Topband: Best Height Above Ground for a Beverage RX Antenna

[Milt Jensen]

----- Original Message ----- 
From: <w8av at aol.com>
> My 550' NE/SW beverage crosses a small ravine and is about 15-20 feet AGL
over this ravine for about 50-60 feet of its total length.  Although it
hears OK, it is a far poorer performer than the other beverages that
maintain roughly the same height AGL over their entire lengths.
>
> 73.................de Goose, W8AV
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My experience with crossing the dry arroyos in the Southwest is that if the
span is more than 1/8 WL and the depth is greater than 15 feet, there is an
induced affect on the Beverage wire such that it believes it is a "long
wire" for the span distance.  Antennas suspended over this type of terrain
are more noisy and lose some of their directive characteristics.

To mitigate this situation I install an earth (ground) extension underneath
the Beverage wire for the length of the span to maintain the same spacing
that the antenna has over level ground.  I have used aluminum electric fence
wire installed in the following manner.

My antennas are 10 feet AGL so I install 4 ground wires at that level
underneath the Beverage wire, from one side of the arroyo to the other.  The
4 ground plane wires are spaced such that two are on each side of the center
line of the Beverage; the outer wire at 10 foot spacing from the center line
and the inner wire at 3 foot spacing.  The resultant overall spacing across
the 4 wires is 7 feet, 6 feet, and 7 feet with the Beverage wire over dead
center.

On each side of the arroyo, all four ground plane wires are attached to one
common 8 foot long ground rod.

This terrain modification technique has allowed me to make much longer
Beverage antennas without degrading performance by crossing deep arroyos
with long spans.  Antennas deployed in this manner then perform with the
same receiving characteristics as their sister antennas which are entirely
deployed over even terrain.

Mis dos dentavos, y YMMV, de Milt - N5IA