NEC-LIST:re: monopole elevation pattern

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

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