Atmospheric radio noise and signals received on directional aerials at high frequencies

Results are presented of amplitude-probability-distribution measurements of atmospheric radio noise received simultaneously on a vertical monopole and on horizontal rhombic aerials at a site in Singapore. Observations were taken at frequencies close to those for which the directional aerials were normally used to receive commercial signals, and by choosing observation periods in relation to thunderstorm activity, two typical communication aerials directed on Hong Kong and Nairobi have been studied under a wide range of receiving conditions. The noise powers received by the omnidirectional and directional aerials are compared, and their relative values are explained in terms of the nonuniform spatial distribution of the noise sources. The effects of the use of directional aerials upon the noise structure are also discussed. In addition, the field strengths of the commercial signals have been examined. The measured improvements in the signal/noise ratio for the rhombic aerials compared with the monopole aerial are discussed in relation to the theoretical improvements to be expected from a knowledge of the gain and directivity of the rhombic aerials.