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Old 14th May 2018, 1:15 pm   #21
rambo1152
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Default Re: TV system differences?

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Originally Posted by Argus25 View Post
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Another thing about 405 vs 625 in the United Kingdom, is all the 405 transmitters operated at VHF and all the 625 transmitters were on UHF, so when the 405 line system was eventually switched off in 1985, the VHF allocations were not re-engineered for 625 as you might have expected, VHF was abandoned as far as TV was concerned.
I didn't know that. So UK made 625 line TV's would not have had VHF tuners in them. All the early NZ ones did and UHF came later. Surprisingly NZ was still running VHF & UHF TV analog when I was last there some months ago. Analog TV transmissions have been gone in AU for some time.

Yes that's right.
The Irish Republic used VHF/625 but not the UK

It was quite a brave decision and a lot of local relays were required, but we ended up with a robust four channel system and ultimately managed to shoehorn a fifth, not quite so robust one in.

Also, the two incumbent networks (BBC and ITV) remained broadcasting on VHF/405 for more than a decade after they had been duplicated on UHF/625 with virtually national coverage, so when they turned 405 off in 1985, it's fair to say nobody really noticed.

Initially there was only one service rolled out on UHF/625. BBC2 was seen by the masses as a rather high brow arty-farty channel, UHF aerials were often called "BBC2 aerials"
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Old 14th May 2018, 3:04 pm   #22
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Default Re: TV system differences?

The different aerial added to the chimney had some snob value... we can afford the new telly and aerial for BBC2!

When the MUSE high definition TV standard was being demonstrated around the place, a common question was "Will I need a new aerial?" and the answer giiven was "No". The demonstrators were puzzled that the questioners were disappointed by this. They wanted to advertise their wealth!

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Old 14th May 2018, 3:15 pm   #23
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Do you mean that UK 405 productions looked bad on the Australian system? That's because they would have been 16mm telerecordings. The 405 system gave very good results on the 405 TVs of the day. It was abandoned for reasons of standardisation within Europe, not because it performed poorly.

Possibly one of the last surviving ITV 405 line recordings- transferred to VHS here (for Wendy's home consumption) and still looks good- eat your heart out Simon Cowell here is the master at work.

https://www.youtube.com/watch?v=Zd_O88adO1w
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Old 14th May 2018, 3:16 pm   #24
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Default Re: TV system differences?

Here's a link to the Pilkington report (Secret!) which set UK TV on course for modernisation, 625 lines, BBC2 (and ITA2 as proposed eventually) and colour.

http://filestore.nationalarchives.go...0-c-62-102.pdf

Interestingly, the report envisages up to 6 625 channels on UHF.

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Old 14th May 2018, 3:23 pm   #25
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Default Re: TV system differences?

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The different aerial added to the chimney had some snob value... we can afford the new telly and aerial for BBC2!
This was also a factor in the early days of satellite TV. BSB installations used a small unobtrusive 'squarial' while Sky installations needed a big white dish (because they were using a satellite cluster not originally intended for direct broadcasting). BSB thought this would give them a big marketing advantage, but the opposite was often the case - people on council estates liked having a great big dish on the side of the house as it showed their neighbours that they could afford a Sky subscription.
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Old 14th May 2018, 3:32 pm   #26
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Default Re: TV system differences?

I did some of the first domestic satellite installations in Cornwall, long time ago now, large steerable dish on a flat roof or horizontal platform, there were only two Birds or so up there then, no Sky as I recall.

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Old 14th May 2018, 3:54 pm   #27
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In the early days of BBC televison transmissions I understand that they changed standards each day, one day 405 and next was some other (possibly 212?) this until 405 was decided upon?
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Old 14th May 2018, 4:06 pm   #28
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Hello Anthony,

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In the early days of BBC televison transmissions I understand that they changed standards each day, one day 405 and next was some other (possibly 212?) this until 405 was decided upon?
The EMI-Marconi 405 line system alternated with the Baird 240 line system on a weekly basis.

