Measurements of the Delay and Direction of Arrival of Echoes from Near-by Short-Wave Transmitters

Observations on pulses radiated by a high-power beam transmitter operating in the short-wave range show that when the receiver is located within the skip zone, echoes are observed having delays of from 1 to 50 milliseconds. These echoes are the result of scattering and three different types may be recognized, each arising from a different source. Echoes of the multiple type were found to occur the most frequently and to have many of the characteristics of signals transmitted over long distances. Components were observed from regions up to 4000 miles distant. Direction-of-arrival measurements using steerable arrays operating on the musa principle indicate that these multiple echoes are scattered from regions along the transmitted beam. Vertical angle-of-arrival measurements using a musa receiving system indicate that the surface of the earth may be the source of scattering. Similarities between multiple echoes and southerly deviated waves from European transmitters have been found which indicate that the same phenomena may be responsible for both.