Abstract
THE paper on the London Television Service read to the Institution of Electrical Engineers on April 21 by T. C. Macnamara and D. C. Birkinshaw describes the television station recently built by the British Broadcasting Corporation in a part of the Alexandra Palace, London, N. The reports of the reception of the transmissions have in general been encouraging. The range of the station, originally estimated to be about 25 miles, has proved to be considerably farther in most cases ; good reception can be obtained up to about 35 miles. Reports of visual receptions have been received from Brighton, South -end, Cambridge and Bedford, the distances of which from the station are 40-60 miles. In these cases reception took place under exceptionally favourable conditions. It has been found that in the ultra-short waves used for television, the interference due to electro-medical apparatus used for high-frequency diathermy is sometimes serious. For example, a North London hospital situated about half a mile from the Alexandra Palace has a spark diathermy machine which when used completely ‘jams’ the reception of the five-metre radio link transmitter at the Palace. The whole of the walls and ceiling of the room were covered with aluminium foil 5 mm. in thickness, applied with a paper backing after the fashion of ordinary wall paper. At one end of the room, which was open, a partition covered with frac12; in. mesh chicken wire was erected and good electrical connexion made between the aluminium foil on the ceiling and walls and the chicken-wire. A similar screen was placed over the window and another was laid on the floor underneath the usual rubber floor material. The treatment effected complete suppression of the interference. If the screened door in the partition was opened by only a few inches, the interference was almost as bad as with the unscreened room. This proves the necessity of taking thorough measures.
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The London Television Service. Nature 141, 781 (1938). https://doi.org/10.1038/141781c0
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DOI: https://doi.org/10.1038/141781c0