Measurement of the electromagnetic field of waves received during trans-oceanic radio transmission

A series of recent experiments is described on the determination of the electric and magnetic field intensities of the waves received at Leghorn, Italy, from the Annapolis, Maryland transmitting station. A pair of large loops, respectively practically parallel and perpendicular to the incoming wave are used. The incoming signals are received by hetero-dyne oscillator and amplified. The substitution method is used for the measurements, whereby the incoming signal is compared to an artificial signal produced in the non-receptive loop by a local oscillator. A thermo-couple and galvanometer in the oscillator circuit, together with a calibrated mutual inductance for coupling to the non-receptive antenna, permit quantitative results. The necessary precautions and procedure are described. Numerical results are given, and it is shown that the field strengths of the incoming waves are much greater than those calculated by the usual transmission formulas.