Ten Years of Technical Progress 

6 May 2022 tbs.pm/75167

 

BBC Yearbook 1933 cover

From the BBC Yearbook for 1933

ON THE introduction of regular broadcasting in Great Britain comparatively little was known as to the power required to cover a definite area at sufficient strength for regular reception by the public. Previous experience was mainly concerned with commercial and service stations, operated by skilled personnel. In general it may be said that a vastly greater power has been found to be necessary than was originally estimated.

THE SYSTEM OF DISTRIBUTION

The first scheme of distribution consisted of eight so-called main stations, those at London, Birmingham, Manchester, Newcastle, Glasgow, Aberdeen, Cardiff, and Bournemouth. The transmitter in each case supplied approximately 1 kW to the aerial, and the effective service range was between 20 and 30 miles [32 to 48km], varying with the nature of the country and the wavelength used. These eight stations, put into operation between November 1922 and October 1923, provided an adequate service for the thickly populated districts in which they were situated, but it was soon found that there were several districts almost equally dense in population, which were entirely outside the area in which good reception could be obtained on a regular day or night basis.

At that time most of the programmes were supplied locally from studios and points situated near to the transmitters. It was not considered practicable or economic to introduce a large number of additional main stations each originating its own programme, and tests were made to see whether it would be possible to extend the supply of programmes to additional stations by means of telephone line connections with existing centres. These tests were successful, and resulted in the establishment of eleven relay stations, working on low power (approximately .12 kW in the aerial), situated in Sheffield, Plymouth, Edinburgh, Liverpool, Leeds, Bradford, Hull, Nottingham, Dundee, Stoke-on-Trent and Swansea. Each of these cities was equipped with a studio so that the origination of programmes locally was possible. These stations were put into operation between November 1923 and December 1924.

However, during 1924 a demand arose for a service for the country districts and towns not served by main or relay stations. Experiments were therefore begun to see whether successful broadcasting could be carried out on a “long” wavelength, which by the use of high power could be made to serve a much greater area than was possible on the “medium” (300-500 metres) band of wavelengths then in use. Accordingly, an experimental station, working on 1600 metres, was established in July 1924 at the Chelmsford works of the Marconi Company, the power being approximately 15 kW in the aerial. There was soon no doubt of the success of this experiment, and the Chelmsford Station was replaced in July 1925 by a permanent long-wave high-power station, known as 5XX, at Borough Hill, near Daventry. This station employed the same wavelength, with a power in the aerial of 25 kW. In the meanwhile it had been decided to serve Northern Ireland by a ninth main station, working on a medium wave and a power of 1 kW; this was situated in Belfast, and was opened in September 1924.

In April 1925, the London Station was moved from Marconi House to the roof of Selfridge’s store in Oxford Street, and the power increased to 2 kW. Thus at the end of 1925 the service was given by eight main stations of 1 kW, and one of 2 kW, eleven relay stations of approximately .12 kW, and a long-wave high-power station of 25 kW.

 

Map of the UK with transmitters marked

The old scheme of distribution is shown in dotted outline. The new scheme (except the new Daventry, 5XX) is shown in full outline. It is anticipated that the new Daventry will provide a service to the whole of the British Isles under normal conditions. The circles on the above map are only comparative representations of the service areas of the various transmitters, since in practice these areas never turn out to be true circles, as the strength of the transmission varies according to the type of country over which it has to travel.

 

As far back as 1924 it became evident that the number of wavelengths available for broadcasting throughout Europe would be insufficient for the needs of all countries, and in consequence during that year the idea arose that it might be possible to work several stations on a single wavelength. Experiments to that end were made in 1925, and during 1926 four of the relay stations were adapted to this method of working, but the accuracy maintained by each station was only of the order of 100-200 parts in a million, which resulted in the area served by each station being very considerably curtailed. During 1927 and 1928 further experiments were made with comparatively elaborate apparatus, capable of maintaining the frequency of each station accurate to within approximately 10-15 parts in a million, and with this more satisfactory standard of common-wave working having been reached, ten low-power stations were eventually put to work on the same wavelength.

