Low mains voltage

On Saturday, 24 November 2018 12:13:41 UTC, Graham. wrote:

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the unusual one linked to was as he described. Nearly all were round dots, usually top right but less often right in the middle.
The dots were the moment the reels changed over. Modernish projectors show a whole film on one large reel so no changeover. Ancient ones have the film on several reels & the projectors must be changed from one to the other at the right moment. The dots show when.
The square/line things were for some other purpose, they were there way too long to be be anything to do with reel changeovers. Probably too modern to have reel changeovers anyway.
NT
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On 24/11/2018 13:22, snipped-for-privacy@gmail.com wrote:

That's cine films. This is about TV.
--
Max Demian

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BBC tended to use a dot at the top LHS which looked like a " mark (two parallel vertical lines).
ITV tended to use one at top RHS which was a square with diagonal scrolling lines that seemed to go from slowly moving at the beginning and end of the cue period, and quicker moving of the scrolling lines in the middle of the period. Sometimes ITV ones were filled with a chequerboard rather than diagonal lines.
It was a staggeringly low-tech solution to the problem. You'd think that the cue signal could be sent in the blanking period (like Teletext) with a decoder at each BBC/ITV region or OB van that could probably be the subject of a Wireless World project :-).
I've not noticed cue dots nowadays, so I presume they have been superseded by an "invisible" form of signalling rather than an in-vision one.
Does DVB-T and DVB-S allow for a datastream that could be used for this sort of signalling, so an off-air receiver can be used instead of needing a dedicated reverse channel (studio to OB) for "and now over to our reporter on the scene" news reports.
I imagine that adverts are cued automatically from a signal at the playout centre (or studio, for live programmes), rather than needing someone to look for a cue dot (whether or not it is visible to the punters) and press the button as soon as they see it.
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On Sat, 24 Nov 2018 18:43:34 +0000, NY wrote:

Well they shouldn't have changed speed because the stripes were generated by a free running 1MHz oscillator.
The original cue dot generators were valve jobs with multivibrators setting the size and position of the dot. As these were prone to thermal drift they had to be checked during line up prior to transmission. Even then they sometimes misbehaved and came up in the wrong place on air!
There was a design concept at one stage to build a detector circuit to detect the 1MHz to automatically run commercials but it didn't get off the ground.
--
TOJ.

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I'm sure I'm not imagining it. They varied from a stripe taking a second or so to pass from one side of the dot to the other, to a rapid flicker, within the same instance of the dot (so not drift of oscillator frequency due to temperature changes etc). It seemed to be very consistent that they started slow, speeded up to a frenzy and then slowed down again.
My challenge now is to find a Youtube video of an old ITV series and play "hunt the cue dot". I'd refer you to Public Eye (early 1970s) which Talking Pictures are currently repeating, but that seems to use a static chequerboard pattern rather than diagonal scrolling stripes.
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On Sat, 24 Nov 2018 20:29:11 +0000, NY wrote:

Well the original generators were as I described. They were hand built in ATV's workshop as they were designed by our deputy Chief Engineer Bernard Marsden. Other ITV companies may have built their own or bought manufactured ones as they became available. Later ones were transistorised and may have had different characteristics. Ours never produced a chequerboard pattern.
--
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https://i.postimg.cc/yxB9Ntgp/Public-Eye-6-13-The-Trouble-with-Jenny.png is an example from Public Eye - Thames, early 1970s. It seemed to alternate between a few seconds of static chequerboard and then a few seconds of fast scrolling of the pattern, then back to steady again - as if the frequency that produced the alternating black and white (with the addition of cross-colour!) was sometimes in sync with the frame rate and sometimes free-running. I'm not sure why all Talking Pictures TV programmes have an initial half-line of black and white dots and dashes, like Teletext, but I've even seen that on modern BBC regional news programmes which have been nowhere near analogue to have teletext or the missing leading and trailing half-lines.
https://i.postimg.cc/W3VC2pnB/A-Bit-of-a-Do-1-01-The-White-Wedding.png and
https://i.postimg.cc/BbqrCZPT/The-Outsider-1-01.png are from A Bit of a Do and The Outsider, both Yorkshire TV programmes from the mid-80s. These are the broad diagonal stripes and they scrolled at a constant speed.
I'll keep my eyes open for examples of broad diagonal stripes which vary the scroll speed - often towards the end of the on period, *apparently* as if they were to alert the person who cued the adverts that the critical off-at-5-seconds event was imminent.
I'm surprised that even the master that was sold to Talking Pictures (for Public Eye) or ITV3 (for A Bit of a Do) had the cue dots burnt in. You'd think that they'd have used a clean copy, rather than one that had been prepared for transmission. The Outsider is a different matter because that was a VHS-from-analogue recording from when it was first transmitted, not a modern repeat on a digital channel. I've just realised an interesting coincidence: both "Do" and "Outsider" were filmed/recorded in and around Knaresborough.
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On Sun, 25 Nov 2018 11:38:16 +0000, NY wrote:

