Test Cards

Test Cards have all but disappeared from tv screens in the twenty-first century, certainly on old-fashioned analogue terrestrial stations, where twenty-four hour programming is the order of the day.

Even when there is a substantial break in the schedules the gap is often filled with headache-inducing trailers, a simple caption or selected pages from a teletext service. On satellite, however, where channels come and go apparently at random, there’s often the odd test card or pattern to be seen – always electronically generated – and these introductory paragraphs are illustrated by some that I found knocking about recently in the Clarke Belt.

So what is the purpose of test cards and why are they so rarely used these days?

Today there’s hardly room in tv schedules to squeeze a test card in sideways, and we are quite used to pressing a few buttons on a remote control to receive any number of programmes instantly. But sixty-odd years ago things were very different.

For a start there was only one channel, and that only broadcast for a few hours in the afternoon and evening. Most people couldn’t afford a telly, and they were hardly going to be persuaded to save up for one if the sets in the shops had blank screens. Even when you bought one, it wouldn’t work straight out of the box. The dealer would have to install it for you, erect an aerial, and perform a complicated series of adjustments before you received your first picture.

Because sets relied on thermionic valves in those days and ran very hot, it was necessary to allow the circuitry to ‘warm up’ properly before your programme was due to start. Since this would most likely be the first show of the evening there had to be something on the screen to assure you that the set was going to work properly.

A simple caption would suffice, but how much better to have a display that would allow the viewer to tweak the user controls – brightness, contrast, horizontal hold, etc, that because of the poor stability of the electronic components inside the set required frequent adjustment.

The broadcasters too needed a test signal that would tell them that the network was functioning properly.

Of course special test generators were available that could be used to make accurate measurements of the performance of every aspect of the studio and distribution equipment, but again, how useful it would be to have a pattern that could give a rough indication of performance (or lack of it) from camera to screen.

And so two siblings were born – the test card and the tuning signal. The tuning signal was a ‘cut-down’ test card that looked quite technical but not too frightening, and included identification and simple tests for brightness and contrast setting on the tv set. Thus it could be radiated prior to the start of programmes giving the viewer the confidence that his set was working, was tuned to the correct channel, and that the programmes were about to start.

The test cards, on the other hand, contained a more rigorous selection of patterns that were of use all the way through the broadcasting chain. The geometrical patterns allowed receivers, monitors and cameras to be adjusted to give a picture of the correct size and shape, while greyscales allowed the brightness, contrast and (in the case of cameras) gamma to be set correctly.

Gratings of fine lines enabled the focus of cameras and receivers to be checked and fine-tuning to be optimised. Larger black and white patches and needle pulses allowed aerials to be adjusted to obviate ghosting, and also showed up defects in transmission lines and vision circuitry. For a full technical description of the function of the various elements of some of the many UK test cards that have been used over the past sixty-odd years, see Not just a pretty face…

All-in-all test cards were an invaluable toolbox for everyone involved in providing a television service at a time when test equipment was very expensive and programmes were few and far between. This altruistic approach has had its day though. As far back as the nineteen-seventies, when energy and cash were suddenly at a premium, the BBC used to turn off its transmitters altogether when no programmes were scheduled and countered complaints from dealers and aerial installers by saying they were not in the business of providing test signals at licence-payers’ expense, though they never went on to explain how one could install an aerial without a working transmitter to aim at.

The BBC’s test cards are undoubtedly aesthetically as well as technically excellent. Each new one has had the same look to it, and all have been adopted by many other broadcasters in the world, starting of course with the UK’s commercial independent television stations that began to appear in 1955. And it was a joy to see colour television sets tuned to Test Card F on BBC1, BBC2 and ITV in a dealer’s showroom giving displays of almost identical quality.

Other countries had their own designs, of course; some taken up by several broadcasters, others unique to their own. The nineteen-sixties and -seventies were a golden era for receiving, identifying and photographing foreign test cards for those with such a disposition.

