[Antennas] Vertical coaxial endfed dipole...

[Jerry Flanders]

The purpose of the "several loops" of the coax is to create a high 
impedance at the operating freq so that the quarter wavelength of coax 
shield nearest the antenna end of the coax is "insulated" (for RF) from the 
feed coax. Anything you do to improve this "insulation" will make the 
antenna's performance more predictable and more in line with the 
conventional half wavelength center fed dipole.

If you have a grid-dip meter or antenna analyzer you could improve it by 
bridging across the coil with a capacitor to make a conventional 
parallel-tuned circuit resonant at the dipoles operating freq. You would 
simply open up the shield of the coax at each side of the coil (the 
"several loops") and connect the capacitor there.

I don't think the FG fishing rod would have any practical effect on the 
antenna's performance. Sounds like a good way to support it to me.

Jerry W4UK

At 12:13 AM 2/20/2002 -0800, Demetre Koumanakos wrote:

>Hi all,
>
>The ARRL handbook describes the construction of an and fed horizontal 
>coaxial dipole. This antenna is nothing more than a L4 radiator wire 
>soldered on the center conductor of a L4 coax cable. On the feed side of 
>the coax several loops of the same coax cable are present to creat a 1:1 balun.
>
>Anyway to the questions:
>
>Has anyone had any experience with such an antenna ?
>
>How would this antenna rate to a center fed dipole ?
>
>I was thinking of building this antenna for 10m, the antenna would be 
>housed inside a fiberglass fishing rod in order to use it as a vertical...
>
>Any tips ? comments ?
>
>73
>
>Demetre - SV1ENS
>
>
>
>
>
>
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>
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