In 1925, also, a scheme was evolved for a system of regional broadcasting by high-power stations situated in the more populous districts. The proposal was to erect high-power stations near London, in the Midlands, the industrial North, the West country, and in Scotland. Each station was to contain two transmitters, sending out two contrasting programmes at sensibly equal strength, so as to make the problem of selection between them as simple as possible from the technical point of view. Some difficulty was experienced in obtaining the Government’s agreement to this scheme, but at the beginning of 1926 permission was obtained to erect a high-power medium-wave station at Daventry, which, in conjunction with the long-wave station already in existence there, would give a service of alternative programmes on an experimental basis over a radius of approximately 80 miles [129km]. The radius served by the long-wave station was, of course, greater than this, but the limit of the area served by two programmes was determined by the strength of the new station, which became known as 5GB. After successful tests had been made, this station was opened for regular service in August 1927.

 

Transmitters on a crowded rooftop

THE ORIGINAL LONDON STATION, 2LO, AT MARCONI HOUSE

 

At about this time — namely, in June 1927 — the B.B.C. appointed a committee, under Dr. W. H. Eccles, F.R.S., to approve, reject, or modify, the scheme of twin regional transmitting stations. In detail the scheme provided for the erection of one station approximately 15 miles [24km] north of London, and a similar station in the Pennines between Manchester and Leeds to serve the industrial areas of the North of England. For Scotland a station was to be built between Edinburgh and Glasgow, and to serve the West of England and Wales a fourth station was to be situated on the Somerset coast. The alternative service to the Midlands was to be provided by the two existing Daventry stations.

The committee of experts reported favourably on the scheme, and eventually the Government’s permission was obtained to proceed. Construction of the London Station therefore began in July 1928, and the station was put into operation on a single programme basis for public reception in October 1929, and on a dual programme basis in March 1930. This was followed by the station for the North Region, which was fully introduced in July 1931, and that for Scotland in September 1932. It is anticipated at the time of writing that the station for Wales and the West of England will be complete in March 1933.

 

Two very tall masts

THE SECOND 2LO TRANSMITTER, ON THE ROOF OF SELFRIDGE’S STORE IN OXFORD STREET

 

It was never expected, however, that these five twin stations could cover the whole of the territory served by the B.B.C. with a reliable service, and the scheme allowed for low-power stations at Aberdeen, Newcastle, Bournemouth, and Plymouth. In addition, the Government’s permission has now been obtained to increase the power of the long-wave station to approximately 100 kW, in order that the service to the districts falling outside the range of the Regional Stations may be improved. Plans are also in hand for increasing the power of the Belfast Station. Future improvements in the scheme of distribution will depend on developments in the international wavelength situation.

THE WAVELENGTH PROBLEM

It has already been mentioned that in 1924 it became evident that the steady increase of the number of broadcasting stations on the continent of Europe was likely to constitute a grave problem, in the near future, from the point of view of mutual interference.

It was observed that if two stations, each employing a power of the order of only 1 kW, were working on wavelength channels so separated that an audible beat was set up between the carrier waves of the two stations, severe interference resulted, even though the distant station might be a thousand miles away. At that time there was no officially standardised band of wavelengths for broadcasting, the existing International Convention having been drawn up prior to the introduction of broadcasting. In general, the Post Office authorities of the various countries had assigned waves between 200 and 550 metres, with a few stations working between 1000 and 2000 metres, of which the Daventry Station was one; but there was no organisation to regulate these wavelength channels on an international basis. Consequently, the B.B.C. invited the other European broadcasters to a conference in London in March 1925, and the outcome of this was the formation of the International Broadcasting Union. Several further conferences led to an International Plan for the allocation of wavelengths to be used by individual organisations, prepared at Geneva in November 1926, and adopted by at least a majority of organisations responsible for broadcasting in Europe.

 

A man sings into a microphone

GEORGE ROBEY IN THE STUDIO AT MARCONI HOUSE

 

This plan met with a considerable measure of success, but it was not adhered to strictly by all countries. At the same time, as progress continued, stations sprung up which were not catered for. In 1927 the International Radiotelegraph Convention of Washington allotted the wavebands of 200-545 metres and 1340-1875 metres for the use of broadcasting stations. Parts of these bands, however, were shared with other services.

