My instincts tell me this is a bad idea, but perhaps others have done this
successfully. I currently have an OB9-5 HF yagi (spec 7.8 ft^2 projected
area) mounted one foot above the top of my tower. The mast is 2 inch OD steel
DOM with 5 ft inside the tower to the rotator and 7 ft above the tower. Can't
find the mast wall thickness at the moment but I think its 0.12 inches. Thrust
bearing is at the top of the tower. I'm considering adding a 40M rotary
dipole (3.4 ft^2) above the yagi. But I need to place it at least 10 ft above
the yagi to minimize coupling, plus I need 3 ft above the dipole for the dipole
truss bracket. That means I need 13 ft "more" mast. Is it possible to splice
an additional 13 ft of DOM onto the existing mast using a steel structural tube
inserted inside the mast pieces and bolted through the masts? If so, how long
should this joint tube be? The tower is a crank-up so I can work up there
comfortably with a man lift when it's cranked down.
tnx for your thoughts.
N3AE
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