The Arizona Game and Fish Department (AGFD) would like to have aircraft warning markers on the guy wires of our 40 m and 50 m towers:
"When guy wires are present, AGFD recommends attaching Bird Flight Diverters (BFDs) at spaced intervals along the length of multiple wires. At a minimum, four Aircraft Warning Markers (spherical or cylindrical, 36 inches in diameter) should be placed 10 meters below the apex and BFDs be placed at 10 meter intervals along the length of each outer wires."
In the following, I calculate the spatial separation between the sonics and a ball mounted on the guy wire closest to the sonics.
The sonic is mounted 73" or 1.85 m from the Rohn towers. The sonic boom is at an angle of 30 degrees with respect to the plane of the closest guy wire (PGW).
Thus the sonic is 1.85 m * sin(30 deg) = 0.93 m from the PGW and the horizontal distance of the sonic from the tower in the PGW is 1.85m * cos(60 deg) = 1.6 m.
The ball is placed 10 m below the top of the tower and the upper guy is attached 5' = 1.5 m below the top of the tower. Thus the ball is 8.5 m below the top of the outer guy and displaced 0.8*8.5 m = 6.8 m horizontally from the tower. It is displaced 6.8 -1.6 = 5.2 m horizontally from the sonic in the PGW.
Since the sonics are at 5 m height intervals, the best case is a 2.5 m vertical separation between the ball and a sonic. I could refine this with the exact heights of the sonics on each tower, but the spatial separation will be principally defined by the 5.2 m horizontal separation. Thus the best case (maximum) separation is sqrt(0.93^2 + 2.5^2 + 5.2^2) = 5.8 m. The worst case is sqrt(0.93^2 + 5.2^2) = 5.3 m. These only differ by 10%.
Wyngaard calculated the flow distortion caused by a sphere with a potential flow (laminar) model. Note that for a turbulent flow, this model is adequate only upwind of the sphere. Downwind of the sphere, the turbulent wake complicates the flow around the sphere (not to mention periodic shedding of the wakes). Upwind of the sphere, the distortion of the mean flow is on the order of 3/2 (a/r)^3 where a is the radius of the sphere and r is the distance from the center of the sphere. Thus for a 36" diameter sphere, the flow distortion is estimated to be 1e-3 in the worst case and 7e-4 in the best case. These are certainly acceptable levels of flow distortion, but these estimates are only valid upwind of the sphere.