A Study of Short-Time Multiple Signals

The echos or multiples of the direct signals from a transmitting station which arrive shortly after the main signal are due to direct-reflection from the Kennelly-Heaviside layer. Those arriving after considerable time (about one-seventh of a second) have travelled around the world. This paper deals with new, intermediate types of multiple signals which arrive at the receiving station from 0.01 to 0.04 second after the direct signal. Groups of these have been associated with paths to the regions of auroral activity, the magnetic and geographic north poles. A classification of these short-time multiple signals is given and resolved into the regular echos and a new wedge-shaped echo. The wedge or hangover multiples may be due to a plurality of paths resulting in successive echos of decreasing amplitude. Surprisingly large fluctuations of path difference of all short-time multiples occur in as short a time as one-quarter second.