The course lines, which were a result of a balance between the radiation patterns from different transmitters, would fluctuate depending on weather conditions, vegetation or snow cover near the station, and even the airborne receiver's antenna angle. Under some conditions, the signals from the A quadrant would "skip" into the N quadrant (or vice versa), causing a false "virtual course" away from any real course line. Also, thunderstorms and other atmospheric disturbances would create electromagnetic interference to disrupt the range signals and produce crackling "static" in the pilots' headsets.[21]