Dear Group:

A popular antenna for LPFM stations is an antenna that I call an OI
antenna (because of its appearance). It consists of about 0.25 wave
lengths (WL) of thick wire shaped into a circle [the O] in the
horizontal plane with about 0.125 WL of thick wire in the vertical plane
connected to each end of the circle [the I]. In other words, it is
essentially a 0.5 WL dipole with one leg extending from the center to
the left in a horizontal circle that then points down while the other
leg extends to the right in a horizontal circle that then points up.

Commercial examples are the Telecom TFC1K and the well built
Dielectric DCR-L. Most often, two of the antennas are used vertically
spaced by 1 WL and driven in phase. All venders characterize the
antenna as being circularly polarized.

1. What is (are) the conventional name for this antenna? I have not
been able to find it in any of my references.

2. When I model one bay of the antenna I find that almost all of the
radiation is vertically polarized. This is not at all surprising in
view of the symmetry of the horizontal element [the O].
What might I be doing wrong?

Speculation: I may not have the dimensions correct though the antenna I
modeled is resonant at 94 MHz. It is possible that venders are equating
omni-directional-in-the-horizontal-plane with circularly polarized.

I have an EZNEC file that I will send to anyone who wishes it.

The impetus for these questions is a determination of an appropriate
offset of these antennas from a large diameter tower.

Thanks in advance for your insight.
73 Mac N8TT
--
J. Mc Laughlin - Michigan USA
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