The beginning of a new service 

4 September 2017 tbs.pm/13582

From the BBC Year-book for 1 November 1929 to 31 October 1930

Receiving technique automatically follows transmission conditions. For example, a broadcast transmitter of low power provides an overwhelmingly strong signal at places in the immediate vicinity of its aerial, and therefore some listeners find that the crudest and most inefficient types of receiving equipment will give satisfactory results. Naturally such listeners do not wish any change to be made which would necessitate their using apparatus of even normal efficiency; neither, perhaps, is it any direct concern of theirs that reception conditions in other districts further from the transmitter may be inferior. In consequence, there must be a small minority who are adversely affected by a change in transmission conditions. An alteration in the system of distribution involves considerable expenditure, and naturally changes are not made unless a definite improvement will result therefrom.

Long before structural work was commenced on the new London Station at Brookmans Park, the extent of the dislocation, resulting from the necessary closing down of the old transmitter in Oxford Street, was considered in relation to the benefits which the new Station would provide. As far as the London area was concerned, it was anticipated that the two difficulties which a comparatively small minority of listeners would experience would be due to the use of either insufficiently sensitive, or selective, receivers.

It was known that the new transmitter, being 15 miles North of Oxford Street, would be definitely weaker in the area around Oxford Street than the old transmitter situated actually in Oxford Street, even though the new transmitter were many times more powerful than the old. Listeners in practically all other districts would be supplied with vastly greater strength, depending upon their distance from the sites of the old and the new transmitters. The second type of dislocation was due to the fact that the new station was built to radiate two contrasted programmes (the old transmitter could radiate only one) and at first listeners having sets with a poor degree of selectivity were expected to have some difficulty in separating the two programmes.

Ernst Jahnke crystal radio receiver, ca. 1924-1926. The radio is tuned to different stations by moving the slider (right) up or down the tuning coil. The device at top is the cat’s whisker detector. Image source: Hihiman via Wikimedia Commons CC-BY-SA

Considering first the sensitivity dislocation factor, it was not thought that valve receivers used by listeners in districts near Oxford Street would experience any serious trouble as the strength provided by the new transmitter, although weaker than that provided by the nearby old transmitter, would be adequate. The B.B.C., therefore, concentrated mainly on an endeavour to help crystal set users whose apparatus was too inefficient to work satisfactorily with an adequate, though not overwhelming, strength of signal. Consequently a pamphlet was prepared explaining in detail the various ways in which a crystal set could be made to give satisfactory results under the new conditions. This pamphlet was entitled “Crystal Sets and the Brookmans Park Transmitter” and publicity was given to the fact that the B.B.C. would supply it free of charge to any listener who cared to apply for it.

Despite the fact that the B.B.C. had given frequently repeated warnings of the forthcoming change in reception conditions, it was feared that a number of listeners would not take any active steps until it actually took place. When the new Station was ready, therefore, a process of “sliding in” was adopted. At first the new Station radiated on normal power, but only outside usual programme hours, namely, for half an hour each morning between 11.30 a.m. and 12 noon and from 12 midnight until 1 a.m. This phase was intended for those who wished to make in advance any changes which their receiving apparatus might require. The transmission of half an hour in the morning, was to give an opportunity for the wireless trade to carry out tests on listeners’ apparatus. The first phase of the introduction was maintained for a fortnight before the second phase was commenced. The second phase was to transmit certain portions of the regular programme from the new transmitter instead of from the old transmitter. Three weeks after the second phase had been introduced the old transmitter in Oxford Street was shut down entirely and the service was taken over by the new transmitter at Brookmans Park. This was on October 21st, 1929.

During the period of introduction the incoming letters from listeners were examined carefully. Many of these, of course, were from listeners who obtained far better reception from the new Station than they had ever obtained from the old transmitter, and who were anxious for the new transmitter to be introduced fully with a minimum of delay. In Fig. 1 a graph is shown giving the number of letters received in each complete week ending on the dates shown on the horizontal axis. Despite the elaborate advance publicity, and the “slide-in” method, it will be seen that the bulk of the correspondence was not received until the actual time of the transference of the full service to the new Station. Subsequently the correspondence, that is complaints and appreciations, gradually died away as listeners accustomed themselves to the new conditions; and by the beginning of December, 1929, any difficulties which existed concerning sensitivity had in the majority of cases been overcome. It was possible then to start introducing the second transmitter.

A pamphlet similar to that for the assistance of those who were experiencing trouble due to the change in signal strength, was also prepared to help those who might find themselves in difficulty in separating the two programmes, this second pamphlet being entitled “The Reception of Alternative Programmes.”

The same method of gradually introducing the second programme was again followed. Fig. 2 is a graph showing the number of letters which were received in each complete week during the period of the introduction of the second programme; again some being appreciations, and others requesting advice concerning individual difficulties. The second transmitter first radiated a scheduled preliminary transmission on December 9th, 1929, at a time when the first transmitter was not working. This was to enable listeners to tune in the second transmitter without complication due to a programme from the first transmitter. It was thought that if both transmitters were working some listeners might have more difficulty in finding and identifying the second programme. Subsequently preliminary transmissions of both programmes were carried out between the hours of 12 noon and 1 p.m. and during the late dance music. On December 22nd, additional preliminary transmissions were introduced before the regular Sunday afternoon programmes; the object being, of course, to enable those who were not at home during the week to ascertain whether or not their receivers could separate the two transmissions satisfactorily.

The letters resulting from these transmissions were far fewer than was anticipated, indicating either that

  1. The degree of selectivity of listeners’ apparatus was far better than was expected, or
  2. That those listeners whose apparatus needed an improvement in selectivity were taking no interest in the tests which were being carried out for their benefit.

Consequently the B.B.C. decided to radiate dual programmes on two evenings in each week. At the same time a questionnaire was published in each issue of the Radio Times for the use of listeners requiring technical information. This had the desired result and correspondence started to pour in, as can be seen from Fig. 2. The full evening bi-weekly preliminary transmissions were maintained for seven weeks, and by February 17th, incoming correspondence was found to be falling away rapidly. It was then possible to introduce the full daily service of contrasted programmes and this step was taken on March 9th — three months after the first preliminary test of dual programme conditions. The increase in correspondence consequent upon the commencement of full alternative programmes was very small (see Fig. 2). This indicates that the majority of those whose apparatus needed an improvement in selectivity had, at some stage or other of the system of gradual introduction, taken the necessary steps, thus fulfilling the object at which the B.B.C. were aiming in adopting the “slide-in” system. Space does not permit a detailed description of the methods which were used to handle quickly and accurately the heavy and helpful incoming correspondence but, in general, there was not more than 2 or 3 days delay in sending the information which individual listeners required.

The opening of the London Dual Programme Station was carried out in a way which it is hoped was as convenient as possible for its listeners — at the same time it provided valuable experience to the B.B.C. which will be used to benefit listeners in the North and other Regional areas.

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