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Old 14th May 2018, 4:11 pm   #29
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As Mike said [in post 3] that was a very wide ranging initial enquiry from the OP [David] in the first place-so wide that I wondered why? Twenty seven responses in less than twenty four hours, that's very impressive! His first enquiry's got none at all I've researched Redifusion in Ramsbottom and Hastings but I didn't know they got out so far with the system at that time

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Old 14th May 2018, 4:15 pm   #30
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Default Re: TV system differences?

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The EMI-Marconi 405 line system alternated with the Baird 240 line system on a weekly basis.
Mind you, the Baird 240-line system was dropped within months.

Original dual standard (405/240) sets extremely rare, though I know of at least one owned by a forum member.

As an aside, another member owns an equally-rare experimental 405-line NTSC colour television.

(I am respecting the privacy of these members by not naming them - GDPR and all that!)
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Old 14th May 2018, 4:26 pm   #31
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Default Re: TV system differences?

We might as well throw in Baird's pre-war [1936] colour tv system [via landline] while we're at it. He's only known for having lost the Mechanical v EMI CRT competition but he was just about to unveil his new electronic version of colour transmission when he died in 1946, just around the corner from here in Bexhill.

We had to wait another 21 years for colour!

Dave

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Old 14th May 2018, 4:37 pm   #32
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Default Re: TV system differences?

3D too: https://www.nms.ac.uk/colourtelevision, but in the end it comes down to practicalities, and market forces.
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Old 14th May 2018, 4:54 pm   #33
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Default Re: TV system differences?

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Possibly one of the last surviving ITV 405 line recordings- transferred to VHS here (for Wendy's home consumption) and still looks good- eat your heart out Simon Cowell here is the master at work.

https://www.youtube.com/watch?v=Zd_O88adO1w
And to think, that within months, maybe weeks of that, ABC would be no more.

Fond memories of Diddy David Hamilton's continuity from Didsbury.
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Old 14th May 2018, 5:27 pm   #34
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Very good quality [recording] Graham and a historical artifact, thanks! It's also a reminder that Britain in 1968 s was still very conservative and not all Flower Power. I didn't like talent shows than [or now] or bland performers but the contemporary colour You Tube footage of Judith Durham with The Seekers, live in Australia, around the same time, changed my mind about them. You're right, there is a direct line from Hughie Greene down to Simon Cowell, in more ways than one There's a much sadder one to the present day as well in Greene's personal life.

"And I mean that most sincerely folks"

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Old 14th May 2018, 10:20 pm   #35
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The EMI-Marconi 405 line system alternated with the Baird 240 line system on a weekly basis.
Thanks for the info Dave
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Old 15th May 2018, 12:26 am   #36
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Hello Anthony,

You're welcome.

Regards,

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Old 15th May 2018, 5:59 am   #37
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As has been observed, the original question is potentially very broad, and a comprehensive answer could go very deep. I think that most of what needs to be said has already been said, so what follows is simply a somewhat different perspective on the analogue case.

Viewed from within the set of analogue TV systems, the various systems, 405, 525, 625 and so on, can look quite different. Viewed from without, they look more like variations on a theme, as follows.

Of the systems that were used for regular broadcasting from more than just one transmitter:

They all had the same basic scanning system with 2:1 interlace.

They had from the start, or were changed relatively early in their lives to have, the same 4:3 aspect ratio.

The number of horizontal lines varied, with 405, 525, 625 and 819 being used.

The field frequency was either 50 or 60 Hz, usually tied to the mains supply frequency in the countries in which they were used, but not exclusively so.

The same basic video waveform was used with time and amplitude separation of the picture and synchronizing information. The form of the synchronizing signals varied somewhat amongst the various systems, and sometimes within subsets with the same line count.

