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Author Topic: Inverted L ground plane  (Read 9653 times)

Offline OgreVorbis

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Inverted L ground plane
« on: August 28, 2019, 1059 UTC »
If I have an inverted L, is it better to put most of the radials under the horizontal section? Should I just use a normal circular pattern around the antenna and don't emphasize under the horizontal?

Should the radials under the horizontal extend out more (as if the end of the horizontal is the center of the antenna)? This should form a jelly bean type shape.

Aside from that, it there anything you would recommend for an inverted L (not to purchase; ideas)?
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Offline Brian

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Re: Inverted L ground plane
« Reply #1 on: August 28, 2019, 1437 UTC »
My inverted L has the radials originating from the vertical section. I think this is best as it's the vertical that does the most radiating. As for whether it should extend out further under the horizontal, I don't know but it certainly won't do any harm.

If you're trying to improve the earth counterpoise, then I believe it's more beneficial to add lots of short radials than just a few long ones.

Offline Josh

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Re: Inverted L ground plane
« Reply #2 on: August 28, 2019, 2045 UTC »
Some run a wire along the ground under the h portion of the L for its entire length, in addition to the radials at the v portion.
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Offline bandarr3000

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Re: Inverted L ground plane
« Reply #3 on: August 29, 2019, 2249 UTC »
Some run a wire along the ground under the h portion of the L for its entire length, in addition to the radials at the v portion.

This is exactly what I do, with good signal reports. 
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Offline Brian

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Re: Inverted L ground plane
« Reply #4 on: August 30, 2019, 1231 UTC »
Some run a wire along the ground under the h portion of the L for its entire length, in addition to the radials at the v portion.

This is exactly what I do, with good signal reports.

And no reason why not.
The purpose of the ground radials is to act like like a mirror of the radiating element which is the vertical section and is why concentrating the radials there is best.
In my own present setup, I can't run a radial the full length of the horizontal anyway as it runs over a neighbours field. I do have about 30 unused radials at the end of the horizontal wire from a previous setup which I may connect to the current setup. The more the better!

I'm lucky that I have a proper Field Intensity Meter (Nems Clarke WX-2E, similar to a Potomac) so any changes I make can be accurately measured.

Offline Josh

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Re: Inverted L ground plane
« Reply #5 on: August 30, 2019, 1814 UTC »
Ya a fsm is great to have for seeing how antennas compare. I went from a 1/4 to 3/4w vert and the angle of radiation dropped dramatically, ie with the same power out and fsm at same location, only antenna was changed, fsm showed a huge increase in signal strength.

The 20w manpacks in use by US sf have a wire antenna kit that includes a spider web ground wire net that is placed under the manpack on the ground, and the inverted L or whatever antenna they deploy goes off to wherever the support is. No direct contact with earth as to the rf ground but it works ok.
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Offline Kage

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Re: Inverted L ground plane
« Reply #6 on: September 05, 2019, 1758 UTC »
I actually replied without actually responding to your post here by accident, didn't even see your post until now here but over on that other forum we use I talked about ground planes for Inverted L's.

There's a claim that placing an equally length wire along the ground as the horizontal; aired part of the vertical section is beneficial. I'm not sure if that's fact though, might take some computer analyses. That horizontal section is not really radiating much anyway so I feel the most important part of that section acts as a loading coil for the vertical section or capacitance hat, and by placing a length of ground plane along the same direction will simply add to aerial capacitance thus probably plays with overall loading efficiency.

Now as far as directional qualities of the L, the long part horizontally longitudinal is the direction with a possible loss of 1dB. Put the length of the inv. L behind the area you want to give the strongest signal, but 1dB is so little it probably will have little effect anyway.

I've also noticed that sloping L's exhibit some interesting features. If you slope the inv. L the sloped section seems to have a far lower angle of radiation, thus if you are on the outskirts of town like me and want to hit your town strongest with frontal ERP, you put the sloping section toward your town and the ground screen same direction.

I may be wrong on some of this, but these are my observations in reality when testing.
« Last Edit: September 05, 2019, 1807 UTC by Kage »
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