There are examples of long-distance reception on the Non-UK Test Cards page.

So how are test cards generated and transmitted?

There are basically three methods of making a test pattern. The obvious one – suggested by the name – is to draw or print the design onto a card and mount it in front of a television camera.
A variation is to make a transparency and mount it in a slide scanner.

Whilst that technique is essential for testing the camera or scanner in question, it can lead to errors when the intention is to test the circuit or receiver.

A second way that was used early in the days of monochrome television was the ‘monoscope’. That was a kind of camera tube that had the test pattern printed in carbon onto an aluminium plate that formed the anode of the tube. That produced much better signals for day-in-day-out test card duty.

Thirdly there are the electronically generated patterns. Using simple electronic circuitry it’s possible to generate a range of useful signals for testing circuits and receivers and such were in use by broadcasters and dealers from the start. But to make a comprehensive test card was a lot more difficult and it was not until the mid and late nineteen-sixties that they began to appear. The earliest was probably the Phillips PM5540 pattern generator as used by NOS in The Netherlands, and by others.

This was followed in the colour era by the Phillips PM5544, the IBA’s ETP1 and the Telefunken FuBK pattern, amongst others.

Nevertheless, a few optical colour cards were used, notably, of course, the BBC/ITA/BREMA Test Card F, and that continued until the end of the century (from 1984 generated from a digital memory rather than a sandwich of mono and colour transparencies mounted in a 35mm slide) until two revamped versions were introduced – the electronically generated Test Card J (4:3) and Test Card W (16:9) that included almost all the features of Test Card F, had the central colour picture digitally remastered from the original colour reversal transparency, and had additional tests required for digital operations. A high-definition version of Test Card W followed that was suitable for the 1080 line standard.


 

Illustrations

The Off-Screen photographs of UK reception were taken from production sets – a Ferguson 19-inch dual-standard receiver and an EKCO 17-inch 405-line set in 1967-8 and a PYE 22-inch colour receiver rather later. Some of the non-UK cards I photographed from receivers converted for 625-line VHF operation – a 12-inch PYE 405-line receiver of 1950 vintage and a home-brew 20-inch 625-line only receiver constructed in 1970 from a design published in Practical Television magazine.

The off-screen pictures of Test Card F were scanned from 35mm slides taken from the Forgestone 22-inch colour receiver kit in 1979, and all the twenty-first century screenshots are from a Sony WEGA 32-inch widescreen receiver photographed with a Hewlett-Packard Photosmart 318 digital ‘snapshot’ camera – a combination that results in frightful moiré interference patterns and some dubious focussing and exposure values.

The colour bars and some simple test patterns were recreated from scratch in Adobe PhotoShop. One or two video screen grabs have come my way, courtesy of Mark Carver and “Dantus” Paolo Pizzo, and other pictures culled from various old books, magazines and leaflets, are included for completeness.

Because some of the off-screen and half-tone shots are a little fuzzy, I have reconstructed some of the cards from scratch in a graphics package. Click on the cards on the left of the page to reveal a full-resolution 405-line (500 x 375) or 625-line (765 x 575) version. (Choose “Open in a new window” in order to compare the reconstruction with the original.)


 

The 30-line era

On 30 September 1929, the BBC was obliged to allow John Logie Baird access to two London medium wave transmitters for the purpose of experimental transmissions in the 30-line standard. These were produced by means of a ‘Nipkow’ scanning disc – a 20-inch diameter aluminium wheel perforated at the rim with thirty tiny holes, each one slightly nearer the centre than the last, so that a ‘raster’ of thirty vertical lines with an aspect ratio of 3:7 was produced. The scanning spot started at the bottom right of the picture, moving rapidly upwards, with subsequent lines appearing to the left, until the spot arrived at the top left-hand corner. A black line was left along the top of the picture as a rudimentary synchronisation signal. A refinement sometimes employed was to make the lines at the centre of the picture closer together than those at the edge in an attempt to improve the apparent resolution. To get an idea of the scale, imagine a clock face. The height of the scanned picture would be represented by the distance between the fourteenth and sixteenth-minute marks. The pictures produced (by viewing a neon light through the disc) were dark, small, flickery and slightly curved.

