Propagation Studies on 45.1, 474, and 2800 Megacycles within and beyond the Horizon

Continuous recordings of field strength on 474 and 2800 megacycles, over a period of 13 months, revealed maximum values three to four times the free-space field at distances of 42.5 and 70.1 miles from the transmitting site atop the Empire State Building, New York City. Recordings on 45.1 megacycles during the same period, on a reduced schedule, did not exhibit the large variation found on the higher frequencies. Refraction was found to be greater in the summertime, the strongest periods occurring at night or in the early morning. Refraction greater than normal was not evident when the average wind velocity was above 13 miles per hour. A study of weather conditions during the periods of strongest refraction indicated that roughly 60 per cent of the gradients were of the frontal type, involving different air masses, and approximately 60 per cent of the gradients were higher than 100 feet above the earth's surface.