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Old 24th Mar 2020, 10:39 am   #21
Nuvistor
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Default Re: 1946 Why 405 lines?

Were the early transmissions restricted to about 2.5Mhz, seem to have read it but cannot find it now?
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Old 24th Mar 2020, 10:44 am   #22
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Default Re: 1946 Why 405 lines?

No disrespect to John Logie Baird and his family, but (IMHO) he has very little to do with 'modern' TV as it emerged in the pre war years. Of course, he was a great catalyst whose efforts and experiments over a long period brought the subject out into the open and inspired others to develop ideas. Even his final wet process attempt with 240 lines was way beyond the EMI developed 405 line system. And it was of course the latter who developed TV 'as we know it'. But the average man in the street thinks it was Baird!
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Old 24th Mar 2020, 10:45 am   #23
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Default Re: 1946 Why 405 lines?

Quote:
Originally Posted by dave walsh View Post
Baird was about to present a new colour electronic system in London but became ill and died [here at Bexhill] in June 1946, before that could take place!
I think Tanuki's 405 line overview looks fairly accurate.

The politics around BBC trials of 405 v 625 line colour in 1966 are even more interesting. The technical conclusion was that 625 was superior but it's clear from the study published in Wireless World that, actually, the members of the public in the viewing audience couldn't really detect any difference . There have been threads on this as well.

Dave W
Yes, on the size screens at the time.
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Old 24th Mar 2020, 10:57 am   #24
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Default Re: 1946 Why 405 lines?

Quote:
Originally Posted by Nuvistor View Post
Were the early transmissions restricted to about 2.5Mhz, seem to have read it but cannot find it now?
Well the AP transmitter gave pretty near 3MHz bandwidth.

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Old 24th Mar 2020, 11:04 am   #25
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Default Re: 1946 Why 405 lines?

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Originally Posted by stevehertz View Post
But the average man in the street thinks it was Baird!
Very true! And very unfair. If there was any single UK citizen who was the father of television development it was A.A. Campbell Swinton, not Baird.

It was Campbell Swinton's design ideas that led to Zworykin's Iconoscope.

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Old 24th Mar 2020, 11:16 am   #26
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Default Re: 1946 Why 405 lines?

405 line television: 5:4 aspect ratio the maximum bandwidth is 2.75Mhz. When the aspect ratio was changed to 4:3 the bandwidth is 3Mhz for the same horizontal definition.

DFWB.

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Old 24th Mar 2020, 11:25 am   #27
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Default Re: 1946 Why 405 lines?

Quote:
Originally Posted by Catkins View Post
C. O. Stanley of Pye is there in the guise of the "Radio Industry Council". Does anyone know the affiliations of the other people mentioned?
F.B. Duncan eventually became Chairman of the Board at Pye.
E.J. Power was Chief Engineer at Murphy Radio.

Don't know about the others

Peter

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Old 24th Mar 2020, 11:32 am   #28
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Default Re: 1946 Why 405 lines?

I don't think the 'spot wobble' helped a lot, you couldn't see the lines so the picture looked out of focus, I think the Ecko T161 had it.

It was possible to get a brilliantly sharp picture on 405 lines, when 625 started certainly initially the picture didn't look as good, possibly due to the extra bandwidth required.

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Old 24th Mar 2020, 11:45 am   #29
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Default Re: 1946 Why 405 lines?

Early problems with 625 was partly due to low gain, the Frame Grid valves in the IF helped and UHF transistor tuners transformed the sets.
The noise factor of the valve tuners at the top end of Band 5 was poor, the difference between 500Mhz and 800Mhz was large.
Then the RBM sets had Black Level Clamp, it improved the picture but some customers could not get used to it.

David,
Thanks for the bandwidth insight, I knew there was something I had read.
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Old 24th Mar 2020, 4:57 pm   #30
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Default Re: 1946 Why 405 lines?

With the greatest of respect to Steve H [a proper chap ] posts 22* and 23* this old trope that the man in the street is deluded about Baird and that he enjoys undeserved glory for further developments always emerges and is misleading in itself. Plus I don't think the "man in the street" ever knew or cared that much about, especially as J L [perhaps conveniently] didn't survive. Much more information has emerged during the last twenty years or so although his "war years" still seem to be a bit of a mystery. That might explain a few things in itself.

I haven't the amazing depth of technical knowledge shown by others on here so I'm reliant on the social history. As a young man I met an elderly Canadian Industrialist who showed my wife and myself around his huge furniture store in Manchester [including] the non public areas]. He told us about his life in London in the thirties, his luxury flat at Hyde Park Corner and his Colour TV! I said to my wife later, "That was interesting but probably all made up by a chap who took a shine to you-we didn't get colour until the late sixties!" Later I heard vague hints about "early" colour and after joining the BVWS more. Then I received a booklet about, Baird issued by the Society, with [as it said] un-retouched reproductions of his pioneering colour cinema transmissions. I didn't grasp at first that this was a GPO landline system but it vindicated the man we met and you know, it was Colour TV...in the 30's.

Baird was never a well man. I've understood from my limited research that he was actually [perhaps shamefully] forced out of his own company. I was always suspicious of the way in which it [apparently] seemed convenient to n ignore him after what was, admittedly, seemed to be a complete miss-step in the pre-war "competition". Perhaps though, he was desperate to re-gain some credibility using the [already outdated] electro-mechanical technology he had developed to a very high level? If he had not been a victim of Reith at school and later the political/business establishment, with [again] Reith using his influence as Dictator General at the BBC things might have been a lot different. It's not in dispute that Baird was never given any real assistance from "the powers that be". He was probably inconvenient to a lot of people's
ambitions.. or presented as such. .g
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Old 24th Mar 2020, 5:16 pm   #31
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Default Re: 1946 Why 405 lines?

