Experiments with Directivity Steering for Fading Reduction

R A P I D fading in radio communication has been recognized for some time as being due to the interaction of distinct components having different transmission times. The possibility that these components might arrive from slightly different directions was suggested by various observed facts, among which was the behavior of sharply directive antennas. It has been noticed in the past that fading was affected by the directivity of the receiving antenna. An example is given in the oscillograph records of Fig. 1 showing observations made by the authors some years ago at Cliffwood, New Jersey. These illustrate a condition of less fading on a large "inverted vee" 1 antenna than on a small nondirectional antenna, using telegraph signals received from station G B K in England. Beating the signal with a local oscillator provided the audio frequency which was recorded. The directive antenna output was recorded on the upper trace while the lower strip recorded the output of the substantially non-directive, comparison antenna. Such observations as these suggest the possibility of controlling and reducing fading by a systematic use of sharp directivity. The present paper reports some experiments in which changes in fading are correlated with changes in the directive pattern of a rhombic antenna 1 made by mechanically changing its shape. It may be reasoned that, where the total differences in the path