Pulse Phase-Change Signaling in the Presence of Ionospheric Multipath Distortion

Ionospherically-propagated high-frequency signals generally arrive by multiple paths having different and graduallychanging time delays which cause multipath distortion. Interference fading and delay-difference smearing are the principle manifestations of this distortion. The technique of alternately transmitting long (1-msec) and short (20-μsec) pulses was developed to study multipath smearing and to determine whether the rates of change of phase would permit the use of phase-change signalling systems. Tests were conducted which confirmed the frequent occurrence of abrupt phase changes during reception of any one pulse, but established that the rate of phase-change between corresponding portions of successive pulses always was gradual. The phase-change signaling system that was developed as a result of this study is described. Data transmission (with millisecond pulses) over distances greater than 3000 km with negligible errors for prolonged periods was observed.