At the risk of again placing my foot on top of my tongue, I think it
bears mentioning that one of the hidden issues in this discussion is
what radiation do you want or need. The radiation pattern of a dipole
at a reasonable height resembles a donut on edge. What this really
means is that gain is a misnomer for the radiation off the ends of a
dipole. There is very little. With enough height there will be
additional gain off the sides of the dipole, compared to a vertical,
with most of the gain centered at 90 deg horizontal off the center of
the dipole. A 1/2 or 1/4 wl vertical's pattern is identical and
rotated so that the donut is flat instead on edge and is centered about
halfway up the vertical. Either a 1/2 wl vertical or a well grounded
1/4 will have some gain but the pattern should be fairly distributed
vertically around 360 deg.
For those who enjoy being confused, I suggest downloading the free EZNEC
trial. The trial also includes a number of antenna types as examples.
As you learn to use the program, you will find the patterns you create
to be interesting but not exact unless you buy the complete program and
start learning how to insert elements such as traps, tuning coils, and
feed lines. As I understand it, and there are many who have a more
complete understanding of the program than I, this will allow you to get
closer to reality but the basic understanding will not change much.
73,
-- John / WA1JG
|