I have some 625 line TV programmes, notably "most Secret War" and Yes (Prime) Minister that I have shrunk to 16:9, as said near enough 405 lines, they look fine on a 25" HD LCD TV.

I have read that EMI went for 405 knowing it wasn't brilliant with their current camera tubes in about 1934 but knew (hoped?) by '36 technology would catch up, it did. Brilliant foresight.
 
Old 24th Mar 2020, 5:42 pm   #32
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Default Re: 1946 Why 405 lines?

Quote:
Originally Posted by stevehertz View Post
Even his final wet process attempt with 240 lines was way beyond the EMI developed 405 line system.
Steve,

That's an interesting statement.

Peter
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Old 24th Mar 2020, 6:10 pm   #33
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Default Re: 1946 Why 405 lines?

There is a lengthy but quite interesting book about JLB at Russell_Burns_-_John_Logie_Baird:_Television_Pioneer_2000.pdf (a Czech web site). If you then click on "Stáhnout pomalu" (download slowly), you can download it without having to register - but be warned, it's 205MB!
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Old 24th Mar 2020, 6:40 pm   #34
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Default Re: 1946 Why 405 lines?

The original EMI standard was to be 243 lines interlaced, the intention was that it would compete with the sequential scanning Baird 240 line system.
The EMI system would offer a flicker free picture.
The EMI line repetition rate would be 6,075c.p.s. Almost matches the Baird 6.000c.p.s. EMI employed five divide-by-three circuits = 243 supplied from the 12,150 c.p.s. master oscillator. Increase the master oscillator frequency to 20.250c.p.s. and replace one of the count down circuits to divide-by-five the result is 405. Of course other parameters have to be considered, 2.7Mc/s video bandwidth being the one needing attention, something not easy to achieve in 1934!

DFWB.
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Old 24th Mar 2020, 6:48 pm   #35
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Default Re: 1946 Why 405 lines?

I recorded a few minutes of 243 line a couple of years ago.

It didn't look at all bad.

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Old 24th Mar 2020, 7:23 pm   #36
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Default Re: 1946 Why 405 lines?

Very good! Certainly of good entertainment value.
405 was incredibly bright and had a sparkle that is difficult to describe but must be seen on a well adjusted receiver. In all my years in the trade I never heard a single customer complain or even mention the line structure, in fact when viewing very close up the line structure was used by customers as a focusing aid and if they could not see them, something was amiss!
Definition was more than adequate even with 21" tubes viewed at a sensible distance.
Regardless of systems our 405 line TV's were viewed with envy by numerous broadcasting engineers from distant parts of the World. RIP Alan Blumlein and the EMI team. You served us very well. John.
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Old 24th Mar 2020, 8:00 pm   #37
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Default Re: 1946 Why 405 lines?

Quote:
Originally Posted by Dave Moll View Post
There is a lengthy but quite interesting book about JLB at Russell_Burns_-_John_Logie_Baird:_Television_Pioneer_2000.pdf (a Czech web site). If you then click on "Stáhnout pomalu" (download slowly), you can download it without having to register - but be warned, it's 205MB!
Thanks Dave, I have several books by Burns. He is an excellent radio and television historian.

Peter
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Old 24th Mar 2020, 8:02 pm   #38
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Default Re: 1946 Why 405 lines?

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405 was incredibly bright and had a sparkle that is difficult to describe
Maybe because of the positive modulation? The odd extra bright bit would be transmitted (good old analogue not knowing!), unlike negative modulation where it would be clipped to stop interference with the syncs..
 
Old 24th Mar 2020, 8:35 pm   #39
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Default Re: 1946 Why 405 lines?

I can remember, as if yesterday, as a young boy whilst on holiday with mum and dad, watching on a Decca type 1000 Sergeant Bilko on the Phil Silvers Show projected onto a 4'X3' screen. I was amazed. All we had at home was a 16" Bush TUG26

The Decca TV definition was better than 16mm home movie quality and the sheer size of screen and brightness was more than entertainment quality.

I knew nothing about 405/625 line structures but don't remember there being line structure or interlace issues. Now a little older, the lack of mean level AGC and a silvered screen must have helped an awful lot.

Having recently watched a 12" Dynatron Falcon of 1949 vintage I can easily see why a projection TV screen size would, as today, be first choice if only then your pocket was deep enough which it seems for many people it was and there were programmes worth watching, Billy Cotton springs to mind.

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Old 24th Mar 2020, 8:38 pm   #40
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Default Re: 1946 Why 405 lines?

I have two leaflets for two different large screen front projection TVs that Decca made in the early 1950's. What was presumably the earlier (no name or number) model's screen size was 3' 6" x 2' 6", the later's (Model 1000), 4' x 3'. For both, "high fidelity" double-sideband models were available for the London area.

The earler model cost £350 complete ( purchase tax included), the Model 1000, £158. 10. 0d. for the base unit, £6. 10.0d for the screen . The earlier was said to give a picture of "cinema quality".

Edit. Post crossed with #39. I was going to ask if anyone had seen these in the flesh!

Last edited by emeritus; 24th Mar 2020 at 8:47 pm.
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