Significant Radiation from Directional Antennas of Broadcast Stations for Determining Sky-Wave Interference at Short Distances

The present practice in the design of directional antennas for broadcast stations to prevent sky-wave interference to another station on the channel at short distances does not necessarily accomplish the purpose. The interference signal has been computed from the radiation along one path at a fixed vertical angle. This practice has been generally followed by consulting engineers and has been acceptable to the Federal Communications Commission. Measurements indicating the length of the path of sky-wave signals received at short distances show that the signals take various paths and are not confined to a single path. Measurements were made by pulse transmissions of the relative time required for skywave signals to arrive at a receiving point some 230 miles from the transmitter. Control was had of the vertical radiation pattern. The records made of the received signal indicate varying heights and conditions of the reflection layer. To assure that no interference is caused by sky-wave signals, in accordance with the Commission\´s Standards of Good Engineering Practice, the Standards must be modified to require proper consideration of the radiation at all angles which constitute the "appropriate vertical vector."