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Custom mounting adapter for 40 MM Square Boom


The 40 MM square boom adapter is suitable for OptiBeam antennas such as the OB 9-5 and OB11-5.  The adapter consists of a 2.5 inch aluminum tube that fits over the boom.   There is a $20  extra charge for this adapter. 


Bill / KM1C tested the 40MM adapter kit on his 3 yagi stack.  Click for his project info.  


Note: although the head of the bolt is at the top, it will actually be on the side of the boom facing down toward the ground.  See pictures below.



Short Boom sample shown drilled for one of the holes.   Slide the adapter over the boom with the larger hole facing down.  The larger hole goes on the side of the boom facing down (toward the ground).  Mark the boom and drill the 4 holes in the boom with a 3/8 drill or slightly larger drill (e.g. 7/16) if necessary to allow the bolts to fit.  Sometimes when drilling if you don't align the holes exactly it may be easier to get the bolts to go thru the round boom section with a 7/16 drill and either is fine.


Tape the thick SS washer to the boom before sliding the adapter over the boom.  The washer goes on the bottom side (facing the ground).


Insert the bolt through the larger 5/8 inch hole.  Tighten the nylon insert lock nut snugly


Adapter in place.  Note: the larger hole and screw head is down to allow maximum clearance to the other parts of the antenna. 

Bill / KM1C ordered the 40MM adapter for his "stackable" TiltPlate with the optional KARLock.  The KARLock latch mounts to the visible tube.  The mast attaches to the backside of the fixed plate.


Another angle


End view showing the square boom in the 2.5 inch tube and one of the adapter bolts is visible. 

Leveling Bolts provide additional separation for phasing tube clearance.   These bolts will be installed when you receive your TiltPlate.  If you are converting from a different type of antenna to the OB9-5 the bolts will be provided along with the adapter.  Here are the details on the bolts and mounting.