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An artical from Wireless World for July 1953 on the arrangements
made for the outside broadcast of the Coronation.
- By T. H. BRIDGEWATER
APART from the sheer size of the operation the deployment of twenty-one cameras, five mobile control rooms, three subsidiary control points, and so on the television broadcast of the Coronation ceremonies presented a number of problems not usually met on the simpler type of outside broadcast. It was also made the occasion to introduce several new technical refinements.
In the ordinary course of events, outside broadcasts originating in the London area are routed into the distribution network via the central control room at Alexandra Palace. On this occasion, with five main sources to be handled simultaneously, it was necessary to install a temporary outside broadcast central control room in Broadcasting House. The last-mentioned was chosen as being the most convenient point into which to bring the Post Office lines carrying vision and sound signals from the five mobile control rooms disposed along the processional route (including, of course, the one at the Abbey). This central point was able to preview the pictures from all these sources and to switch them at will into a single outgoing channel to Alexandra Palace, whence they were distributed to the whole television network in this country and on the Continent.
All this imposed a heavy strain on the resources of the Post Office Engineering Department who ably exloited all the available systems and techniquesvideo on " balanced pair," telephone pair and coaxial, and so onin order to meet this exceptional demand. This they did to such effect that not only were there five circuits in simultaneous use but also adequate reserves for immediate use in the event of breakdown. The Post Office also provided three other vision circuits to carry the outputs from isolated camerason Buckingham Palace roof, on the roof of Abbey House, Tothill Street, and in the Annexe of Westminster Abbeyto their nearest mobile control rooms.
Camera with zoom lens installed over the
West Door in Westminster Abbey. Because
of the low roof the viewfinder had to be
taken off the camera and placed on the floor.
The positioning of cameras had to be carefully worked out several months beforehand in conjunction with the Ministry of Works and the Abbey architects, and in relation to the claims of sound broadcasting, newsreels, press and other interests at the several main sites, particularly at the Victoria Memorial, the Colonial Office and Westminster Abbey. The Abbey presented exceptional problems, the selection of view-points having to be reconciled with the needs of many other parties and with the over-riding requirement that the equipment be not only unobtrusive but, in nearly all cases, out of sight. This led to compromises and to some remarkably cramped and unhandy positions that imposed the severest discomfort and strain on the operators at a time when they would have wished for ease and freedom. For example, in three of the positions the height of the operating box was only about three feet, so that, as will be seen from the picture, the cameraman had not even the space to sit upright, let alone stand.
The event saw the introduction of many more zoom lenses and a total of five were in service. Two of these were of the new Watson type with interchange-ble back elements, giving a choice of two 5:1 magnification rangeswith angles of view of 3 deg to 15 deg and 6 deg to 30 degwhile another, also a new design, came from Taylor, Taylor and Hobson with a range between 5 deg and 25 deg. The B.B.C. has encouraged the development of zoom lenses over a number of years and camera technique is now reaping the benefit of research and design in this important field. Viewers of the Coronation outside broadcast may have noticed the smooth manner in which interesting features in the subject were brought closer, or when the television camera appeared to "catch up" again on some part of the procession that had already receded into the distance.
Another special lens, relatively new to television, was the Dallmeyer 40in "double-folded" telephoto. This was in use at the Victoria Memorial position on a camera facing Buckingham Palace, and since its horizontal angle (in conjunction with an image orthicon pick-up tube) is as little as 1¾ deg a very close view of members of the Royal Family during their appearances on the balcony could be obtained. An angle of this order calls for extreme care in use as any slight shake or vibration even the effect of a puff of wind will result in a greatly exaggerated movement of the image on the screen.
Every effort was made to transmit the clearest possible pictures and a noticeable enhancement of definition came from the use of the new "derivative equalizers," developed by the B.B.C.'s Research Department* and produced in sufficient quantity to equip nearly all the cameras in use on June 2. These equalizers work on the principle of adding to the picture signal derivatives of itself obtained by differentiating circuits, and provide a simple means of adjusting and compensating optical and electrical losses.
Temporary television control room installed
at Broadcasting House, where the pictures
from five mobile control rooms were
previewed and selected.
It was thought desirable to avoid the momentary frame-slips which usually occur when switching between vision sources or cameras whose waveforms are not triggered from the same pulse generators; the number of such interruptions in the course of a long broadcast would have been sufficient to be considerably distracting. Accordingly the B.B.C.'s Designs Department evolved a system of remotely locking each of the eight pulse generators in use by means of a master frequency sent by lines from the Broadcasting House central control point. A phasing control in series with the signal fed to each line permitted precise frame phasing to an accuracy of a very small fraction of one line; hence it was quite feasible to " cut" from one picture source to another without any loss of synchronism.
The relaying of the Coronation broadcast to France, Holland and Western Germany was looked upon by the B.B.C. as a project of the greatest importance and the most careful preparations and tests were made during the preceding six months. It was arranged that the pictures would be the same as those providedfor our home audience, but commentaries in the different languages would be superimposed on the effects and ceremony. French commentators were installed alongside the British at several of the main camera positions and spoke through independent microphones and circuits to a separate control point in a studio at Broadcasting House, thence to Paris.
The vision signals reached their various Continental destinations almost entirely by centimetre-wave links, five of which were installed and operated between London and Cassel (France) by Standard Telephones and Cables, on behalf of the B.B.C. and Radiodiffusion-Television Franchise. A particularly importantindeed essentialfeature was the use of diversity reception on the cross-Channel link, in order to overcome the fading which is such a well-known and troublesome phenomenon on over-sea paths with frequencies of 4,000 Mc/s or higher. From previous experiments, S.T.C. had established the value of using two receivers with their parabolic aerial dishes mounted some fifteen feet apart in the vertical plane. It has been found that when the signal at one receiver is subject to fading, that of the other is steady; thus, with both signals available, a fading-free signal can always be obtained. This method amply justified itself both during the tests preceding the Coronation transmission and on Coronation day itself. There is no doubt that this method will find applications in the future, not only for any further links with the Continent but also for certain O.Bs within the British Isles.
Temporary control room for sound broadcasting in Trafalgar Square.
Each control position manned by an operator was associated with one
commentator, and had a mixer for introducing sound effects.
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