On 22 August 1932, the BBC took over responsibility for the transmissions, having installed a proper studio and control room, operating with equipment that used mirror drums instead of Nipkow discs. Receivers using that technology were also introduced, leading to larger, brighter pictures with straight verticals. The BBC 30-line transmissions continued until September 1935 and included programmes and test patterns. Because of the technical limitations, only the head and shoulders of one actor could appear on the screen at a time. To change shot, a large chequerboard was slid in front of the camera whilst another actor moved into place.

The captions were scanned by means of a second camera mounted in front of a carousel carrying a dozen caption cards. The test patterns were very simple and were not assembled into a composite card as they were to be with high-definition standards.

This pattern is a test of the low-frequency response of the system, comprising as it does two square waves at the line (375Hz) and field (12.5Hz) repetition frequencies. Poor low frequency response resulted in one or more of the three white quarters appearing darker than it should. The best lf response is obtained on a medium wave am signal when the receiver is tuned correctly, so this test would have been a ‘magic eye’ equivalent.

This wedge was a test of the high-frequency response. Only the left-hand side would have appeared clear on a receiver of the time. The converging lines would have blurred to grey well before they joined at the right-hand side. The upper limit of the transmitted frequencies was dependent on the quality of the audio circuits feeding the transmitter, the transmitter itself, and the receiver used to feed the ‘televisor’ display device. 10kHz would have given sufficient vertical resolution to match the 30-line horizontal resolution. Again this pattern would have been used as an indication that the radio was correctly on-station.

This test allowed the viewer to adjust the scanning device in the receiver for correct synchronisation. The circle was not so much for scanning size adjustment since that was fixed by the mechanics of the disc or mirror drum and couldn’t be changed. However, the video signal was transmitted without any synchronising pulses and so it was necessary to adjust the speed and phase of the disc or drum manually to obtain a viewable picture. When the line was horizontal, the circle truly circular and the image stationary and central, the picture was correctly synchronised.

Some receivers had crude built-in synchronisation in the form of a ‘sonic wheel’ which was a metal disc having thirty teeth fitted to the scanning disc drive shaft. It could be synchronised by means of a coil fed with the video signal – the pulses representing the black line at the top of each picture being arranged to coincide with the teeth on the wheel, but its effectiveness depended on the video content.


 

The 405-line era

THE FIRST 405-line era began at 3pm on Monday 2 November 1936 with the start of the official BBC television service from Alexandra Palace and ended abruptly on Friday 1 September 1939 two days before the outbreak of the second world war. At 3pm on Friday 7 June 1946 programmes resumed, almost as if there had been no interruption. The end came on Wednesday 2 January 1985 – albeit a day later in Scotland because of the extra day’s bank holiday there. Apparently there were no complaints about the closedown – BBC1 and ITV had been available in most areas for many years on 625-line UHF in colour, and it seems that almost everyone had equipped themselves with a 625-line receiver by 1985.

More details of the UK 405-line service including some ITA transmitter coverage maps from 1967 may be found on the UK 405-Line Television Network section of this web site, and technical specifications and more detailed history are on World TV Standards.

This section illustrates some of the test cards that were in use on the UK 405-line standard, though I have included UK 625-line monochrome cards, and some international ‘standard’ cards from the same era. There are separate sections for colour and widescreen cards, including some from non-UK broadcasters. Further examples of non-UK test cards and captions, a number of which I received and photographed myself here in Sheffield, can be found on the Non-UK Test Cards page.

TO BEGIN at the beginning… This is Test Card A from the 1936-39 era, one of the few pictures on this page from the first three years of high-definition transmissions, before they were cancelled for the duration of Second World War. It has the bare essentials to qualify as a test card rather than a tuning signal – mid-grey background, horizontal and vertical gratings for focus and hf response, letterbox for lf frequency response, castellations and circle for scan amplitudes and centring, and needle pulses for transient response and multipath reception. Click on the card for a 405-line resolution reconstruction.

