An Echo Interference Method for the Study of Radio Wave Paths

An experimental determination of the rate of change of radio-frequency phase of the separate downcoming echoes has been carried out. The small power crystal-controlled oscillator circuit of the 4,435-kc transmitter operates continuously, the high-power pulse transmission being produced by modulating the power-amplifier circuits. A receiver was operated very near the transmitter, having rapid recovery from the paralyzing effect of the pulse ground wave and sufficient sensitivity to receive the echoes with good amplitude, and having a very slight coupling to the crystal-oscillator circuit such that the crystal "pick-up" was comparable to the echoes received. The echoes showed their changing radio-frequency phase by alternately adding to and subtracting from the constant crystal oscillator pick-up. This "interferometer" is naturally sensitive to small changes in the optical path of the waves. The phase changes are regular, but the time of one 360 deg. phase change on 4,435 kc varies from 1 sec. to 60 sec., or possibly longer during the day and evening, and at times changes between these limits in as short a time as 15 min. When multiple echoes are present, the second and third echoes phase in and out more rapidly than the first echo, but not by an even factor.