FROM THE ARCHIVE OF: Dave Baldwin, The TV Room
This page contains examples of the various tuning signals and test cards used on BBC Television since the 1930s. The feature remains a work-in-progress and we’d be delighted to hear from anyone who has any additional information about any of the items covered here.
Test patterns and tuning signals
Television is a UK invention. On 27th January 1926, John Logie-Baird demonstrated that it was possible to transmit pictures using mechanical scanning apparatus. In 1929, the first experimental television service was broadcast by the BBC in collaboration with The Baird Company, using the Baird 30-line system.
In 1934 came the idea of using patterns to test the equipment. Initially, these were very simple designs, consisting of circles and lines. which tested the picture ratio.
In November 1936, Baird introduced an enhanced version of the mechanical system, capable of 240 lines. However, an electronic system from Marconi-EMI boasted 405 lines. The BBC transmitted each system on alternate weeks, from Alexandra Palace. The Marconi-EMI 405-line system was deemed superior and the BBC discontinued use of the Baird format on 13th February 1937.
1937 also saw the introduction of the first BBC tuning signal. This was used to assist viewers in adjusting the numerous controls on their TV sets to obtain the optimum signal.
Television services were suspended from 1939 until 1946 due to World War II.
With the war over, BBC TV got back up and running, for the few thousand people who could actually view it. And just as before, tuning signals were in use, prior to the start of programmes each day.
Before the end of the decade, the BBC began using patterns specifically designed to assist with aligning studio cameras and testing response. In addition to being used off-air, these designs were also broadcast, and became a useful tool for the TV trade, when setting up domestic TV installations.
The designs were hand-drawn on large pieces of card, typically 2ft x 3ft. Hence the term “Test Card” was coined. They were put to air via a camera. Originally, they were also referred to as “Opacities”.
An alternative to having to dedicate a conventional camera to airing a test card, was a monoscope. This was a special-purpose camera that had the test image painted on the inside screen of the tube. Each tube was only capable of handling one test image. However, the set-up was expensive, difficult to adjust, and was restricted to black and white output. It fell out of favour in the 1960s.
The cards later became “Transparencies” – ranging from 1ft wide, to the 35mm slides that were common during the 1960s, 1970s and 1980s. The term “Test Card” became the common term for these special designs, irrespective of the means by which they were put to air.
Test Card A was the first BBC test card. It debuted in the late-1940s and is credited with being the world’s first television test card to be transmitted.
The 2.5 MC frequency grating was of most interest to engineers, hence its location in the centre of the circle. Although a great improvement on anything previously available, Test Card A and it’s successor, were criticised for not having sufficient testing features.
Test Card B no longer exists. The best remaining image is a photograph of a studio, with a partial view of Test Card B on a stand. BBC engineer George Hersee described it in his 1967 work, but it is believed that no copies of the full card remain in existence.
It was similar to Test Card A but with an extra greyscale strip below the circle. The letterbox just above ‘A’ moved to the top of the card. It was never actually broadcast, but was used for camera line-up at Alexandra Palace.
Test Card C was first broadcast in January 1948. At the time, the aspect ratio of TV broadcasts was 5:4. By the early 1950s, this had changed to 4:3. The design of Test Card C was altered slightly as a consequence.
Some BBC regional transmitter sites used slightly different versions of Test Card C. There were at least three different designs in use at the BBC. Additionally, the ITA used a another design for the ITV Network.
In 1964, two new test cards were introduced. Test Card D was adopted by the BBC and ITV for use on BBC One and throughout the ITV Network. Test Card E was used for the new 625-line BBC Two service.
Test Card D and Test Card E were virtually identical, bar the frequency gratings, which were finer on the latter, to cater for the higher definition offered by the 625 service.
The frequency gratings on Test Card E were sinusoidal, and thus technically more useful than the square waves on previous test cards. However, as a result, some of the gratings looked soft and fuzzy – the lowest grating in particular.
TV dealers complained about this and Test Card E was consequently scrapped, after c. one week on air. It was replaced by a modified version of Test Card C. Unfortunately, we have no examples of the special BBC Two version of Test Card C.
Test Card F, designed by BBC engineer, George Hersee, was introduced in 1967, and aired on the new colour 625-line BBC Two service. This test card features Mr Hersee’s daughter, Carole, pictured alongside Bubbles the clown.
RELATED ARTICLE: How did TCF become such an iconic BBC image?
Since the 1950s, BBC trade test transmissions were accompanied by music compiled from library music publishers. Over the years, virtually every music genre imaginable was featured.
The vast majority of this music was not commercially-available in the UK. However, in 1953 and 1954 some commercially-available recordings were used with Test Card C – these were all on the Oriole label.
In 1954, tracks by the Xavier Cugat Orchestra and the David Carroll Orchestra included vocals – this was unusual for trade test music. For a period in the 1970s and early 1980s, some of the tapes included pop music.
These tracks would have been from an outtake recording, produced outside of the UK. The BBC could transmit this material as library music, as the recording would not have been released commercially in the UK.
