Inverted Veritcal

[KE5FOT]

I'm currently working to upgrade my antenna situation. One option based on my present circumstance that I am considering is whether or not I should build a vertical. However, it may be more convenient in my situation to invert the vertical, use a ground plane with three or four radials slanted toward the feedpoint. Of course, this would mean that I'd have one electrical ground on top attached to the shield of the coax, but then I'd have the actual ground (i.e. mother earth) on the bottom possibly squeezing the radiation pattern a bit more. Not to mention the coax would be running along the antenna for part of the way up.

So my question is, how would an inverted ground plane antenna perform, and how would the feedline's running parallel to it for part of its length affect the radiation pattern. This would a quarter wave vertical for 40 meters.

It's a very unusual idea, I've never heard anyone talk about it, so it makes me wonder if it's an assumed bad idea. I myself wonder where I thought of it, actually . . . imagining it in my head it reminds me of a hat rack.

by the way this antenna is designed to be quick to put up and take down due to neighbors and the threat of hurricanes.

Thanks for any suggestions

Ed

[K1VSK]

I may have misunderstood what you described but it sounds like you intend an essentially top fed vertical?

There is lots written about such designs, all of it bad.

[WB2WIK]

I wouldn't do that.

Why not a real, normal base-fed vertical with a permanent radial field but a tilt-over mount so you can just lay it over if a storm is coming, or when you're not using it? DX Engineering makes such a tilt-over mount which is quite strong and accommodates many vertical designs...and is also cheap!

WB2WIK/6

[KE5FOT]

I would build a proper radial field but I simply don't have the room to do so. My backyard is pretty small.

I agree now having had the night to look over the idea of this inverted ground plane it seems pretty ridiculous. At this point I'm thinking about just going to 2 and 6 meters and working with smaller antennae . . . start small and work my way up to the 33 and 66 foot behemoths. I just don't have room for antennae over 15 feet in size, and I am too stubborn to buy a pre-made antenna.

But if anyone else has seen such a setup used before and has some comments on it I'd still be interested to hear if an inverted ground-plane antenna would work.

[KL7AJ]

Quote[/b] (K1VSK @ Oct. 17 2007,08:46)]I may have misunderstood what you described but it sounds like you intend an essentially top fed vertical?

There is lots written about such designs, all of it bad.

We had just such a beastie on these 74 MHz callboxes we had all over Los Angeles. They never "not worked" but I don't know if they had any advantage or not over our normal coaxial antennas. Warrants some 'vestigation.

eric

[WB2WIK]

Quote[/b] (KE5FOT @ Oct. 17 2007,13:04)]I would build a proper radial field but I simply don't have the room to do so. #My backyard is pretty small. #

How small is it?

I have a 1/4-acre city lot and my backyard is less than half that and mostly occupied by a swimming pool and patio. But there's more than enough room for a lot of antennas, and I have several, almost all of which are way larger than "15 feet."

For one, when you go out in your yard, look up. Does the sky look really, really high? It does, here. That's one direction to go where you should have as much room as I have.

WB2WIK/6

[WA9UAA]

Ed,
Before you give up, look up 'Half Square' as an antenna type. You may have to go up and over something. Another alternative is an end fed vertical, it's a half wave long. Par End-fedz makes them; or, you can do some research on how to build a single band matching circuit. GL
73,
Rob WA9UAA

[G0GQK]

I think for a successful antenna which you require, using the many tried and tested antenna's designed by those who know about wires and waves would be a better idea.

G0GQK

[K6UEY]

One factor to take into consideration a full length ¼wave radiator has a 90° phase shift,that puts the end of the radiator at a voltage point or hi Impedance. To reduce the antenna leakage to ground that portion should be multiple wave lengths above ground. That could present some mechanhical difficulties.
I would suggest a review of the antenna basics and may be then you may have a better grasp on some of the problems you are facing with small real estate. Remember it takes far more real estate to put up a properly mounted monopole antenna than it does a dipole antenna. A Monopole must have the image portion to radiate properly ie.... radial system.A dipole has a 180° phase shift so it supplies its own image portion.

[W5HTW]

There are several commercially made verticals that work well in small space without radials. The GAP Titan comes to mind, but MFJ makes one, as do both Butternut and Comet. Probably Steppir does, as well.

None of them are really cheap, all of them are reasonably easy to install and tune. All of them will stand up to rough weather if installed properly and guyed. No need to take them down unless a hurricane or tornado is approaching.

Verticals, inverted or not, are going to have a far different radiation pattern from a dipole or other horizontal antenna. But they can work very well, especially if your interest lies outside a 500-800 mile radius of your site. Except in the low VHF region, verticals have almost no ground wave, so 10-12 meters they can be OK for very local operation, but as you go lower, they just don't do the trick.

With a small lot you can still put up horizontal antennas, such as a loop, inverted-L, trap Vee, even a G5RV. A slanted wire from the house gable, or a flag pole or tall tree, can do wonders, even if the lower end is couple five feet off the ground. And it will give you local coverage, though it may not be as good for DX.

Good luck!
ed