[ARDF] Does anyone have a good design for a Halo Antenna?

[Dale Hunt WB6BYU]

I agree with Jay's comments. I think there are some
other articles on omnidirectional horizontal antennas on
W4RNL's web site, but I don't have the links handy
at the moment.

Just as a quick check I tried modeling a simple dipole
with the ends bent at right angles to form a 3-sided
square.  (The model had the wires both bent in the same
direction 6" from the feedpoint, with a total length
of 41" for the dipole).  The overall pattern was less
than 5dB from circular.  There are nulls in the pattern
at relatively low angles but these are due to ground
reflection rather than the antenna itself, so installation
shouldn't be a problem.  Input impedance is about 20
ohms:  I suspect most low power transmitters will handle
this, but you may want to add some matching if you are
pushing the final transistor close to its limits.


You may be able to get a more omnidirectional pattern
by shortening the center section, but at the expense of
a lower feedpoint impedance.  However, for practice
sessions simply bending a stiff-wire dipole into something
vaguely like a halo should be quite sufficient.
(I sometimes bend mine around a tree trunk to keep the
ends out of the way.)

My practice antennas are stiff wire dipoles, probably
#14 solid copper house wire, built on the top of a short
piece of lathe with the other end pointed to make a
stake about 18" to 2' high.  The wood stake is used as
the center insulator.  With a MicroHunt transmitter
secured to the stake and some multi-colored survey
flagging it makes a very convenient and portable
practice transmitter that can just be stuck in the
ground wherever desired.  I can carry the whole set of
them in one hand.  I've also secured the stakes to
my ammo can transmitter boxes with a couple big
rubber bands to make a self-contained package.

For competition my next design will be turnstyled loops.
These can be made from light flexible wire with dowels
for spreaders.  By designing the loops for 100 ohm
impedance I can use a pair of 50 ohm cables as a balanced
feedline to each and get a good 50 ohm match when the
two are connected in parallel.  Looks good on the computer,
next step is to actually build one and try it out.

- Dale WB6BYU