27-12-2016, 11:36 PM
The NTSC’s reasons for choosing horizontal polarization were provided in Fink, “Television Standards and Practice”; see chapter X. (See: https://archive.org/stream/televisionsta..._djvu.txt; and: http://www.earlytelevision.org/pdf/telev...ndards.pdf.) This quotation from early in the chapter provides a succinct summary: “By the time the Panel concluded its deliberations, however, sufficient evidence had been assembled to bring about substantial agreement that there was a slight preponderance of advantage for the horizontal direction.”
It would appear that outside of the UK, the NTSC’s precedent was followed, with the addition that in some territories, vertical polarization was also used, typically for secondary transmitters, in situations where the use of orthogonal polarization would ease the problems of channel-sharing. Thus one might say that although horizontal was preferred, vertical was nonetheless acceptable in certain circumstances.
I haven’t seen anything to suggest that the polarization issue was reviewed in the UK when the TV network expansion plans were drawn up. So the continued use of vertical polarization for the main transmitters may simply have been inertial. The BBC’s development work on FM broadcasting had shown horizontal to be better than vertical, particularly in respect of ignition interference rejection. But that does not seems to have influenced the TV case. Or perhaps it was the GPO, who had the final sign-off on transmitter frequencies, power, etc., who made the polarization call. (Later on it was the GPO who dictated that the polarization of ITA TV stations would match those of the respective BBC stations in each area.) The Sutton Coldfield mast was built with horizontally-polarized Band II radiators for future FM use, so the BBC had made its determination by then. Presumably the mast could have been topped with a turnstile stack had horizontal polarization been chosen for the TV transmitter.
The NTSC had also determined that the same polarization should be used for both TV and FM transmissions. Presumably this was the convenience of consumers, who could then use combined receiving aerials. Whether that aspect was considered in the UK is also unknown.
Cheers,
Steve
It would appear that outside of the UK, the NTSC’s precedent was followed, with the addition that in some territories, vertical polarization was also used, typically for secondary transmitters, in situations where the use of orthogonal polarization would ease the problems of channel-sharing. Thus one might say that although horizontal was preferred, vertical was nonetheless acceptable in certain circumstances.
I haven’t seen anything to suggest that the polarization issue was reviewed in the UK when the TV network expansion plans were drawn up. So the continued use of vertical polarization for the main transmitters may simply have been inertial. The BBC’s development work on FM broadcasting had shown horizontal to be better than vertical, particularly in respect of ignition interference rejection. But that does not seems to have influenced the TV case. Or perhaps it was the GPO, who had the final sign-off on transmitter frequencies, power, etc., who made the polarization call. (Later on it was the GPO who dictated that the polarization of ITA TV stations would match those of the respective BBC stations in each area.) The Sutton Coldfield mast was built with horizontally-polarized Band II radiators for future FM use, so the BBC had made its determination by then. Presumably the mast could have been topped with a turnstile stack had horizontal polarization been chosen for the TV transmitter.
The NTSC had also determined that the same polarization should be used for both TV and FM transmissions. Presumably this was the convenience of consumers, who could then use combined receiving aerials. Whether that aspect was considered in the UK is also unknown.
Cheers,
Steve
