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ENGINEERING PAGE
BBC WILL ADHERE TO PROVEN
STANDARDS FOR TELEVISION
་
BY J. T. DICKINSON
A statement made on August 24 this year by the United Kingdom Postmaster-General, Mr. Wil- fred Paling, marked the beginning of a new opoch in British television,
In effect, the statement gave Governmental recogni- tion to the Television Advisory Committees recommendation that there was no technical justification for changing the fundamental transmission standards used since 1936 by the Television Service of the British Broadcasting Corporation.
This decision was important; because television receivers are made to suit particular trans- will not mission systems and reproduce pictures transtnitted) by different systems.
The British standards are bar- Interlaced 405-line ed upon a
subsequent picture, and some television transmissions in other countries have employed stand- ards bused upon larger numbers of times. It has been suggested. therefore, that, by retaining the 405-line pieture, British leleva- slon is unnecessarily handicapped and cannot produce a picture of such good quality ងទ Rystems using more lines.
This inference is fallacious, but is fairly widely believed, because the number of horitzontal lines i a television picture is very com- monly referred to as the "de- finition" of the picture, whereas It is in fact only one factor con- tributing the definition.
Technical Basis
it will be understood, then, that the highest modulation frequency that can be effective. ly transmitted by a given aya-u tem is a much more rollable guide to the quality of that ayatom, and, in fact, this will determina
da. the maximum airable number of horizontal Hines, and any increase in the number of Ilnes above the number determined In this
Instead monaer may
of im proving the plature, result in fosa entisfactory reproduction. When, some 13 years ago, the standards to be adopted for the then projected British high-de- Anition television service wero being considered, it had to be decided what
the highest modulation frequency that could be effectively transmitted on the carrier-wave frequencies likely to be suitable and available for television. If an unnecessarily been band-width had narrow standardised, the quality of the pleture would be restricted and the full possibilities of the system! could not have been used.
But if too wide a band-width
was
Two the new 'C.P.S. Emitron' television cameras boing set up by technicians of the BBC in preparation for televis ing the events at the Empire Pool at the Olympic Games.
of balance
tions, and this lack always results in u less antisfying picture.
out
A
going ahend vary satisfactorily. it la altuated at Button Cold. feld, Warwickshire, and wher completed it will sarva a popu-
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This wide service will be ob tatned by using a vision trans- mitter rated 95 kilowatte peak power-twice that of the Alexandra Palace transmitter and the London that serves Burrounding counties and aerial mounted on a mast 230 metres high.
ar
being
anci
Practical confirmation of this occurred as a result of the re- cent Olympic Games, held in Britain,
Lord Trefgarns, Chairman of tho Television pointed Commitee, Advisory
which statement 1 amplified some parts of the Postmaster-General's statement. The B.B.C. Television Servica
cover of complete gave very
to The transliters aro the
vialtore Games, and
by Electric from London
all over the manufactured world had the opportunity of and Musical Industries, Limited, studying television contending and by Marconi's Wireless Tele- The with wide variety of oondi graph Company, Limited.
very tions, as there as sometimes single vorfal array is of If you consider the manner in were fixed, then it would be cs
and a novel design and distributes both usd sential to
very bright sunshine correspondingly picture is which television
A
the vision and the sound signals other times heavy rain. scanned, you will realise that the higher carler-wave frequencies,
Hoth indoor and outdoor events almost uniformly i all horzontal lines de-, which would make transmitting number of horizontul
more were televised, at midday and in directions. At first the Sutton nincs only what may be called and receiving equipement the vertical definition, and then only when the size of the scan- ning "spot" obeys certain condi- Lions, For any particular num- ber of horizontal lines there are certain limits to the appropriate Jefinition along the lines, because the possibility of being able to resolvu very much aner detail In one direction only does not pro- duce a clearer picture.
The horizontal deftrition mea- sured the ability of tite system to follow rapid changes of light and shudu encountered by the sebrning Leom us it travels along a ne Very ane detail will produce com ponents of corresponding higher frequency in the vision algnal, that is, the electric wave gen- erated by the television camera and, to reproduce these, the sys- ten must be capable of effective- ly transmitting, from the camera to the enthode-ray tube of the receiver, a wider bund of fre- quencies.
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Looking very much like a scene from "The Shape Of Things To Come," this is a mobilo television control room used for the first time in televising events at the Empire Pool during the Olympic Games.
will broadcast expensive, reduce the effective | the evening Visitors from coun- Coldfield station range for given transmitter trics where there is yet no televi- the same programmes as Alex- were evidently impressed, andra Palance, and for this pur- power and greatly Increase the slon risk of "ghost images caused by but the most interesting point pose it has been necessary to pro- familiar with vide eireults over the 200 kilo- the energy reaching the receiving was that visitors aerial by paths of different other television services seemed metres between the stations cap-
believe reluctant to lengths.
that such able of handling the wide vision clear picture were obtainable band-width referred to earlier. with a 405-line system.
New Receivers
Standards Agreed
It is generally agrood now that standards based upon a three- megacycles per
Recond bond
Same As Human Eye
The sale to the public of tele- vision recivers continues to keep pace with the increasing rate of manufacture. Indeed the manu-
width and a 405-line picture also Now, however, the sensitivity represent the best compromise of the most recent British tele- between pleture quality and re-vision cameras is equivalent to eclver cost. The actual choice of that of the humans cyus and they facturers report a flood of ordera for television receivers from the 105 as the number of horzontal are in addition practically at Midlands, following the recent
The result is that liner arises from certain practical chromatic. considerations, including the no- plays may now be televised frcin announcement by the BBC. of
the normal stage the frequencies to be used cessity of having an odd number theatres with of lines for an interlaced picture lighting and without inconveni- Sutton Coldfield, in spite of the
the programirace the fact that nudience in and a convenient ration between enco to the. the line and picture recurrence threatre, and in normal studio not to available in that area until frequencies. Similar computational work the camera lenses may, if the autumn of 1949.
for other published television desired; (be stopped-down", toi standarda in nearly every case give great depth of focus, show marked differences between!
The construction of the rat
the hörzontal and vertical defini- póst wár félevision natation u}
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AGENTS'
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The new addsivers incorporata many Improvemante deriving from: British wartime radar and communications advances. and
these help to produos brighter, atomrer pictures. the same time the receivers are moro' reliable, less bulky, easier to maintain and have fewer controla to adjust than provi- ously.
Unlike in the United States, practically all-television recolvers in Britain are in private homes and -it-is rare to find one in a restaurant, bar or club.
11
[fact le recognised In the presenta-
tion
of the programmes, which ure produced and timed in manner appropriate to amali audiencesót-bdividial families. It has also resulted in a relative- ly amal demand for projection. recolvers, although those are
viewed tubes are perfectly ad- equate for normal home audi.
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