Some Experiments in Short Distance Short-Wave Radio Transmission

Some experiments in short-wave radio transmission over a distance of 55 miles are described, the results of which are interpreted to indicate the presence of strong "sky" waves, with "ground" waves of negligible amplitude in comparison with the "sky" waves as received. Upon decreasing the transmitter wavelength, at a given time of day, a minimum wavelength was reached below which no communication could be obtained; this wavelength is termed the "cut-off" wavelength. The average value of the cut-off wavelength, for various times of day, is given for several different months. The minimum observed wavelength upon which communication was possible was 28 meters. A series of experiments in which an orientable half-wavelength antenna was employed served to indicate definitely an optimum position of the antenna for transmission over the 55-mile distance. The indicated transmission path left the transmitter at an angle of approximately 65 degrees to the horizontal. In long distance communication the position of the antenna was found to have no appreciable effect.