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

[Jay Hennigan]

Matthew Robbins wrote:
> I'm looking for a simple, durable, and easy-to-build halo antenna design for 2m.
> 
> I've been reading about them, and some of the stuff says building
> Halos is as easy-as-pie, and other stuff says it is really
> complicated, touchy, and it's all just trial-and-error. I'm planning
> to build five of them, so I'm hoping for the former.
> 
> I'm interested in Halos because I want horizontal polarization without
> the size of a turnstile (or eggbeater).

Google is your friend.

http://www.kr1st.com/2mhalo.htm
http://home.comcast.net/~buck0/2m_halo.htm
http://www.hamuniverse.com/loop.html
http://members.aol.com/n2kbk/2mhalo.html

General notes:

Nothing magic going on here.  These are basically dipoles bent into a 
circle.

Thicker material results in broader bandwidth.  More rugged but also 
heavier and presents more wind load.

There's a voltage point across the ends, so the gap should be well 
insulated.  Actual gap distance not too critical, about an inch or so is 
fine.

Some designs use disks, etc. as the elements of a capacitor across the 
gap for fine-tuning.  Probably not needed for low power with relatively 
thick elements.

Most designs are gamma-match but anything that works for a dipole will 
work here.  The hairpin loops for tape-measure beams, etc. may be a good 
choice.

Consider a bead balun at the feedpoint to prevent the coax braid from 
acting as a radiator and distorting the pattern.

The N2KBK design looks like it could be done with tape-measure material 
or similar.

For ARDF use,  I would definitely test it by setting up a receiver with 
s-meter or whoopie mode some distance away.  Rotate the antenna through 
360 degrees to ensure that the radiation pattern is near omni, or at 
least not too wonky.  How you route the feedline may have an effect 
here, especially with a sub-optimal match or balun.

As with any design...

Good
Fast
Cheap

You can generally optimize a maximum of two of the above.  :-)

--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
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