The bandwidth allowed for the video signal varied with the line counts and field rates. The more lines per picture and the more fields per second, the higher was the required bandwidth for a given horizontal definition. The “hard” limit on vision bandwidth was imposed by the transmission system.

Each of the basic systems had an associated transmission system, in some cases, as with 625 lines, several associated transmission systems.

For all transmission systems within the set:

They used channels of defined bandwidth and pattern within the VHF and UHF bands.

They used separate carriers for vision and sound. The relative positioning of those two carriers varied with transmission system. The majority had vision carrier low, sound carrier high, but a minority were the other way around. The latter group included all 405-line and some 625- and 819-line transmissions.

Vision was transmitted by amplitude modulation (AM) with preservation of the DC component.

They had from the start, or were changed relatively early in their lives to have vestigial (asymmetric) sideband AM. Whether the lower or upper sideband was vestigial was determined by whether the vision carrier was low or high within the channel.

Inclusion of the DC component allowed the vision modulation to be in either a positive (modulation depth increasing with picture brightness) or negative (modulation depth decreasing with increasing picture brightness) sense. Most transmission systems were negative but some were positive. The latter group included all 405-line, all 819-line and some 625-line transmission systems.

Vision bandwidth, being that allowed for the full sideband, varied by line-count and within a set of given line-count systems. Those actually used were as follows:

405 lines: 3.0 MHz.
525 lines Originally 4.0 MHz, later 4.2 MHz.
625 lines: 4.0 (later 4.2), 5.0, 5.5 and 6.0 MHz.
819 lines: 5.0 and 10.4 MHz.

The sound could be transmitted by either amplitude modulation (AM) or frequency modulation (FM). FM was the majority choice. Audio pre-emphasis (50, 75 or 100 microseconds) was always used with FM, and sometimes (50 microseconds) with AM. In practice, FM sound was always associated with negative vision modulation systems, and AM sound with positive vision modulation systems.

The power ratios of the vision and sound carriers varied amongst the systems, and different broadcasting authorities used different ratios for nominally the same system.

Both horizontal and vertical polarizations were used for transmitting aerials, and later circular polarization was also used. In the UK, vertical polarization was primary for the 405-line system, with horizontal also used to obtain orthogonal separation of co-channel transmitters. Elsewhere, horizontal was primary, with vertical used in some countries, but not all, to obtain orthogonal separation.

To that list one could add the various colour systems that were "piggybacked" on to some of the existing monochrome systems. NTSC, SECAM and PAL were also variations on a theme, with subvariants to suit specific monochrome transmission systems. Later the various means of transmitting stereo and multi-channel sound were also “adds-on” of distinct varieties rather than being variations on a theme.

In respect of the 405-line system, I think that it was Schoenberg of EMI who decided to step up to what was an unprecedented line count at the time. This had about the same line frequency as the RCA 343-line, 60 Hz experimental system. To the extent that line frequency was a better indicator than line count of the degree-of-difficulty, then EMI was moving to the edge of, but not going beyond, what was known to be possible at the time.

The 525-line system was the outcome of the deliberations of the first NTSC in 1941. (The first NTSC was distinct from the better-known 2nd NTSC that developed the eponymous colour system in 1953, although many members worked on both.) The first NTSC considered all possibilities, the only “given” being that the channel width was fixed at 6 MHz. Also, the 60 Hz power supply frequency was a persuasive and non-variable factor. On line count, the initial leaning was towards 441, as had been used for the RMA experimental system. But Donald Fink, a major and influential member of the first NTSC, proposed 525 lines on the basis that as there was some flexibility in the trade-off between vertical and horizontal definition, the line count should be sufficient to ensure flatness of field and avoidance of “lininess”, which 441 lines did not do. NTSC chose negative vision modulation with vestigial lower sideband and vision carrier at the lower end of the channel, FM sound, the use of equalizing pulses in the synchronizing signal, and horizontal transmitter polarization, imputing advantages – not necessarily major – to all and so to some extent established these as norms.

