Have a 55 ft tower rated at 18 sq ft (TX 455) a 15 ft mast and a 150 LB - 17 sqft multiband beam (SteppIR DB36). Question is how far up the mast should I mount the antenna? Would like to get to at least a half wave over ground for 40 meters (60-62 ft) or 7 foot of mast. Fred K3BHX