On 5 May 1975 the South African Broadcasting Corporation (SABC) began
experimental broadcasts in the main cities of South Africa. Many viewers will
remember staring at the mesmerising colour test pattern in their sitting rooms.
Once a common sight, test patterns are now only rarely seen partly because
they are no longer intended to assist viewers in the calibration of their television
sets, but mainly due to the fact that most television stations run programming
24/7.
The history of television test signals dates back to 27 January 1926 when John
Logie-Baird first demonstrated that it was possible to transmit pictures using his
mechanical scanning apparatus in Britain.
It wasn’t until 1929 that the first experimental television service was broadcast
by the BBC in collaboration with The Baird Company. At this time transmission
took place for 30 minutes per day using the Baird 30-line system.
It was around 1934 that the first simple test patterns were generated to test
the equipment. These consisted of a simple circle and line chart, which tested
the picture ratio and the first wedge-shaped “frequency grating’ for testing high-
frequency response.
Between 1939 and 1946 there was no television due to the war. After the war,
Britain’s 3 350 TV viewers tuned into some new test signals and to the first ever
BBC Clock. It was around this time that the BBC generated the first true “Test
Card’. Test Card A was designed to aid the aligning of studio cameras and signal
response. It was also broadcast to aid the field engineers who were setting up
television sets. “Test Cards’ were so called because the original ones were
indeed cards, usually hand-drawn on large pieces of card. Typically they would
measure 2ft by 3ft and a large camera would be placed in front of them.
North America
In North America, most stations ran the now infamous Indian Head Test Card
personalised with a station ident, originally a piece of artwork in card format.
RCA then developed an electronic test card generator called a monoscope. This
was made up of cathode ray tubes with a metal plate onto which the image of
the Indian Head was etched, which burnt a permanent image into the tubes. The
monoscope had a UHF signal output that was fed into the transmitter.
The Indian Head monoscope was also used in Canada, Sweden, the then
Rhodesia Television (now Zimbabwe Broadcasting Corporation) during British
colonial times and was also used by Venezuelan TV in South America. Towards
the end of the Indian Head TV era (around the late 1970s), there was no nightly
test pattern on some stations in the US, typically when automatic logging and
remote transmitter controls allowed shutdown of power immediately after the
formal sign-off.
In the 1970s, Philips introduced the PM5544 test generator. The test pattern
was not just an electronically generated version of a colour image – the signal
from which it derived contained some deliberate deviations or violations of the
TV standard which were designed to cause obvious aberrations in specific areas
of the pattern if the receiver had any amplitude or phase distortion in its Phase
Alternating Line (PAL) decoder. How the pattern was distorted gave a clear
indication of what part of the PAL circuit was not working so the TV repairman
could fix the problem.
Today
Today, modern TV sets such as LCD and plasma sets rarely need adjustment as
the use of digital interconnect standards operate without the issues inherent to
analogue broadcasting. But the bottom line is that the financial imperatives of
commercial television broadcasting mean that air time is now typically filled with
programmes and commercials (such as infomercials) 24 hours a day, and non-
commercial broadcasters have to match this.
There are, believe it or not, groups of “test pattern fanatics’ who monitor and log
the use of test patterns when they occur. For example, did you know that
Hungary’s RTL KLUB, Iceland’s RUV and Latvian Television all run test patterns
between broadcast hours? Most Asian countries including China, Nepal,
Philippines, Malaysia and Indonesia also do the same, but test cards are no
longer broadcast in Thailand when Thai PBS stopped broadcasting them in
January 2011.
Iconic
Perhaps the most iconic of all test cards was Test Card F. First broadcast on 2
July 1967 (the day after the first colour pictures appeared to the public on
television) Test Card F was created by BBC engineer George Hersee. The central
image on the card featured his eight-year-old daughter Carole, playing noughts
and crosses with a clown doll, Bubbles the Clown, surrounded by various
greyscales and colour test signals needed to ensure a correct picture. Like other
test cards, it was usually shown while no programmes were being broadcast,
but it was the first to be transmitted in colour in the UK and the first to feature a
person. It was used on television around the world for more than four decades.
Text Card X
In modern times Test Card F has been replaced by Test Card X, which can be
viewed for 90 seconds every two hours as part of the BBC HD preview slot when
programming is not on air. The test card, when viewed, is enhanced with 5.1
surround sound tests. The card is a rescanned HD version of Test Card F artwork
and Miss Hersee, who is now 50 years old and who was paid around £100 by
the BBC when the image first appeared, is thought to hold the record for the
most TV appearances by a single person!
