Tropospheric path loss measurements at 400 mc over distances 25-830 miles

An analysis is presented of more than 16,000 hours of 400 MC propagation data taken by Lincoln Laboratory at seven overland receiving sites ranging from 94 to 830 miles plus 340 hours of overwater data taken in cooperation with the Naval Research Laboratory. On the basis of over 200 hours of wintertime data, overwater transmission appears to be 5 to 10 DB better than overland transmission. Fading rate and fading range are more variable in the range under 250 miles. Parabolic antennas up to 60 feet in diameter show no gain degradation on the average and it is believed that much larger antennas can be used. The rate at which the path loss increases is quite variable with distance. For the winter months, the attenuation rate is as low as 0.1 DB per mile between 350 and 450 miles, while between 600 and 830 miles the rate averages 0.19 DB per mile. On the baiss of the data presented in this report, it is evident that tropospheric transmission will support single hop, multi-channel voice transmission circuits for distances as great as 600 miles. This can be accomplished by the use of high power transmitters, very large antennas, single side band modulation and diversity reception.