Early development of the BBC’s
colour television service
This is an extract from “Twenty-five
Years of BBC Television”,
BBC Engineering Division Monograph No 39: October 1961
By Sir Harold Bishop, C.B.E.,
F.C.G.I., M.I.E.E., M.I.Mech.E.
Director of Engineering, British Broadcasting Corporation
This is document was
made available to the general public in 1961 and is reproduced here with thanks
to the BBC.
6.2 Colour Television
The BBC has been carrying out research and
development on colour television since the resumption of the television service
after the war. In the early post-war years an experimental sequential system
with mechanical colour separation was developed, and a considerable amount of
research was carried out on the fundamentals of trichromatic colorimetry as
applied to television.
By 1953, the consensus of opinion was (as
it still is) that no public colour television service could be contemplated
unless it were compatible, i.e. the transmissions were of a form which would
enable existing monochrome receivers to produce black-and-white pictures. It
seemed unlikely that compatibility would be achieved with any system which was
not effectively simultaneous, and the first report of the Television Advisory
Committee pointed out that the impossibility of increasing the channel spacing
in Band 1 (41-68 Mc/s) would necessitate a fully compatible system if colour
transmissions were made in this band. Towards the end of 1953 the BBC Research
Department began the development of an adaptation of the American N.T.S.C. fully
compatible simultaneous colour television system to the British 405-line
On 7 October 1954, the first 'compatible'
type of colour television picture was radiated from the medium-power transmitter
at Alexandra Palace. The pictures included slides and 16-mm motion pictures, and
the details of the standards employed on this occasion differed little from
those employed regularly from 1955 until the present time. On this historic
occasion only one colour television receiver, so far as is known, displayed the
pictures, but there was a fair-sized audience viewing the compatible
black-and-white pictures in their homes on normal domestic television receivers.
Although many hundreds of tests were subsequently necessary to prove the point,
it seemed to the observers of this first transmission, which was a co-operative
effort of the Research Department of Marconi's Wireless Telegraph Co. Ltd and
the BBC Engineering Division, that in this adapted N.T.S.C. system there existed
a standard capable of providing excellent colour pictures and compatible ones of
During the winter of 1955-6 a regular
series of transmissions was radiated from the medium-power transmitter at
Alexandra Palace, with the primary purpose of testing the compatibility of the
pictures on a comparatively large sample of domestic receivers. Again, only
slides and pictures from 16-mm motion film were used, this time the equipment
being of BBC design and manufacture. In the meantime Studio A at Alexandra
Palace had been equipped with a single three-tube colour camera of Marconi
design, and the first occasions on which colour pictures including scenes from
the studio were broadcast occurred on 3, 4, and 5 April 1956 during a special
demonstration for delegates of Study Group IX of the C.C.l.R., who were visiting
this country as part of a world-wide assessment of the state of development of
colour television. The programme of this demonstration was probably the most
comprehensive which has yet been given, and was as follows:
Colour pictures were first shown using
three separate full-bandwidth links to convey the R, G, and B signals, in order
to show the performance of the R.C.A. 21-in shadow mask tube independently of
the N.T.S.C.-type coding and decoding system. Pictures were then shown after
passing the signals through the coding and decoding circuits in the following
1. Composite video signal over a single
cable link (to estimate the effectiveness of the Band-sharing system).
2. Chrominance and luminance over separate
cable links (to estimate whether the transmission of luminance in a separate
channel might improve picture quality).
3. Sound and composite vision signals
transmitted by radio on the Band I, Channel 1 frequencies. (To observe whether
any deterioration of picture quality or mutual interference between sound and
vision were noticeable.)
The effects of varying the bandwidth of
the 'I' or in- phase component of the chrominance signal, of impulsive and
random noise interference and of varying errors in subcarrier phase, were also
In all cases where a 'Y' or luminance
signal was available the picture was also presented on a black-and-white
receiver having the same picture size.
By the autumn of 1956, Studio A at
Alexandra Palace had been equipped with a second experimental colour camera and,
a little later, a 35-mm Cintel film scanner was installed to supplement the
slide and 16-mm film scanner. With this equipment and with the enthusiastic help
of a small group of programme staff, an ambitious and comprehensive series of
programmes was broadcast, this time from the Crystal Palace transmitter, in the
winter of 1956-7 and was observed in people's homes on specially developed
experimental colour receivers and also, of course, on a large number of
black-and-white domestic sets. The details of this series of tests and the
results obtained therefrom have been fully described in Monograph No. 18. On 30
and 31 January 1957, a special programme was broadcast and shown to a large
audience of Members of both Houses of Parliament on six receivers installed in a
room in the House of Lords.
During the winter of 1957-8 a further
series of experimental programmes was broadcast from the studio at Alexandra
Palace and was seen by a rather bigger audience on colour receivers than in the
previous year. At the conclusion of these tests in 1958 the studio at Alexandra
Palace was dismantled and the cameras installed temporarily in a van which
carried out two outside broadcasts. The slide and film-scanning equipment was
moved to the Lime Grove Studios whence a regular series of transmissions outside
normal programme time has been given, beginning in the autumn of 1958 and
continuing with only short breaks to the present time.
The BBC demonstrated colour television to
the public for the first time at the National Radio Show at Earls Court in 1961.
Live transmissions from a glass-sided studio as well as film transmissions were
demonstrated on six 21-in. monitors. Each colour monitor had a 21-in.
black-and-white monitor alongside it to demonstrate compatibility. Only a small
minority of the public or of dealers had seen any colour television previously,
and both groups were favourably impressed.
6.3 Television Broadcasting on UHF
In 1956 the Television Advisory Committee
recommended that transmissions should be carried out in the ultra-high frequency
bands (Nos. IV and V) to assess the potentialities of these bands for television
broadcasting, and experimental transmitters for both bands were in- stalled at
the Crystal Palace television station. The Band IV tests were carried out with a
low-power transmitter radiating square-wave-modulated signals at 495 Mc/s, but
the Band V installation included transmitters for both vision and sound, with a
vision transmitter power of about 10 kW and an e.r.p. of 125 kW from a helical
aerial at a height of 690 ft. The transmitters could be modified to work either
on a 405-line system (with a.m. sound) or a C.C.I.R. 625-line system (with f.m.
sound), the vision carrier frequency being 654-25 Mc/s in both cases. In
addition to the BBC a number of other organizations participated in these field
trials, which were the most comprehensive series of UHF television propagation
tests yet conducted in any country. The trials are fully described in another
BBC publication, and the mobile field-strength measuring laboratory developed by
the BBC is described in an earlier BBC Engineering Monograph."
The main conclusions of the trials which
applied equally to a 405-line or a 625-line service were that over a terrain
such as south-east England, the first-class service area of a Band V transmitter
with an e.r.p. of 1,000 kW would be comparable in size to, but more irregular in
shape than, that given by the present Band I transmitter with an e.r.p. of 170
kW at 45 Mc/s.
The second-class service area obtained
would also be of approximately the same actual size as that given by the Band I
station but, on the higher frequencies, the topography would materially modify
the shape of the area with respect to the present Band I coverage, with
consequent changes in the numbers of viewers served.
Owing to the greater dependence of the
Band V signal on topography, the contours of both the first- and second- class
service areas would be more irregular in the case of Band V, and this would
increase the number of transmitters needed to give national coverage.
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