Elevation System for EME Arrays
By Edward R. Cole, AL7EB
Overveiw: This is a brief description of the custom built system I designed for elevating four 2 meter crossed yagis for a small standard eme array. The antennas, 2m-xpol-20s, and the 12 x12 foot H-frame are manufactured by M2. The elevation system consists of a custom made bracket and a commercial TVRO satellite dish actuator.
Note: This is not a detailed step-by-step article, but more a general description of the design with a plan diagram and a couple pictures. From this, I believe someone might build an acceptable system by incorporating my ideas into his own particular equipment.
Description: My eme antenna system is mounted on a 40 foot Rohn-25 tower, using a Hazer lift system, a Ham-III azimuth rotator, a seven foot 2 inch, schedule-80 steel mast with the custom elevation system attached near the top.
The elevation assembly is constructed from two-inch square steel tubing (see drawing) and was constructed by a local welding shop to my specification. It consists of a 16 inch high by 36-inch wide rectangular frame to which a U-shaped bracket is welded. The U-shaped bracket projects 10 inches horizontally in front of the 16x36 frame and is welded in place. Midway on this is located a dual flange for attaching the actuator body with a ½ inch bolt.
On each end of the rectangular frame, two pillow block bearings for a 1-1/4 inch shaft are mounted with bolts and locknuts. Three pittman arms are constructed from 2x2 tubing. The outboard arms are 10 inch long and the center arm is 12 inches. All three are drilled to accept a 1-1/4 inch diameter solid steel shaft. The arms are positioned, aligned in the same plane and welded. This makes up the moveable part of the elevation system. All three arms are drilled to accept 4-inch standard DB Products antenna clamps. The 3-inch aluminum crossboom of the H-frame is attached to the arms with the clamps. Appropriate spacers are used and the brackets double nutted. The actuator arm attaches to a double flange on the center arm. When the arm extends, the antenna array is elevated by rotating the pittman arms about the shaft. 90-degree movement is possible. The elevation assembly attaches to the two-inch vertical mast using three DB clamps.
To ensure that the cross boom does not slip I drilled and tapped the center clamp plate into the boom to accept a short 5/16 bolt. In case of severe impediment of movement, this bolt should act as a shear pin (1/4 inch would probably suffice; I used what I had on hand).
The welding shop painted the bracket gray to keep from rusting. Construction in Alaska is expensive. The bracket including all material except the actuator cost me $500. It is heavy at near 70 lbs. (without the actuator). You could probably use thinner walled square tubing to bring down the weight. It has been up since mid-March 1999 and works flawlessly. Having the Hazer is very convenient for making adjustments to the antennas. Everything was mounted at the ground using a ten-foot stepladder.
I hope you find this design interesting. I am still constructing my array and don’t expect to be active on 2m eme till this fall. I still have an 8877 amplifier to build.
See you on the Moon!
73, Ed
Published in EME Symposium-99
