was chosen to allow maximum use of the three Band I channels for the first network. Two out of the seven main transmitters were vertical, the others horizontal. Even so, co-channel main transmitters were not closely spaced, and had mountain ranges between them.
Cheers,
Steve
In the USA, the use of orthogonal polarization might have created difficulties. In the more populated northeast, some viewers were likely in range of the transmitters of two (or more) urban centres, so having some horizontal and some vertical, a difference likely between adjacent centres, would have created unwelcome difficulties for them. Also, perhaps inevitably, horizontal and vertical would not have been seen as equal alternatives, with horizontal most likely seen as the better option. So, in a competitive market, broadcasters assigned vertical polarization may have seen this as being saddled with a disadvantage. Hence channel assignment planning was done on the basis of all transmitters being horizontally polarized, with physical separation and offsets being the means by which co-channel interference was minimized.
In Europe with its generally higher population density and more closely spaced urban centres, co-channel interference was likely to be a bigger problem, to the extent that the benefits of orthogonal polarization were sufficiently desirable to overcome any perceived disadvantages. As far as I know, and the UK excepted, those countries adopting orthogonal polarization saw horizontal as primary and vertical as secondary. In the New Zealand case, I’d guess – and it’s only a guess – that orthogonal polarization was chosen to allow maximum use of the three Band I channels for the first network. Two out of the seven main transmitters were vertical, the others horizontal. Even so, co-channel main transmitters were not closely spaced, and had mountain ranges between them.
Cheers,
Steve
