On Saturday, 24 November 2018 12:13:41 UTC, Graham. wrote:
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.
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
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I've not noticed cue dots nowadays, so I presume they have been superseded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.
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
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.
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.
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
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
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.
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
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.
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?
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
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
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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.
[email address is not usable -- followup in the newsgroup]
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
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.
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