Naval radio direction-finding

An account is given of the progress in naval radio direction-finding both on land and in H.M. Ships during the last ten years. On land, the Admiralty has been specially concerned in highfrequency (3?30 Mc/s) direction-finding. Some parts of the very-high-frequency range (30?300 Mc/s) are also of interest, notably in the band used for communication with fighter aircraft, 100 to 156 Mc/s. In the field of h.f. direction-finding, the factors limiting the accuracy at present obtainable with the standard Adcock-type apparatus are critically reviewed. Brief descriptions are given of several new systems in h.f. direction-finding on land, in which it is suggested further research would be profitable. The paper describes further developments in ship-board m.f. direction-finding, and the research and development work carried out in the h.f., v.h.f., u.h.f. (300?3000 Mc/s) and s.h.f. (3000?30000 Mc/s) bands. It is shown that accurate direction-finding on high frequencies in ships offers considerably greater difficulties as compared with those encountered on m.f. This is due to the greater disturbances caused by the secondary fields radiated by various parts of the ship´s structure and rigging. It is also shown how the essential conditions have been derived for siting the direction-finder aerial in a position where the effects of secondary radiation will not excessively degrade the performance. The paper considers the principles of design employed in the ship-board h.f. direction-finder and explains how the various requirements of accuracy, sensitivity, coverage of the whole h.f. band with a minimum of design and operating complexity, reliability, sensefinding and quickness in operation, involve a compromise in which the highest performance in any one particular is unattainable. The essential performance data are given for the apparatus widely fitted during the recent war. The various aspects of research and development in v.h.f. directionfinders for ships are considered and it- is shown that the ship conditions are less adverse in the v.h.f. case than they are in h.f. direction-finding. In keeping the paper to a reasonable length, only a brief introduction is given to the work done in the wide field of u.h.f. and s.h.f. directionfinding. Many of the techniques in these frequency bands merge with those of radar, with the important difference that direction-finding must always attempt to cover the widest possible frequency range with the simplest possible apparatus. The applications of radio direction-finding to naval purposes are briefly stated.