Hello Marconi 390:
Yes i tried to make a I-10K without out ground plane radials, as a customer wanted a few. After seeing the results, the SWR was dependent on the mast length, and tunning was erritic. So after measuring all this I never looked back, the ground plane radials work to well to trade off for the convience of putting up a I-10K in a tall tree. This testing also reveled some neat to know stuff about the matching circuits.
This reminded me, many years ago trying to install a Sigma 4, 3/4 wavelength antenna. I had it tuned to low SWR but when I raised it to the operating heigth, the SWR went nutzoid into the Red on the SWR meter. And the Gamma Matching hardware had to be modified to get it to work, it had a intermittent connection. That was a real charm to have a intermittent connection in the antenna tuning section after it was raised up and all the guy wires where secured. I got the SWR down to a reasonable level by reducing the mast heigth, to what looked like a 3rd Mulitable length of 9 feet, how wounderful, that wasn't in the instructions. Boy did I want to choke somebody over all that!
Oh by the way I have several Sigma 4 Antennas in the aluminum scrape barrel, maybe I need to post a picture of this, on the web site. Everytime I walk by the barrel, I smile knowing that some poor soul will NOT have a hair pulling contest with them.
If you look at the manufactures diagram of the Impedance Matching circuit of these fiberglass sticks, how else would you think the energy doesn't use the outside of the coax as a counterpoise, or the other half of the antenna. The manufacture pamplet says a 1/2 wavelength over a 1/4 wavelength.
By insulating the mast will not change anything, due to again the coax is the counterpoise. Now if you installed the fiberglass stick
so that the mast was insulated, from the mast and the coax was placed inside the metal mast as to shield the coax, that might be a good antenna comparison test to do.
One other thing that I have helped with these none ground plane antennas was to add a Toroid Core 2.4 inches ( Amidon FT240-77 avialable at
www.amidoncorp.com/aai_ferritecores.htm ) with about 15 turns of coax around the core, and taped into place. This choked was placed at 102 to 104 inches below the antenna connector, on the coax itself. The coax was RG8X so it could wound around the core without exceding the bend radials spec I think. This showed some increase in antenna performance, per the user. I have not tested this myself. As I am pretty maxed out for time.
I have been asked to build a 4 element yagi beam antenna that was designed to be mounted Horz, with a I-10K Antenna, using the 4 elememt yagi beam, Boom and Elements as the ground plane radilas. Now thats a grerat idea I think, and maybe some day I'll try that design.
Jay in the Mojave
www.a1antennas.com
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