On May 29, 9:31*am, "JB" wrote:


The 1/4 wave ground plane has a useless pattern. *Main lobe at about 30
degrees above horizon, but broad enough to be usable and simple to build.

The 1/4 GP with sloping radials and the 1/2 wave are so close in
performance to almost be unnoticeable if both are mounted in
the air say at 30 ft. The two antennas will have almost the same
pattern at almost the same exact angle. When modeling both
at 30 ft, the GP's maximum is at 2.7 degrees, vs 2.6 degrees
for the 1/2 wave. "145 MHZ".
The GP's performance will vary a bit due to the number of
radials, but in general the difference between the two antennas
will amount to about .3 to .5 DB. Not much.
This does not take into account common mode currents.
In some cases, I bet it's possible for a 1/4 GP to outperform
a J-pole if the J pole has no decoupling from the line.
Myself, I've never used a J-pole. I prefer a gamma loop
type match if I build a base fed 1/2 wave. I don't like
the matching device to be parallel with the radiating element.
Most of my "simple" 2m verticals are 1/4 wave GP's.. :/
I have one in the attic hung from the rafters. It has either
6 or 8 radials.. I forgot which.. Been a long time since I've
been up there. If you use more than 3-4 radials which is
the norm, you will see an increase in performance.
I think more due to better decoupling of the line rather
than less ground loss. At 30 ft, ground loss is not much
of an issue as long as the antenna is complete. Just one
radial will make for a 1/2 wave vertical dipole of sorts, and
ground loss should not be much of an issue at several
wavelengths in the air. So... I think the increase in
performance is more due to better decoupling from the line.
Either type can use further decoupling techniques for
improved performance. The GP will usually use a 2nd
set of radials 1/4 wave below the main radial set.
The same scheme can be used for the 1/2 wave if
common mode currents are a problem and skewing
the pattern up off the horizon.
In many cases, decoupling of the line is more important
to gain at a low angle than element length.
Does no good to use a longer element if line currents
skew the pattern upwards.