Abstract :
A series of measurements on transmissions of 3.2cm wavelength at ranges far beyond the radio horizon has been made over various paths, at arbitrary periods of time. These have established the existence of an essentially permanent extra diffraction signal field Whilst its level does not change appreciably with time, the character of this signal can vary from that typical of a scattering process to that due to a coherent mode of propagation. Further, although the observed signal attenuation rate with distance is similar to that expected for a scattered field, the average level is found to be some 10¿15 dB below that predicted from theory There appear to be factors affecting the long range propagation of 3.2cm waves through the lower atmosphere which are incompletely understood. Although no extensive analysis of meteorological conditions has been made, there is some evidence to show that the existence of extensive well-pronounced anticyclonic systems results in poor propagation conditions for the extra-diffraction signals.
