Abstract :
The paper describes a method of measuring the angle of incidence of downcoming short waves in which the phase difference between the e.m.f.´s in two similar horizontal aerials at the same height above the ground is determined from the trace on the fluorescent screen of a cathode-ray oscillograph, to the deflecting plates of which are applied the two aerial e.m.f.´s after similar amplification by receivers of the type developed at the Radio Research Station for cathode-ray direction-finding. As the main object in view is the measurement of the downcoming angles of 20-metre waves from Lawrenceville, New York, working on the radio-telephone circuit to London, the aerial system used is designed for most efficient operation on this wavelength: but it is found quite practicable to use it on wavelengths up to 64 metres and also for signals from directions not widely divergent from that of the straight line at right angles to the aerials. The results obtained show that, over the period January?April, 1933, one main ray accompanied by other and smaller-amplitude rays is, in general, received at Slough from the 20-metre Lawrenceville stations during their normal working period. The average angle of incidence of this main ray is 72? (measured to the normal to the ground). Throughout the first four months of the year, the angle of incidence remained fairly constant over the working period, but, from about the beginning of April, 1933, the angle of incidence of the one main ray which was still present began to grow throughout the day. At the commencement of transmission, at noon G.M.T., the angle of incidence is of the same order as that obtaining throughout the day in the ?winter? months. The angle increases gradually until values of 80? to 85? are obtained towards sunset. A drop in average field strength of the transmissions has also been noted since April. The deduction that one main ray accompanied by smaller-amplitude rays is generally present in the downcoming radiation - from Lawrenceville has been confirmed by the preliminary results of some short-duration 20-metre pulse transmissions from that station.
