Put together a 40m GP Ground Mounted Vertical. The vert elemenet is a 33' chunk of wire supported by a tree limb. Started with 4 40' radials but soon learned that that wasn't the best plan. I have read so much about the radials ... big debate was how many , 8 sounds optimal but 4 is OK... not much gained going beyond 8 maybe a db or so. Another thing was the length of the radials ... read that longer is better, read that ground mounted antennas like that the radials dont make a whole lot of difference that the currents flow through the earth..yeah right!
My antenna is sitting on a gravel hill ... maybe 18" of top soil. So I have a lousy ground and the radials are going to come into play! The 30 Meter 1/4 GP had a flat SWR and I cut both the vert element and radials the same 23' length. I was a little leery of the 39' radials for the 40 meter antenna ....
When I first fired up the new antenna it was resonate at 6.7 MHz with a VSWR of 1.6. The 30 meter was almost flat when I first cut it. Made the initial cut on the vert el to get the antenna optimized for 6.9 MHz then wondered what would happen if I started shortening the radials.
freq initial -1' radial -1' radial -3" vert el -1' radial
6.6 2 1.9 1.9 2.1 2.1
6.7 1.7 1.6 1.5 1.7 1.7
6.8 1.6 1.5 1.4 1.5 1.4
6.9 1.5 1.5 1.3 1.4 1.3
7.0 1.6 1.5 1.4 1.4 1.25
7.1 1.7 1.5 1.5 1.4 1.3
7.2 1.7 1.7 1.6 1.5 1.4
7.3 2 1.9 1.8 1.7 1.6
So after the initial measurements I took 2' off the radials then 3" off the vert el then another foot off the radials . Decided to keep on trimming to see how low will it go.
freq -1' radial -1' radial -1' radial -1'radial
6.6 1.7 1.8 1.9 2.1
6.8 1.5 1.5 1.5 1.6
6.9 1.3 1.3 1.2 1.2
7.0 1.25 1.2 1.1 1.05
7.1 1.3 1.2 1.1 1.05
7.2 1.4 1.3 1.2 1.1
7.3 1.5 1.5 1.4 1.3
So I trimmed 7' off the radials so they are around 33' and trimmed about a foot in total off the vert around 32' .
I am just trying to make the antennas as efficient as possible.
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