Abstract: Calculation of the passive interference protection distance from transmission lines to small-bore short-wave radio direction-finding stations is critical for engineering design. Based on the operating frequency of the short-wave direction-finding stations, this paper analyzes the effects of the passive interference of single-base tower's height on the short-wave direction-finding stations when the resonant frequencies are λ/4 and 3λ/4 respectively. Then it further concludes a computing method for calculating the passive interference protection distance from multi-circuit transmission lines to the short-wave direction-finding stations on the condition that the total error of direction-finding equipment is less than 1 degree. This approach not only offers more rational, complete and precise protective measures for the electromagnetic compatible problems between transmission lines and short-wave direction-finding stations, but also provides a reference for future engineering design of transmission lines and a basis for preparation of the new industrial standard-Code for Protective Design of Radio Stations against Effect from DC Overhead Transmissiion Line.

Key words: transmission lines, direction-finding stations, passive interference, direction-finding error limit, protective distance