6 Element Yagi

University of Alberta observatory domes

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Antenna Elements

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6 Element Yagi Antenna

This antenna antenna design consists of wire mounted on pieces of 3/4 inch plywood drilled out to slide onto a galvanized metal pipe that serves as the boom. The elements on the setting blocks are then set in position with set screws (ordinary wood screws). The original antenna was actually designed to work at 108 MHz rather than the 92.1 MHz it actually detected meteors at. Not great, but it shows that even a poorly made antenna can be used to detect meteors.

There are six elements that need to be cut to the proper length and spaced at specified distances from one another for the antenna to be "tuned" to the observing frequency.

See the table at this link to see the length of the antenna elements and the spacing between them for given frequencies. Lengths and spacings are given for the FM radio band. Or you can use the formulas on the How to Build an Antenna page to calculate the dimensions for your antenna.

See the instructions on how to make the antenna elements. You will need these to fasten to the top of the adjusting blocks. Once you have cut and labeled all the elements, you need to mount them to the metal boom using setting blocks.
The setting block can be made from any sturdy wood such as 3/4 inch plywood. It should be at least 3/4 inch thick. Cut 6 pieces approximately 20 cm square. Drill a hole slightly larger than the outside diameter of the boom you are using so that the block can slip over the boom easily. Don't make the hole too large otherwise the block can move too easily on the boom. Use an exterior grade stain or paint to finish the blocks to protect them from the weather. You won't need much and suitable left over stain or paint can probably be acquired from home.
Each adjusting block needs to have two 2 inch wood screws added to it as set screws. Pre-drill 2 holes in the bottom of each adjusting block positioned so the screws enter the centre hole at either side as shown in the illustration. Make sure the drill holes are centred on the wood and that the pre-drilled holes are smaller than the diameter of the screws. This will allow the screws to set snugly. Screw the wood screws in far enough that they are just about to enter the centre hole.

 
Slide the adjusting blocks onto the boom placing them at the spacings that you marked on the boom from the Dimension Table for your frequency. Mark each block so you know what element, D1, Reflector, etc., should be attached to which block. Secure the blocks at the correct spacing by tightening the set screws being careful not to over-tighten them. Attach the 

elements to the top of the block using cable clamps of a suitable size.

 

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We gratefully acknowledge the financial support of the 

Edmonton Centre of the Royal Astronomical Society of Canada, Department of Physics (University of Alberta)

and the

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