Then circa 1944 the Russians adapted the NTSC system to suit a 50 Hz field frequency, which meant 625 lines for approximately the same line frequency. With what turned out to be very good foresight, they chose an 8 MHz channel, with 6 MHz vision bandwidth, apparently in order to match 16 mm film horizontal definition. Regular broadcasting started in 1948.

The French went for very high definition with their 819-line system in 1949, but eventually moved to 625 lines. The 819-line system used positive modulation and AM sound, and originally had vision carrier-high channels. Why this was so I am not sure. But the existing 441-line single transmitter service was that way, so perhaps it was done for commonality.

The Western Europeans picked up on the Russian work, but did not like the 8 MHz channel. Evidently there was some debate, with some suggesting that that the American 6 MHz channel, as had been used for an American-supplied 625-line experimental transmitter in Torino, would be appropriate. Eventually a compromise 7 MHz channel was agreed later in 1950. This turned out to be lacking in foresight. By the time that European UHF TV allocations were being planned in the second half of the 1950s, the 8 MHz channel was adopted, and this allowed the France and the UK to develop improved 625-line systems that exploited this channel width. Discussion of the multitude of 625-line variants and why they were the way they were would I think be too much of a digression.

Both the 525- and 625-line systems lasted until the digital era, so could be seen as “Goldilocks” choices. If one looks at the progression of analogue TV systems, using line frequency as a single parameter measuring their development state, then the major points on the curve were:

343/60 and 405/50 (441/50 would also fit here)

441/60 – essentially experimental (the 50 Hz counterpart would have been 525/50)

525/60 and 625/50

819/50.

The plateau was reached at 525/60 and 625/50. 819/50 was an isolated peak on the plateau, a peak too far one might say.

The UK was an early mover and thus locked in to a system that was still on the upward part of the learning curve. But its later entry to 625/50 meant that it could use a refined version.

So we could say that 405 was an early system, about the best that could have been done at the time, but short of what soon became practicable.

625 was a stasis system which, although not the best that could possibly be done in the analogue era, was about the optimum choice, representing the best trade-off amongst all competing factors until digital arrived.


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Old 15th May 2018, 6:08 am   #38
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The EMI-Marconi 405 line system alternated with the Baird 240 line system on a weekly basis.
If you want to compare then scroll down on this page.

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Old 15th May 2018, 6:28 am   #39
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Do you mean that UK 405 productions looked bad on the Australian system? That's because they would have been 16mm telerecordings. The 405 system gave very good results on the 405 TVs of the day. It was abandoned for reasons of standardisation within Europe, not because it performed poorly.
My recollection is that in the 1960s in New Zealand, most overseas TV programmes came in as 16 mm films. Some were originated that way, and some apparently were transferred from videotape or perhaps recorded on film from live transmissions.

According to my memory, those from the USA were not too bad. The typical giveaway as to their video origin was the presence of image orthicon artefacts, such as black fringing around bright parts of a scene.

Those from the UK were sometimes not very good at all, and I seem to recall that Granada programmes were the worst. The problem was poor vertical definition, to the point where images looked blurred. I’d guess that the transfer to film was done using 405-line monitors with significant spot-wobble to avoid visible lines and to obtain reasonable flatness of field. As the British TV companies moved to 625 lines for production, the problem went away.

Sound quality was different too. The American programmes seemed to have been recorded at a higher level, with some peak clipping evident. The British programmes were typically recorded at a lower level, with background hiss often apparent, particularly noticeable when one fed the TV sound (direct from the demodulator) into a hi-fi system. The levels as transmitted and received were not materially different, as there would have been gain equalization at the studio. Rather I am inferring a recording level difference from the results.


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Old 15th May 2018, 10:23 am   #40
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Perceived poor performance of the 405-line 'system A' generally derives from the interposition of 16mm 'telerecording', and not from direct viewing of the television signal, which, on tube sizes up to 17", is virtually indistinguishable from 625.
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