Halos are slightly less than a half wave around in circumference. They
rely on the residual capacitance to be canceled by a gamma match, T
match, or utilized with an inductive stub in a beta match. The
feedpoint impedance and resonant point reflects the capacitance
between the ends opposite the feedpoint. Slight changes to this
capacitance, usually due to rain, snow, or vibration can move the
feedpoint impedance out of resonance.
The radiation pattern of a halo is not circular; the radiation to the
sides are down about 2 dB or so from the radiation from the ends.
The PAR triangles are slightly larger than a half wave and have
greater separation between the ends. The feedpoint impedance is
inductive, cancelled by series capacitors. The end capacitance has
much less effect on the feedpoint impedance. PAR also include a
current mode (choke) balun in the matching unit. Most halo makers do
not. The pattern of the PAR is nearly circular, with only a half dB or
so variation between the ends and the sides.
The inverted vee is an underrated antenna for 6 meters. I think it is
superior to either the halo or the PAR triangle and not much more
trouble to erect. The radiation off the ends is a few dB down from
broadside, but the radiation broadside is 2 dB or so up on the halo.
It is lots cheaper as well.
While the halos have their place in mobile or portable operation, the
inverted vee is not much more trouble than either to erect in a
permanent situation, and will provide superior performance to either.
- Duffey
--
KK6MC
James Duffey
Cedar Crest NM
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