Radio direction-finding on wavelengths between 2 and 3 metres (100 to 150 Mc/s)

Abstract

This paper describes a preliminary investigation of radio direction-finding on wavelengths between 2 m. and 3 m. (100 to 150 Mc./s.) with the aid of instruments fitted with rotating aerial systems similar to those used in earlier work in the band 6 m. to 10 m. (30 to 50 Mc./s.). The sensitivities of the loop and Adcock direction-finders used are such that bearings with a swing of ±5° can be obtained with field strengths of 20 and 40 μV per metre respectively. The reciprocal error of the instruments has been reduced to 1°, and the polarization error can be kept below 5° for angles of incidence and polarization to the vertical of 60°, although readjustment of the compensation arrangement is required to maintain this over an appreciable wave-band. The two direction-finders have been operated at various distances up to 30 miles from an experimental transmitter developing 100 watts on a wavelength of 3 m., and the average errors varied from about 10° at 1 mile to 3.5° at 20 miles with a vertical transmitting aerial. These errors are somewhat larger than the corresponding values found for the longer-wave band of m. to 10 m. (30 to 50 Mc./s.). When an attempt was made to use a direction-finder inside a wooden hut, the observations were found to be subject to an octantal error 2° to 5° amplitude, the value increasing as the wavelength was reduced. This error was found to be due to reflection effects from the walls of the hut, and experiments made with various wooden boards showed that it depended upon the nature of the wood and direction of the grain. A synthetic material with no grain direction was found to have only a small effect.