[TenTec] vertical radials

[David Kelley]

Mike,

For in-ground radials you don't need to worry about getting the lengths
exactly right.  As someone else said, the longer the better, but if you
have settled on 1/4 wave (free space length) as a good compromise
between cost and performance, you only need to make the radials
approximately 1/4 wave long.  A few feet one way or the other will not
make a noticeable difference.

In the case of a ground-mounted vertical, current flows through the
ground radially outward (and inward) from the ground connection point.
Theoretically, that current extends out to infinity (or all the way around
the earth).  However, the current is most concentrated near your
antenna and decreases approximately inversely proportionally with
distance (i.e., it varies as 1/r, where r is distance to the base of the
antenna).  The reason we place radials near the base of vertical
antennas is to improve the conductivity of the ground where the
current is most concentrated, not to create a resonant structure for
the "missing half" of the antenna.  Since the ground is a partial
conductor, the antenna structure doesn't "end" at the radial tips; it
keeps going all the way around the world (and down into the ground,
for that matter, although the skin effect forces most of the current to
flow near the surface).  Improving the conductivity in the region of
high current concentration cuts down on losses.

As someone else said, consult the ARRL Antenna Book or the
technical section of the ARRL web site for information on the
optimum combination of number of radials vs. radial length for a given
total amount of wire.  Don't worry about what the actual length comes
out to be.

73,
Dave NB4J

>what length of wire for 1/4 wave?
>
>I figure on using the old 468/freq and then taking the result and dividing
>by two. to get a 1/4 wave
>
>would that be correct?
>
>since I have about 3 acres to put the antenna up, I plan on renting a
>trencher they use to put in the invisible dog fence. this thing cuts, places
>the wire in the trench and then covers it up.. about $35 for a day...
>
>
>Mike Bryce, WB8VGE
>SunLight Energy Systems

--
David F. Kelley, Ph.D.
Assistant Professor
Electrical Engineering Dept.
Bucknell University
Lewisburg, PA 17837
(570) 577-1313
dkelley at bucknell.edu