Wednesday, August 19, 2015

A new beam antenna build at N6QW ~ Part 9

Project Update

I have become great friends with the local UPS delivery man assigned to my route. He keeps dropping off packages and religiously inquires about the status of my beam antenna project. So the blog readers I am sure would also like to know the current status. Essentially the rotor mechanism will be located at the base and the entire mast and beam will rotate.

The Configuration

 Diagrammatically the antenna installation will look like the sketch below:
 Starting with the base which will be 1 foot cube of reinforced concrete using rebar this will provide a platform to anchor the rotator and vertical mast. The rotator will sit on a US Tower RP-3 Base Plate which is elevated approximately 3inches from the top of the base using commercial L brackets from Simpson Products. The L Brackets are anchored into the concrete using three 1/2 Inch by 8" long anchor bolts.

The Yaesu Model G450 (good for 10 Sq. Ft. of wind load) is bottom mounted on the US Tower RP-3 Plate Mounting assembly which has been elevated 3 inches so the control cable connector clears the  concrete base. Spiderbeam sells adapter sections for the top and bottom of the mast. At the bottom section one is used to provide a smooth transition from the rotor to the mast. A similar section is employed at the top of the mast to facilitate mounting in the boom to mast bracket.

Two sets of guy wires that are strategically located along the vertical mast assembly keep the mast assembly vertical. SpiderBeam recommends the use of a special material for the guy wires which evidently have some sort of magical properties. In addition I am adding a house bracket to steady the assembly at about the 9 foot level and this assembly is nothing more than a section of PVC pipe. I am of the opinion this sleeve bearing will assist in absorbing any side load torque as a result of rotation.

The Mosley Beam model MP-32, itself is a two element tri-bander which is custom built. The Forward Gain is slightly better than 3 DB on 20 Meters and has a Front to Back Ratio of 20 DB. The driven element is from a TA-32 which can take the legal limit and the other element is from a TA-32 Jr. This enables the beam to have a lighter overall weight yet be able to take the legal limit. I have a homebrew 3CPX1500A7 amp built for 20 Meters and I wanted to be able to use that amp without worrying about smoking the beam!

The beam is yet to arrive but in several days I will start on the foundation. Unfortunately I must take down my current antenna and that will put me off the air for a short period of time.

Stay Tuned de N6QW

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