Antenna


Howard Fidel
 

At my QTH we have restrictions on antenna height, no more then 7' above the roof line. My property is such that I did not have a place to put up a 40 meter dipole. I was hoping to put a multiband dipole. To achieve this, I combined two different antenna designs I found online. For the 40 meter part I adopted W5VM's shorty 40 design, which is under 38' long. From the same coax I added additional dipoles for the 20 15 and 10 meter bands using a modification the classic fan construction. 
The antenna is hung from the top of my chimney, about 25' of the ground to a tree on the property edge mounted at a point about 7' lower then the chimney mounted end. There were 2 surprises when I tested this. According to W5VM, the loading coil should be tapped 3 turns from the center for the drive point.  I designed the coil so I could test this tap, and 1 turn more and 1 turn less. All of these had SWRs over 2 to 1. Since it was easy to try, I moved the drive point to the end of the coil, and the SWR came down to an acceptable 1.6 to 1. The second surprise is that the SWR on the high end of the 80 meter band is also quite usable at as low as 1.5 to 1. 
The other unorthodox thing that I did was use 75 ohm RG6 coax, which if very inexpensive, I picked up 100' for $6. My design notes are attached on a spreadsheet. If anyone is interested I can post pictures.
Howard

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