EXTERNAL LINK: there’s much more about the music that accompanied the test card at The Test Card Circle website.
The test card was also accompanied by a test tone on many occasions. Until the 1970s, the tone would be inserted for short periods at regular intervals during the day. By the 1980s, music was played with the test card for much of the day, with tone being restricted to short periods each morning, when the test card first appeared.
There were different tones for BBC One and BBC Two: BBC One used 1KHz, and BBC Two 440Hz. The use of different tones on each channel was mainly just so that engineers (and viewers of a certain disposition) could easily identify each channel.
Originally, the tones originated at Broadcasting House (the home of radio). We’re not sure exactly how they were generated there. In later years (around the start of the 1980s), some units were built that took in 5MHz from Rubidium oscillators, and synthesised the above audio frequencies precisely. The kit was still there as late as 2009 and still worked.
However, since the introduction of the ‘VALID’ test signal (colour bars with a rotating central pattern and synchronised blip on the sound, made by Vistek (now ProBel)), the BBC uses 997Hz for the main programme stereo, and 440Hz for the second stereo – often used for Clean Effects.
The problem with precise 1KHz is that only some of all the possible digital levels are used. 997, however, is such an odd number, that it cycles through all the levels, thus fully exercising any DACs. But it is close enough to 1KHz so as not to be audibly different.
Test Card F was broadcast from a 35mm slide, using a Rank Cintel slide scanner. It was actually a dual-layer slide – one layer for the monochrome areas, the other for the colour parts – very carefully aligned and sealed in a glass slide-holder. There was no BBC One-branded slide version of Test Card F.
The ‘BBC 2 COLOUR’ test card slide was used on BBC One and BBC Two. However, when Test Card F was aired on BBC One, a ‘BBC 1’ caption was electronically superimposed, covering up the ‘BBC 2 COLOUR’ text.
The Rank Cintel slide scanner was a large and expensive piece of equipment, but probably of more importance, technically, is that it would be near impossible to keep two scanners aligned identically to match each other.
Like all standards, their absolute accuracy is not as important as the fact that everybody agrees. Hence, it was far better to use just one scanner, and overlay a ‘BBC 1’ caption on the feed that was used for the BBC One transmissions, as this resulted in a consistent test signal for both networks.
Test Card F was generally broadcast for longer periods during daytime hours on BBC Two than on BBC One. The latter’s schedule often being filled by programmes for schools and children.
The BBC One caption overlay was a little crude by modern standards. It was produced by a dedicated unit that had the relevant parts from an ‘Anchor’ machine (an early form of electronic caption generator, before the introduction of Astons and Ryleys).
In 1980, the BBC began an experimental Ceefax In-Vision service. Gaps in the schedule which previously would have been occupied by trade test transmission, were now being filled by a selection of teletext pages.
The In-Vision broadcasts – offering a digest of news, sport, travel and TV listings – were largely restricted to short, early morning slots, with the test card continuing to play the more prominent role during gaps in the programme schedule.
With TV sets becoming more reliable and members of the trade now having test signal generators available to them, the days of the trade test transmission were numbered. The BBC was also keen to promote its teletext service and BBC editorial teams wanted to make better use of the dead airtime.
RELATED ARTICLE: The history of Pages from Ceefax.
RELATED ARTICLE: The BBC test card and in-vision teletext.
In early May 1983 daytime trade test transmissions were replaced by Pages from Ceefax. The test card was now largely restricted to brief early morning slots, shortly after transmitters came back on air following overnight closedowns.
Weekdays, Test Card F would be broadcast for seven-and-a-half minutes, between 5.52am and 6am on BBC One (preceded by a period of pulse and bar, accompanied by tone).
It would also be broadcast for seven-and-a-half minutes on Saturday and Sunday mornings, before the first programme of the day. The test card would also have a seven-and-a-half minute outing on BBC Two each day, prior to the start of programmes or Pages from Ceefax.
Occasionally, there were technical issues with the ‘in-vision’ Ceefax transmission: we are unable to verify the cause of the issues but there were certainly problems with the Ceefax transmission system over the years – particularly in the 1980s. And perhaps the in-vision teletext generator misbehaved occasionally too.
Whatever the reason for the lack of availability of Ceefax, Test Card F or Test Card G (more on that shortly), would be brought in as a substitute.
The test cards also stepped in during some periods of industrial action, where Ceefax content (particularly news, weather, sport, business and travel) was unavailable, although apology captions were also occasionally deployed in such situations.
RELATED ARTICLE: The history of the BBC trade test transmission (part 2/4).
RELATED ARTICLE: The history of the BBC trade test transmission (part 3/4).
RELATED ARTICLE: The history of the BBC trade test transmission (part 4/4).
With thanks to Dave Baldwin for the 1980s/1990s recordings from which many of the stills were obtained. Thanks also to Andy Emmerson, for the black and white test cards. Our thanks to Andrew Nairn for his input regarding test card usage.
PICTURED: BBC Test Card J. COPYRIGHT: BBC.
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