Updated: 7th September 2019.
The project to replace the Noddy-based clock caption device (where a camera was placed in front of a mechanical clock and colour added by a colour synthesiser) was initiated in 1979 after John Shelley spotted an article in the Engineering Weekly Information Sheet, where the various problems with keeping the clock camera correctly adjusted were outlined. John sent a handwritten note to Richard Russell of the Designs Department saying simply “This all seems pretty primitive. Is there a possibility that we could generate the clock caption electronically?”.
When built, the new electronic kit was put on display at the BBC’s stand at the IBC (International Broadcasting Convention) in Brighton in 1980.
On the 39th anniversary of the on-air launch of the new channel clock, we’re sharing the following long since forgotten article, produced by BBC Engineering, which provides some fascinating insights about the technology behind this iconic BBC clock.
From Saturday 6th September, the clock seen on BBC Two has been produced electronically. The BBC One clock is expected to ‘go electronic’ next year. The new BBC system, designed by Richard Russell of the Designs Department, has done away with the need for cameras, slide scanners and mechanical clocks. Richard Russell says “the new clock has been designed to take up less space, to be less costly to operate and to be more reliable and to offer better resolution than the system it has replaced.”BBC Eng Inf (1980)
The picture the viewer sees is made up of the clock and the BBC logo, showing him which channel he is watching. The network logo for BBC Two is generated using run-length encoding, where the data is stored in a programmable read-only memory (PROM). Run-length encoding is where, instead of telling each picture element what colour it should be, it is only necessary at each colour change to tell the system how long the colour will last, i.e., its ‘run-length’. Although theoretically 1,024 colour changes could take place on each line, this is limited by the size and speed of the data memory. The use of a buffer memory permits at least 64 changes on each line.
The run-length data for the BBC Two logo has been produced by John Mitchell of the Television Investigation Section. Robin Vinson and Ewen MacLaine of the Computer Graphics Workshop produced the data for the Open University symbol on BBC Two, which is also generated by the new equipment.
The logo generator can operate in two modes. The first limits the system to four different colours and reduces the size of the memory needed to a minimum. The other makes 32 different colours possible but as a result needs a much larger memory. For example, it needs about 4 kilobytes of memory storage to display a simple logo.
An additional feature of the BBC logo generator is that it can be used to produce simple animation. Although it is mainly intended to produce fixed patterns by reading run-length data from a PROM, movement can be achieved by using a microprocessor to make real-time alterations to the data held in a random access memory (RAM). The system reads the data from the RAM by means of direct memory access (DMA).
The main part of the picture – the electronically generated clock – is made up of two components: the fixed elements on the clock face and its moving hands. The fixed elements – hour markers, the circle and the centre spot – are stored in a PROM as a series of horizontal position coordinates which are read out in sync with the television waveform. The size of the memory required is reduced by using horizontal and vertical symmetry.
The data for the clock hands is stored in a RAM. A microprocessor controlled by an erasable programmable read-only memory (EPROM) keeps track of the time and every second calculates the correct angle of the hour, minute and second hands.
The BBC designers had to get over the problem that when the hands made only a small angle to the horizontal, the television line structure breaks the edge of the hands up into a staircase. The BBC’s answer is to feed the hand signals through analogue processing circuitry which adjusts the rise and fall times of the waveform according to the angle of each hand. The microprocessor then selects the rise time to give the best optical effect on the viewers’ screen.
All the equipment needs is mixed blanking and mixed sync pulses together with AC mains power. However, time reference pulses and logo-selection signals for remote control can be used as optional inputs. Without an external time reference signal, the clock derives its reference from either incoming television pulses or from its own internal oscillator. The outputs are standard 0.7 volt peak-to-peak RGB and a composite monochrome output suitable for feeding to a colour synthesiser.
The clock can be set to any time. It can be corrected in one-second intervals or by the hour – useful for the twice yearly changes between GMT and BST.
The on air launch of the electronic clock did not mark the end of service for its mechanical counterpart. There were still occasional sightings of the physical model post-6th September 1980. However, it’s not clear why this happened. A fault with the new clock kit or BBC Two had temporarily moved to the back-up network control facility, which hadn’t yet been equipped with the new clock equipment?
It is our understanding that the electronic clock kit was delivered to the presentation departments in Northern Ireland, Scotland and Wales in late-1984. The units provided BBC One and BBC Two clock capabilities. The new look BBC One was intended to launch on 1st January 1985, so the new equipment for the updated BBC One symbol and the electronic clocks was delivered to Belfast, Glasgow and Cardiff to meet that date. BBC One Northern Ireland launched an electronic clock a few months ahead of Scotland and Wales – making them the only national region to use an electronic clock sporting the 1981 – 1985 design.
The BBC Two electronic clock delivered to the national regions apparently did not include any regional branding. We have heard anecdotal evidence of the BBC Two clock being used on air by BBC Two Scotland. But no reports of the BBC Two clocks (the 1980 – 1986 design) being put out on air by BBC Northern Ireland and BBC Wales. If you know different, let us know.
Clean Feed contributor Andrew Nairn confirmed that the Scottish electronic stripy ‘2’ clock was definitely used on air in early 1985 – and potentially earlier. Local opts on BBC Two were not uncommon, for Gaelic programmes, party conference coverage and other live programmes that couldn’t be transmitted on BBC One Scotland. As the Glasgow pres department would’ve had the new BBC Two clock equipment available from late-1984, there’s nothing to say they wouldn’t have started using it right away.
Here’s the BBC Wales mechanical model. It was used on both channels.
And a video clip showing the clock in working order in 2011:
Also, when the BBC Two clock design was updated in March 1986, the nations were not supplied with updated kit. Instead, they had to make do with a recoloured version of the 1980 clock design, with the new BBC Two logo. The ‘TWO’ logo was displayed in a similar style to that of the BBC Two Open University symbol. We are aware of at least one sighting of this clock on BBC Two Northern Ireland. Unlike the 1986 – 1991 ‘TWO’ idents in the nations, the equivalent clock had no regional branding. Any appearances on BBC Two Scotland and BBC Two Wales? Let us know.
Includes a reproduction of an article from BBC Eng Inf (1980) - the quarterly magazine for BBC Engineering staff. COPYRIGHT: BBC.FEATURE IMAGE:
PICTURED: BBC Two 1980 clock (recreation). SUPPLIED BY: created using facilities at 625.uk.com. COPYRIGHT: BBC.