Re: NEC-LIST:re: monopole elevation pattern

Chuck, All

This problem has probably been noodled for about a century now. Seems
much confusion exists on how to improve horizon launch for V-pol with finite
groundplanes.

Did you or any others consider elevating the groundplane and if so, would you
(could you) share your conclusions including any details such as terminating or
tapering (bending) the far tips?

dan bathker

At 07:25 AM 3/18/2002 -0600, Chuck Vandament wrote:
>Frank, et.al.
>We have pondered this problem for many years. What you are describing is
>the sky-wave part of the pattern. The monopole launches a strong surface
>wave even though the far-field pattern shows a null at the horizon.
>
>We were on a team with Collins Radio/RCA for a proposal to the govt. for an
>over-the-horizon radar at hf. The spec called for a lower half-power point
>at 3 deg. above the horizon. The antenna was a broadside array with
>monopoles in front of a reflector screen. The ground screen extended
>1000ft toward the front and also off the sides for the array scan angles.
>The ground screen was made from 20ft wide rolls of welded wire fencing
>(galvanized zing on steel) with welded seams. We measured scale models
>and were convinced that we could meet the spec. GE won the contract so we
>never saw our design materialize.
>
>We did get an improvement in that low takeoff angle over the classical
>monopole by using a sleeve-monopole. The monopole was 1-inch aluminum pipe
>standing inside the sleeve. The sleeve was 3-1/8 aluminum pipe. The
>sleeve was grounded at the base and extended to about one-third of the full
>height of the monopole. The monopole was fed at the base, just above the
>insulator. (for homebuilders, a glass coke bottle makes a great base
>insulator - but cork it so it doesn't fill up with water)
>
>Frank, if you find a way to get a low takeoff angle with a reasonable
>length of ground screen, I hope you will publish the results.
>
>Smilin' Chuck Vandament
>--
>The NEC-List mailing list <nec-list_at_gweep.ca>
>http://www.gweep.ca/mailman/listinfo.cgi/nec-list

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