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homebrew 70cm oscar yagi
First I like to thank the following.
N4CZT Doug, For getting me involed in Amateur satellite. These guys helped me make my mind up on what I wanted to do. K9STH Glen KA4DPO John WA9SVD Larry KL7AJ Eric W9GB Gregory, For helping me with some vital information I been searching for months now trying to find a good design for a circular polarized 70cm yagi. All I could find is bits and pieces. I took those bits and put them all together and this is the results. This is a 10 X 10, total 20 element yagi. Will edit this post as it moves along. These first four pics shows how the boom is drilled. I made a simple jig to hold the boom on the milling table. Mark boom on two locations (vertical and horizontal). You and lay the boom in a piece of long angle iron to get it straight. Align the bit with the mark and your hole will be at 90 degrees each time. My boom is 1 inch x 72 inches. All elements are 3/16 except driven. It will be 3/8" Elements are insulated from boom. To reduce noise. Driven element will have "gamma match" Element length: Ref- 12 15/16 drv- 12 3/4 D1- 11 15/16 D2- 11 13/16 D3- 11 5/8 D4- 11 9/16 D5- 11 1/2 D6- 11 7/16 D7- 11 3/8 D8- This one in still in question. 11 5/16 would be the next down step. 11 15/16 would blunt the pattern alot to take the sharpness off. 11 1/2 may be the better choice. Spacing: Ref= 0 Drv= 0-5 3/4 D1= 0-8 1/2 D2= 0-13 1/8 D3= 0-18 3/8 D4= 0-25 1/8 D5= 0-32 5/8 D6= 0-40 3/4 D7= 0-49 1/2 D8= 0-58 1/2 Horizontal plane will mount first. Vertical plane will be shifted forward by 1/4 wave length. Phasing harness will be two 75 ohm cables 1/4 wave length each. Most antennas are on the same plane. You have to install a 1/4 wave length jumper to get circular polarization. You feed it 90 degrees out of phase. Since the vertical elements at shifted forward 1/4 wave length (90 degrees electrical in space), the phasing harness is equal on each side, should give identical transformation of antenna impedance. |
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