VHF TV.

[colly0410]

If there was no sporadic E or tropo propagation on band 1 then IMO it would have been more or less perfect for TV. I suppose in the early 50's in the UK with just the main high power TX's running it was perfect, the trouble started when they fired up lower powered TX's reusing the same 5 channels. It must have been a nightmare job being a channel planner back then, especially when the Continental TX's fired up with different line standards..

[Murphyv310]

It was all good fun though. Up here all 5 Band 1 channels had something on them all year from other BBC transmitters, during lifts it was great, reversing detectors and twiddling the line hold.

[colly0410]

Here just north of Nottingham I only got a picture on ch's 4 from Sutton Coldfield & 2 from Holme Moss, 1,3 & 5 were just snow - until a lift, when you'd usually get BBC London on 1, South or Scotland on 3 & West/South Wales on 5. Never got Divis, Pontop Pike or any other region AFAIK. Received BBC Wales on ch 6 a few times..

[Terry]

When the first Bush sets came out with dual standard IF strips, it was possible to convert them to VHF 625-lines by the simple practice of inserting two screwdrivers between the connecting tags of the bottom two sections of the vertical switch, thus connecting the tuner HT and IF respectively.

Sporadic E always seemed to rotate in a clockwise direction so might start of with Norway before progressing to Russia and West Germany. It then seemed to jump a bit round to Spain, which often provided reception throughout the afternoon. Most of what we received was on channels E2 and E4 and as one faded, often the other would replace it!

I did see RAI (Italy) once in 1966. It must have been tropospheric reception because it was much too stable for Sporadic E.

Eventually the test card faded and was replaced by a very attractive blonde continuity announcer! She was followed by the Eurovision caption but, on this occasion, the originating source shown in the centre was BBC/ITA. This was followed by the caption WORLD CUP '66 and the match began ...

So, over a thousand miles there then another thousand or so back!

[colly0410]

I'm wondering how much difference using both vertical & horizontal polarisation on band 1 in the UK made? Read somewhere that it reduced co-channel interference by up to 10 decibels, was this a bit of wishful thinking? I'm thinking that the polarisation would get twisted a bit by hills, trees, etc..

[Synchrodyne]

For background, have a look here:
  
http://www.itu.int/en/ITU-R/terrestrial/..._Annex.pdf; go to page 63.

The conclusion was that orthogonal polarization was worthwhile doing to reduce co-channel interference.  It was acknowledged that results could be variable by site.  The measured median benefit was 18 dB, with 90% of sites at or above 10 dB.

The UK situation may have been an extreme one, in that Band I at least was “overstuffed” to the point where non-trivial mutual interference was inevitable.

This item from Wireless World 1966 February about the opening of the Gloucester channel 1H relay is telling.

   

It included the comment:  “For satisfactory reception of BBC-1 transmissions very careful positioning of the aerial may be necessary to avoid interference from other stations using this channel – particularly the high power station at Crystal Palace.”

Cheers,

Steve

[colly0410]

Thyank's for the PDF thing, other stuff in it interesting as well. Says horizontal pol best for UHF because aerials are more directive, I expect that's why UK UHF main stations are all horizontal, the lower power stations are vertical (well most are) as not so important I presume. It's about a 75/25 mix of horizontal (Waltham) & vertical (Nottingham) round here. I'm on Waltham now with a loft aerial as when I was on Nottingham every time it Thundered it would go off & stay off for ages, Waltham go's off for a few seconds then comes back on again. I can see the Nottingham TX & it gives a slightly stronger signal but not as reliable as Waltham..

[colly0410]

Read that some Countries only used horizontal polarisation i.e. USA, Canada IIRC, wonder why they didn't mix it like UK & New Zealand did/still do?

[Synchrodyne]

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

[colly0410]

Ah yes, I can see the problems of mixing it up in America now: A new station starting up & being made to use vertical pol & people saying "I'm not buying a new vertical antenna just to watch that station" & the station owners would moan & whinge of unfairness. Would be a bit like British people not upgrading the TV & aerial for BBC2 in the 60's/70's, my parents an example.

On the co-channel spacing topic I'm wonder how the ITA got away with Winter Hill in Lancashire & Black Mountain near Belfast both using channel 9, albeit cross polarised. I'd have though channel 8 would have been better for co-channel interference prevention, but what do I know? I'm a thicko..