What is the effect of having a semi-circle of radials beneath a
vertical antenna instead of a complete circle? For example if your
vertical is near a property line. I vaguely remember reading that the
azimuth pattern would no longer be omni-directional and there would be
a change in the elevation of the main lobe. But my memory is hazy and I
can't find anything on the web.

On 23 ago, 23:06, "R.K. AJ4BF" wrote:
What is the effect of having a semi-circle of radials beneath a
vertical antenna instead of a complete circle? For example if your
vertical is near a property line. I vaguely remember reading that the
azimuth pattern would no longer be omni-directional and there would be
a change in the elevation of the main lobe. But my memory is hazy and I
can't find anything on the web.

Hello,

When your radiator is about a halve wave (or multiple of), the azimuth
radiation pattern is mainly determined by the radiator (as current fed
to radial network is far below the current in the radiator).

I assume that you radials are close to the ground or touching the
ground (soil).
In case of shorter antennas, current in the radials will be
significant. In that case you are right, the azimuth pattern will no
longer be circular. There will be more radiation in a direction
opposite to where are no radials. I believe that you will not notice
the difference between semi circular or full circular radial network
because of directivity.

Regarding elevation pattern, the soil properties will be dominant. So
I would not worry about your ground network.

The real part of the ground impedance will be higher (with respect to
a full star configuration), so depending on the radiation resistance
of you vertical, the radiation efficiency may be lower.

Best regards,

Wim
PA3DJS
www.tetech.nl

R.K. AJ4BF wrote:
What is the effect of having a semi-circle of radials beneath a
vertical antenna instead of a complete circle? For example if your
vertical is near a property line. I vaguely remember reading that the
azimuth pattern would no longer be omni-directional and there would be
a change in the elevation of the main lobe. But my memory is hazy and I
can't find anything on the web.


It will have some effect, but less than you might think. I put up a
vertical on one side of my yard, and put in a set of radials that were
as long as I could get them in every direction. Some of them aren't
perfectly radial either, there is the occasional bend in some of them.

It's one of those things that if possible, they should be arranged in a
perfect radial pattern all around the antenna. But as Hams, we don't
always have the chance to have things perfect.

I would say that if you could get some short radials down in the
deficient direction it would be best, but if not, put it up anyway and
have some fun.

- 73 de Mike KB3EIA -