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Abstract

The Blaw-Knox mast radiator was erected at Droitwich for radiating the 261 metre European Service by vertical polarisation, in place of the horizontally polarised system which had been in use since 1940.

This report gives the results of field-strength measurements taken on the existing Βι¶ΉΤΌΕΔ and Forces transmissions and shows that considerable additional distortion of the 391 m. and 296 m. polar diagrams may be caused by the Blaw-Knox mast with certain base impedance conditions. The final condition of connection of the Blaw-Knox mast, which was arrived at after experiments had been carried out to cure cross-modulation effects between the 261 m. transmission and the Βι¶ΉΤΌΕΔ and Forces transmission, gives polar diagrams for the Βι¶ΉΤΌΕΔ and Forces transmitters not greatly different from those existing before the erection of the mast.

The 261 m. polar diagram of radiation from the Blaw-Knox mast itself is adversely affected by the other masts and aerials on the site. Experiments are described, which attempted to effect an improvement in some directions but were unsuccessful. It is concluded that only satisfactory method of improving the radiation in a south-easterly and southerly direction would be either to re-site the Blaw-Knox mast or to use another aerial for this service.

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