Somewhere I got the following formula for a cylindrical equivalent to triangular tower like Rohn 45. Equivalent Cylindrical Diameter = 2 * CUBEROOT [(D * F^2)/2] where D = tube diameter and F = Face width. For Rohn 45, D = 1.25" and F = 18", so cylindrical diameter equivalent = 11.7446" Does anyone know where this came from or if it is valid? 73, Bill W4ZV