Between 2 November 1936 and 7 February 1937 the EMI 405-line system alternated week-by-week with the Baird 240-line 25 frames per second system on a trial basis. The Baird system had an aspect ratio of 4:3, while that of the EMI system was 5:4 until 1950. Since Test Card A has a definite 4:3 aspect ratio it could be inferred that it was used for the Baird system but in fact all the cards I have come across seem to be designed for 4:3, including some shown below which were introduced in 1946 and 1949.

Just above the black circle in Test Card A is a set of fine horizontal lines at a pitch of about 1/360 of the height of the card. The 405-line picture (377 lines high) might just have resolved these, but the Baird 240-line picture would not have. A 405-line receiver would not have resolved the ‘3 MC’ vertical bars since the transmitted vision bandwidth was 2.5MHz, but they would have shown up on studio monitors. The video frequencies used by the 240/25 system were only a quarter of those required by 405/50 though. A mere 857kHz would have sufficed for the Baird system, which means that Test Card A was certainly not designed for that standard.

Despite the scarcity of programmes at the time (a couple of hours in the afternoon and evening) Test Card A was rarely seen. What was more often transmitted, continuing into the ‘fifties and ‘sixties, was this first-ever electronic test pattern known as the cruciform (or ‘art bars’ – short for ‘artificial’ – in the trade). Although extremely simple to generate, it had several functions: firstly as check on picture centring, secondly as a test of high frequency response (the vertical edges of the cross should be sharp) and thirdly to indicate low frequency response (the black and white areas should be uniform, and not turn grey towards the right).

Also from that period – around 1938 – are these early BBC tuning signals cum station idents.

SO WHAT of Test Card B? It was similar to Test Card A, but with the letterbox shifted to the top in place of the central frequency gratings and replaced with a strip of coloured squares from an Ilford panchromatic response chart at the bottom. This was to assess the spectral response of the camera, but it produced a non-linear brightness staircase on the picture which confused technicians. No complete copy of this card appears to have survived.

However, the firm Cathodeon introduced a range of monoscope test patterns labelled B to G. C and G were the standard cards shown below, D was based on the RMA Resolution Chart 1946 also shown below and F was a simple line-drawing resolution chart. Pattern B was this view of King’s College Chapel, Cambridge. Cathodeon were a subsidiary of Pye which was based in that city. Test Card B it ain’t, but it’s the nearest thing with an official B designation that we have. Brian Summers has a 1MB pdf file of the Cathodeon illustrated brochure of Monicon tubes on his comprehensive Museum of the Broadcast Television Camera website.

Like Test Card A, Test Card B was designed primarily as a studio-based chart for the alignment and adjustment of cameras, rather than domestic receivers, and so was probably never put to air. Neither has any peak white indication or proper contrast wedge and the grey background would have been adjusted for around 80% white on the waveform monitor, as in the reconstructions, in order to avoid overshoot on the frequency gratings. The ‘letterbox’ probably comprised a strip of very low reflectance material such as velour that acted as a black-level reference for the cameras as it would appear darker than the other markings on the chart.

THESE CARDS are simple designs from the very early days of the ITA. They were radiated from a temporary transmitter housed in a caravan with ‘experimental’ call sign G9AED operated by Belling and Lee, the aerial manufacturers, but later acquired by the ITA. The ITA card was transmitted in 1955 from the Croydon site, and the G9AED one was from Winter Hill in 1956, each prior to the start of the full service, and they comprise tests needed by aerial installers rather than anyone wanting to adjust receiving or transmitting circuitry.

One of the captions pictured on the left invited viewers to send in reception reports. Robin Benson did just that and was rewarded with this QSL (radio-ese for confirmation of reception) card, which he has kindly allowed me to put here.

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