TV and FM interference by windmills. Final report, 1 January 1976--21 December 1976

A preliminary but wide ranging investigation of the effects of a horizontal axis windmill on the reception of TV and FM signals in its vicinity is described. It is shown that the rotating blades produce a time varying amplitude modulation of the total signal received, and that for an antenna so located as to pick up the specular or forward scattering off the blades, the modulation can produce severe distortion of the video portion of a TV signal reproduction. The distortion is worst at the higher frequencies, and therefore poses more of a problem at UHF than at VHF. No interference to the audio signal nor to any FM transmission has been observed. Based on laboratory studies as well as field tests, a modulation level has been established at which the video interference is judged ''severe'' (or objectionable), and this threshold of interference is substantially independent of the primary field strength. A theory has been developed to compute the interference zone about a windmill for any given TV transmitter, and the results are in good agreement with those obtained from field tests using the operational windmill at the NASA Plum Brook Facility.