In January 1929, a new plan of allocations was prepared by the Union at Brussels, which had as its object the bringing up to date of the original Geneva Plan. This plan also attained some measure of success, but it was not universally adhered to. Consequently, in June 1929, a conference of European Governmental representatives was convened at Prague, and the resulting Prague Plan was eventually agreed to by the majority of Governments. This plan at least prevented chaos developing in the ether owing to the increasing number and power of the stations. The outstanding difficulty at the present time is caused by the fact that there are too few long-wave channels to satisfy the needs of Europe generally. For this and other reasons, it is anticipated that there will be a further conference on the same basis as that held at Prague, in the spring of 1933, following on the meeting of the International Radiotelegraph Convention in the autumn of 1932 at Madrid.

STUDIO TECHNIQUE

In parallel with development on the transmission side it has been necessary to develop the design of studios and the apparatus associated with them—namely, microphones, amplifiers, and control systems. When the London Station started regular broadcasting, there was one 20 ft. x 20 ft. [6x6m] studio situated in Marconi House. The next step was a move to Savoy Hill, which permitted the gradual construction of some nine studios, the biggest of which measured 45 ft. X 26 ft [14x8m]. The latest step has been the construction of Broadcasting House, which was complete and in full operation in June 1932. This building contains twenty-two studios, the largest of which, the Concert Hall, measures 106 ft. X 42 ft [32x13m].

In the early days the practice was to prevent entirely the reflection of sound from the walls of the studio, in order to avoid what was then considered unpleasant reverberation. The presence of this reverberation is now, however, considered essential for good reproduction, and the unpleasantness of the early days was mainly due to deficiencies in microphones and associated apparatus, and in the receiving apparatus used by listeners. Thus, gradually, the amount of sound-absorbing material in studios has been reduced and its acoustic suitability improved, until a stage has been reached to-day which allows of the scientific design of a studio to give equal reverberation time at all the important audio-frequencies, predetermined and arranged to suit the dimensions of the studio and the purpose for which it will be used.

 

A studio

THE LARGEST STUDIO AT SAVOY HILL (“NO. 1”)

 

Similar development has also taken place in connection with the whole of the rest of the plant used for broadcasting, which includes speech-input equipment and telephone-line connections (the latter rented from the Post Office), as well as the transmitters themselves.

From the earliest days the B.B.C. has continually laid the greatest stress on high quality of reproduction, and has, in fact, been a pioneer amongst other broadcasting authorities in this respect. This has entailed the careful control of depth of modulation, to the extent of reducing the strength of reception of stations of given power, as compared with similar stations which modulate more deeply at the expense of quality.

In the provinces, studios and plant have been developed on the same principle. At the present time up to date studios and equipment exist in Manchester and Edinburgh, while studios on modern lines, with entirely new equipment, are in course of construction at Birmingham, Cardiff, Belfast, Glasgow, Leeds, and Bristol. The guiding principle in the design of the whole of the B.B.C. technical plant has been to produce quality which shall make possible the appreciation of the higher forms of music and dramatic art.

TELEVISION

Since 1926 the B.B.C. has taken all practicable steps to make use of modern development in television, and after a long period of entirely experimental transmissions a series of television transmissions on the Baird system has been instituted from the new headquarters at Broadcasting House. This may be described as one step beyond the purely experimental stage. At the same time, every opportunity of improving technique is being taken. Future progress must depend on this.

SHORT-WAVE TRANSMISSIONS

The possibility of supplying broadcast programmes direct to overseas Dominions and Colonies was under consideration as early as 1926, and in November 1927 experimental transmissions were instituted from the Chelmsford Works of the Marconi Company, in order to determine whether the somewhat indifferent quality of reception available from such transmissions was acceptable to listeners overseas. These transmissions met with some success, and resulted in the decision in November 1931 to build a short-wave station for the transmission of regular programmes to the Dominions and Colonies. Future development will, of course, depend on the success of this station, although the service need no longer be regarded as experimental.

 

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