Abstract :
The paper constitutes a theoretical and experimental investigation of the principal forms of the spaced-aerial or Adcock direction-finder. The analysis is concerned mainly with the determination of two important properties of the systems, namely their performance under the influence of downcoming waves and their efficiency as receivers of wireless energy. These characteristics are reduced to quantitative form by introducing the two factors named respectively ?standard-wave error? and ?pick-up factor,? and the various aerial-system modifications are studied with the object of showing how these factors may be predicted for any given system and how they vary with the dimensions, wavelength, and other characteristics, and also with the constants of the ground on which the aerials are erected. The four principal aerial systems dealt with are the ?U? type, the elevated type, the coupled type, and the balanced type. The ?standard -wave error? of the type of direction-finders which is based on the principle of the closed loop or coil is first derived theoretically; it is found to be approximately 35? for a large range of wavelengths, and to be independent of ground conductivity and dimensions of the loop within, wide limits. Experimental confirmation of this is obtained on short waves (20 to 50 m). The theory of the ?U? type is then considered and the method of calculating the standard-wave error for any given case is worked out. The agreement between values obtained in this way and the experimental results is satisfactory. The effect of screening the horizontal members of the system is discussed, but no quantitative formula for calculating the effect of the screen is found to be obtainable. A description is next given of a series of experiments with the ?U? type on short waves, the system being tested by means of locally-generated downcoming waves of variable polarization. This method was employed to measure the effect of screening and burying the horizontal limb of the ?U- ? aerial, as well as to determine the standard-wave error of the unscreened system. Turning to the elevated type, after a brief theoretical discussion, experiments with the rotating form of this system are described; these include determinations of the standard-wave error by means of an elevated transmitter of variable polarization, an investigation of the effect of shortening the lower limbs of the dipoles, and an investigation of the effect of increasing the height of the apparatus above the ground. A working formula is obtained for calculating the standard-wave error for a system of this type. The next modification dealt with is the coupled type, the various forms of which are described and illustrated. A description is given of a medium-wave direction-finder which was constructed to work on this principle. This was tested by means of downcoming waves from a kite transmitter and also by a local injection method. A formula for calculating the performance of the coupled type of aerial is derived from theory based on these experiments. The balanced type, which is next considered, is described in detail and the results of the tests made with the kite transmitter are given. A combination of the coupled and balanced systems, named the balanced-coupled type, is then described. This system was found to have a standard-wave error too low to be measured. Practical tables are given for each system, showing the standard-wave errors for various wavelengths, aerial-system dimensions, and soil conductivities. These tables show that the systems vary very greatly in performance with the conditions and with the details of their design. The pick-up factors of the various systems are dealt with in a separate section. The case of the loop or coil aerial is first dealt with and is used as a standard of reference for the other systems. Each of the spaced-aerial systems is then examined in turn with regard to its properties in this respect. The paper concludes with a comparative table