I see what you mean. Ours never looked like that. I would think you would need a number of counters to produce that chequerboard and ours didn't have any, remember this was pre-semiconductor era.
The Do and Outsider are like ours but must be much later units as they are on colour programs. Our originals were on 405 of course.
--
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I suppose an oscillator at an exact multiple of (n+1)/2 line frequency, derived by multiplying the line frequency (*), so it keeps in sync, would produce a static chequerboard because on every line there would be a static pattern of black and white, but alternate lines would have a half-pattern offset from its neighbour. If it was required to animate pattern to draw attention to an imminent change of state, just tweak the frequency by a few Hz either way to make the pattern crawl left or right.
The one weakness with static or constant-speed cue dots is that they don't give accurate warning of the change. OK, it's exactly 60 seconds from start to end of cue dot, and exactly 5 seconds from disappearance to switching to adverts, but what if someone happens to miss the start of the cue dot and therefore doesn't know when to start their stopwatch. At least a changing state of cue dot says "watch attentively now, ready to press the button the moment the dot disappears".
(*) Or subdividing a much higher "dot clock" from a higher frequency clock crystal.
Intriguingly, the Yorkshire TV ident at the beginning of the episode of The Outsider had a very brief 2-frame instance of a circular film cue dot which might be on the beginning of all YTV's programmes if they use that same bit of film for the ident on all their programmes.
Going back to the Thames ident on Public Eye, it was interesting to see how much more drab the London skyline of their ident looked in black and white that the more well-known colour version. And the fanfare used on some episodes sounded to have a bit of wobble on some notes. Given that the film ident would be rock-steady for proper synchronisation with TV, I can only assume that the cornet player fluffed a few notes on that recording, before it was later replaced by a better performance. The first series of Public Eye that Talking Pictures have been showing was (IIRC) from the very early days after Thames and LWT took over from ABC, so Thames were probably still finding their feet.
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Cue dots predated Teletext by a great many years. Certainly used in the 405 era.
--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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Yes but blanking periods (if not Teletext to make use of them) have been there since the beginning of TV - out of necessity in order to let the field and frame ramp circuits reset themselves. I imagine if analogue TV was being designed now, those periods could be made a lot shorter with digitally-controlled counters to perform the sweep of the electron gun rather than RC networks to define the period.
Between OB van and studio, they often used Sound in Sync to avoid needing a separate sound channel, and I imagine that involved encoding a few bits of sound at even line- and frame-end so as to achieve the required bit rate for the sound. Trouble is, that wouldn't make it through to broadcast TV, so you couldn't use an off-air TV for cueing. Was S-i-S used by all broadcasters, or was it specific to BBC?
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In the days when cue dots were invented, I suspect that domestic receivers would have been easily upset by spurious things in the blanking period. Even when teletext came out (about 20 years later), some sets were upset by it.

Again we are in a much later period. SiS was a BBC development, but was licenced to somebody (I think Pye) for manufacture, so could hav ebeen used by anbody
--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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On Sat, 24 Nov 2018 18:43:34 -0000, NY wrote:

Off air cues for live TV these days are not really practical. The round trip time from a live OB back to the OB off air is around 8 seconds...
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Dave.
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It was to give timings to cue in the following (live) programme. My memory says on a -30 secs (approx), off at -10 secs, on again at -5secs.
--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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On Sat, 24 Nov 2018 14:06:55 +0000, charles wrote:

That may have been the BBC system. In ITV the dot went on at 1 min before commercial break and off at 5 secs before. We ran commercial film reels on a 5 sec preroll.
--
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On Thursday, 22 November 2018 16:39:23 UTC, NY wrote:

easy way to get to the tea/biscuits/loo first

bad psu regulation, maybe near flat batteries

There's probably software somewhere to fix it, albeit at loss of effective bit rate.
NT
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On Thursday, 22 November 2018 14:33:10 UTC, NY wrote:

I have a 1950s TV. I can understand why mains lock was still needed. Yes it was nice looking consumer goods, but in some ways it's primitive. 1930s techology screen, not even an ion trap.

That was normal in B&W TVs.
NT
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The ripple was visible, probably not in the EHT (which has a large capacitor, formed by the post deflection amplification electrode and the earthed backing on the tube), but in the line scan amplitude, usually resulting in a barely perceptable ripple scrolling slowly up or down the screen.

I think it was 1968 when I first saw colour. A great aunt had a colour set and we went around there. Had to wait quite a while before there was a program broadcast in colour - most were still in B&W at the time, but there was just an occasional colour program.
--
Andrew Gabriel
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On Thursday, 22 November 2018 14:47:15 UTC, Andrew Gabriel wrote:

PSU regulation became popular in the 80s. A minority used it before then, but most just designed the circuitry to cope with varying HT.
NT
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In article
snipped-for-privacy@privacy.net says...

Originally, TV sync pulse generators were mains locked because slight hum is not noticeable when it is stationary but highly visible as soon as it starts to move!
A lot of this was probably linked to the problems of manufacturing the large value electrolytic capacitors required to eliminate all of the ripple but things had improved by the 60s.
The problem was the anticipated launch of colour TV which has to be crystal locked to the subcarrier so, as all colour TV was to be on 625-lines, BBC2 was crystal locked from the start.There were still lots of elderly TVs around in the early 60s which couldn't handle non mains locked signals so the change to the 405 line services was delayed, as Charles said.
--

Terry

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